# Mechanical Behaviour Questions and Answers – Factors Affecting Creep Behaviour

This set of Mechanical Behaviour Assessment Questions and Answers focuses on “Factors Affecting Creep Behaviour”.

1. ____________ favors the creep resistance of the metal.
a) Lower SFE
b) High temperature
c) High stress
d) Pre-strain

Explanation: Lower stacking fault energy favors the creep resistance of the metal. Because cross slip of screw dislocations become difficult.

2. BCC metals have ___________ stacking fault energy.
a) Zero
b) Very low
c) Medium
d) Very high

Explanation: BCC metals have very high Stacking fault energy. Hence dislocations do not dissociate into particles. Cross glide is very easy.

3. Sherby and Burke equation shows that ___________ diffusivity and ___________ E favors low creep rate.
a) High, high
b) High, low
c) Low, high
d) Low, low

Explanation: Diffusivity gives rise to creep. The same results are shown in the equation. Low diffusivity and high E favor low creep rate.

4. __________ favors low creep rate.
a) Low E
b) High diffusivity
c) Low SFE
d) High stress

Explanation: Low SFE favors low creep rate. High E, low diffusivity and low applied stress favor low creep rate.

5. When does annealed condition is preferred over cold worked condition?
a) At low temperature
b) For short holding time
c) Very high temperature
d) For medium temperature

Explanation: The beneficial effect of cold working diminishes at the higher temperature. For service either at very high temperature or for a very long time annealed condition is preferred.
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6. Which of the following elements gives a maximum increase in recrystallization temperature in Al?
a) Si
b) Mg
c) Cu
d) Mn

Explanation: Mn increases recrystallization temperature by 180 to 200˚C. Si, Mg or Cu increase just by 50 to 80˚C.

7. Which element have the least effect on increase creep resistant in aluminum?
a) Mn
b) Fe
c) Cu
d) Cr

Explanation: Cu increases recrystallization temperature to 50 to 80˚C only. While Mn, Fe and Cr increase it by 180 to 200˚C.

8. Which element gives highest strain ageing effect in steel?
a) C
b) N
c) Mo
d) Al

Explanation: N gives strain ageing effect more than carbon in steel. This effect is due to the size difference of solute and solvent.

9. What is service temperature limitation for precipitation hardened alloys?
a) Melting temperature
b) Solvus temperature
c) Recrystallization temperature
d) Growth temperature

Explanation: Near solvus temperature, precipitate particles start to overage. It leads to decrease in strength.

10. Which compounds are widely used as second phase dispersoids?
a) Borides
b) Aluminides
c) Silisides
d) Oxides

Explanation: Oxides are among the most stable compounds at elevated temperature. These are easily available so most widely used.

11. Sintered aluminum product can retain its strength up to about ___________
a) 0.2 Tm
b) 0.4 Tm
c) 0.6 Tm
d) 0.9 Tm

Explanation: Sintered aluminum product retains its strength upto 0.9 Tm. Here Tm is melting temperature in Kelvin.

12. Fine grained structure is preferred always for creep conditions.
a) True
b) False

Explanation: Below equicohesive temperature, fine grained structure is preferred. While above it, coarse grain structure is preferred.

13. Quenched steel have poor creep properties.
a) True
b) False

Explanation: These have unstable martensite. Which change its dimensions on heating. So this is poor in creep conditions.

14. Which steel is preferred in creep conditions?
a) Normalized
b) Overaged
c) Annealed
d) Quenched

Explanation: Normalized steel has optimum creep properties. Next, best is an annealed steel.

15. Which steelmaking method gives the best creep properties?
a) Induction
b) Arc furnace
c) Twin hearth
d) Open hearth

Explanation: Induction and vacuum melting givers best creep properties. Arc furnace is second next best to induction.

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