Glossary of Terms

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Glossary of Terms

1-butanol. See n-butyl alcohol. chromatic aberration for two colors. See also alloy system. A complete series of compositions 2-butoxyethanol. See butyl cellosolve. achromatic objective. produced by mixing in all proportions any achromatic objective. Objective are achromatic group of two or more components, at least one when corrected chromatically for two colors, of which is a metal. A generally red and green, and spherically for alpha (␣) The low-temperature allotrope of ti- light of one color, usually in the yellow-green tanium with a hexagonal close-packed crystal aberration. Any error that causes image degra- portion of the spectrum. structure that occurs below the b transus. dation. Such an error may be chromatic, acicular alpha. A product of nucleation and alpha-beta structure. A microstructure contain- spherical, astigmatic, or comatic and can regrowth from b to the lower-temperature allo- ing ␣ and b as the principal phases at a specific sult from design, execution, or both. See also trope ␣ phase. It may have a needlelike ap- temperature. See also beta. astigmatism, chromatic aberration, coma, and pearance in a photomicrograph and may have alpha brass. A solid-solution phase of one or spherical aberration. needle, lenticular, or flattened bar morphology more alloying elements in copper having the abrasion. The process of grinding or wearing in three dimensions. See also alpha. same crystal lattice as copper. away through the use of abrasives; a rough- acid extraction. Removal of phases by disso- alpha case. The oxygen-, nitrogen-, or carbon- ening or scratching of a surface due to abra- lution of the matrix metal in an acid. See also enriched ␣-stabilized surface resulting from sive wear. extraction. elevated-temperature exposure. See also al- abrasion artifact. A false structure introduced adhesive wear. The removal of material from a pha stabilizer. during an abrasion stage of a surface-prepa- surface by the welding together and subse- alpha double prime (orthorhombic marten- ration sequence. quent shearing of a minute area of two sur- site). A supersaturated, nonequilibrium ortho- abrasion fluid. A liquid added to an abrasion faces that slide across each other under pres- rhombic phase formed by a diffusionless system. The liquid may act as a lubricant, as sure. Contrast with abrasive wear. transformation of the b phase in certain alloys. a coolant, or as a means of flushing abrasion age hardening. Hardening by aging, usually af- alpha iron. Solid phase of pure iron that is stable debris from the abrasion track. ter rapid cooling or cold working. See also below 910 C (1670 F), possesses the body- abrasion process. An abrasive machining pro- aging. centered cubic lattice, and is ferromagnetic cedure in which the surface of the workpiece aging. A change in properties that occurs at am- below 768 C (1415 F). is rubbed against a two-dimensional array of bient or moderately elevated temperatures af- alpha prime (hexagonal martensite). A super- abrasive particles under approximately con- ter hot working, heat treating, or cold working saturated, nonequilibrium hexagonal ␣ phase stant load. (strain aging). The change in properties is of- formed by a diffusionless transformation of abrasion rate. The rate at which material is re- ten due to a phase change (precipitation) but the b phase. It is often difficult to distinguish moved from a surface during abrasion. It is does not alter chemical composition. See also from acicular ␣, although the latter is usually usually expressed in terms of the thickness re- age hardening, artificial aging, interrupted less well defined and frequently has curved, moved per unit of time or distance traversed. aging, natural aging, overaging, precipitation instead of straight, sides. abrasive. A substance capable of removing ma- hardening, precipitation heat treatment, pro- alpha stabilizer. An alloying element that dis- terial from another substance in machining, gressive aging, quench aging, step aging, and solves preferentially in the ␣ phase and raises abrasion, or polishing that usually takes the strain aging. the ␣-b transformation temperature. form of several small, irregularly shaped par- alignment. A mechanical or electrical adjust- alpha transus. The temperature that designates ticles of a hard material. ment of the components of an optical device the phase boundary between the ␣ and ␣ b abrasive machining. A machining process in so that the path of the radiating beam coin- fields. which the points of abrasive particles are used cides with the optical axis or other predeter- aluminum chloride, anhydrous. as machining tools. Grinding is a typical abra- mined path in the system. See also magnetic Solid; AlCl3; sive machining process. reacts violently with water, evolving HCl gas; alignment, mechanical alignment, and voltage • abrasive wear. The removal of material from a alignment. use of hydrated form, AlCl3 6H2O, is pre- surface when hard particles slide or roll across allotriomorphic crystal. A crystal having a nor- ferred. the surface under pressure. The particles may mal lattice structure but an outward shape that ammonium molybdate. Crystals; also called be loose or may be part of another surface in is imperfect, because it is determined to some ammonium paramolybdate or heptamolyb- • contact with the surface being abraded. Con- extent by the surroundings. The grains in a date; (NH4)6Mo7O42 4H2O; can be used inter- trast with adhesive wear. metallic aggregate are allotriomorphic crys- changeably with “molybdic acid, 85%.” a-butyl alcohol. Liquid; normal butyl alcohol; tals. Compare with idiomorphic crystal. amplifier. A negative lens used instead of an also called butyl alcohol and 1-butanol. allotropy. The property by which certain ele- eyepiece to project under magnification the accelerating potential. A relatively high voltage ments may exist in more than one crystal image formed by an objective. The amplifier applied between the cathode and anode of an structure. See also polymorphism. is designed for flatness of field and should be electron gun to accelerate electrons. alloying element. An element added to and re- used with an apochromatic objective. achromatic. Free of color. A lens or objective is maining in a metal that changes structure and analyzer. An optical device capable of produc- achromatic when corrected for longitudinal properties. ing plane-polarized light. It is used for detect- 1116 / Reference Information

ing the effect of the object on plane-polarized aperture (optical). In optical microscopy, the axis (crystal). The edge of the unit cell of a light produced by the polarizer. working diameter of a lens or a mirror. See space lattice. Any one axis of any one lattice angle of reflection. (1) Reflection: the angle be- also angular aperture. is defined in length and direction relative to tween the reflected beam and the normal to aplanatic. Corrected for spherical aberration and other axes of that lattice. the reflecting surfaces. See also normal. (2) coma. Diffraction: the angle between the diffracted apochromatic objective. Objectives corrected beam and the diffracting planes. chromatically for three colors and spherically angstrom unit (A˚ ). A unit of linear measure for two colors are called apochromats. These B equal to 1010 m, or 0.1 nm. Although not an corrections are superior to those of the ach- accepted SI unit, it is occasionally used for romatic series of lenses. Because apochromats backing film. A film used as auxiliary support small distances, such as interatomic distances, are not well corrected for lateral color, special for the thin replica or specimen-supporting and some wavelengths. eyepieces are used to compensate. See also film. angular aperture. In optical microscopy, the an- achromatic. back reflection. The diffraction of x-rays at a gle between the most divergent rays that can artifact. A feature of artificial character, such as Bragg angle approaching 90. pass through a lens to form the image of an a scratch or a piece of dust on a metallographic bainite. A eutectoid transformation product of object. See also aperture (optical). specimen, that can be erroneously interpreted ferrite and a fine dispersion of carbide gener- anisotropy. Characterized by having different as a real feature. See also abrasion artifact, ally formed below 450 to 500 C (840 to 930 values of a property in different directions. mounting artifact, and polishing artifact. F). Upper bainite is an aggregate that con- annealing. A generic term denoting a treat- artificial aging. Aging above room temperature. tains parallel lath-shaped units of ferrite, pro- ment—heating to and holding at a suitable Compare with natural aging. duces the so-called “feathery” appearance in temperature, followed by cooling at a suitable astigmatism. A defect in a lens or optical system optical microscopy, and is formed above ap- rate—used primarily to soften metallic mate- that causes rays in one plane parallel to the proximately 350 C (660 F). Lower bainite, rials but also to produce desired changes si- optical axis to focus at a distance different which has an acicular appearance similar to multaneously in other properties or in micro- from those in the plane at right angles to it. tempered martensite, is formed below approx- structure. When applied only for the relief of ASTM grain size number. See grain size. imately 350 C (660 F). stress, the process is called stress relieving or athermal. Not isothermal. Changing rather than banding. Inhomogeneous distribution of alloy- stress-relief annealing. In ferrous alloys, an- constant temperature conditions. ing elements or phases aligned in filaments or nealing is carried out above the upper critical atomic replica. A thin replica devoid of struc- plates parallel to the direction of working. See temperature, but the time-temperature cycles ture on the molecular level. It is prepared by also ferrite-pearlite banding and segregation vary widely in maximum temperature attained the vacuum or hydrolytic deposition of metals banding. and cooling rate used, depending on compo- or simple compounds of low molecular barrel distortion. See negative distortion. sition, material condition, and desired results. weight. See also replica. basal plane. That plane of a hexagonal or te- See also black annealing, blue annealing, box atomic scattering factor, f. The ratio of the am- tragonal crystal perpendicular to the axis of highest symmetry. Its Miller indices are (001). annealing, bright annealing, cycle annealing, plitude of the wave scattered by an atom to basketweave. Alpha platelets with or without in- flame annealing, graphitizing, isothermal an- that scattered by a single electron. terweaved b platelets that occur in colonies in nealing, malleabilizing, process annealing, attack polishing. Simultaneous etching and me- a Widmansta¨tten structure. quench annealing, spheroidizing, and subcrit- chanical polishing. benzalkonium chloride. Crystals; essentially ical annealing. In nonferrous alloys, anneal- austempering. Cooling (quenching) an austen- alkyl-dimethyl-benzyl-ammonium chloride. ing cycles are designed to remove part or all itized steel at a rate high enough to suppress May not be readily available in this form; see the effects of cold working (recrystallization formation of high-temperature transformation zephiran chloride. may or may be involved), cause complete co- products, then holding the steel at a tempera- beta (b) The high-temperature allotrope of tita- alescence of precipitates from the solid solu- ture below that for pearlite formation and nium with a body-centered cubic crystal struc- tion in relatively coarse form, or both, de- above that for martensite formation until ture that occurs above the b transus. pending on composition and material transformation to an essentially bainitic struc- beta eutectoid stabilizer. An alloying element condition. See also anneal to temper, final an- ture is complete. that dissolves preferentially in the b phase, nealing, intermediate annealing, recrystalli- austenite. Generally, a solid solution of one or lowers the ␣-b to b transformation tempera- zation annealing, and stress relieving. more alloying elements in a face-centered cu- ture, and results in b decomposition to ␣ plus annealing carbon. See temper carbon. bic polymorph of iron (c-iron). Specifically, a compound. This eutectoid reaction can be annealing twin. A twin formed in a crystal dur- in carbon steels, the interstitial solid solution sluggish for some alloys. ing recrystallization. of carbon in c-iron. beta fleck. Alpha-lean region in the ␣-b micro- annealing twin bands. See twin bands. austenitic grain size. The size attained by the structure significantly larger than the primary anneal to temper. A final partial anneal that grains in steel when heated to the austenitic ␣ width. This b-rich area has a b transus mea- softens a cold-worked nonferrous alloy to a region. This may be revealed by appropriate surably below that of the matrix. Beta flecks specified level of hardness or tensile strength. etching of cross sections after cooling to room have reduced amounts of primary ␣ that may anode aperture. In electron microscopy, the temperature. exhibit a morphology different from the pri- opening in the accelerating voltage anode austenitizing. Forming austenite by heating a mary ␣ in the surrounding ␣-b matrix. shield of an electron gun through which the ferrous alloy into the transformation range beta isomorphous stabilizer. An alloying ele- electrons must pass to illuminate or irradiate (partial austenitizing) or above the transfor- ment that dissolves preferentially in the b the specimen. mation range (complete austenitizing). phase, lowers the ␣-b to b transformation tem- anodic etching. Reveals the microstructure by average grain diameter. The mean diameter of perature without a eutectoid reaction, and selective anodic dissolution of the polished an equiaxed grain section whose size repre- forms a continuous series of solid solution surface using a direct current. Variation with sents all the grain sections in the aggregate with b-titanium. layer formation: anodizing. being measured. See also grain size. beta structure. Structurally analogous body- aperture (electron). See anode aperture, con- axial ratio. The ratio of the length of one axis centered cubic phases (similar to b-brass) or denser aperture, and physical objective aper- to that of another, for example, c/a, or the con- electron compounds that have ratios of three ture. tinued ratio of three axes, such as a:b:c. valence electrons to two atoms. Glossary of Terms / 1117 beta transus. The minimum temperature above box annealing. Annealing of a metal or alloy in a gaseous atmosphere having a composition which equilibrium ␣ does not exist. For b eu- a sealed container under conditions that min- that results in simultaneous absorption of car- tectoid additions, the b transus ordinarily is imize oxidation. See also black annealing. bon and nitrogen by the surface and, by dif- applied to hypoeutectoid compositions or Bragg angle. The angle between the incident fusion, creates a concentration gradient. The those that lie to the left of the eutectoid com- beam and the lattice planes considered. process is completed by cooling at a rate that position. Bragg equation. nk 2d sin h, where n is the produces the desired properties in the work- bifilar eyepiece. A filar eyepiece with motion in order of reflection, k is the wavelength of x- piece. two mutually perpendicular directions. rays, d is the distance between lattice planes, carbon potential. A measure of the capacity of binary alloy. Any specific composition in a bi- and h is the Bragg angle. See also order (in x- an environment containing active carbon to al- nary system. ray reflection). ter or maintain, under prescribed conditions, binary system. The complete series of compo- Bragg method. A method of x-ray diffraction in the carbon concentration in a steel. sitions produced by mixing a pair of compo- which a single crystal is mounted on a spec- carbon restoration. Replacing the carbon lost nents in all proportions. trometer with a crystal face parallel to the axis in the surface layer during previous process- binodal curve. In a two-dimensional phase di- of the instrument. ing by carburizing this layer to the original agram, a continuous line consisting of both of bright annealing. Annealing in a protective me- carbon level. the pair of conjugate boundaries of a two- dium to prevent discoloration of the bright carburizing. A case-hardening process in which phase equilibrium that join without inflection surface. an austenitized ferrous material contacts a car- at a critical point. See also miscibility gap. bright-field illumination. For reflected light, bonaceous atmosphere having sufficient car- birefringence. A double-refraction phenomenon the form of illumination that causes specularly bon potential to cause absorption of carbon at in anisotropic materials in which an unpolar- reflected surfaces normal to the axis of the mi- the surface and, by diffusion, to create a con- ized beam of light is divided into two beams croscope to appear bright. For transmission centration gradient. with different directions and relative velocities electron microscopy, the illumination of an case. That portion of a ferrous alloy, extending of propagation. The amount of energy trans- object so that it appears on a bright back- inward from the surface, whose composition mitted along an optical path through a crystal ground. has been altered during case hardening. Typ- that exhibits birefringence becomes a function brittle fracture. Rapid fracture preceded by lit- ically considered to be the portion of an alloy of crystalline orientation. tle or no plastic deformation. (a) whose composition has been measurably bivariant equilibrium. A stable state among brittleness. The tendency of a material to frac- altered from the original composition, (b) that several phases equal to the number of com- ture without first undergoing significant plas- appears dark when etched, or (c) that has a ponents in a system and in which any two of tic deformation. higher hardness value than the core. Contrast the external variables of temperature, pres- buffer. A substance added to aqueous solutions with core. sure, or concentration may be varied without to maintain a constant hydrogen-ion concen- case hardening. A generic term covering sev- necessarily changing the number of phases. tration even in the presence of acids or alkalis. eral processes applicable to steel that change Sometimes termed divariant equilibrium. burning. (1) During austenitizing, permanent the chemical composition of the surface layer black annealing. Box annealing of ferrous alloy damage of a metal or alloy by heating to cause by absorption of carbon, nitrogen, or both and, sheet, strip, or wire. incipient melting or intergranular oxidation. by diffusion, create a concentration gradient. blackbody. A hypothetical “body” that com- See also overheating. (2) During subcritical See also carbonitriding, carburizing, cyanid- pletely absorbs all incident radiant energy, in- annealing, particularly in continuous annealing, nitriding, nitrocarburizing, and quench dependent of wavelength and direction, that ing, production of a severely decarburized and hardening. grain-coarsened surface layer that results from is, neither reflects nor transmits any of the in- cast replica. A reproduction of a surface in plas- excessively prolonged heating to an exces- cident radiant energy. tic made by the evaporation of the solvent sively high temperature. (3) In grinding, suf- blocky alpha. Alpha phase that is considerably from a solution of the plastic or by polymer- ficient heating of the workpiece to cause dis- larger and more polygonal in appearance than ization of a monomer on the surface. See also coloration or to change the microstructure by the primary ␣ in the sample. It may arise from replica. tempering or hardening. extended exposure high in the ␣-b phase field cast structure. The metallographic structure of burnishing. Smoothing surfaces through fric- or by slow cooling through the b transus dur- a casting evidenced by shape and orientation tional contact between the workpiece and ing forging or heat treating. It may be removed of grains as well as segregation of impurities. some hard pieces of material, such as hard- by b recrystallization, or all-b working, fol- cathodic etching. See ion etching. ened steel balls. lowed by further ␣-b work, and may accom- cell block (CB). A contiguous group of cells in ␣ butyl carbitol. Liquid; diethylene glycol mon- pany grain-boundary . obutyl ether. which the same set of glide systems operates. blowholes. A hole produced in a casting or weld butyl cellosolve. Liquid; ethylene glycol mon- cell boundaries. Low-angle dislocation bound- by gas trapped during solidification. obutyl ether; also called 2-butoxyethanol. aries that surround the cells and are classified blue annealing. Heating hot-rolled ferrous sheet as incidental dislocation boundary. in an open furnace to a temperature within the cellosolve. Liquid; ethylene glycol monoethyl transformation range, then cooling in air to C ether. soften the metal. A bluish oxide surface layer cementite. A very hard and brittle iron-carbon forms. capping (of abrasive particles). A mechanism compound, Fe3C, also known as iron carbide. body-centered. Having an atom or group of at- of deterioration of abrasive points in which the It is characterized by its orthorhombic crystal 1 1 1 oms separated by a translation of ⁄2, ⁄2, ⁄2 points become covered by caps of adherent structure. Its occurrence as a phase in steels from a similar atom or group of atoms. The abrasion debris. alters chemical composition by the presence number of atoms in a body-centered cell must carbide. A compound of carbon with one or of manganese and other carbide-forming ele- be a multiple of 2. more metallic elements. ments. boundary grain. In the Jeffries’ method for carbitol. Liquid; diethylene glycol monoethyl chemical polishing. A process that produces a grain size measurement, a grain that is inter- ether. polished surface by the action of a chemical sected by the boundary of the standard area carbonitriding. A case-hardening process in etching solution. The etching solution is com- and is therefore counted only as one-half of a which a suitable ferrous material is heated pounded so that peaks in the topography of grain. above the lower transformation temperature in the surface are dissolved preferentially. 1118 / Reference Information

