This set of Mechanical Behaviour Multiple Choice Questions & Answers (MCQs) focuses on “Creep Resistant Materials”.
1. In ferrite the self-diffusion coefficient _________ with increasing carbon content.
c) Remains constant
d) First increases, then decrease
Explanation: In ferrite the self-diffusion coefficient increases with increasing carbon content. Strain or creep rate is influenced by diffusivity.
2. Which method improves creep resistance but not strength?
a) Solution strengthening
c) Grain coarsening
d) Precipitation hardening
Explanation: At temperatures greater than cohesive, coarse grain structure is preferred. Other methods of creep resistance improve strength too.
3. What is the most important method of improving creep strength?
a) Solid solution strengthening
b) Precipitation hardening
c) Dispersion hardening
Explanation: Dispersion hardening is the most important method of improving creep strength. These improve service temperature as high as 0.9 Tm.
4. _________ are difficult to weld.
a) Austenitic steels
b) Ferritic steels
d) Cast iron
Explanation: Ferritic steels are difficult to weld. It is because of the formation of chromium carbide on grain boundaries. This phenomenon is known as weld decay.
5. What is the advantage of ferritic steels?
b) Oxidation resistant
c) Sub-zero temperature
Explanation: Ferritic steels are good oxidation resistant. These are difficult to weld. These undergo ductile brittle transition so can’t be used on subzero temperatures.
6. Ferritic steels are susceptible to 475°C embrittlement when chromium exceeds _________
Explanation: Ferritic steels are susceptible to 475°C embrittlement when chromium exceeds 13%. The higher amount of chromium causes welding susceptibility.
7. Which of the following is not a superalloy category?
Explanation: Superalloys are broadly classified into 3 categories. These are iron-base, nickel-base and cobalt-base.
8. Which of the following is a superalloy category?
Explanation: Lead, tin and zinc all have low melting temperatures. Their alloys can’t be used as superalloys. Iron-base, nickel-base and cobalt-base alloys are superalloys.
9. Protective action against corrosion is provided by _________
Explanation: Cr2O3 or Al2O3 surface films provide protection against corrosion in superalloys. CO2, Cl2 on the other hand, are of corrosive nature.
10. What is the largest use for superalloys?
d) Gas turbines
Explanation: The largest use for superalloys is in the gas turbine industry. High temperature oxidation resistance is main property.
11. In the alloy Incoloy 901, part of the iron is replaced by _________ to improve high temperature stability.
Explanation: In the alloy Incoloy 901, part of the iron is replaced by Nickel to improve high temperature stability. These alloys are Nickel-iron base alloys.
12. Nickel base superalloys have _________ solid solution matrix.
Explanation: Nickel base superalloys contain iron and chromium as the major alloying element. Microstructure consists of FCC solid solution matrix.
13. Which material can’t be used above 1000°C?
Explanation: Lead has melting point of 327°C. It can’t be used on high temperatures. Refractory metals are used above 1000°C.
14. Titanium alloys can be used up to 1000°C.
Explanation: Titanium alloys are not used above 600°C. Because these are susceptible to embrittlement and surface oxidation.
15. Ni is used to stabilize FCC structure in iron-base superalloys.
Explanation: Iron-base alloys contain about 15% Cr and 25% Ni. Cr provides corrosion resistance and Ni provides FCC structure.
Sanfoundry Global Education & Learning Series – Mechanical Behaviour & Testing of Materials.
To practice all areas of Mechanical Behaviour & Testing of Materials, here is complete set of 1000+ Multiple Choice Questions and Answers.