MAT E 202 - FINAL EXAM QUESTIONS WITH VERIFIED SOLUTIONS LATEST UPDATE 2026

MAT E 202 - FINAL EXAM QUESTIONS WITH VERIFIED SOLUTIONS LATEST UPDATE 2026 Diffusion - Answers atoms tend to migrate from regions of high concentration to regions of low concentration Self-diffusion - Answers migration of host atoms in pure atoms Vacancy diffusion - Answers atoms and vacancies exchange positions applies to host and substitutional impurity atoms What is the diffusion rate of vacancy diffusion dependent on? - Answers number of vacancies activation energy to exchange Interstitial diffusion - Answers small, interstitial atoms move from one interstitial position to an adjacent one Which diffusion mechanism is more rapid, vacancy diffusion or interstitial diffusion? - Answers interstitial What is an example of interstitial diffusion? - Answers case hardening: diffusing carbon atoms in the outer surface of iron (steel) to harden the surface - improves wear resistance and fatigue failure Is diffusion dependent or independent of time? - Answers time dependent Is rate of diffusion (flux) dependent or independent of time? - Answers independent of time How is diffusion related to temperature? - Answers increases with increasing temp, exponential Slip - Answers plastic deformation occurs by motion of dislocations Dislocation motion - Answers movement of extra half-plane of atoms by breaking and reforming of interatomic bonds Slip systems - Answers combination of slip plane and slip direction Slip plane - Answers crystallographic plane on which slip occurs most easily plane with high planar density Slip direction - Answers crystallographic direction along which slip occurs most easily direction with high linear density Applied tensile stress - Answers shear stress component when slip plane oriented neither perpendicular or parallel to stress direction When does slip occur on a single crystal slip system? - Answers when resolved shear stress is greater than critical resolved shear stress Polycrystalline materials - Answers many grains, often random crystallographic orientations What is the grain structure of a polycrystalline material before rolling? - Answers grains equiaxed and randomly oriented properties isotropic What is the grain structure of a polycrystalline material after rolling? - Answers grains elongated properties somewhat anisotropic For a metal to physically deform, - Answers dislocations must move Reduce dislocation mobility = - Answers metal strengthens/hardens Increase dislocation mobility = - Answers metal weakens/softens Why does a metal weaken when dislocation motion increases? - Answers greater forces are acting which creates dislocations What are the four mechanisms to strengthen/harden metals and decrease mobility? - Answers 1. grain size reduction 2. solid solution strengthening 3. strain hardening (cold working) 4. precipitation hardening How do grain boundaries affect dislocation motion? - Answers act as barriers where slip planes must change directions (takes energy and forces discontinuity) How does reducing grain size, strength/harden metals and decreases mobility? - Answers increases grain boundary area which creates more barriers to dislocation motion increases yield strength, tensile strength and hardness How do lattice strains around dislocations strength/harden metals and decreases mobility - Answers slows down the dislocations by adding barriers which overall increases yield strength Strain hardening - Answers plastically deforming metals at room temperature to strengthen/harden them As %CW increases what happens to yield strength, TS and ductility? - Answers yield strength, TS increase ductility decrease How is dislocation density affected by deformation? - Answers increases with increasing deformation How is the distance between dislocation affected by increasing dislocation density? - Answers decreases Precipitation hardening - Answers choose an alloy (Cu, Al) heat treat alloy to nucleate and grow size, spacing and inherent strength of precipitates will dictate strength of alloy For precipitation hardening what do you assume? - Answers constant volume fraction Precipitate shear - Answers strength increases with larger R and f Dislocation bowing - Answers strength increases with decreasing R and increasing f Annealing - Answers heat treatment cold worked metals brings about changes in structure and properties What does annealing do to tensile strength and ductility? - Answers decreases tensile strength and increases ductility What are the 3 stages of annealing? - Answers Recovery, recrystallization and grain growth Recovery - Answers reduction of internal stresses reduction of dislocation density to annihilation of dislocations (line up) Recrystallization - Answers nucleation of new grains have low dislocation densities small in size consume and replace parent CW grains Recrystallization temperature - Answers temperature at which recrystallization just reaches completion in one hour Hot working - Answers deformation above recrystallization temperature Cold working - Answers deformation below recrystallization temperature Grain growth - Answers occurs as heat treatment continues average grain size increases small grains shrink (ultimately disappear) large grains continue to grow Metals having small grains - Answers relatively strong and tough at low temperatures Metals having large grains - Answers good creep resistance at relatively high temperatures Solution - Answers one phase Mixture - Answers more than one phase Solubility limit - Answers maximum concentration for which only a single phase solution exists Components - Answers the elements or compounds which are present in the alloy Phases - Answers the physically and chemically distinct material regions that form Phase diagrams - Answers indicate phases a function of T, C and P Eutectic reaction - Answers liquid transforms into 2 solids phases Hypoeutectic - Answers before euctectic Hypereutectic - Answers after eutectic Eutectoid - Answers one solid phase transforms to two other solid phases Does hypoeutectoid steel have proeutectoid cementite or ferrite? - Answers ferrite Does hypereutectoid steel have proeutectoid cementite or ferrite? - Answers cementite Nucleation - Answers nuclei act as templates on which crystals grow for nucleus to form rate of addition of atoms to nucleus must be faster than rate of loss once nucleated, growth proceeds until equilibrium is attained What increases the driving force to nucleate? - Answers increasing delta T (supercooling) Small supercooling - Answers slow nucleation rate few nuclei large crystals Large undercooling - Answers rapid nucleation rate many nuclei small crystals Homogeneous nucleation - Answers nuclei form in the bulk of liquid metal requires considerable supercooling Heterogeneous nucleation - Answers much easier since stable "nucleating surface" is already present only very slight supercooling Small undercooling produces a low transformation rate because - Answers nucleation rate is low High undercooling produces a low transformation rate because - Answers growth rate is low Diffusionless transformation - Answers single metastable phase: martensite Diffusional - Answers ferrite and cementite: 2 phase microconstituents