Chinese-script eutectic. A configuration of eu- tice spacings are usually different, strains of- rected chromatically, these eyepieces are over- tectic constituents, found particularly in some ten exist at the interface. corrected. See also apochromatic objective. cast alloys of aluminum containing iron and coherent scattering. A type of x-ray or electron complex silicate inclusions. A general term de- silicon and in magnesium alloys containing scattering in which the phase of the scattered scribing silicate inclusions containing visible silicon, that resembles the characters in Chi- beam has a definite (not random) relationship constituents in addition to the silicate matrix. nese script. to the phase of the incident beam. Also termed An example is corundum or spinel crystals oc- chlorine extraction. Removal of phases by for- unmodified scattering. See also incoherent curring in a silicate matrix in steel. mation of a volatile chloride. See also extrac- scattering. condenser. A system of lenses or mirrors de- tion. cold etching. Development of microstructure at signed to collect, control, and concentrate chromatic aberration. A defect in a lens or lens room temperature and below. light. system that results in different focal lengths of cold-worked structure. A microstructure re- condenser aperture. In electron microscopy, an the lens for radiation of diverse wavelengths. sulting from plastic deformation of a metal or opening in the condenser lens controlling the The dispersive power of a simple positive lens alloy below its recrystallization temperature. number of electrons entering the lens and the focuses light from the blue end of the spec- collimation. The operation of controlling a beam angular aperture of the illuminating beam. trum at a shorter distance than light from the of radiation so that its rays are as nearly par- condenser lens. A device used to focus radiation red end. An image produced by such a lens allel as possible. in or near the plane of the object. will exhibit color fringes around the border of collodian replica. A replica of a surface cast in conjugate phases. Those states of matter of the image. The difference in position along the nitrocellulose. unique composition that coexist at equilib- axis for the focal points of light is called lon- colonies. Regions within prior-b grains with ␣ rium at a single point in temperature and pres- gitudinal chromatic aberration. The difference platelets having nearly identical orientations. sure. For example, the two coexisting phases in magnification due to variations in position In commercially pure titanium, colonies often of a two-phase equilibrium. of the principal points for light of different have serrated boundaries. Colonies arise as conjugate planes. Two planes of an optical sys- wavelengths, also a difference in focal length, transformation products during cooling from tem such that one is the image of the other. is known as lateral chromatic aberration. the b field at cooling rates that induce platelet constituent. A phase or combination of phases nucleation and growth. chromic acid. Dark-red crystals or flakes; CrO3; that occurs in a characteristic configuration in also called chromic anhydride, chromic acid color filter. A device that transmits principally a a microstructure. anhydride, and chromium trioxide. See chro- predetermined range of wavelengths. See also constitutional diagram. See phase diagram. mic oxide. contrast filter and filter. continuous phase. The phase that forms the chromic anhydride. See chromic acid. color temperature. The temperature in degrees background or matrix in which the other phase chromic oxide. Fine green powder; Cr O ;a Kelvin at which a blackbody must be operated or phases may be dispersed. 2 3 to provide a color equivalent to that of the polishing abrasive; do not confuse with CrO3, continuous precipitation. Precipitation from a which is a strong acid and a component of source in question. See also blackbody. supersaturated solid solution in which the pre- many etchants. columnar structure. A coarse structure of par- cipitate particles grow by long-range diffusion cleavage. Transgranular brittle fracture of crystal allel, elongated grains formed by unidirec- without recrystallization of the matrix. Con- by crack propagation across a crystallographic tional growth that is most often observed in tinuous precipitates grow from nuclei distrib- plane of low index. castings but sometimes seen in structures. uted more or less uniformly throughout the This results from diffusional growth accom- cleavage crack. A crack that extends along a matrix. They usually are randomly oriented panied by a solid-state transformation. plane of easy cleavage in a crystalline mate- but may form a Widmansta¨tten structure. Also coma. A lens aberration occurring in the part of rial. called general precipitation. Compare with the image field that is some distance from the cleavage fracture. A fracture, usually of a po- discontinuous precipitation, and localized principal axis of the system. It results from lycrystalline metal, in which most of the precipitation. different magnification in the various lens grains have failed by cleavage, resulting in continuous spectrum (x-rays). The polychro- zones. Extra-axial object points appear as bright reflecting facets. See also crystalline matic radiation emitted by the target of an x- short, cometlike images, with the brighter fracture. ray tube. It contains all wavelengths above a small head toward the center of the field (posi- cleavage plane. A characteristic crystallo- certain minimum value, known as the short tive coma) or away from the center (negative graphic plane or set of planes in a crystal on coma). wavelength limit. which cleavage fracture occurs easily. combined carbon. That part of the total carbon contrast enhancement (electron optics). An close-packed. A geometric arrangement in in steel or cast iron present as other than free improvement in electron image contrast by the which a collection of equally sized spheres carbon. use of an objective aperture diaphragm, (atoms) may be packed together in a minimum comet tails (on a polished surface). A group of shadow casting, or other means. See also total volume. comparatively deep unidirectional scratches shadowing. coalescence. Growth of grains at the expense of that form adjacent to a microstructural discon- contrast filter. A color filter, usually with strong the remainder by absorption or the growth of tinuity during mechanical polishing. They absorption, that uses the special absorption a phase or particle at the expense of the re- have the general shape of a comet tail. Comet bands of the objective to control the contrast mainder by absorption or reprecipitation. tails form only when a unidirectional motion of the image by exaggerating or diminishing coarse grains. Grains larger than normal for the is maintained between the surface being pol- the brightness difference between differently particular wrought metal or alloy or of a size ished and the polishing cloth. colored areas. that produces a surface roughening known as comparison standard. A standard micrograph contrast perception. The ability to differentiate orange peel or alligator skin. or a series of micrographs, usually taken at 75 various components of the object structure by coated abrasive product. A two-body abrasion to 100, used to determine grain size by di- various intensity levels in the image. device in which a backing paper or cloth is rect comparison with the image. controlled etching. Electrolytic etching with se- coated with a layer of abrasive grits, that are compensating eyepiece. An eyepiece designed lection of suitable etchant and voltage result- cemented to the backing. for use with apochromatic objectives. They ing in a balance between current and dissolved coherent precipitate. A precipitated particle of are also used to advantage with high-power metal ions. a second phase whose lattice maintains reg- (oil-immersion) achromatic objectives. Be- controlled rolling. A hot-rolling process in istry with the matrix lattice. Because the lat- cause apochromatic objectives are undercor- which the temperature of the steel is closely Glossary of Terms / 1119

