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Home , Work hardening

Syllabus for ME463/MSC408 2014

Jan 15 Organization of the course. Organization of atoms, bonding, energy levels and density of states, lattices and crystal structures. Jan 20 MLK day Jan 22: Crystal directions and planes (Miller indices), stereographic projections. Crystal structures of Metals. Diamond and graphite structures. Coordination in ionic compounds. AB compounds. Imperfections: point, line, plane, volume. This is all of Chapter 1. Start chapter 2. Phase concept, Phase stability. Hypothetical phases. Free energy and temperature. Free energy and composition. Mechanisms of phase changes. Kinetics. Jan 27: Nucleation in liquids. Nucleation in solids. Interfaces between phases. Interphases. Two phase equilibria. Three phase equilibria—eutectic reaction. Peritectic reactions. Intermediate phases. Limitations of phase diagrams. Example phase diagrams: Cu-Zn, Fe-C (oh no, not again), Cu-Pb and the monotectic reaction L1α + L2.(like a eutectic but one product is still liquid) Jan 29: Ternary phase diagrams: fully miscible and ternary eutectics. Ternary eutectics with solid solutions. Ternaries with peritectic. Ternaries with intermetallics theory: Size, electrochemical, valency effects. Primary solubility boundary. Electronic structure affects the phases. Interstitial solid solutions.

