ME-303 Materials Technology - Dec 2023 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
   aWhat is co-ordination number? Find the co-ordination number for simple cubic, face central cubic and HCP systems.
   How to answer

   • Definition of coordination number (number of nearest equidistant neighbors to a central atom).
   • Determination for Simple Cubic (SC): Coordination number = 6.
   • Determination for Face-Centered Cubic (FCC): Coordination number = 12.
   • Determination for Hexagonal Close-Packed (HCP): Coordination number = 12.
2. 7 Marks
   bExplain the governing rules for the formation of substitutional solid solutions.
   How to answer

   • Mention Hume-Rothery rules for solid solubility.
   • Atomic size factor: difference in atomic radii must be less than ~15%.
   • Crystal structure rule: same crystal structure for complete solubility.
   • Electronegativity factor: similar electronegativity to prevent compound formation.
   • Relative valency rule: higher valency solvent dissolves more solute than vice-versa.
3. 7 Marks
   aExplain the relationship between equilibrium diagrams and properties of alloys.
   How to answer

   • Significance of equilibrium (phase) diagrams in predicting microstructures.
   • Variation of mechanical properties (tensile strength, hardness, ductility, electrical conductivity) with alloy composition.
   • Properties across solid solution regions vs two-phase/eutectic regions.
   • Correlating phase morphology with final bulk properties.
4. 7 Marks
   bDraw $\text{Fe-Fe}_3\text{C}$ phase diagram and explain the phase transformation reactions in the diagram.
   How to answer

   • Neat sketch of the Fe-Fe3C equilibrium phase diagram up to 6.67% C with temperatures and phase labels.
   • Explain Eutectic reaction: Liquid (4.3% C) at 1147°C to Austenite + Cementite (Ledeburite).
   • Explain Eutectoid reaction: Austenite (0.76% C) at 727°C to Ferrite + Cementite (Pearlite).
   • Explain Peritectic reaction: Liquid (0.53% C) + $\delta$-ferrite (0.09% C) at 1495°C to Austenite (0.17% C).
5. 7 Marks
   aWhat is quench severity? Explain its role on hardenings of steels.
   How to answer

   • Definition of quench severity (Grossmann's H-value, heat-extracting capability of quenching medium).
   • Different quenching media and their relative severities (brine, water, oil, air, still vs agitated).
   • Role in achieving critical cooling rate to form martensite.
   • Effects on depth of hardening, residual stresses, and distortion/cracking.
6. 7 Marks
   bExplain the role of solvus curve in phase diagrams for age hard-enable alloys.
   How to answer

   • Definition of solvus curve (boundary separating a single-phase solid solution from a two-phase mixture).
   • Requirement for age hardening: decreasing solid solubility of solute in solvent with decreasing temperature.
   • Role in solution heat treatment (heating above solvus into single-phase field).
   • Role in quenching and subsequent aging (precipitation of fine second-phase particles below solvus).
7. 7 Marks
   aDraw the partial Al-Cu phase diagram (up to 10% Cu) and explain engineering significance of Al with 4-5% Cu.
   How to answer

   • Sketch partial Al-Cu phase diagram from 0 to 10 wt% Cu showing $\alpha$ solid solution, solvus curve, maximum solubility 5.65% at 548°C, and $\alpha + \theta$ ($\text{CuAl}_2$) region.
   • Engineering significance of 4-5% Cu alloys (e.g., Duralumin): ideal composition for age hardening.
   • High strength-to-weight ratio achieved via solution treatment, quenching, and aging.
   • Major engineering applications (aerospace, automotive structures).
8. 7 Marks
   bExplain how the property of aluminium alloys changes on age-hardening?
   How to answer

   • Three stages of age hardening: solution treatment, quenching, artificial/natural aging.
   • Formation of GP zones and intermediate coherent precipitates pinning dislocations.
   • Changes in properties: increase in yield strength, tensile strength, and hardness.
   • Simultaneous decrease in ductility and toughness.
   • Effect of overaging (coalescence of precipitates causing loss of hardness/strength).
9. 7 Marks
   aExplain fatigue limit (fatigue test) using S-N diagram.
   How to answer

   • Definition of fatigue and endurance/fatigue limit.
   • Description of fatigue testing (rotating beam or cyclic stress).
   • Sketch of S-N curve (stress amplitude $S$ vs log number of cycles $N$).
   • Distinction between ferrous metals exhibiting a distinct horizontal endurance limit and non-ferrous metals that do not.
10. 7 Marks
    bWhat is the effect of grain size on mechanical properties?
    How to answer