controlled, particularly during the final rolling cross direction. See transverse direction. uity so that none can enter the objective passes, to produce a fine-grain microstructure. cross rolling. A hot-rolling process in which directly. In electron microscopy, the image is cooling curve. A graph showing the relationship rolling reduction proceeds perpendicular to formed using only electrons scattered by the between time and temperature during the and parallel to the length of the original slab. object. cooling of a material. It is used to find the crystal. A solid composed of atoms, ions, or Debye ring. A continuous circle, concentric temperatures at which phase changes occur. A molecules arranged in a pattern that is periodic about the undeviated beam, produced by mon- property or function other than time may oc- in three dimensions. ochromatic x-ray diffraction from a randomly casionally be used—for example, thermal ex- crystal analysis. A method for determining oriented crystalline powder. An analogous ef- pansion. crystal structure, for example, the size and fect is obtained using electron diffraction. cooling rate. The average slope of the time-tem- shape of the unit cell and the location of all Debye-Scherrer method. A method of x-ray perature curve taken over a specified time and atoms within the unit cell. diffraction using monochromatic radiation temperature interval. crystal-figure etching. Discontinuity in etching and a polycrystalline specimen mounted on core. (1) In a ferrous alloy that has undergone depending on crystal orientation. Distinctive the axis of a cylindrical strip of film. See also case hardening, that portion of the alloy struc- sectional figures form at polished surfaces. powder method. ture not part of the case. Typically considered Closely related to dislocation etching. decarburization. Loss of carbon from the sur- to be the portion that (a) appears light when crystalline fracture. A pattern of brightly re- face of a ferrous alloy as a result of heating in etched, (b) has an unaltered chemical com- flecting crystal facets on the fracture surface a medium that reacts with carbon. position, or (c) has a hardness value lower of a polycrystalline metal resulting from decoration (of dislocations). Segregation of than that of the case. (2) A specially formed cleavage fracture of many individual crystals. solute atoms to the line of a dislocation in a material inserted in a mold to shape the inte- Contrast with fibrous fracture. crystal. In ferrite, the dislocations may be rior or other part of a casting that cannot be crystallite. A crystalline grain not bounded by decorated with carbon or nitrogen atoms. shaped as easily by the pattern. habit planes. deep etching. Macroetching, especially for coring. A variation in composition between the crystal system. One of seven groups into which steels, to determine the overall character of the center and surface of a unit of structure, such all crystals may be divided: triclinic, mono- material (presence of imperfections such as as a dendrite, a grain, or a carbide particle, that clinic, orthorhombic, hexagonal, rhombo- seam defects, rolling defects, forging bursts, results from nonequilibrium growth over a hedral, tetragonal, and cubic. remnant shrinkage voids, cracks, and coring). temperature range. cube texture. A texture found in wrought metals define (x-rays). To limit a beam of x-rays by corundum. A naturally occurring, impure ␣-alu- in the cubic system in which nearly all the passage through apertures to obtain a parallel, minum oxide. A purer form of the oxide than crystal grains have a plane of the type (100) divergent, or convergent beam. emery. parallel or nearly parallel of the plane of work- definition. The clarity or sharpness of a micro- critical cooling rate. The minimum rate of con- ing and a direction of the type [001] parallel scopic image. tinuous cooling for preventing undesirable or nearly parallel to the direction of elonga- deformation bands. Parts of a crystal that have transformations. For steel, unless otherwise tion. rotated differently during deformation to pro- specified, it is the slowest rate at which aus- cubic. Having three mutually perpendicular axes duce bands of varied orientation within indi- tenite can be cooled from above critical tem- of equal length. vidual grains. deformation lines. perature to prevent its transformation above cupping. The condition sometimes occurring in Thin bands or lines produced the martensite start temperature. heavily cold-worked rods and wires in which by cold working in grains of some metals, particularly those of face-centered cubic struc- critical curve. In a binary or higher-order phase the outside fibers remain intact and the central ture. They are not removed by repolishing and diagram, a line along which the phases of a zone has failed in a series of cup-and-cone re-etching. heterogeneous equilibrium become identical. fractures. degrees of freedom. The number of independent critical illumination. The formation of an image cupric ammonium chloride. Crystals; a double variables, such as temperature, pressure, or of the light source in the object field. salt, CuCl •2NH Cl•2H O; if not available, 2 4 2 concentration, within the phases present that critical point. (1) The temperature or pressure substitute 0.6 g CuCl •2H O plus 0.4 g NH Cl 2 2 4 may be adjusted independently without caus- at which a change in crystal structure, phase, for each gram of the double salt. ing a phase change in an alloy system at equi- or physical properties occurs. Also termed curvature of field. A property of a lens that librium. transformation temperature. (2) In an equilib- causes the image of a plane to be focused into delta ferrite. Designation commonly assigned rium diagram, that combination of composi- a curved surface instead of a plane. to d-iron that indicates inclusion of elements tion, temperature, and pressure at which the cyaniding. A case-hardening process in which a in solid solution. Small amounts of carbon and phases of an inhomogeneous system are in ferrous material is heated above the lower large amounts of other alloying elements equilibrium. transformation temperature range in a molten markedly affect the high- and low-temperature critical pressure. That pressure above which the salt containing cyanide to cause simultaneous limit of equilibrium. liquid and vapor states are no longer distin- absorption of carbon and nitrogen at the sur- delta iron. Solid phase of pure iron that is stable guishable. face and, by diffusion, create a concentration from 1400 to 1539 C (2550 to 2800 F) and critical rake angle. The rake angle at which the gradient. Quench hardening completes the possesses the body-centered cubic lattice. action of a V-point tool changes from cutting process. dendrite. A crystal with a treelike branching pat- to plowing. cycle annealing. An annealing process that uses tern. It is most evident in cast metals slowly critical strain. That strain resulting in the for- a predetermined and closely controlled time- cooled through the solidification range. mation of very large grains during recrystal- temperature cycle to produce specific proper- dendritic segregation. Inhomogeneous distri- lization. ties or microstructures. bution of alloying elements through the arms critical surface. In a ternary or higher-order of dendrites. phase diagram, the area on which the phases dense dislocation wall. A single, nearly planar, in equilibrium become identical. D deformation-induced boundary, classified as a critical temperature. That temperature above geometrically necessary boundary, enclosing which the vapor phase cannot be condensed dark-field illumination. The illumination of an a cell block at small-to-intermediate strains. to liquid by an increase in pressure. Synony- object such that it appears bright and the sur- deoxidation products. Those nonmetallic inclu- mous with critical point if pressure is con- rounding field dark. This results from illumi- sions that form as a result of adding deoxidiz- stant. nating the object with rays of sufficient obliq- ing agents to molten metal. 1120 / Reference Information depletion. Selective removal of one component bearings, in which interdiffusion between the jection, such as dirt in or near the electron of an alloy, usually from the surface or pref- various components has taken place. beam. erentially from grain-boundary regions. discontinuous precipitation. Precipitation from drop etching. Placing a drop of an etchant on a depth of field. The depth in the subject over a supersaturated solid solution in which the selected area of the sample surface to develop which features can be seen to be acceptably in precipitate particles grow by short-range dif- the alloying microconstituents (drip reaction). focus in the final image produced by a micro- fusion, accompanied by recrystallization of dry etching. Development of microstructure un- scope. the matrix in the region of precipitation. Dis- der the influence of gases. deviation (x-ray). The angle between the dif- continuous precipitates grow into the matrix dry objective. Any microscope objective de- fracted beam and the transmitted incident from nuclei near grain boundaries, forming signed for use without liquid between the beam. It is equal to twice the Bragg angle h. cells of alternate lamellae of precipitate and cover glass and the objective or, in the case of devitrification. Crystallization of an amorphous depleted (and recrystallized) matrix. Often re- metallurgical objectives, in the space between substance. ferred to as cellular or nodular precipitation. objective and specimen. dezincification. A type of corrosion in which Compare with continuous precipitation and duplex grain size. The simultaneous presence zinc is selectively leached from zinc-contain- localized precipitation. of two grain sizes in substantial amounts, with ing alloys. This occurs most commonly in dislocation. A linear imperfection in a crystal- one grain size appreciably larger than the oth- copper-zinc alloys. line array of atoms. The two basic types rec- ers. Also termed mixed grain size. diethylene glycol. Syrupy liquid; also called ognized are (a) an edge dislocation that cor- duplex microstructure. A two-phase structure. 2,2-oxydiethanol and dihydroxydiethyl ether; responds to the row of mismatched atoms (HOCH2CH2)2O; more viscous than ethylene along the edge formed by an extra, partial glycol—otherwise similar in behavior. plane of atoms within the body of a crystal E diethylene glycol monobutyl ether. See butyl and (b) a screw dislocation that corresponds carbitol. to the axis of a spiral structure in a crystal and edge-trailing technique. A unidirectional mo- diethylene glycol monoethyl ether. See carbi- is characterized by a distortion joining nor- tion perpendicular to and toward one edge of tol. mally parallel lines together to form a contin- the specimen during abrasion or polishing diethyl ether. See ether. uous helical ramp (with a pitch of one inter- used to improve edge retention. differential interference contrast illumina- planar distance) winding about the elastic electron scatter. The scatter of electrons tion. A microscopic technique using a beam- dislocation. A mixed dislocation, which is any by an object without loss of energy, usually splitting double-quartz prism, that is, a mod- combination of a screw dislocation and an an interaction between electrons and atoms. ified Wollaston prism placed ahead of the edge dislocation, is prevalent. electrical discharge machining. Removal of objective together with a polarizer and ana- dislocation etching. Etching of exit points of stock from an electrically conductive material lyzer in the 90 crossed positions. The two dislocations on a surface. Depends on the by rapid, repetitive spark discharge through a light beams are made to coincide at the focal strain field ranging over a distance of several dielectric fluid flowing between the workpiece plane of the objective, revealing height differ- atoms. Etching of dislocations is caused by and a shaped electrode. ences as variations in color. The prism can be their strain field ranging over a distance of electrochemical (chemical) etching. General moved, shifting the interference image several atoms. Crystal figures (etch pits) are expression for all developments of micro- through the range of Newtonian colors. formed at the exiting points. For example, etch structure through reduction and oxidation (re- diffraction. (1) A modification that radiation un- pits for cubic materials are cube faced. dox reactions). dergoes, for example, in passing by the edge disordered structure. The crystal structure of a electrolytic etching. See anodic etching. of opaque bodies or through narrow slits, in solid solution in which the atoms of different electrolytic extraction. Removal of phases by which the rays appear to be deflected. (2) Co- elements are randomly distributed relative to using an electrolytic cell containing an elec- herent scattering of x-rays by the atoms of a the available lattice sites. Contrast with or- trolyte that preferentially dissolves the metal crystal that necessarily results in beams in dered structure. matrix. See also extraction. characteristic directions. Sometimes termed electrolytic polishing. An electrochemical pol- dispersoid. Finely divided particles of relatively reflection. (3) The scattering of electrons by ishing process in which the metal to be pol- insoluble constituents visible in the micro- any crystalline material through discrete an- ished is made the anode in an electrolytic cell structure of certain alloys. gles depending only on the lattice spacings of where preferential dissolution at high points dissociation. As applied to heterogeneous equi- the material and the velocity of the electrons. in the surface topography produces a specu- libria, the transformation of one phase into diffraction grating. An artificially produced pe- larly reflective surface. two or more new phases of different compo- riodic array of scattering centers capable of electromagnetic focusing device. See focusing sition. producing a pattern of diffracted energy, such device. as accurately ruled lines on a plane surface. dissociation pressure. At a designated tempera- electromagnetic lens. An electromagnet de- diffraction pattern (x-rays). The spatial ar- ture, the pressure at which a phase will trans- signed to produce a suitably shaped magnetic rangement and relative intensities of diffracted form into two or more new phases of different field for the focusing and deflection of elec- beams. composition. trons or other charged particles in electron- diffraction ring. The diffraction pattern pro- dissolution etching. Development of micro- optical instrumentation. duced by a given set of planes from randomly structure by surface removal. electromechanical polishing. An attack-polish- oriented crystalline material. See also Debye divariant equilibrium. See bivariant equilib- ing method in which the chemical action of ring. rium. the polishing fluid is enhanced or controlled diffusion. (1) Spreading of a constituent in a gas, divorced eutectic. A structure in which the com- by the application of an electric current be- liquid, or solid that tends to make the components of a eutectic appear to be entirely tween the specimen and polishing wheel. position of all parts uniform. (2) The sponta- separate. electron. An elementary particle that is the nega- neous movement of atoms or molecules to double etching. Use of two etching solutions in tively charged constituent of ordinary matter. new sites within a material. sequence. The second etchant emphasizes a The electron is the lightest known particle diffusion zone. The zone of variable composi- particular microstructural feature. possessing an electric charge. Its rest mass is 28 1 tion at the junction between two different ma- drift. In electron optics, motion of the electron me 9.1 10 g, approximately ⁄1836 of terials, such as in welds or between the surface beam or image due to current, voltage, or the mass of the proton or neutron, which are, layer and the core of clad materials or sleeve specimen instabilities or to charging of a pro- respectively, the positively charged and neu- Glossary of Terms / 1121

tral constituents of ordinary matter. The emery. A naturally occurring, impure ␣-alumi- ethylene glycol monoethyl ether. See cello- charge of the electron is e 4.8 1010 num oxide. A less pure form of the oxide than solve. esu 1.6 1019 C. corundum. ethyl ether. See ether. electron beam. A stream of electrons in an elec- enantiotropy. The relation of crystal forms of eutectic. (1) An isothermal reversible reaction in tron-optical system. the same substance in which one form is stable which a liquid solution is converted into two electron diffraction. The phenomenon, or the above a certain temperature and the other form or more intimately mixed solids on cooling; technique, of producing diffraction patterns is stable below that temperature. For example, the number of solids formed equals the num- through the incidence of electrons on matter. ferrite and austenite are enantiotropic in fer- ber of components in the system. (2) An alloy electron gun. A device for producing and ac- rous alloys. having the composition indicated by the eu- celerating a beam of electrons. end-centered. Having an atom or group of at- tectic point on an equilibrium diagram. (3) An 1 electron image. A representation of an object oms separated by a translation of the type ⁄2, alloy structure of intermixed solid constituents 1 formed by a beam of electrons focused by an ⁄2, 0 from a similar atom or group of atoms. formed by a eutectic reaction. electron-optical system. See also image. The number of atoms in an end-centered cell eutectic arrest. In a cooling or heating curve, an electron lens. A device for focusing an electron must be a multiple of 2. approximately isothermal segment corre- beam to produce an image of an object. epitaxy. Oriented growth of a crystalline sub- sponding to the time interval during which the electron micrograph. A reproduction of an im- stance on a substrate with the same crystal ori- heat of transformation from the liquid phase age formed by the action of an electron beam entation. to two or more solid phases is evolving. on a photographic emulsion. epsilon (e). Designation generally assigned to eutectic carbides. Carbide formed during freez- electron microscope. An electron-optical device intermetallic, metal-metalloid, and metal-non- ing as one of the mutually insoluble phases that produces a magnified image of an object. metallic compounds found in ferrous alloy participating in the eutectic reaction of a hypereutectic tool steel. See also hypereutectic Detail may be revealed by selective transmis- systems, for example, Fe3Mo2, FeSi, and Fe3P. sion, reflection, or emission of electrons by the epsilon carbide. Carbide with hexagonal close- alloy. object. See also scanning electron microscope packed lattice that precipitates during the first eutectic-cell etching. Development of eutectic and transmission electron microscope. stage of tempering of primary martensite. Its cells (grains). electron microscope column. The assembly of composition corresponds to the empirical for- eutectic point. The composition of a liquid phase in univariant equilibrium with two or gun, lenses, specimen, and viewing and plate mula Fe2.4C. chambers. epsilon structure. Structurally analogous close- more solid phases; the lowest melting alloy of electron microscopy. The study of materials by packed phases or electron compounds that a composition series. means of an electron microscope. have ratios of seven valence electrons to four eutectoid. (1) An isothermal, reversible trans- electron microscopy impression. See impres- atoms. formation in which a solid solution is con- sion. equiaxed grain structure. A structure in which verted into two or more intimately mixed sol- electron-optical axis. The path of an electron the grains have approximately the same di- ids. The number of solids formed equals the through an electron-optical system, along mensions in all directions. number of components in the system. (2) An which it suffers no deflection due to lens equilibrium. A state of dynamic balance be- alloy having the composition indicated by the fields. This axis does not necessarily coincide tween the opposing actions, reactions, or ve- eutectoid point on an equilibrium diagram. (3) with the mechanical axis of the system. locities of a reversible process. An alloy structure of intermixed solid constit- electron-optical system. A combination of parts equilibrium diagram. A graph of the tempera- uents formed by a eutectoid transformation. evaporation. capable of producing and controlling a beam ture, pressure, and composition limits of phase The vaporization of a material by heating, usually in a vacuum. In electron mi- of electrons to yield an image of an object. fields in an alloy system as they exist under croscopy, this process is used for shadowing electron probe. A narrow beam of electrons conditions of thermodynamical equilibrium. or to produce thin support films by conden- used to scan or illuminate an object or screen. In metal systems, pressure is usually consid- sation of the vapors of metals or salts. electron trajectory. The path of an electron. ered constant. Compare with phase diagram. Ewald sphere. A geometric construction, of ra- electron velocity. The rate of motion of an elec- etchant. A chemical solution used to etch a dius equal to the reciprocal of the wavelength tron. metal to reveal structural details. of the incident radiation, with its surface at the electron wavelength. The wavelength necessary etch cracks. Shallow cracks in hardened steel origin of the reciprocal lattice. Any crystal to account for the deviation of electron rays containing high residual surface stresses, pro- plane will reflect if the corresponding recip- in crystals by wave-diffraction theory. It is nu- duced by etching in an embrittling acid. rocal lattice point lies on the surface of this merically equal to the quotient of Planck’s etch figures. Characteristic markings produced sphere. constant divided by the electron momentum. on crystal surfaces by chemical attack, usually exogenous inclusions. Nonmetallic inclusions electropolishing. See electrolytic polishing. having facets parallel to low-index crystallo- generally large in size and representing acci- electrostatic focusing device. See focusing de- graphic planes. dental contamination from materials, such as vice. etching. Subjecting the surface of a metal to fireclay refractories. electrostatic immersion lens. See immersion preferential chemical or electrolytic attack to extinction. A decrease in the intensity of the dif- objective. reveal structural details for metallographic ex- fracted beam caused by perfection or near per- electrostatic lens. A lens producing a potential amination. fection of crystal structure. See also primary field capable of deflecting electron rays to etch rinsing. Pouring the etchant over a tilted extinction and secondary extinction. form an image of an object. sample surface until the structure is revealed. extinction coefficient. The ratio of the diffracted elongated alpha. A fibrous structure brought Used for etching with severe gas evolution. beam intensity when extinction is present to about by unidirectional metalworking. It may ether. Liquid; also called ethyl ether and diethyl the diffracted beam intensity when extinction be enhanced by the prior presence of blocky ether; very low flash point; highly explosive; is absent. It applies to primary or secondary and/or grain-boundary ␣. boiling point is 34.4 C (94 F). extinction. elongated grain. A grain with one principal axis ethylene glycol. Syrupy liquid; also called 1,2- extraction. A general term denoting chemical significantly longer than either of the other ethanediol and dihydroxyethane; (CH2)2/ methods of isolating phases from the metal two. (OH)2. Less viscous than diethylene glycol; matrix. embedded abrasive. Fragments of abrasive par- otherwise similar in behavior. eyepiece. A lens or system of lenses for increas- ticles forced into the surface of a workpiece ethylene glycol monobutyl ether. Liquid; also ing magnification in a microscope by magni- during grinding, abrasion, or polishing. called 2-butoxyethanol or butyl cellosolve. fying the image formed by the objective. 1122 / Reference Information