Feb 3: Electrochemical compounds. Size factor compounds. AB2 Laves phases. Ordering and disorder This finishes chapter 2. Start Chapter 3 on solidification. Freezing of a pure metal. Latent heat. Subcritical and supercritical nuclei. Nucleation and Growth. Undercooling. Homogeneous nucleation. Heterogeneous nucleation. Feb 5: Continuous growth vs lateral growth vs dendritic growth. Screw perpetual spiral step. Dendrite growth and the stability of planar fronts. Temperature gradients. Forms of cast structure. Columnar growth, equiaxed cores. Dissolved gasses and pores. Segregation. Rejected impurities. Directional solidification. Single crystal growth. Coring and Cellular microsegregation. Zone refining. Feb 10 Eutectic solidification, continuous casting, microstructure of welds. Metallic glass -- when you care enough to supercool too much! Rapid solidification and quasicrystals of pentagonal symmetry. . We know the concept. Now we deal with details. Edge, Screw, mixed. Burgers vector, tangent vector, and Burgers circuit. Mechanisms for slip and climb. Slipped and unslipped boundary. Details of dislocation dislocation intersections. Strain fields around dislocations…edge and screw. that arise from changes in strain energy due to motion. Feb 12:Dislocation in ionic crystals. Dislocations attracted to free surfaces and grain boundaries. Not thermodynamically stable…..equilibrium is zero dislocation density. Extended dislocations and stacking faults that join them. Cross slip. Dissociation of dislocation into Shockley partials. Alloying elements and stacking fault energy. Constricting of stacking faults to allow cross slip. Sessile dislocations. Knowing your dislocation vectors—the Thompson tetrahedral. Frank Loops. Stair rod dislocations. Quenched systems and dislocation tetrahedral will be in chapter 6. Dislocation glide and climb. Dislocations and SF in BCC crystals. Dislocation behavior in ordered structures. That is the end of Chapt 4. Feb 17: Skip Chapter 5 on Characterization. Start Chapt 6 on point defects. Vacancies and interstitials in metals. Vacancy capture by quenching and interstitial production by irradiation. Point defects in non-metal crystals. Concentrations of point defects during . Clustering of vacancies to form dislocation loops (prismatic), tetrahedra formation, void formation. Swelling due to irradiation that produces voids. Stability of dislocation loops. Irradiation induced segregation. Kirkendall phenomena Vacancy flux drag on solutes. Irradiation as a means of promoting order. Feb 19: Diffusion….first the laws of Fick---down the concentration gradient but for a different reason. Random walk as the origin of diffusion. Steady diffusion. Second law is non-steady diffusion. Solution involves error function. Temperature dependence of diffusion. Carburization Homogenizations (for the very patient) Thin film diffusion. Interstitial diffusion. Substitutional diffusion. Substitutional alloys. Kirkendall effect, diffusion couples, and the use of Markers and Mantano interface. Grain boundary diffusion. Dislocation Pipe diffusion. Segregation of alloy elements to near free surfaces. Surface diffusion…when the species is able to move on the surface. Feb 24: Diffusion under very high pressure. Diffusion induced stresses. Anelasticity and internal friction. Snoek peaks. Torsion pendulum of Ke. The damping of iron due to carbon motion in the octahedral holes. Skip chapter 8 Start Chapter 9 PLASTIC via dislocation motions. We already know generally about tensile tests, , impact test, tests and fatigue tests from the mechanics of how they are done….this chapter looks at why we get the responses. We will start with the expressions for necking in tensile bars. Elastic deformation-the atomic springs approach with cross bracing. Isotropic material Moduli relations. Definitions of displacement fields, strain fields. Strain at a point and stress at a point. Hooke’s law for cubic crystals. Independent elastic constants. Some comments on the lower symmetry systems. Mention of Nye. Anisotropy of metal crystals. Plastic macro deformation criteria: Tresca and von Mises. The effective stress and strain. Micro plastic deformation Feb. 26: Slip and twinning. Resolved shear stress on a dislocation. Schmidt factors. Law of critical resolved shear stress. Multiple slip. Rotations due to slip. Work hardening and slip. Dislocation mobility. Dislocation velocity and its measurement. Edges and screws move at different rates. Temperature and strain rate both affect stress. Pierels-Nabarro stress. Strain rate sensitivity experiments. Dislocation source operation. Orowan equation derivation will be postponed to chapter 11. March 3: Discontinuous yielding. Yield points and crystal structure. Yielding in ordered alloys. Dislocation solute interactions. Solute strengthening. Dislocation locking and temperature. Kinetics of strain ageing. Dynamic strain ageing. Portevin LeChatelier effect. Interstitial dislocation interactions. of very small metal volumes.When there are not enough dislocations to deform smoothly. Mechanical twinning. Nucleation and growth of twins. Effects of impurities and prestrain on twinning. Dislocation mechanisms for twinning. Twinning and fracture. March 5 Atomistic Modelling of mechanical properties. Multiscale modeling. Simulation of defects. Molecular statics and molecular dynamics. Monte Carlo methods. Chapter 10. Surface energy measurement by zero creep rate. Anisotropy of surface energy. Grain boundaries as interfaces: Small angle boundaries as arrays of dislocations. Tilt and twist. Misorientation effect on GB energy. Coincident site lattice. Special boundaries. Annealing Twin boundaries. Developing preferred orientations via slip—migration of the slip vector and slip plane normal. Measuring texture. Pole figure. Wire textures and sheet textures. March 17: Role of grain boundary constraint in plastic deformation. Hall Petch relation. Superplasticity. Very small grain sizes. Creep enhancement via small grains. Start chapt 11 Work hardening and Annealing. Taylor model of stresses due to loops. Derivation of Orowan equation. Work hardening of single crystals. The three stage work hardening curve. Dislocation microstructures that develop. Loop patches, dipoles and multipoles. Work hardening in polycrystals. Dispersion hardened alloys. Work hardening in ordered alloys and role of anti phase domain boundaries. March 19: General effects of Annealing and the three stages of Annealing. Plot the strength as a measure of degree of annealing and look for peaks. RECOVERY: RECRYSTALLIZATION. Boundary mobility. Nucleation and growth as the controlling physics of recrystallization. Factors that influence recrystallization. Grain growth…..only starts after the system has completed primary recrystallization. Duplex temperatures to promote abnormal grain growth. Straight sides on grains and parallel grain boundaries are the signature of annealing twins in FCC. Textures can develop during recrystallization….new grains have orientation relationship with old ones so textures can accumulate. March 24: Chapter 12 is on Transformations but this is usually done very well in ME280 so we will skip. Start chapter 13 on Precipitation hardening. Supersaturated solid solution. Modified phase diagrams for coherent precipitate formation. Temperature and solute content effects. Guinier Preston zones. Coherency and loss of coherency. Mechanisms of precipitation hardening: particle deformability. Coherency strain hardening. Chemical hardening via sheared precipitates. March 26: Dispersion hardening. Cutting of ordered particles. Prismatic loop formation during deformation in Al-Cu. Quenching rate effects. Cold work effects. Trace alloying elements. Duplex aging. Precipitate free zones. Particle coarsening. Spinodal decomposition and UPHILL diffusion. Competition between chemical and mechanical energies leads to dominant wavelengths. Start Chapter 14 on specific alloys. April 9: We will treat very briefly plain carbon , alloy steels, and stainless steels and HSLA steels since they are well covered in the prerequisite course. We will discuss maraging steels and dual phase steels. We will talk about mechanically alloyed steels. We will examine cast irons, superalloys, Titanium alloys. Structural intermetallics. Aluminum Lithium alloys and mechanically alloyed aluminum. Copper alloys. CDA brasses. Chapter 15 Starts with creep and covers deformation mechanism maps. April 14: Metal Fatigue from the mechanical engineer’s point of view and the structural changes that cause it from the Materials scientist’s point of view. Persistent slip bands. The physics of crack formation. Crack growth. Fatigue striations. Voiding and fracture. Ductile void growth, particle matrix decohesion. Rupture. Voiding and fracture at high temperatures. April 16: In class closed book midterm exam. There will be no homework after the exam; instead, work on your project paper. April 21: Fracture Toughness starting with the Giffith Criterion. Size effects of Fracture Toughness. Ductile brittle transition and cleavage. Dislocation models of microcracks. Factors affecting brittleness of steel. Hydrogen embrittlement in steel. Intergranular fracture. Fracture mechanism maps. Crack Growth under fatigue loading. April 23: Start Chapter 16 Free energy of oxide formation. Thermodynamics vs kinetics Oxidation kinetics, parabolic oxidation, logarithmic and linear oxidation laws. Parameters affecting oxidation rates. Lattice vacancies and oxidation. Oxidation resistance imparted by alloying. April 28: Aqueous Corrosion. Electrochemistry of corrosion . electrochemical and galvanic series. Polarization. Pourbaix diagrams. Corrosion protection and corrosion inhibitors. Sacrificial protection. Anodizing. Intergranular attack and the related stress corrosion cracking. The many different types of localized corrosion. April 30: Coatings and modification of surfaces. Chemical and physical vapor deposition. Particle bombardment and ion implantation. Diamond like films. Laser processing of surfaces. Project paper due this day during class.