This set of Manufacturing Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Imperfection and Defects In Solid”.
b) Line imperfections
c) Volume imperfections
d) Surface imperfections
Explanation: The simplest of the point defects is a vacancy, vacant lattice site. This could occur an atom is being missing from its lattice site. All crystalline solids contains vacancies, in fact, it is impossible for a material to be free of these vacancies, making them to call equilibrium defects. For reference, all the imperfections in solids are being tabulated below:
| IMPERFECTIONS IN SOLIDS | |||
|---|---|---|---|
| Point Imperfections (Zero-Dimensional) | Line Imperfections (One-Dimensional) | Surface Imperfections (Two-Dimensional) | Volume Imperfections(Three-Dimensional) |
| Vacancies | Dislocations | Surface | Voids |
| Interstitial Impurities | Disclinations | Grain boundaries | Cracks |
| Substitutional Impurities | Twin boundaries | Inclusions | |
| Schottky defect | Stacking faults | Precipitates | |
| Frenkel defect | Interphase boundary | Twins | |
2. Substitution of a foreign atom in the site of parent atom in the crystal is a?
a) Vacancy defect
b) Substitution impurity
c) Volume imperfection
d) Vacancy defect
Explanation: When an impurity atom of equal to atomic size of the host atom is being replaced or substituted for the host atoms, is called substitutional impurity.
3. Edge dislocation imperfection is a sub type of _____________
a) Point imperfections
b) Line imperfections
c) Volume imperfections
d) Surface imperfections
Explanation: A dislocation is a one-dimensional or linear defect around which some of the atoms are misaligned. Edge dislocation is a type of dislocation, where an extra portion of plane of atoms, the edge terminates within the crystal.
4. Displacement of an ion from regular location to interstitial location is known as ____________
a) Vacancy defect
b) Line imperfection
c) Schottky’s defect
d) Frenkel defect
Explanation: Frenkel defect, named after its discoverer “Yakov Frenkel”, forms when an atom leaves its regular position thus creating a vacancy there, and becomes interstitial by positioning itself into nearby interstitial location. Usually small ion (cation) undergoes this phenomenon.
5. When a pair of cation and anion are missing in a crystal, it is called ____________
a) Vacancy defect
b) Line imperfection
c) Schottky’s defect
d) Frenkel defect
Explanation: Schottky’s defect, named after its discoverer “Walter H. Schottky”, forms when two atoms of opposite charge (anion and cation) leaves their regular atomic positions thus creating two vacancies. As two atoms of opposite charges are leaving, there is no change in overall charge of the material with Schottky’s defect. Schottky’s defect is known for its presence in ionic crystals.
6. Which one of the following is not a zero-dimensional defect?
a) Vacancy defect
b) Substitution imperfection
c) Schottky’s defect
d) Screw dislocation
Explanation: Screw dislocation is a type of dislocations (linear or one-dimensional defects) which thought to be formed by a shear stress that is applied to produce the distortion in a spiral manner inside the crystal, indicating burgers vector parallel to this dislocation type.
7. Twin or Twinning is a category of ________
a) Point imperfections
b) Line imperfections
c) Volume imperfections
d) Surface imperfections8. As the grain size of a metal increases, its strength ________
a) Decreases
b) Increases
c) Remains constant
d) No effect of grain size on strength
Explanation: Strength of a metal is directly proportional to its ability resist plastic deformation, thus resisting its dislocation movement. As one can relate that, more the number of grain boundaries (fine is the grain size), more is the obstruction to the movement of dislocation, thus more is the strength of a metal. So, if grain size increases, its strength decreases. This phenomenon can be best understood with the help of Hall-Petch relation.
9. As the grain size of a meal increases, its ductility ________
a) Decreases
b) Increases
c) Remains constant
d) No effect of grain size on ductility
Explanation: Fine the grain size (lower the grain size), more is the number of grain boundaries, thus more is the yield strength, thus more is the ductility. So, if grain size increases, its ductility decreases.
10. Phenomenon of cross slip occurs in ________
a) Point imperfections
b) Line imperfections
c) Volume imperfections
d) Surface imperfections
Explanation: When we apply a stress, it causes screw dislocations to move from one slip plane to another slip plane, which is known as its cross slip. Cross slip is one of the primary mechanisms that causes plastic deformation in metals.