This set of Mechanical Behaviour Multiple Choice Questions & Answers (MCQs) focuses on “Surface Imperfections”.
1. Which one of the following, is not exhibited by atoms present in the free surface?
a) Improper coordination number
b) Disrupted atomic bonding
c) Higher free energy
d) Less reactive than atoms present in the material
Explanation: Atoms present in the free surface have atoms only in one side, so these have improper coordination number, disrupted atomic bonding and higher free energy. These are more reactive than the bulk atoms.
2. Which property is deteriorated by increasing grain boundary area?
b) Corrosion resistance
Explanation: Strength, hardness and toughness of material increase with the decrease in grain size which is explained by the Hall-Petch relationship. Grain boundaries are the areas of high free energy, which decrease corrosion resistance.
3. Grain boundary improves ________
a) Electrical conductivity
b) Thermal conductivity
c) Creep strength
Explanation: Grain boundaries improve toughness of material by checking the dislocation motion. Electrical conductivity, thermal conductivity and creep strength deteriorate by increasing grain boundary area.
4. What is the range of mis orientation angle in high angle grain boundaries?
a) More than 10°
b) 5 – 10°
c) 1 – 5°
d) Less than 1°
Explanation: Grain boundaries, having a misorientation angle more than 10°, are categorized as high angle grain boundaries. While grain boundaries, having angle less than 10°, are categorized as low angle grain boundaries. An angle less than 1° is known as sub boundaries.
5. What is the most common etchant used to reveal grain structure of aluminium alloys?
d) Adler etchant
Explanation: Keller’s etchant is used for aluminium alloys. Its composition is 190 ml of distilled water, 5 ml nitric acid, 3 ml of hydrochloric acid and 2 ml of hydrofluoric acid. The immersion time is kept 10 to 30 seconds.
6. Nital etchant is used for revealing microstructure of _______
a) Cast iron
d) Zinc alloys
Explanation: Nital is used for etching cast iron. Composition of nital is 100 ml ethanol and 1 – 10 ml nitric acid. Immersion time varies from seconds to few minutes depending on the composition of cast iron.
7. Mechanical twins are commonly observed in _____ while annealing twins are observed in ______
a) FCC, BCC
b) BCC, HCP
c) FCC, HCP
d) HCP, FCC
Explanation: HCP is more likely to form mechanical twins because they have less number of slip systems. While FCC has more number of slip systems.
8. A low angle grain boundary formed by an array of edge dislocations is referred to as ______ boundary.
Explanation: The array of edge dislocations forms tilt between adjacent grains. This grain boundary is referred as tilt boundary.
9. A low angle grain boundary, formed by set of _______ dislocations, is defined as twist boundary.
Explanation: The set of screw dislocations gives twisting of lattice with respect to the adjacent lattice. The grain boundary, thus formed, is referred as twist boundary.
10. High angle grain boundaries provide easy atom diffusion in a solid state.
Explanation: In high angle grain boundaries, atoms are found in somewhat disordered state, which provides vacancies and facilitates easy diffusion of atoms.
11. What is the stacking sequence for FCC structure?
Explanation: Stacking sequence for FCC structure is ABCA because the fourth plane shows resemblance to the first plane. ABABAB is stacking sequence for HCP and BCC. Stacking sequence for simple cubic is AAA.
12. Stacking fault energy of silver is _____
a) 40 – 50 mJm-2
b) 70 – 80 mJm-2
c) 10 – 20 mJm-2
d) 20 – 30 mJm-2
Explanation: Silver has SFE 20 – 30 mJm-2. That’s why, it is less ductile than copper, which has SFE 70 – 78 mJm-2.
13. Higher Stacking fault energy materials face more difficulty in cross slip and climb.
Explanation: In high SFE materials, due to no stacking faults, screw dislocations cross slip easily. These also deform by glide of dislocations.
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.