F ing. In fracture surfaces, flakes appear as of concentration, with pressure and tempera- bright, silvery areas with a coarse texture. In ture constant. face (crystal). An idiomorphic plane surface on deep acid-etched transverse sections, they ap- free ferrite. See proeutectoid ferrite. a crystal. pear as discontinuities that are usually in the freezing point. See melting point. face-centered. Having atoms or groups of atoms midway to center location of the section. Also frequency (x-ray). The number of alternations 1 1 1 1 termed hairline cracks and shatter cracks. per second of the electric vector of the x-ray separated by translations of ⁄2, ⁄2,0; ⁄2,0, ⁄2 1 1 flame annealing. Annealing in which the heat is beam. It is equal to the velocity divided by the and 0, ⁄2, ⁄2 from a similar atom or group of atoms. The number of atoms in a face-cen- applied directly by a flame. wavelength. tered cell must be a multiple of 4. flow lines. Texture showing the direction of Fresnel fringes. A class of diffraction fringes • metal flow during hot or cold working. Flow formed when the source of illumination and ferric nitrate. Crystals; Fe(NO3)3 9H2O; there is no anhydrous form of this salt. lines often can be revealed by etching the sur- the viewing screen are at a finite distance from ferrite. Generally, a solid solution of one or face or a section of a metal part. a diffracting edge. In the electron microscope, more elements in body-centered cubic iron. In focal length. The distance from the second prin- these fringes are best seen when the object is plain carbon steels, the interstitial solid solu- cipal point to the point on the axis at which slightly out of focus. tion of carbon in ␣-iron. parallel rays entering the lens will converge or focus. ferrite-pearlite banding. Inhomogeneous dis- G tribution of ferrite and pearlite aligned in fil- focal spot. That area on the target of an x-ray aments or plates parallel to the direction of tube that is bombarded by electrons. working. focus. A point at which rays originating from a gamma iron. Solid nonmagnetic phase of pure point in the object converge or from which iron that is stable from 910 to 1400 C (1670 ferritic grain size. The grain size of the ferritic matrix of a steel. they diverge or appear to diverge under the to 2550 F) and possesses the face-centered cubic lattice. ferritizing anneal. The process of producing a influence of a lens or diffracting system. gamma structure. Structurally analogous predominantly ferritic matrix in a ferrous alloy focusing device (electrons). A device that effec- phases or electron compounds having ratios of through an appropriate heat treatment. tively increases the angular aperture of the 21 valence electrons to 13 atoms. This is gen- fiber. (1) The characteristic of wrought metal electron beam illuminating the object, render- erally a large, complex cubic structure. that indicates directional properties. It is re- ing the focusing more critical. gelatin replica. A reproduction of a surface pre- vealed by etching a longitudinal section or focusing (x-rays). The operation of producing a pared in a film composed of gelatin. See also manifested by the fibrous appearance of a convergent beam in which all rays meet in a replica. fracture. It is caused chiefly by extension of point or line. general precipitate. A precipitate that is dis- the metallic and nonmetallic constituents of forged structure. The macrostructure through a persed throughout the matrix. See also contin- the metal in the direction of working. (2) The suitable section of a forging that reveals direction of working. uous precipitation. pattern of preferred orientation of metal crys- geometrically necessary boundary. Boundaries tals after a given deformation process. Formvar. A plastic material used for the preparation of replicas or for specimen-supporting whose angular misorientations are controlled fiber texture. A texture characterized by having by the difference in glide-induced lattice ro- only one preferred crystallographic direction. membranes. Formvar replica. A reproduction of a surface in tations in the adjoining volumes. fibrous fracture. A fracture whose surface is Gibbs free energy. The maximum useful work a plastic Formvar film. See also replica. characterized by a dull gray or silky appear- obtainable from a chemical system without fractography. Descriptive treatment of fracture, ance. Contrast with crystalline fracture. net change in temperature or pressure. especially in metals, with specific reference to fibrous structure. (1) In forgings, a structure re- Gibbs triangle. An equilateral triangle used for photography of the fracture surface. vealed as laminations, not necessarily detri- plotting composition in a ternary system. fracture grain size. Grain size determined by mental, on an etched section or as a ropy ap- glancing angle. The angle (usually small) be- comparing a fracture of a specimen with a set pearance on a fracture. (2) In wrought iron, a tween an incident x-ray beam and the surface of standard fractures. For steel, a fully mar- structure consisting of slag fibers embedded of the specimen. tensitic specimen is generally used, and the in ferrite. (3) In rolled steel plate stock, a uni- glide. See slip. form, lamination-free, fine-grained structure depth of hardening and the prior-austenitic glycerol. Syrupy liquid; also called glycerin or on a fractured surface. grain size are determined. glycerine; C3H5 (OH)3; contains up to 5% (by filar eyepiece. An eyepiece having in its focal fragmentation. The subdivision of a grain into weight) H2O. plane a fiducial line that can be moved using small, discrete crystallite outlined by a heavily graded abrasive. An abrasive powder in which a calibrated micrometer screw. Useful for ac- deformed network of intersecting slip bands the sizes of the individual particles are con- curate determination of linear dimensions. as a result of cold working. These small crys- fined to certain specified limits. Also termed filar micrometer. tals or fragments differ in orientation and tend grain. An individual crystal in a polycrystalline filter. A device that modifies the light from the to rotate to a stable orientation determined by metal or alloy, including twinned regions or light source. the systems. subgrains if present. final annealing. The last anneal given a nonfer- freckling. A type of segregation revealed as dark grain boundary. An interface separating two rous alloy before shipment. spots on a macroetched specimen of a con- grains at which the orientation of the lattice final polishing. A polishing process in which the sumable-electrode vacuum-arc-remelted al- changes from that of one grain to that of the primary objective is to produce a final surface loy. other. When the orientation change is very suitable for microscopic examination. free carbon. The part of the total carbon content small, the boundary is sometimes referred to flake graphite. An irregularly shaped body, usu- in steel or cast iron present in elemental form as a subboundary structure. ally appearing as long, curved plates of gra- as graphite. grain-boundary etching. Development of inter- phitic carbon, such as that found in gray cast free-energy diagram. A graph of the variation sections of grain faces with the polished sur- irons. with concentration of the Gibbs free energy at face. Because of severe, localized crystal de- flakes. Short, discontinuous internal cracks in constant pressure and temperature. formation, grain boundaries have higher ferrous metals attributed to stresses produced free-energy surface. In a ternary or higher-order dissolution potential than grains themselves. by localized transformation and hydrogen-sol- free-energy diagram, the locus of points rep- Accumulation of impurities in grain bound- ubility effects during cooling after hot work- resenting the Gibbs free energy as a function aries increases this effect. Glossary of Terms / 1123

1 2 1 2 1 1 grain-boundary liquation. An advanced stage grit size. Nominal size of abrasive particles in a 0, 0) and ( ⁄3, ⁄3, ⁄2)or(⁄3, ⁄3, ⁄2). (2) One of of overheating in which material in the region grinding wheel, corresponding to the number the two ways in which spherical objects can of austenitic grain boundaries melts. Also of openings per linear inch in a screen through be most closely packed together so that the termed burning. which the particles can pass. close-packed planes are alternately staggered grain-boundary sulfide precipitation. An in- Guinier-Preston (G-P) zone. A small precipi- in the order A-B-A-B-A-B. termediate stage of overheating in which sul- tation domain in a supersaturated metallic high aluminum defect. An ␣-stabilized region fide inclusions are redistributed to the austen- solid solution. A G-P zone has no well-defined in titanium containing an abnormally large itic grain boundaries by partial solution at the crystalline structure of its own and contains amount of aluminum that may span a large overheating temperature and reprecipitation an abnormally high concentration of solute at- number of b grains. It contains an inordinate during subsequent cooling. oms. The formation of G-P zones constitutes fraction of primary ␣ but has a microhardness grain coarsening. A heat treatment that pro- the first stage of precipitation and is usually only slightly higher than the adjacent matrix. duces excessively large austenitic grains. accompanied by a change in properties of the Also termed type II defects. solid solution in which they occur. grain-contrast etching. Etching the surface of high interstitial defect. Interstitially stabilized the grains according to their crystal orienta- ␣-phase region in titanium of substantially tion. They become distinct by the different re- H higher hardness than surrounding material. It flectivity caused by reaction layers or surface arises from very high local nitrogen or oxygen roughness. concentrations that increase the b transus and grain fineness number. A weighted average habit plane. The plane or system of planes of a produce the high-hardness, often brittle ␣ grain size of a granular material. The Ameri- crystalline phase along which some phenom- phase. Such a defect is often accompanied by can Foundrymen’s Society grain fineness enon, such as twinning or transformation, oc- a void resulting from thermomechanical number is calculated with prescribed weight- curs. ing factors from the standard screen analysis. hairline cracks. See flakes. working. Also termed type I or low-density grain flow. Fiberlike lines on polished and hardenability. The relative ability of a ferrous interstitial defects, although they are not nec- etched sections of forgings caused by orien- alloy to form martensite when quenched from essarily low density. tation of the constituents of the metal in the a temperature above the upper critical tem- homogenizing. Holding at high temperature to direction of working during forging. Grain perature. Hardenability is commonly mea- eliminate or decrease chemical segregation by flow produced by proper die design can im- sured as the distance below a quenched sur- diffusion. prove required mechanical properties of forg- face at which the metal exhibits a specific hot cathode gun. See thermionic cathode gun. ings. hardness—50 HRC, for example—or a spe- hot crack. See solidification shrinkage crack. grain growth. An increase in the grain size of a cific percentage of martensite in the micro- hot etching. Development and stabilization of metal, usually as a result of heating at an el- structure. the microstructure at elevated temperature in evated temperature. hardening. Increasing hardness by suitable etchants or gases. grain size. (1) A measure of the areas or vol- treatment, usually involving heating and cool- hot quenching. An imprecise term for various ing. See also age hardening, case hardening, umes of grains in a polycrystalline metal or quenching procedures in which a quenching induction hardening, precipitation hardening, alloy, usually expressed as an average when medium is maintained at a prescribed tem- and quench hardening. the individual sizes are fairly uniform. In met- perature above 70 C (160 F). als containing two or more phases, the grain heat-affected zone. That portion of the base metal that was not melted during brazing, cut- hot-worked structure. The structure of a ma- size refers to that of the matrix unless other- terial worked at a temperature higher than the wise specified. Grain size is reported in terms ting, or welding but whose microstructure and mechanical properties were altered by the recrystallization temperature. of number of grains per unit area or volume, heat. hot working. Deformation under conditions that average diameter, or as a number derived from heat tinting. Formation of interference film on result in crystallization. area measurements. (2) For grinding wheels, a metal surface through thermal oxidation in hydride phase. The phase TiH formed in tita- see the preferred term grit size. x air or other gases, usually at elevated tem- nium when the hydrogen content exceeds the granular fracture. An irregular surface pro- perature. solubility limit, generally locally due to some duced when metal fractures. This fracture is herringbone pattern. The term chevron pattern special circumstance. characterized by a rough, grainlike appear- is sometimes used interchangeably with the ance. It can be subclassified into transgranular hypereutectic alloy. In an alloy system exhib- term herringbone pattern. However, there are and intergranular forms. This fracture is fre- iting a eutectic, any alloy whose composition differences in appearance. First, a chevron quently called crystalline fracture, but the im- has an excess of alloying element compared pattern is a macroscale pattern, while a her- with the eutectic composition and whose equi- plication that the metal failed because it crys- ringbone pattern is a microscale pattern. Sec- tallized is misleading, because all metals are librium microstructure contains some eutectic ondly, a herringbone pattern, although it is a structure. crystalline in the solid state. series of nested Vs, is created by the different graphite. The polymorph of carbon with a hex- hypereutectoid alloy. In an alloy system exhib- mechanism of a central spine created by cleav- iting a eutectoid, any alloy whose composition agonal crystal structure. See also flake graph- age on a {100} plane and continued intermit- has an excess of alloying element compared ite, nodular graphite, rosette graphite, and tent lateral crack expansion of the crack on with the eutectoid composition and whose spheroidal graphite. {1,1,2} twinning planes. graphitization. Formation of graphite in iron or heterogeneous equilibrium. In a chemical sys- equilibrium microstructure contains some eu- steel. Primary graphitization refers to forma- tem, a state of dynamic balance among two or tectoid structure. tion of graphite during solidification; second- more homogeneous phases capable of stable hypoeutectic alloy. In an alloy system exhibit- ary graphitization, later formation during heat coexistence in mutual or sequential contact. ing a eutectic, any alloy whose composition treatment. hexagonal (lattices for crystals). Having two has an excess of base metal compared with the eutectic composition and whose equilibrium graphitizing. Annealing a ferrous alloy such equal coplanar axes, a1 and a2,at120 to each that some or all the carbon precipitates as other and a third axis, c, at right angles to the microstructure contains some eutectic struc- graphite. other two; c may or may not equal a1 and a2. ture. grinding. Removing material from a workpiece hexagonal close-packed. (1) A structure con- hypoeutectoid alloy. In an alloy system exhib- using a grinding wheel or abrasive belt. taining two atoms per unit cell located at (0, iting a eutectoid, any alloy whose composition 1124 / Reference Information

