This set of Corrosion Engineering Multiple Choice Questions & Answers (MCQs) focuses on “High Temperature Materials”.
1. Metals that follow linear oxidation kinetics at low temperatures tend to oxidize catastrophicallyat high temperatures.
a) True
b) False
View Answer
Explanation: Metals that follows linear oxidation kinetics at low temperature tend to oxidize catastrophically at high temperatures. It is due to the rapid exothermic reactions at the surfaces at high temperatures.
2. Which of the following metals results in the ignition in extreme cases?
a) Sodium
b) Magnesium
c) Niobium
d) Sodium, magnesium, and niobium
View Answer
Explanation: If the rate of heat transfer from metal to surroundings is less than heat evolution from oxide formation then it increases the surface temperature of metals. This leads to the ignition of metals and it includes sodium, magnesium, and niobium.
3. Which of the following metals results in the formation of volatile oxides?
a) Molybdenum
b) Tungsten
c) Osmium, tungsten, molybdenum, and Vanadium
d) Vanadium
View Answer
Explanation: Volatile oxides are the oxides that get evaporate within the fractions of seconds after their formation. Metals that form volatile oxides include osmium, tungsten, molybdenum, and vanadium.
4. Which of the following is/are true regarding internal corrosion?
a) Corrosion products precipitate in the metal matrix
b) Corrosion products precipitate in the metal matrix and metals such as Fe, Ni, and Co are highly prone to internal corrosion
c) Corrosion occurs on external surfaces of metals
d) It is due to the stable corrosion products of base metals
View Answer
Explanation: Internal corrosion is due to the one or more dilute alloying elements form more stable oxides than the base metal and preferentially forms corrosion in the metal matrix. Iron, nickel, and cobalt are the base metals that are prone to internal corrosion.
5. Dilute alloying elements of base metals exhibiting a relatively high solubility and diffusivity for atomic oxygen are subject to internal corrosion.
a) True
b) False
View Answer
Explanation: Dilute alloying elements of base metals exhibiting a relatively high solubility and diffusivity for atomic oxygen are subject to internal corrosion. It is due to the formation of preferential stable oxides than the base metals.
6. Which of the following mechanical properties is/are important in structural applications of metals?
a) Tensile strength
b) Yield strength
c) Ductility and Elasticity
d) Tensile strength, Yield strength, Ductility, and Fracture toughness
View Answer
Explanation: Mechanical properties that are important in structural applications of metals are:
i. Tensile strength
ii. Yield strength
iii. Ductility
iv. Fracture toughness.
7. Which of the following is/are correct regarding creep?
a) It is the continuous plastic elongation of metal under constant load
b) It is the high-temperature mechanical effect of a metal
c) It is the continuous plastic elongation of metal under constant load at high temperature and it can be minimized by the fraction of grain boundaries
d) It can be minimized by reducing the fraction of grain boundaries
View Answer
Explanation: It is defined as the continuous plastic elongation of metal under constant load at high temperatures. Creep rate is then expressed as percent elongation in a given time. It can be minimized by reducing the fraction of grain boundaries.
8. Which of the following is/are true regarding stress rupture?
a) The stress required to cause a rupture in a predetermined time at a constant temperature
b) It is important in short-term high-temperature applications
c) Stress rupture is an important mechanical property for gas turbine or rocket engines
d) The stress required to cause a rupture in short-term high-temperature applications at a predetermined time is known as stress rupture and it is an important mechanical property for gas turbines and rocket engines
View Answer
Explanation: Stress rupture is defined as the amount of stress that is required to cause a rupture in short-term high-temperature applications at a predetermined time. It is an important mechanical property for gas turbines and rocket engines.
9. Which of the following is/are the adequate high-temperature mechanical properties to avoid fracture?
a) Low creep rate and high stress-rupture strength
b) High stress-rupture strength, low creep rate, and high fracture toughness
c) High stress-rupture strength and high fracture toughness
d) Low creep rate and high fracture toughness
View Answer
Explanation: Low creep rate, high stress-rupture strength, and high fracture toughness are the adequate high-temperature mechanical properties to avoid fracture.
10. Which of the following strengthening mechanisms is/are used to attain high-temperature strength?
a) Solid-solution strengthening
b) Precipitation hardening
c) Dispersion hardening
d) Solid-solution strengthening, precipitation hardening or dispersion hardening
View Answer
Explanation: Strengthening mechanism that is used to attain high-temperature strength are:
i. Solid-solution strengthening
ii. Precipitation hardening
iii. Dispersion hardening.
11. Which of the following metallurgical changes that affect the structural stability of metals at high temperatures?
a) Grain growth, phase changes, precipitation dissolution and precipitation over aging
b) Grain growth and phase changes
c) Precipitation dissolution and precipitation over aging
d) Phase changes, precipitation dissolution and precipitation over aging
View Answer
Explanation: Metallurgical changes that affect the structural stability of metals at high temperature are:
i. Grain growth
ii. Phase changes
iii. Precipitation dissolution
iv. Precipitation over aging.
12. Which of the following nickel-based alloys is/are superalloys?
a) Hastelloy C-276
b) Inconel 718
c) Hastelloy C-276, Inconel 718 and Hastelloy HX
d) Hastelloy HX
View Answer
Explanation: Superalloys or high-performance alloys are the alloys that can resist extreme conditions such as high temperature, high stress, high wear, and corrosive atmospheres. Nickel-based alloys are widely used as superalloys that include Hastelloy C-276, Inconel 718, and Hastelloy HX.
13. Which of the following is/are the high melting point metals?
a) Molybdenum
b) Tungsten
c) Columbium
d) Molybdenum, tungsten, columbium, and tantalum
View Answer
Explanation: Metals – Melting points
i. Tungsten – 6170°F
ii. Tantalum – 5430°F
iii. Molybdenum – 4750°F
iv. Columbium – 4380°F.
14. Which of the following is/are the limitations of high-temperature non-metallic materials?
a) Lack of ductility
b) Less resistance to thermal shock
c) Weldability, less resistance to thermal shock, lack of ductility and formability
d) Weldability and formability
View Answer
Explanation: Limitations of high-temperature non-metallic materials are:
i. Lack of ductility
ii. Less resistance to thermal shock
iii. Lack of ductility
iv. Formability
v. Weldability.
Sanfoundry Global Education & Learning Series – Corrosion Engineering.
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