ASM Handbook, Volume 9: Metallography and Microstructures Copyright © 2004 ASM International® G.F. Vander Voort, editor All rights reserved. www.asminternational.org 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 re- growth 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 ЊC (1670 ЊF), 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 ЊC (1415 ЊF). 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 b ם ␣ the phase boundary between the ␣ and 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 -m, or 0.1 nm. Although not an corrections are superior to those of the ach 10מequal to 10 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 90Њ. 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 ЊC (840 to 930 values of a property in different directions. mounting artifact, and polishing artifact. ЊF). 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- Њ Њ 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- Њ Њ 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.