has an excess of base metal compared with the but may be any substance foreign to and es- intermetallic compound. An intermediate eutectoid composition and whose equilibrium sentially insoluble in the matrix. phase in an alloy system having a narrow microstructure contains some eutectoid struc- incoherent scattering. The deflection of elec- range of homogeneity and relatively simple ture. trons by electrons or atoms that results in a stoichiometric proportions. Nearly all are brit- loss of kinetic energy by the incident electron. tle and of stoichiometric composition. See also coherent scattering. intermetallic phases. Compounds, or interme- I indentation. See impression. diate solid solutions, containing two or more indices. See Miller indices. metals that usually have compositions, char- identification (selective) etching. Etching for indigenous inclusions. See deoxidation prod- acteristic properties, and crystal structures dif- the identification of particular microconsti- ucts. ferent from those of the pure components of tuents without attacking any others. induction hardening. A surface-hardening pro- the system. idiomorphic crystal. Single crystals that have cess in which only the surface layer of a suit- internal oxidation. Preferential in situ oxidation grown without restraint so that the habit able ferrous workpiece is heated by electrical of certain components of phases within the planes are clearly developed. induction to above the upper transformation bulk of a solid alloy accomplished by diffu- illumination. See bright-field illumination, temperature and immediately quenched. sion of oxygen into the body. This is com- dark-field illumination, differential interfer- induction heating. Heating by electrical induc- monly used to prepare electrical contact ma- ence contrast illumination, and polarized light tion. terials. illumination. inelastic electron scatter. See incoherent scat- interplanar distance. The perpendicular dis- image. A representation of an object produced tering. tance between adjacent parallel lattice planes. by radiation, usually with a lens or mirror sys- inflection point. Position on a curved line, such interrupted aging. Aging at two or more tem- tem. as a phase boundary, at which the direction of peratures by steps and cooling to room tem- image rotation. In electron optics, the angular curvature is reversed. perature after each step. Compare with pro- shift of the electron image of an object about intensity (x-rays). The energy per unit of time gressive aging and step aging. the optic axis induced by the tangential com- of a beam per unit area perpendicular to the interrupted quenching. Quenching in which ponent of force exerted on the electrons per- direction of propagation. the metal object being quenched is removed pendicular to the direction of motion in the intensity of scattering. The energy per unit time from the quenching medium while the object field of a magnetic lens. per unit area of the general radiation diffracted is at a temperature substantially higher than immersion etching. The sample is immersed in by matter. Its value depends on the scattering that of the quenching medium. the etchant with the polished surface up and power of the individual atoms of the material, interstitial solid solution. A type of solid so- is agitated. This is the most common etching the scattering angle, and the wavelength of the lution that sometimes forms in alloy systems method. radiation. having two elements of widely different immersion etching (cyclic). Alternate immer- intercept method. A quantitative metallo- atomic sizes. Elements of small atomic size, sion into two etchants: 1, the actual etchant; graphic technique in which the desired quan- such as carbon, hydrogen, and nitrogen, often 2, solution to dissolve the layer formed during tity, such as grain size or amount of precipi- dissolve in solid metals to form this solid so- the etching process of 1. tate, is expressed as the number of times per lution. The space lattice is similar to that of immersion lens. See immersion objective. unit length a straight line on a metallographic the pure metal, and the atoms of carbon, hy- immersion objective. An objective in which a image crosses particles of the feature being drogen, and nitrogen occupy the spaces or in- medium of high refractive index is used in the measured. terstices between the metal atoms. object space to increase the numerical aperture intercrystalline. Between crystals or between intracrystalline. Within or across crystals or and therefore the resolving power of the lens. grains. Also termed intergranular. grains. Same as transcrystalline and transgran- immersion objective (electron optics). A lens intercrystalline cracks. Cracks or fractures that ular. system in which the object space is at a po- occur between the grains or crystals in a po- intracrystalline cracking. See transcrystalline tential or in a medium of index of refraction lycrystalline aggregate. cracking. different from that of the image space. interdendritic. Located within the branches of inverse segregation. A concentration of low- imperfection. In crystallography, any deviation a dendrite or between the boundaries of two melting constituents in those regions in which from an ideal space lattice. or more dendrites. solidification first occurs. impression. (1) In electron microscopy, the re- interdendritic porosity. Voids occurring be- inverted microscope. A microscope arranged so production of the surface contours of a spec- tween the dendrites in cast metal. that the line of sight is directed upward imen formed in a plastic material after the ap- interference. The effect of a combination of through the objective to the object. plication of pressure, heat, or both. (2) In wave trains of various phases and amplitudes. ion etching. Surface removal by bombarding hardness testing, the imprint or dent made in interference filter. A combination of several with accelerated ions in vacuum (1 to 10 kV). the specimen by the indenter of a hardness- thin optical films to form a layered coating for isometric. A crystal form in which the unit di- measuring device. transmitting or reflecting a narrow band of mension on all three axes is the same. impression replica. A surface replica made by wavelengths by interference effects. isomorphous. Having the same crystal structure. impression. See also impression and replica. intergranular. See intercrystalline. This usually refers to intermediate phases that impurities. Undesirable elements or compounds intergranular beta. Beta phase situated be- form a continuous series of solid solutions. in a material. tween ␣ grains. It may be at grain corners, as isomorphous system. A complete series of incidental dislocation boundary. A dislocation in the case of equiaxed ␣-type microstructures mixtures in all proportions of two or more boundary formed by the mutual and statistical in alloys having low b-stabilizer contents. components in which unlimited mutual solu- trapping of glide dislocations and supple- intermediate annealing. Annealing wrought bility exists in the liquid and solid states. mented by forest dislocations. metal at one or more stages during manufac- isothermal annealing. Austenitizing a ferrous inclusion count. Determination of the number, ture and before final thermal treatment. alloy, then cooling to and holding at a tem- kind, size, and distribution of nonmetallic in- intermediate phase. In a chemical system, a dis- perature at which austenite transforms to a clusions. tinguishable homogeneous substance whose relatively soft ferrite-carbide aggregate. See inclusions. Particles of foreign material in a me- composition range of existence does not ex- also austenitizing. tallic matrix. The particles are usually com- tend to any of the pure components of the sys- isothermal transformation. A change in phase pounds, such as oxides, sulfides, or silicates, tem. at any constant temperature. Glossary of Terms / 1125 isothermal transformation (IT) diagram. A lattice. (1) A space lattice is a set of equal and drite as a result of interdendritic shrinkage diagram that shows the isothermal time re- adjoining parallellopipeds formed by dividing during solidification from liquid. This type of quired for transformation of austenite to begin space by three sets of parallel planes, the deviation may vary in orientation from a few and to finish as a function of temperature. planes in any one set being equally spaced. minutes to as much as two degrees of arc. (2) Same as time-temperature-transformation There are seven ways of so dividing space, A type of substructure consisting of elongated (TTT) diagram or S-curve. corresponding to the seven crystal systems. subgrains. isotropic. Having equal values of properties in The unit parallelopiped is usually chosen as line indices. The Miller indices of the set of all directions. Quasi-isotropic refers to mate- the unit cell of the system. See also crystal planes producing a diffraction line. rial in which statistical uniformity exists, such system. (2) A point lattice is a set of points in liquation. Partial melting of an alloy, usually as as polycrystalline metals. space located so that each point has identical a result of coring or other compositional het- isotropy. The condition of having the same val- surroundings. There are 14 ways of so arrang- erogeneities. ues of properties in all directions. ing points in space, corresponding to the 14 liquidus. In a phase diagram, the locus of points Bravais lattices. See the article “Crystal Struc- representing the temperatures at which vari- ture” in this Volume. ous components begin to freeze during cool- J lattice constants. See lattice parameter. ing or finish melting during heating. See also lattice parameter. The length of any side of a solidus. Jeffries’ method. A method for determining unit cell of a given crystal structure. The term localized precipitation. Precipitation from a su- grain size based on counting grains in a pre- is also used for the fractional coordinates x, y, persaturated solid solution similar to contin- scribed area. and z of lattice points when these are variable. uous precipitation, except that the precipitate Laue equations. The three simultaneous equa- particles form at preferred locations, such as tions that state the conditions to be met for along slip planes, grain boundaries, or inco- K diffraction from a three-dimensional network herent twin boundaries. of diffraction centers. longitudinal direction. That direction parallel to Kikuchi lines. Light and dark lines superim- Laue method (for crystal analysis). A method the direction of maximum elongation in a posed on the background of a single-crystal of x-ray diffraction using a beam of white ra- worked material. See also normal direction electron-diffraction pattern caused by diffrac- diation, a fixed single-crystal specimen, and a and transverse direction. tion of diffusely scattered electrons within the flat photographic film usually normal to the long-term etching. Etching times of a few min- crystal; the pattern provides information on incident beam. If the film is located on the utes to hours. the structure of the crystal. same side of the specimen as the x-ray source, Lu¨ders lines or bands. Elongated surface mark- kink band (deformation). In polycrystalline the method is known as the back reflection ings or depressions caused by localized plastic materials, a volume of crystal that has rotated Laue method; if on the other side, as the trans- deformation that results from discontinuous physically to accommodate differential defor- mission Laue method. (inhomogeneous) yielding. mation between adjoining parts of a grain ledeburite. A eutectic structure formed below while the band itself has deformed homoge- 1148 C (2098 F) consisting of austenite and neously. This occurs by regular bending of the cementite in metastable equilibrium in alloys M slip lamellae along the boundaries of the band. of iron and carbon containing greater than 2% K radiation. Characteristic x-rays produced by but less than 6.67% C. Further slow cooling macroetching. Etching a metal surface to accen- an atom when a vacancy in the K shell is filled causes decomposition of the austenite into fer- tuate or reveal macroscopic structural details by one of the outer electrons. rite and cementite (pearlite) as a result of the (such as grain flow, segregation, porosity, or K series. The set of x-ray wavelengths compris- eutectoid reaction. cracks) with the unaided eye or at a magnifi- lever rule. A method that can be applied to any ing K radiation. cation of 50 or less. two-phase field of a binary phase diagram to macrograph. A graphic reproduction of a pre- determine the amounts of the different phases pared surface of a specimen at a magnification L present at a given temperature in a given alloy. not exceeding 25. A horizontal line, referred to as a tie line, rep- macroscopic. Visible at magnifications to 25. lamellar boundaries. A single, nearly planar resents the lever, and the alloy composition its macrostructure. The structure of metals as re- boundary, classified as a geometrically nec- fulcrum. The intersection of the tie line with vealed by macroscopic examination of the essary boundary, enclosing a narrow cell the boundaries of the two-phase field fixes the etched surface of a polished specimen. block at large strains. compositions of the coexisting phases, and the magnetic alignment. lamellar tear. A system of cracks or disconti- amounts of the phases are proportional to the An alignment of the elec- nuities aligned generally parallel to the segments of the tie line between the alloy and tron-optical axis of the electron microscope so worked surface of a plate. This is usually as- the phase compositions. that the image rotates about a point in the cen- sociated with a fusion weld in thick plate. levigation. A process by which a powder is sepa- ter of the viewing screen when the current lamination. An abnormal structure resulting in rated into a fraction with a restricted range of flowing through a lens is varied. See also a separation or weakness aligned generally particle sizes. alignment. parallel to the worked surface of the metal. light-field illumination. See bright-field illu- magnetic lens. A device for focusing an electron lap. (1) A flat surface that holds an abrasive for mination. beam using a magnetic field. polishing operations. (2) A surface imperfec- light filter. See color filter. magnetic shielding. In electron microscopy, tion on worked metal caused by folding over limited solid solution. A crystalline miscibility shielding for the purpose of preventing extra- a fin overfill or similar surface condition, then series whose composition range does not ex- neous magnetic fields from affecting the elec- impressing this into the surface by subsequent tend all the way between the components of tron beam in the microscope. working without welding it. the system; that is, the system is not isomor- magnetite. The oxide of iron of intermediate va- lath martensite. Martensite formed partly in phous. lence that has a composition close to the stoi- steels containing less than approximately line (in x-ray diffraction patterns). An array of chiometric composition Fe3O4. 1.0% C and solely in steels containing less small diffraction spots arranged so that they magnification. The ratio of the length of a line than approximately 0.5% C as parallel arrays appear to form a continuous line on the film. in the image plane, for example, ground glass of packets of lath-shaped units 0.1 to 0.3 lm lineage structure. (1) Deviations from perfect or photographic plate, to the length of the thick. alignment of parallel arms of a columnar den- same line in the object. Magnifications are 1126 / Reference Information

usually expressed in linear terms and in units mechanical twin. A twin formed in a metal dur- microscope. An instrument capable of produc- called diameters. ing plastic deformation by simple shear of the ing a magnified image of a small object. malleabilizing. Annealing white cast iron so that structure. microscopic. Visible at magnifications above some or all of the combined carbon is trans- melting point. The temperature at which a pure 25. formed into graphite or, in some instances, so metal, compound, or eutectic changes from microsegregation. Segregation within a grain, that part of the carbon is removed completely. solid to liquid; the temperature at which the crystal, or small particle. See also coring. martempering. (1) A hardening procedure in liquid and the solid are in equilibrium. microstructure. The structure of a prepared sur- which an austenitized ferrous material is melting pressure. At a stated temperature, the face of a metal revealed by a microscope at a quenched into an appropriate medium at a pressure at which the solid phases of an ele- magnification exceeding 25. temperature just above the martensite start ment or congruently melting compound may Miller-Bravais indices. Indices used for the temperature of the material, held in the me- coexist at equilibrium with liquid of the same hexagonal system. They involve the use of a dium until the temperature is uniform composition. fourth axis, a , coplanar with and at 120 to throughout, although not long enough for melting temperature. See melting point. 3 a1 and a2. bainite to form, then cooled in air. The treat- membrane. Any thin sheet or layer. Miller indices (for lattice planes). The recip- ment is frequently followed by tempering. (2) metallograph. An optical instrument designed rocals of the fractional intercepts a plane When the process is applied to carburized ma- for visual observation and photomicrography makes on the three axes. The symbols are terial, the controlling martensite start tempera- of prepared surfaces of opaque materials at (hkl). magnifications of 25 to approximately ture is that of the case. This variation of the mirror illuminator. A thin, half-round opaque process is frequently called marquenching. 2000. The instrument consists of a high-in- mirror interposed in a microscope for direct- martensite. A generic term for microstructures tensity illuminating source, a microscope, and ing an intense oblique beam of light to the formed by diffusionless phase transformation a camera bellows. On some instruments, pro- object. The light incident on the object passes in which the parent and product phases have visions are made for examination of specimen through one half of the aperture of the objec- a specific crystallographic relationship. Mar- surfaces using polarized light, phase contrast, tive, and the light reflected from the object tensite is characterized by an acicular pattern oblique illumination, dark-field illumination, in the microstructure in ferrous and nonferrous and bright-field illumination. passes through the other half aperture of the alloys. In alloys in which the solute atoms oc- metallography. The science dealing with the objective. cupy interstitial positions in the martensitic constitution and structure of metals and alloys miscibility gap. A region of multiphase equilib- lattice, such as carbon in iron, the structure is as revealed to the unaided eye or by using rium. It is commonly applied to the specific hard and highly strained; however, if the sol- such tools as low-power magnification, opti- case in which an otherwise continuous series ute atoms occupy substitutional positions, cal microscopy, electron microscopy, and dif- of liquid or solid solutions is interrupted over such as nickel in iron, the martensite is soft fraction or x-ray techniques. a limited temperature range by a two-phase and ductile. The amount of high-temperature metal shadowing. The enhancement of contrast field terminating at a critical point. See also phase that transforms to martensite on cooling in a microscope by vacuum depositing a dense binodal curve. depends to a large extent on the lowest tem- metal onto the specimen at an angle generally mixed grain size. See duplex grain size. perature attained, there being a distinct start- not perpendicular to the surface of the speci- molybdic acid, 85%. Crystals or powder containing the equivalent of 85% MoO . This ing temperature (Ms) and a temperature at men. See also shadowing. 3 which the transformation is essentially com- metastable. Possessing a state of pseudoequili- misnamed chemical consists mostly of am- plete (M ), which is the martensite finish tem- brium that has a free energy higher than that monium molybdate, or paramolybdate, which f • perature. See also transformation tempera- of the true equilibrium state. is (NH4)6Mo7O24 4H2O; the two chemicals ture. metastable beta. A b-phase composition that can be used interchangeably. See ammonium martensite range. The interval between the can be partially or completely transformed to molybdate. ␣ martensite start (Ms) and martensite finish martensite, , or eutectoid decomposition monochromatic (homogeneous). Of the same (Mf) temperatures. products with thermal or strain-energy acti- wavelength. martensitic. A platelike constituent having an vation during subsequent processing or ser- monochromatic objective. An objective, usu- appearance and a mechanism of formation vice exposure. ally of fused quartz, that has been corrected similar to that of martensite. microbands. Thin, sheetlike volumes of con- for use with monochromatic light only. matrix. The continuous or principal phase in stant thickness in which cooperative slip oc- monoclinic. Having three axes of any length, which another constituent is dispersed. curs on a fine scale. They are an instability with two included angles equal to 90 and one McQuaid-Ehn grain size. The austenitic grain that carry exclusively the deformation at me- included angle not equal to 90. size developed in steels by carburizing at 927 dium strains when normal homogeneous slip monotropism. The ability of a solid to exist in C (1700 F), followed by slow cooling. Eight is precluded. The sheets are aligned at 55 two or more forms (crystal structures) but in standard McQuaid-Ehn grain sizes rate the to the compression direction and are confined which one form is the stable modification at structure, from No. 8, the finest, to No. 1, the to individual grains, which usually contain all temperatures and pressures. Ferrite and coarsest. two sets of bands. Compare with shear bands. martensite are a monotropic pair below the mechanical alignment. A method of aligning Platelike region formed by two closely spaced temperature at which austenite begins to form, the geometrical axis of the electron micro- dense dislocation walls and defining the edge for example, in steels. Alternate spelling is scope by relative physical movement of the of a cell block. monotrophism. components, usually as a step preceding mag- microcrack. A crack of microscopic propor- mosaic crystal. An imperfect single crystal netic or voltage alignment. See also align- tions. ment. microetching. Development of microstructure composed of regions that are slightly disori- mechanical polishing. A process that yields a for microscopic examination. The usual mag- ented relative to each other. specularly reflecting surface entirely by the nification exceeds 25 (50 in Europe). mosaic structure. In crystals, a substructure in action of machining tools, which are usually microfissure. See microcrack. which adjoining regions have only slightly the points of abrasive particles. micrograph. A graphic reproduction of the pre- different orientations. mechanical stage. A device provided for ad- pared surface of a specimen at a magnification mounting. A means by which a specimen may justing the position of a specimen, usually by greater than 25. be held during preparation of a section sur- translation in two directions at right angles to microporosity. Extremely fine porosity in cast- face. The specimen can be embedded in plas- each other. ings. tic or secured mechanically in clamps. Glossary of Terms / 1127 mounting artifact. A false structure introduced nitrocarburizing. Any of several case-harden- product; often thought to be a transition phase during the mounting stages of a surface-prep- ing processes in which nitrogen and carbon during the formation of ␣ from b. It occurs in aration sequence. are absorbed into the surface layers of a fer- metastable b alloys and can lead to severe em- multiple etching. Sequential etching of a micro- rous material at temperatures below the lower brittlement. It typically occurs during aging at section, with specific reagents attacking dis- critical temperature and, by diffusion, create a low temperature but can also be induced by tinct microconstituents. concentration gradient. Compare with carbon- high hydrostatic pressures. muriatic acid. Liquid; technical-grade HCl. itriding. optical etching. Development of microstructure nodular graphite. Rounded clusters of tem- under application of special illumination tech- pered carbon, such as that obtained in malle- niques, such as dark-field illumination, differ- N able cast iron as a result of the thermal decom- ential interference contrast illumination, position of cementite. phase contrast illumination, and polarized napped cloth. A woven cloth in which some nodular pearlite. Pearlite that has grown as a light illumination. fibers are aligned approximately normal to colony with an approximately spherical mor- order (in x-ray reflection). The factor n in the one of its surfaces. phology. Bragg equation. In x-ray reflection from a natural aging. Spontaneous aging of supersat- nonmetallic inclusions. See inclusions. crystal, the order is an integral number that is urated solid solution at room temperature. See normal. An imaginary line forming right angles the path difference measured in wavelengths also aging. with a surface or other lines sometimes called between reflections from adjacent planes. n-butyl alcohol. Liquid; normal butyl alcohol; the perpendicular. It is used as a basis for de- order-disorder transformation. A phase also called butyl alcohol and 1-butanol. termining angles of incidence reflection and change among two solid solutions having the negative distortion. The distortion in the image refraction. See also angle of reflection. same crystal structure but in which the atoms that occurs when the magnification in the cen- normal direction. That direction perpendicular of one phase (disordered) are randomly dis- ter of the field exceeds that in the edge of the to the plane of working in a worked material. tributed; in the other, the different kinds of field. Also termed barrel distortion. Contrast See also longitudinal direction and transverse atoms occur in a regular sequence on the crys- with positive distortion. direction. tal lattice, that is, in an ordered arrangement. negative eyepiece. An eyepiece in which the real normalizing. Heating a ferrous alloy to suitable ordered structure. That crystal structure of a image of the object forms between the lens temperature above the transformation range, solid solution in which the atoms of different elements of the eyepiece. then cooling in air to a temperature substan- elements seek preferred lattice positions. Con- negative replica. A method of reproducing a tially below the transformation range. See also trast with disordered structure. surface obtained by the direct contact of the transformation temperature. orientation (crystal). Arrangements in space of replicating material with the specimen. Using normal segregation. A concentration of alloy- the axes of the lattice of a crystal with respect this technique, contour of the replica surface ing components or constituents having lower to a chosen reference or coordinate system. is reversed with respect to that of the original. melting points in those regions that are the last See also preferred orientation. See also replica. to solidify. orthochromatic filter. A color filter that modi- network etching. Formation of networks, es- nucleation. Initiation of a phase transformation fies the illumination quality reaching the film pecially in mild steels, after etching in nitric at discrete sites, with the new phase growing so that the brightness of colored objects will acid. These networks relate to subgrain from the nuclei. See also nucleus. be relatively the same in the resultant black- boundaries. nucleus. (1) The first structurally stable particle and-white positive. network structure. A structure in which one capable of initiating recrystallization of a orthorhombic. Having three mutually perpen- constituent occurs primarily at the grain phase or the growth of a new phase. It is sepa- dicular axes of unequal lengths. boundaries, partially or completely envelop- rated from the matrix by an interface. (2) The overaging. Aging under conditions of time and ing the grains of the other constituents. heavy central core of an atom in which most temperature greater than those required to ob- Neumann band. A mechanical twin in ferrite. of the mass and the total positive electrical tain maximum change in a certain property. neutral filter. (1) A color filter that reduces the charge are concentrated. See also aging. intensity of the transmitted illumination with- numerical aperture. The product of the lowest overheating. (1) In ferrous alloys, heating to an out affecting its hue. (2) A color filter having index of refraction in the object space multi- excessively high temperature so that the prop- identical transmission at all wavelengths throughout the spectrum. Such an ideal filter plied by the sine of half the angular aperture erties/structure undergo modification. The re- does not exist in practice. of the objective. sulting structure is very coarse grained. Unlike Nicol prism. A prism used for polarizing or an- burning, it may be possible to restore the original properties/structure by further heat alyzing light made by cementing together two O pieces of calcite using Canada balsam so that treatment, mechanical working, or both. (2) In the extraordinary ray from the first piece aluminum alloys, overheating produces struc- passes through the second piece, while the or- objective. The primary magnifying system of a tures that show areas of resolidified eutectic dinary ray is reflected to the side into an ab- microscope. A system, generally of lenses and or other evidence indicating the metal has sorbing layer of black paint. No light passes less frequently of mirrors, that forms a real, been heated within the melting range. through when two Nicol prisms are crossed. inverted, and magnified image of the object. oxidation grain size. (1) Grain size determined nitride-carbide inclusion types. A compound objective aperture. See aperture (electron) and by holding a specimen at a suitably elevated aperture (optical). temperature in a mildly oxidizing atmosphere. with the general formula Mx(C,N)y observed generally as colored idiomorphic cubic crys- oblique evaporation shadowing. The conden- The specimen is polished before oxidation and tals, where M includes titanium, niobium, tan- sation of evaporated material onto a substrate etched afterwards. (2) Refers to the method talum, and zirconium. that is inclined to the direct line of the vapor involving heating a polished steel specimen to nitriding. A case-hardening process that intro- stream to produce shadows. See also shad- a specified temperature, followed by quench- duces nitrogen into the surface layer of a fer- owing. ing and repolishing. The grain boundaries are rous material by holding it at a suitable tem- oblique illumination. Illumination from light sharply defined by the presence of iron oxide. perature in a nitrogenous atmosphere, usually inclined at an oblique angle to the optical axis. oxide film replica. A thin film of an oxide of ammonia or molten cyanide of appropriate ocular. See eyepiece. the specimen to be examined. The replica is composition. Quenching is not required to omega phase. A nonequilibrium, submicro- prepared by air, oxygen, chemical, or electro- produce a hard case. scopic phase that forms as a nucleation growth chemical oxidation of the parent metal and is 1128 / Reference Information

