This set of Engineering Materials & Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Mechanisms of Creep & Creep Resistant Materials”.
1. Creep occurs at a temperature above ________
a) 0.16 Tm
b) 0.22 Tm
c) 0.4 Tm
d) 0.91 Tm
Explanation: Creep is defined as the permanent deformation of a material due to the application of steady load. It is appreciable only at temperatures above 0.4 Tm.
2. __________ experiences creep at room temperature.
Explanation: Room temperature is about the same as that of the melting point of lead. Therefore, nickel experiences creep at that temperature under its own load. The room temperature of iron and copper is 0.16 Tm and 0.22 Tm respectively, at which creep does not occur.
3. _______ is known as steady-state creep.
a) Primary creep
b) Secondary creep
c) Tertiary creep
d) Quaternary creep
Explanation: Creep occurs in three stages known as primary, secondary, and tertiary creep. Secondary creep is also known as steady-state creep since the rate of work and recoveries are equal.
4. Which of the following does not affect creep?
a) Grain size
b) Thermal stability
c) Chemical reactions
d) Crystal structure
Explanation: Coarse-grained materials and those having higher thermal stability generally affect creep resistance of a material. The chemical reaction involved and work hardening also influence the creep resistance.
5. The time required for the occurrence of creep is known as _________
a) Creep resistance
b) Creep life
c) Creep limit
d) Creep recurrence
Explanation: Creep life is defined as the time required for the occurrence of creep fracture in a material under static load. Creep limit is defined as the maximum static stress that will result in creep. Creep resistance is known as the resistance offered by the material over creep.
6. Which of the following will be rendered useless for prevention of creep?
a) Coarse-grained material
b) Strain hardening
c) Precipitation hardening
Explanation: Creep fracture can be prevented by using coarse-grained materials and treatment by strain hardening a precipitation hardening. The material must be free from residual stresses and can also be heat treated.
7. MgO and Al2O3 can be used at high temperature creep resistance due to _________
a) High melting point
b) High oxygen concentration
c) Low density
d) Chemical stability
Explanation: Creep starts to occur at a temperature higher than 0.4 Tm. Therefore, high melting point materials like MgO and Al2O3 are used for high-temperature operations.
8. Iron base alloys have melting point around __________
Explanation: The most commonly used high-temperature alloys are iron base, nickel base, and cobalt base alloys. Each of these alloys possesses a high melting point temperature of around 1500oC.
9. Strengthening of an iron base, nickel bade, and cobalt base alloys is done by __________
a) Precipitation hardening
b) Grain boundary hardening
c) Dispersion hardening
d) Transformation hardening
Explanation: Iron base, nickel base, and cobalt base alloys have creep resistance around a temperature of 0.5 Tm. Their creep resistance can be improved by a heat treatment process known as dispersion hardening.
10. Why can’t cold working be used for strengthening in case of plastic deformation?
b) Thermal instability
c) Lowers tensile strength
d) Introduces coarsening
Explanation: At temperatures above 0.4 Tm, recrystallization occurs readily. This results in the loss of strength of the cold-worked material. Therefore, for plastic deformation, cold working is generally avoided for creep resistance.
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