ME-303 Materials Technology - Jun 2024 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 7 Marks
   aDescribe with examples, atomic packing factor for FCC and BCC crystal.
   How to answer

   • Define Atomic Packing Factor (APF) with formula
   • Derive APF for BCC structure: relation between lattice parameter a and atomic radius r ($4r = \sqrt{3}a$), effective number of atoms ($n=2$), calculated APF = 0.68
   • Derive APF for FCC structure: relation between a and r ($4r = \sqrt{2}a$), effective number of atoms ($n=4$), calculated APF = 0.74
   • Provide examples of metals possessing BCC (e.g., Fe, Cr, W) and FCC (e.g., Cu, Al, Ni) structures
2. 7 Marks
   bExplain 'Miller Indices' for denoting crystal planes.
   How to answer

   • Define Miller Indices for crystal planes
   • State step-by-step procedure: determine intercepts along axes, take reciprocals, reduce to smallest integers $(h k l)$
   • Rules for handling negative intercepts and parallel planes (intercept at infinity)
   • Give a neat sketch/example of common planes like $(100)$, $(110)$, or $(111)$ in a cubic system
3. 4 Marks
   aDifferentiate between primary creep, secondary creep and tertiary creep. Describe ductility and malleability.
   How to answer

   • Draw typical creep curve (strain vs. time)
   • Tabulate/compare primary (transient, decreasing creep rate), secondary (steady state, constant minimum creep rate), and tertiary (accelerating creep rate leading to rupture)
   • Define ductility: ability to undergo permanent deformation under tensile stress without fracture (e.g., drawing into wires)
   • Define malleability: ability to deform under compressive stress without fracture (e.g., hammering or rolling into thin sheets)
4. 7 Marks
   bExplain the elastic, anelastic and visco elastic behaviour of material.
   How to answer

   • Define elastic behaviour: instantaneous and completely reversible strain upon stress removal (Hooke's law)
   • Define anelastic behaviour: time-dependent recoverable deformation with energy dissipation (damping)
   • Define viscoelastic behaviour: simultaneous combination of viscous (fluid-like) and elastic (solid-like) response, exhibiting creep and stress relaxation
   • Provide mechanical models (spring, dashpot, Maxwell/Voigt models) and stress-strain/time diagrams
5. 14 Marks
   Describe the working of iron-carbon diagram and give advantages and limitations of these diagram when applied to heat treatment.
   How to answer

   • Sketch the Iron-Carbon ($Fe-Fe_3C$) phase diagram up to 6.67% C with key temperatures ($727^\circ\text{C}$, $1147^\circ\text{C}$, $1495^\circ\text{C}$) and phases (ferrite, austenite, cementite)
   • Explain key isothermal transformation reactions: eutectoid (0.76% C), eutectic (4.3% C), and peritectic (0.16% C)
   • Advantages in heat treatment: establishes baseline austenitizing temperatures for annealing, normalizing, and hardening based on critical lines ($A_1, A_3, A_{cm}$)
   • Limitations in heat treatment: diagram is only valid under equilibrium (very slow) cooling conditions; fails to predict non-equilibrium phases like martensite or bainite; does not give kinetics/time required for transformations (necessitating TTT diagrams)
6. 7 Marks
   aExplain the term pearlite, cementite and martensite.
   How to answer

   • Define Cementite: iron carbide ($Fe_3C$), extremely hard and brittle intermetallic compound containing 6.67% C
   • Define Pearlite: lamellar two-phase mixture composed of alternating layers of ferrite ($\\alpha$) and cementite formed by eutectoid decomposition at $727^\circ\text{C}$
   • Define Martensite: supersaturated solid solution of carbon in body-centered tetragonal (BCT) iron formed by diffusionless, athermal shear transformation upon rapid quenching
   • Briefly describe mechanical properties and microstructural features of each phase
7. 7 Marks
   bWhat are the objects of heat treatment? List various heat treatment process.
   How to answer

   • State objectives of heat treatment: relieving internal stresses, refining grain size, improving machinability, altering mechanical properties (hardness, tensile strength, ductility, toughness), improving wear and corrosion resistance
   • List various heat treatment processes: Annealing (Full, Process, Stress-relief, Spheroidizing)
   • Normalizing
   • Hardening (Quenching)
   • Tempering
   • Austempering and Martempering
   • Surface and Case Hardening processes
8. 7 Marks
   aState and explain the difference between case hardening and surface hardening. Name the various case hardening and surface hardening processes.
   How to answer