subsequently freed mechanically or chemi- system as they actually exist under the specific oration of the solvent from a solution of plas- cally for examination. See also replica. conditions of heating or cooling (synonymous tic, polymerization of a monomer, or solidifi- oxide-type inclusions. Oxide compounds oc- with constitutional diagram). A phase diagram cation of a plastic on the surface. See also curring as nonmetallic inclusions in metals, may be an equilibrium diagram, an approxi- replica. usually as a result of deoxidizing additions. In mation to an equilibrium diagram, or a rep- platelet alpha structure. Acicular alpha of a wrought steel products, they may occur as a resentation of metastable conditions of coarser variety, usually with low aspect ratios. stringer formation composed of distinct gran- phases. Compare with equilibrium diagram. This microstructures arises from cooling ␣ or ular or crystalline-appearing particles. phase rule. The maximum number of phases (P) ␣-b alloys from temperatures at which a sig- that may coexist at equilibrium is two, plus nificant fraction of b phase exists. the number of components (C) in the mixture, plate martensite. Martensite formed partly in P minus the number of degrees of freedom (F): steel containing more than approximately P F C 2. 0.5% C and solely in steel containing more pancake grain structure. A structure in which photomicrograph. A micrograph made by pho- than approximately 1.0% C that appear as len- the lengths and widths of individual grains are tographic means. ticular-shaped plates on irrational habit planes physical etching. large compared to their thicknesses. Development of microstruc- near {225}A, or {259}A in high-carbon steels parameter (in crystals). See lattice parameter. ture through removal of atoms from the sur- (0.9% C). parfocal eyepiece. Eyepieces, with common fo- face or lowering the grain-surface potential. polarized light illumination. A method of il- cal planes, that are interchangeable without re- physical objective aperture. In electron mi- lumination in which the incident light is plane focusing. croscopy, a metal diaphragm centrally pierced polarized before it impinges on the specimen. pattern. See diffraction pattern. with a small hole used to limit the cone of polarizer. A Nicol prism, polarizing film, or pearlite. A metastable eutectoid-transformation electrons accepted by the objective lens. This similar device into which normal light passes product consisting of alternating lamellae of improves image contrast, because highly scat- and from which polarized light emerges. ferrite and cementite resulting from the trans- tered electrons are prevented from arriving at pole figure (crystalline aggregates). A graph of formation of austenite at temperatures above the Gaussian image plane and therefore cannot the crystal orientations present in an aggre- the bainite range. contribute to background fog. gate. pearlitic structure. A microstructure resem- picric acid. Crystals; 2,4,6-trinitrophenol; crys- polished surface. A surface that reflects a large bling that of the pearlite constituent in steel. tals of the laboratory chemical contain 10 to proportion of the incident light in a specular Therefore, it is a lamellar structure of varying 15% H2O; explosive; its crystalline metallic manner. degrees of coarseness. salts are even more explosive; do not use polishing. A mechanical, chemical, or electro- peritectic. An isothermal reversible reaction in grades that do not have the 10 to 15% H2O lytic process or combination thereof used to which a liquid phase reacts with a solid phase content. prepare a smooth, reflective surface suitable to produce another solid phase. pincushion distortion. See positive distortion. for microstructural examination that is free of peritectic equilibrium. A reversible univariant pinhole eyepiece. An eyepiece, or a cap to place artifacts or damage introduced during prior transformation in which a solid phase stable over an eyepiece, that has a small central ap- sectioning or grinding. only at lower temperature decomposes into a erture instead of an eye lens. It is used in ad- polishing artifact. A false structure introduced liquid and a solid phase that are conjugate at justing or aligning microscopes. during a polishing stage of a surface-prepa- pinhole ocular. pinhole eyepiece. higher temperature, or conversely. See ration sequence. pinholes. (1) Very small holes that are some- peritectoid equilibrium. A reversible univar- polishing rate. The rate at which material is re- times found as a type of porosity in a casting iant transformation in which a solid phase sta- moved from a surface during polishing. It is because of the microshrinkage or gas evolu- ble only at low temperature decomposes with usually expressed in terms of the thickness re- tion during solidification. In wrought prod- rising temperature into two or more conjugate moved per unit of time or distance traversed. ucts, due to removal of inclusions or micro- solid phases. polycrystalline. Comprising an aggregate of constituents during macroetching of perpendicular section. A section cut perpendic- more than one crystal and usually a large num- transverse sections. (2) In photography, a very ular to a surface of interest in a specimen. ber of crystals. small circular aperture. Compare with taper section. polymorphism. A general term for the ability of pinhole system. A group of two or more pin- petrography. The study of nonmetallic matter holes arranged to define a beam. a solid to exist in more than one form. In met- under suitable microscopes to determine plane (crystal). An idiomorphic face of a crys- als, alloys, and similar substances, this usually structural relationships and to identify the tal. Any atom-containing plane in a crystal. means the ability to exist in two or more crys- phases or minerals present. With transparent plane glass illuminator. A thin, transparent, flat tal structures, or in an amorphous state and at materials, the determination of the optical glass disk interposed in a microscope or a lens least one crystal structure. See also allotropy, properties, such as the indices of refraction imaging system to direct light to the object enantiotropy, and monotropism. and the behavior in transmitted polarized without reducing the useful aperture of the porosity. Holes in a solid, not necessarily con- light, are means of identification. With opaque lens system. nected. materials, the color, hardness, reflectivity, plane of working. The plane of maximum area positive distortion. The distortion in the image shape, and etching behavior in polished sec- extension. that results when the magnification in the cen- tions are means of identification. planimetric method. See Jeffries’ method. ter of the field is less than that at the edge of phase. A physically homogeneous and distinct plasma etching. High-frequency electromag- the field. Also termed pincushion distortion. portion of a material system. netic vibrations produce radicals in a gas mix- Contrast with negative distortion. phase contrast illumination. A special method ture that react with the sample surface and positive eyepiece. An eyepiece in which the real of controlled illumination ideally suited to ob- cause its removal. image of the object is formed below the lower serving thin, transparent objects whose struc- plastic deformation. Deformation that remains lens elements of the eyepiece. tural details vary only slightly in thickness or or will remain permanent after release of the positive replica. A replica whose contours cor- refractive index. This can also be applied to stress that caused it. respond directly to the surface being repli- the examination of opaque materials to deter- plasticity. The capacity of a metal to deform no- cated. Contrast with negative replica. mine surface elevation changes. nelastically without rupturing. potentiometer. An instrument that measures phase diagram. A graph of the temperature and plastic replica. A reproduction in plastic of the electromotive force by balancing against it an composition limits of phase fields in an alloy surface to be studied. It is prepared by evap- equal and opposite electromotive force across Glossary of Terms / 1129

