Anna University Phase Transformers and Mechanical Metallurgy Exam Paper



IV Semester Metallurgical Engineering


Time : Three hours                                                                        Maximum : 100 marks

Answer ALL questions.

PART A — (10 ´ 2 = 20 marks)

1.         Define Fracture Toughness.

2.         What is Arrhenius equation? What are its uses?

3.         Give two examples for precipitation hardenable steels.

4.         Show the relationship between critical stress intensity factor KIC and thickness of the material.

5.         Why heterogeneous nucleation occurs more readily than homogeneous nucleation?

6.         What is the effect of applied stress on martensite formation?

7.         What are the essential conditions for precipitation hardening?

8.         What is low cycle fatigue? Give two examples where this is significant.

9.         State the factors that influence creep rate in metals.

10.      What are the different types of martensites in steels?

PART B — (5 ´ 16 = 80 marks)

11.      (i)      What are the steps in precipitation hardening?                                      (6)

             (ii)     Explain the mechanism and stages in the strengthening of alloys by precipitation hardening with a suitable example.         (6)

             (iii)   Compare dispersion strengthening and precipitation strengthening. Give one example for each.                                                    (4)

12.      (a)     (i)      Derive an expression for the critical free energy change of a spherical particle homogeneously nucleating from the melt.                                     (10)

                       (ii)    Discuss how the activation energy for a reaction can be determined graphically.                                                       (6)


             (b)     (i)      Discuss the mechanism of pearlite formation in steels.                (8)

                       (ii)    Discuss uphill diffusion with suitable examples.                           (8)

13.      (a)     (i)      What are the characteristics of martensitic transformation? Discuss with reference to steels.                                                                                                  (10)

                       (ii)    Discuss briefly martensitic transformation in non–ferrous alloys.(6)


             (b)     (i)      What is shape memory effect in alloys? Give two examples and applications for shape memory alloys.                (10)

                       (ii)    What is thermoelastic martensite?                                                   (6)

14.      (a)     (i)      Discuss strengthening of metal by grain size control.                   (8)

                       (ii)    What are the factors that can control the grain size of steels?     (8)


             (b)     What are the different modes of fracture? Explain  stress intensity factor. Discuss the factors that influence fracture toughness. (16)

15.      (a)     State Griffith’s theory of brittle fracture and derive the Griffith’s equation. Explain Orowan’s modification suggested to Griffith’s equation.


             (b)     (i)      Explain low cycle fatigue and high cycle fatigue with the use of Coffin–Manson law and Basquin’s law.                  (10)

                       (ii)    Discuss the mechanism of creep failure in metals.                        (6)


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