Material Science & Metallurgy
From transcript: 20ME440 Material Science and Metallurgy (A)
Cheat sheet
Formulas
Definitions
- Crystal structure
- FCC, BCC, HCP packing & slip systems → ductility
- Dislocation
- Line defect enabling plastic slip at stresses << theoretical
- Grain boundary
- Obstacle to slip — refine grains to strengthen
- Phase diagram
- Equilibrium phases vs T, composition
- Eutectic / eutectoid
- Liquid→two solids; solid→two solids (Fe–C: 727°C pearlite)
- Martensite
- Diffusionless BCT from quench — hard, brittle until tempered
- Annealing
- Softening + recrystallization; relieve residual stress
- Normalizing
- Air cool from austenite — refine grains, uniform structure
- Tempering
- Reheat martensite — toughness up, hardness down
- Precipitation hardening
- GP zones/precipitates impede dislocations (Al alloys)
- Crystal structures
- FCC, BCC, HCP — slip systems affect ductility
- Heat treatment
- Anneal, normalize, quench, temper — control microstructure
Topic-wise short notes
Structure–property relations
- Slip systems: FCC many → ductile; HCP few → anisotropic/brittle tendency.
- Strengthening: solid solution, strain harden, grain refine, precipitate, disperse.
- Fracture: ductile dimples vs brittle cleavage; fatigue striations.
- Creep: time-dependent strain at high T/Tm ; rupture life curves.
- Corrosion & wear as 'property' in service selection.
Heat treatment & metallurgy
- Austenitize → quench → temper path for martensitic steels.
- Case hardening: carburize/nitride for hard surface, tough core.
- Hardenability ≠ hardness: ability to form martensite deep.
- Cast iron: graphite morphology (flake/nodular) controls properties.
- Al/Cu/Ti: know precipitation vs work-hardening families.
Crystal structure & defects
- Point, line, surface, volume defects — each alters properties differently.
- Vacancies enable diffusion; climb of dislocations at high T.
Phase diagrams & heat treatment
- Lever rule only in two-phase field at equilibrium.
- Nonequilibrium cooling shifts effective diagrams — segregation, coring.
Selection & charts
- Ashby charts: E–ρ, σy–ρ for light stiff/strong design.
- Cost, corrosion, fab route often dominate pure strength.
- Recyclability & supply risk increasingly part of selection.
Exam traps & quick notes
- Steels: eutectoid ~0.76% C; TTT/CCT for pearlite/bainite/martensite.
- Interview: pick material by strength/weight, corrosion, cost, fabricability (DFM).
- AeroJC: balsa, carbon, Monokote — specific strength & process limits.
- Cold work ↑ strength ↓ ductility; anneal reverses.
- Fe–C landmarks: eutectoid 0.76%C @727°C; cementite Fe3C.
- TTT isothermal; CCT continuous cooling — industrial quenches follow CCT.
- Alloy steels: Cr, Mo, Ni for hardenability/toughness/corrosion.
- Polymers: Tg vs Tm; ceramics: brittle, high T, ionic/covalent.
- Composites: rule of mixtures for E along fibers (isostrain).
Comprehensive notes
Structure–property relations
Dislocations, strengthening mechanisms (solid solution, precipitation, cold work, grain size).
External: DoITPoMS micrographs ↗ ASM materials topics ↗
Heat treatment & metallurgy
Iron–carbon diagram reading; hardenability (Jominy); non-ferrous alloys overview.
External: NPTEL Material Science ↗
Crystal structure & defects
FCC/BCC/HCP; slip systems explain ductility. Vacancies, dislocations, grain boundaries. Hall–Petch: finer grains → higher yield.
External: NPTEL ↗ Engineering Toolbox ↗
Phase diagrams & heat treatment
Lever rule; Fe–C diagram landmarks. Anneal/normalize/quench/temper pathways; TTT vs CCT. Hardenability (Jominy). Non-ferrous: Al alloys precipitation hardening basics.
External: NPTEL ↗ Engineering Toolbox ↗
Interview Q&A for this subject
Q: Why does cold work strengthen metals?
A: Dislocation density rises; they impede each other — strength up, ductility down; anneal recovers.
External: ASQ / quality ↗ MIT OCW ↗