   • Differentiate based on composition: case hardening alters surface chemical composition via diffusion of elements (C, N), while thermal surface hardening changes microstructure via localized heating and quenching without changing chemical composition
   • List case hardening processes: Carburizing (pack, gas, liquid), Nitriding, Cyaniding, Carbonitriding
   • List surface hardening processes: Flame hardening, Induction hardening, Laser beam hardening, Electron beam hardening
9. 7 Marks
   bDescribe the martensite transformation in steel.
   How to answer

   • Define martensitic transformation: diffusionless (military/athermal) displacive transformation from austenite (FCC) to martensite (BCT)
   • Explain the mechanism (Bain model): rapid shear deformation trapping interstitial carbon atoms in the octahedral sites along the c-axis
   • Explain transformation kinetics: dependency on temperature rather than time, governed by $M_s$ (martensite start) and $M_f$ (martensite finish) temperatures
   • Describe factors affecting transformation: carbon content, alloy elements, critical cooling rate
10. 7 Marks
    aDefine the term Hardenability. What factors affect hardenability? Describe a method for determining the hardenability of steel.
    How to answer

    • Define hardenability: the depth to which a steel can be hardened upon quenching from austenitizing temperature (distinct from hardness)
    • List factors affecting hardenability: carbon content, alloying elements (Cr, Mn, Mo, Ni), prior austenite grain size, quenching medium
    • Describe the Jominy End-Quench Test: cylindrical specimen standardized dimensions ($25.4\text{ mm} \times 102\text{ mm}$), heating to austenitizing temperature, quenching exclusively at bottom end face with water jet
    • Explain measurement of hardness (HRC) along flats ground on sides as a function of distance from the quenched end to plot hardenability curve
11. 7 Marks
    bWhat is Fatigue failure? How is a fatigue test carried out?
    How to answer

    • Define fatigue failure: progressive, structural failure occurring under cyclic, fluctuating, or repeated stress levels well below the static yield strength
    • Describe fatigue testing method (RR Moore rotating bending fatigue machine): specimen subjected to pure bending while rotating, creating alternating tension and compression
    • Explain how the test is conducted over various stress amplitudes until specimen fractures or reaches specified number of cycles ($10^7$)
    • Sketch and explain the S-N curve (Wöhler curve) highlighting fatigue strength and endurance limit
12. 7 Marks
    aWhat are the commercial alloys of the aluminium? Briefly describe their compositions and uses.
    How to answer

    • Classify commercial aluminium alloys into cast and wrought, or heat-treatable and non-heat treatable alloys
    • Describe Duralumin: ~4% Cu, 0.5% Mg, 0.5% Mn, balance Al; high strength-to-weight ratio; used in aircraft structures, rivets
    • Describe Y-alloy: ~4% Cu, 2% Ni, 1.5% Mg, balance Al; retains strength at elevated temperatures; used in IC engine pistons and cylinder heads
    • Describe Magnalium (Al-Mg) and Hindalium / Al-Si casting alloys (Silumin) with their respective compositions and applications
13. 7 Marks
    bWhat is Babbitt? Write the composition and uses.
    How to answer

    • Define Babbitt metal: soft white metal bearing alloy with microstructure consisting of hard intermetallic particles embedded in a softer matrix
    • Tin-based Babbitt composition: ~88% Sn, 8% Sb, 4% Cu
    • Lead-based Babbitt composition: ~75% Pb, 15% Sb, 10% Sn
    • Applications: plain bearings, journal bearings in automotive engines, turbines, railway axle boxes
14. 7 Marks
    aDescribe different chemical reagents.
    How to answer

    • Define chemical reagents in materials testing / metallography (etchants used to reveal grain boundaries, phase distributions, inclusions)
    • Nital: 1-5% nitric acid in ethanol, used for carbon and low-alloy steels to reveal ferrite and pearlite boundaries
    • Picral: 4% picric acid in ethanol, used for steels to resolve fine pearlite and carbides
    • Keller's reagent: $HNO_3$, $HCl$, $HF$ in water, used for aluminium and its alloys
    • Aqua regia or Villella's reagent: for stainless steels and heat-resistant alloys
15. 7 Marks
    bDescribe volumetric and gravimetric analysis.
    How to answer

    • Define volumetric (titrimetric) analysis: quantitative determination of an unknown concentration by measuring volume of standard solution consumed until endpoint/equivalence point is reached
    • Steps in volumetric analysis: preparation of standard solution, titration with indicator, endpoint detection, calculation ($N_1 V_1 = N_2 V_2$)
    • Define gravimetric analysis: quantitative determination of an analyte based on measuring the mass of a pure precipitate or residue
    • Steps in gravimetric analysis: sample dissolution, precipitation, filtration, washing, drying/ignition, weighing to constant mass
    • Compare the two methods in terms of accuracy, time taken, and typical applications in metallurgical testing