a calibrated resistance carrying a definite cur- sion. Grains may be distorted by subsequent quantitative measurements of micrographs or rent. subtransus deformation. Beta grain bound- metallographic images. Quantities so mea- potentiostat. An instrument that automatically aries may be obscured by a superimposed ␣- sured include volume concentration of phases, maintains an electrode in an electrolyte at a b microstructure and detectable only by spe- grain size, particle size, mean free path be- constant potential or controlled potentials cial techniques. tween like particles or secondary phases, and relative to a suitable reference electrode. process annealing. A heat treatment used to surface-area-to-volume ratio of microconsti- potentiostatic etching. Anodic development of soften metal for further cold working. In fer- tuents, particles, or grains. microstructure at a constant potential. Adjust- rous sheet and wire industries, heating to a quasi-isotropic. See isotropic. ing the potential makes possible a defined temperature close to but below the lower limit quaternary system. The complete series of etching of singular phases. of the transformation range and subsequently compositions produced by mixing four com- powder method. Any method of x-ray diffrac- cooling for working. In the nonferrous indus- ponents in all proportions. tion involving a polycrystalline and preferably tries, heating above the recrystallization tem- quench aging. Aging induced from rapid cool- randomly oriented powder specimen and a peratures at a time and temperature sufficient ing after solution heat treatment. narrow beam of the monochromatic radiation. to permit the desired subsequent cold work- quench annealing. Annealing an austenitic fer- precipitation. Separation of a new phase from ing. rous alloy by solution heat treatment followed solid or liquid solution, usually with changing proeutectoid (phase). Particles of a phase that by rapid quenching. conditions of temperature, pressure, or both. precipitate during cooling after austenitizing quench hardening. (1) Hardening suitable ␣-b precipitation etching. Development of micro- but before the eutectoid transformation takes alloys—most often certain copper or titanium structure through formation of reaction prod- place. alloys—by solution treating and quenching to ucts at the surface of the microsection. See proeutectoid carbide. Primary crystals of ce- develop a martensite-like structure. (2) In fer- also staining. mentite formed directly from the decomposi- rous alloys, hardening by austenitizing, then precipitation hardening. Hardening caused by tion of austenite exclusive of that cementite cooling at a rate so that a substantial amount precipitation of a constituent from a supersat- resulting from the eutectoid reaction. of austenite transforms to martensite. urated solid solution. See also age hardening proeutectoid ferrite. Primary crystals of ferrite quenching crack. Cracks formed as a result of and aging. formed directly from the decomposition of thermal stresses produced by rapid cooling precipitation heat treatment. Artificial aging in austenite exclusive of that ferrite resulting from a high temperature. which a constituent precipitates from a super- from the eutectoid reaction. saturated solid solution. progressive aging. Aging by increasing the tem- preferred orientation. A condition of a poly- perature in steps or continuously during the R crystalline aggregate in which the crystal ori- aging cycle. Compare with interrupted aging entations are not random but tend to align in and step aging. random orientation. A condition of a polycrys- a specific direction in the bulk material that is projection distance. Distance from the eyepiece talline aggregate in which the orientations of completely related to the direction of working. to the image screen. the constituent crystals are completely random See also texture. projection lens. The final lens in the electron relative to each other. Contrast with preferred preshadowed replica. A replica formed by the microscope corresponding to an ocular or pro- orientation. application of shadowing material to the sur- jector in a compound optical microscope. This recalescence. The increase in temperature that face to be replicated. It is formed before the lens forms a real image on the viewing screen occurs after undercooling, because the rate of thin replica film is cast or otherwise deposited or photographic film. liberation of heat during transformation of a on the surface. See also shadowing. P-T diagram. A two-dimensional graph of material exceeds the rate of dissipation of primary (x-ray). The beam incident on the phase relationships in a system of any order heat. specimen. by means of the pressure and temperature recarburizing. (1) Increasing the carbon content primary alpha. Alpha phase in a crystallo- variables. of molten cast iron or steel by adding carbo- graphic structure that is retained from the last P-T-X diagram. A three-dimensional graph of naceous material, high-carbon pig iron, or a high-temperature ␣-b working or heat treat- the phase relationships in a binary system by high-carbon alloy. (2) Carburizing a metal part ment. The morphology of ␣ is influenced by means of the pressure, temperature, and con- to return surface carbon lost in processing. the prior thermomechanical history. centration variables. reciprocal lattice. A lattice of points, each rep- primary crystals. The first type of crystals that P-X diagram. A two-dimensional graph of the resenting a set of planes in the crystal lattice, separate from a melt during solidification. isothermal phase relationships in a binary sys- so that a vector from the origin of the recip- primary etching. Develops the cast microstruc- tem; the coordinates of the graph are pressure rocal lattice to any point is normal to the crys- tures, including coring. and concentration. tal planes represented by that point and has a primary extinction. A decrease in intensity of P-X projection. A two-dimensional graph of the length that is the reciprocal of the plane spac- a diffracted x-ray beam caused by perfection phase relationships in a binary system pro- ing. of crystal structure extending over such a dis- duced by making an orthographic projection recovery. Reduction or removal of strain-hard- tance (approximately 1 lm or greater) that in- of the phase boundaries of a P-T-X diagram ening effects, without motion of large-angle terference between multiply reflected beams on a pressure-concentration plane. grain boundaries. inside the crystal decreases the intensity of the pyrophosphoric acid. Crystals of viscous liq- recrystallization. (1) A change from one crystal externally diffracted beam. uid; H4P2O7, anhydrous; hydrolyzes to H3PO4 structure to another, such as that occurring on print etching (printing). A carrier material is slowly in cold H2O and rapidly in hot H2O. heating or cooling through a critical tempera- soaked with an etching solution and pressed ture. (2) Formation of a new, strain-free grain onto the sample surface. The etchant reacts structure from the structure existing in cold- with one of the microstructural constituents, Q worked metal. forming substances that affect the carrier ma- recrystallization annealing. Annealing cold- terial. The result is a direct imprint as a life- quadrivariant equilibrium. A stable state worked metal to produce a new grain structure size image. It is used for the identification of among several conjugate phases equal to two without a phase change. specific elements, for example, sulfur (sulfur less than the number of components, that is, recrystallization temperature. The approxi- prints). having four degrees of freedom. mate minimum temperature at which recrys- prior-beta grain size. Size of b grains estab- quantitative metallography. Determination of tallization of a cold-worked metal occurs lished during the most recent b-field excur- specific characteristics of a microstructure by within a specified time. 1130 / Reference Information recrystallized grain size. (1) The grain size de- layer of significant damage produced during segregation (coring) etching. Development of veloped by heating cold-worked metal. The earlier machining and abrasion stages of a me- segregation (coring) mainly in macrostructu- time and temperature are selected so that, al- tallographic preparation sequence. A second- res and microstructures of castings. though recrystallization is complete, essen- ary objective is to produce a finish of such selective etching. See identification (selective) tially no grain growth occurs. (2) In aluminum quality that a final polish can be produced eas- etching. and magnesium alloys, the grain size after re- ily. sensitive tint plate. A gypsum plate used in con- crystallization, without regard to grain growth junction with polarizing filters to provide very or the recrystallization conditions. sensitive detection of birefringence and dou- reflection (x-ray). See diffraction. S ble refraction. reflection method. The technique of producing serial sectioning. A technique in which an iden- a diffraction pattern by x-rays or electrons that saturated gun. A self-biased electron gun in tified area on a section surface is observed re- have been reflected from a specimen surface. which electron emission is limited by space peatedly after successive layers of known refractive index (electrons). The ratio of elec- charge rather than filament temperature. thickness have been removed from the sur- tron wavelength in free space to its wave- S bands. A coarse slip band that intersects par- face. It is used to construct a three-dimen- length in a material medium. allel groups of dense dislocation walls or la- sional morphology of structural features. regular reflection. See specular reflection. mellar boundaries. A string of S-shaped per- shadow angle. The angle between the line of replica. A reproduction of a surface in a mate- turbations in lamellar boundaries. The length motion of the evaporated atoms and the sur- rial. It is usually accomplished by depositing of an S-band is generally shorter than a grain face being shadowed. The angle analogous to a thin film of suitable material, such as plastic, diameter. the angle of incidence in optics. It may be onto the specimen surface. This film is sub- scale. A layer of oxidation products formed on specified as arc tangent a so that a is in the sequently extracted and examined by trans- a metal at high temperature. ratio between the height of the object casting mission electron microscopy. See also atomic scanning electron microscope. An electron mi- the shadow over the length of the shadow. See replica, cast replica, collodian replica, Form- croscope in which the image is formed by a also shadowing. var replica, gelatin replica, impression rep- beam operating in synchronism with an elec- shadow cast replica. A replica that has been lica, negative replica, oxide film replica, plas- tron probe scanning the object. The intensity shadowed. See also shadowing. tic replica, positive replica, preshadowed of the image-forming beam is proportional to shadowing. A process by which a metal or salt replica, tape replica method (faxfilm), and va- the scattering or secondary emission of the is deposited on a specimen at an angle from a por-deposited replica. specimen where the probe strikes it. heated filament in a vacuum to enhance image replicate. In electron microscopy, to reproduce scattering (x-ray). A general term including co- contrast by inhibiting the deposition of the using a replica. herent scattering and incoherent scattering. shadowing material behind projections. See residual elements. Small quantities of elements scoring. Marring or scratching of a smooth sur- also metal shadowing, oblique evaporation unintentionally present in an alloy. face. It is most often caused by sliding contact shadowing, and shadow angle. resolution. The capacity of an optical or radia- with a mating member having a hard projec- shadow microscope. An electron microscope tion system to separate closely spaced forms tion or embedded particle on its surface. that forms a shadow image of an object using or entities; in addition, the degree to which scratch. A groove produced in a surface by an electrons emanating from a point source lo- such forms or entities can be discriminated. abrasive point. cated close to the object. Resolution is usually specified as the mini- scratch trace. A line of etch markings produced shales. Abrasive particles of platelike shape. The mum distance by which two lines or points in on a surface at the site of a pre-existing term is applied particularly to diamond abra- the object must be separated before they can scratch, the physical groove of the scratch sives. be revealed as separate lines or points in the having been removed. The scratch trace de- shape resolution. An electron image exhibits image. See also resolving power and shape velops when the deformed material extending shape resolution when a polygon can be rec- resolution. beneath the scratch has not been removed with ognized as such in the image. Roughly, the resolving power. The ability of a given lens sys- the scratch groove and when the residual de- particle diameter—defined as the diameter of tem to reveal fine detail in an object. See also formed material is attacked preferentially dur- a circle of the same area as the particle—must resolution. ing etching. exceed the resolution by a factor equal to the retardation plate. A plate placed in the path of seam. An unwelded fold or lap on the surface of number of sides on the polygon. a beam of polarized light for the purpose of a metal that appears as a crack. This is usually shatter cracks. See flakes. introducing a difference in phase. Usually the result of defects in casting or working that shear bands. Bands in which deformation has quarter-wave or half-wave plates are used, but have not welded shut. been concentrated inhomogeneously in sheets if the light passes through them twice, the secondary etching. Development of microstruc- that extend across regional groups of grains. phase difference is doubled. tures deviating from the primary structure Only one system is usually present in each rhombohedral. Having three equal axes, with through transformation and heat treatment in regional group of grains, different systems be- the included angles equal to each other but not the solid state. ing present in adjoining groups. The bands are equal to 90. secondary extinction. A decrease in the inten- noncrystallographic and form on planes of rolling direction (in rolled metals). See longi- sity of a diffracted x-ray beam caused by par- maximum shear stress (55 to the compression tudinal direction. allelism or near-parallelism of mosaic blocks direction). They carry most of the deformation rosette. (1) Rounded configuration of microcon- in a mosaic crystal; the lower blocks are par- at large strains. Compare with microbands. A stituents arranged in whorls or radiating from tially screened from the incident radiation by region of intense local shear that spans several a center. (2) Strain gages arranged to indicate the upper blocks, which have reflected some grains. at a single position strains in three different of it. shelling. A mechanism of deterioration of coated directions. secondary x-rays. The x-rays emitted by a spec- abrasive products in which entire abrasive rosette graphite. Arrangement of graphite imen irradiated by a primary beam. grains are removed from the cement coating flakes in which the flakes extend radially from segregation. Nonuniform distribution of alloy- that held the abrasive to the backing layer of the center of crystallized areas in gray cast ing elements, impurities, or phases. the product. iron. segregation banding. Inhomogeneous distribu- shielding. In an electron-optical instrument, the rough-polishing process. A polishing process tion of alloying elements aligned in filaments protection of the electron beam from distor- having the primary objective of removing the or plates parallel to the direction of working. tion due to extraneous electric and magnetic Glossary of Terms / 1131

fields. Because the metallic column of the mi- solid solution. A solid crystalline phase contain- specimen distortion (electron optics). A physi- croscope is at ground potential, it provides ing two or more chemical species in concen- cal change in the specimen caused by desic- electrostatic shielding. Magnetic shields may trations that may vary between limits imposed cation or heating by the electron beam. be made of a high-permeability material. by the phase equilibrium. specimen grid. See specimen screen. shortness. A form of brittleness in metal. It is solidus. In a phase diagram, the locus of points specimen holder (electron optics). A device designated as “cold,” “hot,” and “red” to in- representing the temperatures at which vari- that supports the specimen and specimen dicate the temperature range in which the brit- ous components finish freezing on cooling or screen in the correct position in the specimen tleness occurs. begin to melt on heating. chamber of the microscope. short-term etching. Etching times of seconds to solute. The component of a liquid or solid so- specimen screen (electron optics). A disk of a few minutes. lution that is present to the lesser or minor fine screen, usually 200-mesh stainless steel, shrink etching. Precipitation on grain surfaces. extent; the component that is dissolved in the copper, or nickel, that supports the replica or Shrinkage takes place during drying, which solvent. specimen support film for observation in the cracks the layer formed during etching. Crack solution. In a chemical system, a phase existing microscope. orientation depends on the underlying struc- over a range of composition. specimen stage. The part of the microscope that ture. solution heat treatment. A heat treatment in supports the specimen holder and specimen in sigma (r). Solid phase found originally in binary which an alloy is heated to a suitable tem- the microscope and can be moved in a plane iron-chromium alloys that is in stable equilib- perature, held at that temperature long enough perpendicular to the optic axis from outside rium below 820 C (1510 F). It is now used to cause one or more constituents to enter into the column. to identify any structure having the same com- solid solution, then cooled rapidly enough to specimen strain. A distortion of the specimen plex body-centered crystal structure. hold these constituents in solution. resulting from stresses occurring during prep- silicate-type inclusions. Inclusions composed solvent. The component of a liquid or solid so- aration or observation. In electron metallog- essentially of silicate glass, normally plastic at lution that is present to the greater or major raphy, strain may be caused by stretching dur- forging and hot-rolling temperatures, that ap- extent; the component that dissolves the sol- ing removal of a replica or during subsequent pear in steel in the wrought condition as small ute. washing or drying. elongated inclusions usually dark in color un- solvus. In a phase or equilibrium diagram, the specular reflection. The condition in which all der reflected light as normally observed. locus of points representing the temperature at the incident light is reflected at the same angle simple (lattices). Having similar atoms or which solid phases with various compositions as the angle of the incident light relative to the groups of atoms separated by integral trans- coexist with other solid phases, that is, the normal at the point of incidence. The reflec- lations only. limits of solid solubility. tion surface then appears bright, or mirrorlike, skid-polishing process. A mechanical polishing sorbite (obsolete). A fine mixture of ferrite and when viewed with the naked eye. Sometimes process in which the surface to be polished is cementite produced by regulating the rate of termed regular reflection. made to skid across a layer of paste, consisting cooling of steel or by tempering steel after spherical aberration. The zonal aberrations of of the abrasive and the polishing fluid, without hardening. The former is very fine pearlite a lens referred to an axial point. When rays contacting the fibers of the polishing cloth. that is difficult to resolve under the micro- from a point on the axis passing through the slag. A nonmetallic product resulting from mu- scope; the latter is tempered martensite. outer lens zones are focused closer to the lens tual dissolution of flux and nonmetallic im- source (x-rays). The area emitting primary x- than rays passing the central zones, the lens purities in smelting and refining operations. rays in a diffraction experiment. The actual suffers positive spherical aberration. If the slip. Plastic deformation by the irreversible shear source is always the focal spot of the x-ray condition is reversed, that is, the outer zones displacement (translation) of one part of a tube, but the virtual source may be a slit or have a longer focal length than the inner crystal relative to another in a definite crys- pinhole, depending on the conditions of the zones, the lens has negative spherical aberra- tallographic direction and usually on a specific experiment. tion. In the first instance, the lens is uncor- crystallographic plane. Sometimes termed space-charge aberration. An aberration result- rected or undercorrected; in the second, over- glide. ing from the mutual repulsion of the electrons corrected. slip band. A group of parallel slip lines so in a beam. This aberration is most noticeable spherical projection. A projection in which the closely spaced as to appear as a single line in low-voltage, high-current beams. This re- orientation of a crystal plane is represented by when observed under an optical microscope. pulsion acts as a negative lens, causing rays, the point at which the plane normal intersects See also slip line. which were originally parallel, to diverge. a sphere drawn with the crystal as the center. slip direction. The crystallographic direction in space lattice. See lattice. spheroidal graphite. Graphite of spheroidal which the translation of slip takes place. spacing (lattice planes). See interplanar dis- shape with a polycrystalline radial structure. slip line. The trace of the slip plane on the view- tance. This structure can be obtained, for example, ing surface; the trace is usually observable spatial grain size. The average size of the three- by adding cerium or magnesium to the melt. only if the surface has been polished before dimensional grains, as opposed to the more spheroidite. An aggregate of iron or alloy car- deformation. The usual observation on metal conventional grain size determined by a sim- bides of essentially spherical shape dispersed crystals (under an optical microscope) is of a ple average of observations made on a cross throughout a matrix of ferrite. cluster of slip lines known as a slip band. section of the material. spheroidized structure. A microstructure con- slip plane. The crystallographic plane in which specimen chamber (electron optics). The com- sisting of a matrix containing spheroidal par- slip occurs in a crystal. partment located in the column of the electron ticles of another constituent. slivers. Abrasive particles of rodlike shape with microscope in which the specimen is placed spheroidizing. Heating and cooling to produce an aspect ratio greater that 3. The term is ap- for observation. a spheroidal or globular form of carbide in plied particularly to diamond abrasives. specimen charge (electron optics). The electri- steel. solidification range. The temperature range be- cal charge resulting from the impingement of spinodal curve. A graph of the realizable limit tween the liquidus and the solidus. electrons on a nonconducting specimen. of the supersaturation of a solution. solidification shrinkage crack. A crack that specimen contamination (electron optics). The spinodal structure. A fine, homogeneous mix- forms, usually at elevated temperature, be- contamination of the specimen caused by the ture of two phases that form by the growth of cause of the shrinkage stresses accumulating condensation on it of residual vapors in the composition waves in a solid solution during during solidification of a metal casting. Also microscope under the influence of electron suitable heat treatment. The phases of a spi- termed hot crack. bombardment. nodal structure differ in composition from 1132 / Reference Information