    • Hall-Petch equation: $\sigma_y = \sigma_0 + k_y d^{-1/2}$.
    • Effect of fine grain size: increased yield strength, tensile strength, and toughness/ductility at room temperature due to grain boundary barrier to dislocations.
    • Effect at high temperatures: coarse grains provide better creep resistance by reducing grain boundary sliding.
11. 7 Marks
    aWhat is the difference between carburizing and nitriding? Define creep. What is the effect of temperature on creep?
    How to answer

    • Comparison of carburizing and nitriding (temperature, medium, post-quench need, case depth, distortion).
    • Definition of creep (time-dependent permanent deformation under constant mechanical stress at elevated temperatures).
    • Effect of temperature on creep: higher temperature accelerates creep rate and shortens rupture time by promoting diffusion and dislocation climb.
12. 7 Marks
    bHow TTT diagram is obtained? What is its importance over Iron Carbon equilibrium diagram?
    How to answer

    • Experimental procedure to obtain TTT diagram (austenitizing, rapid quenching to subcritical isothermal baths, holding for various times, quenching to room temp, metallographic analysis).
    • Importance of TTT over Fe-C diagram: Fe-C represents equilibrium/slow cooling only, whereas TTT considers cooling rates and time (kinetics).
    • Enables prediction of non-equilibrium phases like bainite and martensite essential for heat treatments (austempering, martempering).
13. 7 Marks
    aDraw the stress-strain diagram for a mild-steel specimen and also, mark the points and classify them, Define the term Hardenability and give the factor affecting Hardenability.
    How to answer

    • Sketch standard tensile stress-strain curve for mild steel.
    • Label key points: Proportional limit, Elastic limit, Upper yield point, Lower yield point, Ultimate tensile strength, Fracture/rupture point.
    • Define Hardenability: depth up to which steel can be hardened by formation of martensite upon quenching.
    • Factors affecting hardenability: carbon content, alloying elements, austenitic grain size, quenching medium and cooling rate.
14. 7 Marks
    bWhat are the influences of alloying $\text{Al}$, $\text{Cr}$, $\text{Ni}$, $\text{Mo}$, $\text{Si}$, $\text{Mn}$, $\text{V}$ and $\text{Cu}$ in steel? Explain in brief?
    How to answer

    • Al: Deoxidizer, grain refiner, aids nitriding.
    • Cr: Improves corrosion resistance, wear resistance, hardenability.
    • Ni: Enhances toughness, especially at low temperatures; austenite stabilizer.
    • Mo: Inhibits temper embrittlement, improves high-temperature creep strength and hardenability.
    • Si: Strong deoxidizer, increases yield strength, used in spring and electrical steels.
    • Mn: Deoxidizer, combines with sulfur to prevent hot shortness, improves hardenability.
    • V: Refines grain size, forms hard carbides, enhances wear resistance and strength.
    • Cu: Improves atmospheric corrosion resistance.
15. 5 Marks
    aShown by graph Brittle and Ductile fracture of materials, Explain in brief Griffith's Theory of Brittle fracture.
    How to answer

    • Sketches/graphs illustrating ductile vs brittle fracture (stress-strain behavior or cup-and-cone vs cleavage flat surfaces).
    • Fundamental concept of Griffith's theory: balance between decrease in elastic strain energy and increase in surface energy as a crack propagates.
    • Griffith's fracture stress formula: $\sigma_f = \sqrt{\frac{2E\gamma}{\pi a}}$.
    • Significance of critical crack length $a$ in determining fracture.
16. 5 Marks
    bHow do you draw a creep curve by conducting suitable creep test? Explain different stages of a creep curve.
    How to answer

    • Description of creep test setup: tensile specimen under constant load in a furnace at elevated temperature measuring strain over time.
    • Sketch of strain vs time creep curve.
    • Instantaneous elastic strain upon loading.
    • Primary (transient) creep: decreasing strain rate due to work hardening.
    • Secondary (steady-state) creep: constant strain rate due to dynamic balance between strain hardening and recovery.
    • Tertiary creep: accelerating strain rate leading to necking and rupture.
17. 4 Marks
    cDistinguish between low carbon, medium carbon and high carbon steels.
    How to answer

    • Carbon content ranges: Low carbon (< 0.25% C), Medium carbon (0.25% - 0.60% C), High carbon (0.60% - 1.4% C).
    • Mechanical properties: Low carbon (high ductility, soft, easily welded), Medium carbon (balanced strength and ductility, heat treatable), High carbon (high hardness and wear resistance, brittle).
    • Typical applications: Low carbon (sheet metal, structural beams), Medium carbon (gears, axles, crankshafts), High carbon (cutting tools, dies, springs).