each other and from the parent phase but have stretcher strains. Elongated markings that ap- without the transformation taking place. Also the same crystal structure as the parent phase. pear on the surfaces of some materials when termed undercooling. sputtering. The production of specimens in the they are deformed just past the yield point. superheating. (1) Heating a phase to a tempera- form of thin films by deposition from a cath- These markings lie approximately parallel to ture above that of a phase transformation with- ode subjected to positive-ion bombardment. the direction of maximum shear stress and are out the transformation taking place. (2) Heat- stage. A device for holding a specimen in the the result of localized yielding. See also Lu¨- ing molten metal to a temperature above the desired position in the optical path. ders lines. normal casting temperature to obtain more staining. Precipitation etching that causes con- stringer. A microstructural configuration of al- complete refining or greater fluidity. trast by distinctive staining of microconsti- loy constituents or foreign nonmetallic mate- superlattice. See ordered structure. tuents; different interference colors originate rial lined up in the direction of working. swabbing. Wiping the sample surface with cot- from surface layers of varying thickness. Iden- structure. As applied to a crystal, the shape and ton saturated with the etchant; this will si- tifies inhomogeneities. size of the unit cell and the location of all at- multaneously remove undesired reaction standard grain-size micrograph. A micro- oms within the unit cell. As applied to micro- products. graph taken of a known grain size at a known structure, the size, shape, and arrangement of syntectic equilibrium. A reversible univariant magnification that is used to determine grain phases. transformation in which a solid phase that is size by direct comparison with another microstructure factor, F. The ratio of the amplitude stable only at lower temperature decomposes graph or with the image of a specimen. of the wave scattered by all the atoms of a unit into two conjugate liquid phases that remain steadite. A hard structural constituent of cast cell to the amplitude of the wave scattered by stable at higher temperature. iron that consists of a binary eutectic of ferrite, a single electron. system (crystal). See crystal system. containing some phosphorus in solution, and subboundary structure (subgrain structure). iron phosphide (Fe3P). The eutectic consists A network of low-angle boundaries, usually of 10.2% P and 89.8% Fe. The melting tem- with misorientations less than 1 within the T perature is 1050 C (1920 F). main grains of a microstructure. step aging. Aging at two or more temperatures subcritical annealing. An annealing treatment tape replica method (faxfilm). A method of by steps, without cooling to room temperature in which a steel is heated to a temperature be- producing a replica by pressing the softened after each step. Compare with interrupted ag- low the A1 temperature, then cooled slowly to surface of tape or plastic sheet material onto ing and progressive aging. room temperature. See also transformation the surface to be replicated. stepdown test. A test involving the preparation temperature. taper section. A section made at an acute angle of a series of machined steps progressing in- subgrain. A portion of a crystal or grain slightly to a surface of interest, achieving a geomet- ward from the surface of a bar for the purpose different in orientation from adjoining por- rical magnification of depth. A sectioning an- of detecting by visual inspection the internal tions of the same crystal. Generally, adjoining gle of 5 43 achieves a depth magnification laminations caused by inclusion segregates. subgrains are separated by low-angle bound- of 10:1. stereo angle. One half of the angle through aries. Nearly empty volumes surrounded by target (x-ray). That part of an x-ray tube that which the specimen is tilted when taking a higher-angle boundaries that fill spaces exter- the electrons strike and from which x-rays are pair of stereoscopic micrographs. The axis of nal to the cell blocks. emitted. rotation lies in the plane of the specimen. submicroscopic. Below the resolution of the mi- temper carbon. Clusters of finely divided stereoscopic micrographs. A pair of micro- croscope. graphite, such as that found in malleable iron, graphs of the same area but taken from dif- substitutional element. An alloying element that are formed as a result of decomposition ferent angles so that the two micrographs, with an atomic size and other features similar of cementite, for example, by heating white when properly mounted and viewed, reveal to the solvent that can replace or substitute for cast iron above the ferrite-austenite transfor- the structures of the objects in their three-di- the solvent atoms in the lattice and form a sig- mation temperature and holding at these tem- mensional relationships. nificant region of solid solution in the phase peratures for a considerable period of time. stereoscopic specimen holder. A specimen diagram. Also termed annealing carbon. See also nod- holder designed for the purpose of making ste- substitutional solid solution. A solid solution ular graphite. reoscopic micrographs. It makes possible the in which the solvent and solute atoms are lo- tempered layer. tilting of the specimen through the stereo an- A surface or subsurface layer cated randomly at the atom sites in the crystal gle. in a steel specimen that has been tempered by strain aging. Aging induced by cold work. structure of the solution. heating during some stage of the preparation strain etching. Etching that provides informa- substrate. The layer of metal underlying a coat- sequence. When observed in a section after tion on deformed and undeformed areas if ing, regardless of whether the layer is base etching, the layer appears darker than the base present side by side. Strained areas show in- metal. material. creased segregation of precipitates. sulfide spheroidization. A stage of overheating tempered martensite. The decomposition prod- strain hardening. An increase in hardness and in which sulfide inclusions are partly or com- ucts that result from heating martensite below strength caused by plastic deformation at tem- pletely spheroidized. the ferrite-austenite transformation tempera- peratures below the recrystallization range. sulfide-type inclusions. In steels, nonmetallic ture. Under the optical microscope, darkening strain markings. Manifestations of prior plastic inclusions composed essentially of manga- of the martensite needles is observed in the deformation visible after etching of a metal- nese iron sulfide solid solutions (Fe,Mn)S. initial stages of tempering. Prolonged temper- lographic section. These markings may be re- They are characterized by plasticity at hot- ing at high temperatures produces spheroidi- ferred to as slip strain markings, twin strain rolling and forging temperatures and, in the zed carbides in a matrix of ferrite. At the markings, and so on, to indicate the specific hot-worked product, appear as dove-gray higher resolution of the electron microscope, deformation mechanism of which they are a elongated inclusions varying from a threadlike the initial stage of tempering is observed to manifestation. to oval outline. result in a structure containing a precipitate of stress relieving. Heating to a suitable tempera- sulfur print. A macrographic method of exam- fine e iron carbide particles. At approximately ture, holding long enough to reduce residual ining distribution of sulfide inclusions. See 260 C (500 F), a transition occurs to a struc- stresses, then cooling slowly enough to min- also print etching. ture of larger and elongated cementite parti- imize the development of new residual supercooling. Cooling to a temperature below cles in a ferrite matrix. With further tempering stresses. that of an equilibrium phase transformation at higher temperatures, the cementite particles Glossary of Terms / 1133

become spheroidal, decreased in number, and Ac1. The temperature at which austenite begins produced by tempering martensite at approx- increased in size. to form during heating. imately 400 C (750 F). The term is variously tempering. In heat treatment, reheating hard- Ac3. The temperature at which transformation of and erroneously applied to bainite and nodular ened steel to some temperature below the eu- ferrite to austenite is complete during heating. fine pearlite. Confusion arose because of the tectoid temperature to decrease hardness and/ Ac4. The temperature at which austenite trans- similarity in appearance among the three or increase toughness. forms to d-ferrite during heating. structures before the advent of high-power mi- temper rolling. Light cold rolling of sheet steel Ae1,Ae3,Aecm,Ae4. The temperatures of phase croscopy. With reference to tool steels, syn- to improve flatness, to minimize the formation changes at equilibrium. onymous with upper bainite. of stretcher strains, and to obtain a specified Arcm. In hypereutectoid steel, the temperature at twin. Two portions of a crystal with a definite hardness or temper. which precipitation of cementite begins dur- orientation relationship; one may be regarded terminal solid solution. In a multicomponent ing cooling. as the parent, the other as the twin. The ori- system, any solid phase of limited composi- Ar1. The temperature at which transformation of entation of the twin is a mirror image of the tion range that includes the composition of austenite to ferrite or to ferrite plus cementite orientation of the parent across a twinning one of the components of the system. is complete during cooling. plane or an orientation that can be derived by ternary system. The complete series of com- Ar3. The temperature at which austenite begins rotating the twin portion about a twinning positions produced by mixing three compo- to transform to ferrite during cooling. axis. See also annealing twin and mechanical nents in all proportions. Ar4. The temperature at which d-ferrite trans- twin. tetragonal. Having three mutually perpendicu- forms to austenite during cooling. twin bands. Bands across the crystal grain, ob- lar axes, two equal in length and unequal to Ms. The temperature at which transformation of served on a polished and etched section, the third. austenite to martensite begins during cooling. where crystallographic orientations have a texture. In a polycrystalline aggregate, the state Mf. The temperature, during cooling, at which mirror-image relationship to the orientation of of distribution of crystal orientations. In the transformation of austenite to martensite is the matrix grain across a composition plane usual sense, it is synonymous with preferred substantially complete. that is usually parallel to the sides of the band. orientation, in which the distribution is not transformed beta. A local or continuous struc- T-X diagram. A two-dimensional graph of the random. ture consisting of decomposition products isobaric phase relationship in a binary system; thermal etching. Annealing the specimen in a arising by nucleation and growth processes the coordinates of the graph are temperature vacuum or inert atmosphere. This is a pre- during cooling from above the local or overall and concentration. ferred technique for high-temperature micros- b transus. Primary and regrowth ␣ may be copy and for ceramics. present. Transformed b typically consists of ␣ thermionic cathode gun. An electron gun that platelets that may or may not be separated by U derives its electrons from a heated filament, b phase. which may also serve as the cathode. Also transgranular. See intracrystalline. ultramicroscopic. See submicroscopic. termed hot cathode gun. transition phase. A nonequilibrium state that unary system. Composed of one component. thermionic emission. The ejection of a stream appears in a chemical system in the course of undercooling. See supercooling. of electrons from a hot cathode, usually under transformation between two equilibrium unit cell. A parallelepiped element of crystal the influence of an electrostatic field. states. structure, containing a certain number of at- thermocouple. Two dissimilar electrical con- transition structure. In precipitation from solid oms, the repetition of which through space ductors so joined as to produce a thermal elec- solution, a metastable precipitate that is co- will build up the complete crystal. See also tromotive force when the junctions are at dif- herent with the matrix. lattice. ferent temperatures. transmission electron microscope. A micro- univariant equilibrium. A stable state among time-temperature curve. A curve produced by scope in which the image-forming rays pass several phases equal to one more than the plotting time against temperature. through (are transmitted by) the specimen be- number of components, that is, having one de- time-temperature-transformation (TTT) dia- ing observed. gree of freedom. gram. See isothermal transformation (IT) di- transmission method. A method of x-ray or agram. electron diffraction in which the recorded dif- tinting. See heat tinting. fracted beams emerge on the same side of the transcrystalline. See intracrystalline. specimen as the transmitted primary beam. V transcrystalline cracking. Cracking or fractur- transverse direction. Literally, “across,” usu- ing that occurs through or across a crystal. ally signifying a direction or plane perpendic- vacancy. A structural imperfection in which an Also termed intracrystalline cracking. ular to the direction of working. In rolled plate individual atom site is temporarily unoccu- transformation ranges. Those ranges of tem- or sheet, the direction across the width is often pied. perature within which austenite forms during called long transverse, and the direction vapor-deposited replica. A replica formed of a heating and transforms during cooling. The through the thickness, short transverse. See metal or a salt by the condensation of the va- two ranges are distinct, sometimes overlap- also longitudinal direction and normal direc- pors of the material onto the surface to be rep- ping but never coinciding. The limiting tem- tion. licated. peratures of the ranges depend on the com- triclinic. Having three axes of any length, none variability. The number of degrees of freedom position of the alloy and on the rate of change of the included angles being equal to one an- of a heterogeneous phase equilibrium. Also of temperature, particularly during cooling. other or equal to 90. termed variance. See also transformation temperature. triple curve. In a P-T diagram, a line represent- variance. See variability. transformation temperature. The temperature ing the sequence of pressure and temperature veining. A subboundary structure that can be de- at which a change in phase occurs. The term values along which two conjugate phases oc- lineated because of the presence of a greater- is sometimes used to denote the limiting tem- cur in univariant equilibrium. than-average concentration of precipitate or perature of a transformation range. The fol- triple point. The intersection of the boundaries solute atoms. lowing symbols are used for iron and steels: of three adjoining grains, as observed in a sec- vertical illumination. Light incident on an ob- Accm. In hypereutectoid steel, the temperature at tion. ject from the objective side so that smooth which the solution of cementite in austenite is troostite. A previously unresolvable, rapidly planes perpendicular to the optical axis of the complete during heating. etching, fine aggregate of carbide and ferrite objective appear bright. 1134 / Reference Information vibratory polishing. A mechanical polishing including plastic deformation induced by ma- Z process in which the specimen is made to chining or surface rubbing, heating during a move around the polishing cloth by imparting preparation stage to such an extent that the zephiran chloride. Aqueous solution; a propri- a suitable vibratory motion to the polishing layer is austenitized and then hardened during etary material produced in grades containing system. cooling, and diffusion of extraneous elements approximately 12 and 17% (by weight) ben- voltage alignment. A condition of alignment of into the surface. zalkonium chloride (alkyl-dimethyl-benzyl- an electron microscope so that the image ex- Widmansta¨tten structure. A structure charac- ammonium chloride) as the active constituent, pands or contracts symmetrically about the terized by a geometrical pattern resulting from plus some ammonium acetate; also called se- center of the viewing screen when the accel- the formation of a new phase along certain phiran chloride; available from pharmacies or erating voltage is changed. See also align- crystallographic planes of the parent solid so- pharmaceutical distributors. See benzalkon- ment. lution. The orientation of the lattice in the new ium chloride. V-X diagram. A graph of the isothermal or iso- phase is related crystallographically to the ori- zone. Any group of crystal planes that are all baric phase relationships in a binary system, entation of the lattice in the parent phase. The parallel to one line, which is called the zone the coordinates of the graph being specific structure was originally observed in meteor- axis. volume and concentration. ites but is readily produced in many alloys, such as titanium, by appropriate heat treatment. SELECTED REFERENCES wipe etching. See swabbing. W work hardening. See strain hardening. ● B. Bramfitt and A. Benscoter, Glossary, Met- working distance. The distance between the allographer’s Guide: Practices and Proce- wavelength (x-rays). The minimum distance be- surface of the specimen being examined and dures for Irons and Steels, ASM Interna- tween points at which the electric vector of an the front surface of the objective lens. tional, 2002 ● J.R. Davis, Ed., ASM Materials Engineering electromagnetic wave has the same value. It Dictionary, ASM International, 1992 is measured along the direction of propagation ● G. Petzow, Metallographic Etching, 2nd ed., of the wave, and it is equal to the velocity ASM International, 1999 divided by the frequency. See also electron ● L.E. Samuels, Metallographic Polishing by wavelength. Mechanical Methods, 4th ed., ASM Interna- weld structure. The microstructure of a weld X tional, 2003 deposit and heat-affected base metal. See also ● L.E. Samuels, Optical Microscopy of Carbon heat-affected zone. x-radiation. Electromagnetic radiation of the Steels, ASM International, 1999 wet etching. Development of microstructure same nature as visible light but having a wave- ● “Standard Definitions of Terms Relating to 1 with liquids, such as acids, bases, neutral so- length approximately ⁄1000 that of visible Heat Treatment of Metals,” E 44, Annual lutions, or mixtures of solutions. light. Commonly referred to as x-rays. Book of ASTM Standards, Vol 03.03, ASTM white-etching layer. A surface layer in a steel x-rays. See x-radiation. International that, as viewed in a section after etching, ap- x-ray tube. A device for the production of x- ● “Standard Definitions of Terms Relating to pears whiter than the base metal. The presence rays by the impact of high-speed electrons on Metallography,” E 7, Annual Book of ASTM of the layer may be due to a number of causes, a metal target. Standards, Vol 03.03, ASTM International