University of Ontario Institute of Technology

ENGR 2220A

Quiz 3

1)Which ONE of the following statements is correct?

1. Smaller substitution atoms generate a compressive stress field in their immediate vicinity
2. Larger substitution atoms generate a tensile stress field in their immediate vicinity
3. Larger substitution atoms generate a compressive stress field in their immediate vicinity
4. Interstitial atoms generate a tensile stress field in their immediate vicinity

2. Which ONE of the following statements is correct?

1. Smaller substitution atoms generate a compressive stress field in their immediate vicinity
2. Larger substitution atoms generate a tensile stress field in their immediate vicinity
3. Interstitial atoms generate a tensile stress field in their immediate vicinity
4. Interstitial atoms generate a compressive stress field in their immediate vicinity

3. Diffusion is FASTER: (Choose ONE).

1. in materials with close-packed structures
2. in materials metallic bonding
3. when the diffusing atoms are smaller
4. in higher density materials

4. Interstitial diffusion is:

1. Slower than substitutional diffusion as the small atoms in the interstices do not have enough energy to easily move across the lattices
2. Faster than regular diffusion as it occurs only at higher temperatures
3. Slower than regular diffusion as the larger host atoms offer greater resistance to movement
4. Faster than substitutional diffusion as the small atoms in the interstices have many location to which they can move to.

5. The solubility of a solute in general

1. decreases with increasing pressure
2. decreases with increasing temperature
3. is higher when crystal structures of constituents are similar
4. is lower when the atom sizes are similar

6. The crystalline materials deform at a much smaller force than theoretical force required to deform crystals due to the presence of:

1. Twin boundaries
2. Vacancies
3. Impur ities
4. Dislocations

7. Which of the following statements is correct?

1. Slip in crystal plane occurs when the sheer stresses become larger than the yield strength
2. Slip in crystal plane occurs when the resolved sheer stresses become larger than the critical resolved shear stress
3. Slip in crystal plane occurs when the critical resolved sheer stresses become larger than the resolved shear stress

4. Slip in crystal plane occurs when the yield stresses become larger than the sheer stresses

8. Dislocations are created due to:

1. Increase in temperature of metals
2. accumulation of Vacancies in metals
3. slow heat treatment of metals
4. plastic deformation of metals

9. Case hardening is an example of

1. Brownian diffusion
2. Interstitial diffusion
3. Substitutional diffusion
4. Inter-molecular diffusion

10. Fick’s first law states that the number of diffusing atoms is:

1. inversely proportional to the area through which they are diffusing
2. directly proportional to the area through which diffusion is taking place
3. inversely proportional to the concentration gradient

11. The diffusion coefficient is

1. inversely proportional to the absolute temperature of the material
2. exponentially proportional to the absolute temperature of the material
3. directly proportional to the absolute temperature of the material

12. Plastic deformation occurs at stresses much smaller than the theoretical strengths of perfect crystals

1. due to the presence of large number of vacancies
2. due to the presence of grain boundaries
3. due to the process of cold working
4. due to the presence of dislocations

13. Dislocation movements is easier in

1. Materials having covalent bonds
2. Materials having metallic bonds
3. Materials having ionic bonds

14. Which of the following in NOT a crystalline dislocation:

1. Edge dislocation
2. Joint dislocation
3. Screw dislocation
4. Mixed dislocation

15. Dislocations move when

1. Critical resolved sheer stress exceeds the yield strength of the material
2. Yield strength of the material is lower than the critical resolved sheer stress.
3. The resolved stress in slip direction exceeds the critical resolved sheer stress

16. Critical resolved sheer stress is a material property and is

1. twice the magnitude of the yield strength
2. twice the magnitude of the tensile strength
3. one half the magnitude of the tensile strength
4. one half the magnitude of the yield strength

17. Which of the following is NOT a strengthening mechanism?

1. Increasing the number of vacancies
2. Formation of solid solutions
3. Grain size reduction
4. Inclusion of precipitates

18. Recovery by heating refers to

1. Reduction in grain size in cold worked metals
2. Increase in grain size in cold worked metals
3. Reduction in dislocation density in cold worked metals
4. Increase in dislocation density in cold worked metals

19. Re-crystallization by heating refers to

1. Reduction in grain size in cold worked metals
2. Increase in grain size in cold worked metals
3. Reduction in dislocation density in cold worked metals
4. Increase in dislocation density in cold worked metals

20. Which ONE of the following statements is correct?

1. Small solute atoms tend to segregate towards the tensile field of a dislocation
2. Large solute atoms tend to segregate towards the tensile field of a dislocation
3. Large solute atoms tend to segregate towards the compressive field of a dislocation

21 Which ONE of the following statements is correct?

1. Smaller substitution atoms generate a tensile stress field in their immediate vicinity
2. Larger substitution atoms generate a tensile stress field in their immediate vicinity.
3. Smaller substitution atoms generate a compressive stress field in their immediate vicinity.
4. Interstitial atoms generate a tensile stress field in their immediate vicinity.

22. Interstitial point defect occurs when:

1. An impurity atom displaces a host atom from its lattice position and occupies that space
2. An impurity atom dislodges host atoms along grain boundaries and occupies that space
3. An impur ity atom resides in the space between the lattice positions without displacing any host atom
4. An impurity atom diffuses into the extra spaces between the grain boundaries

23. The solubility of a solute in general

1. decreases when the atomic radii are similar.

2. Increases when the crystalline structure of both solvent and solute is dissimilar
3. Decreases when the crystalline structure of both solvent and solute is similar
4. Increases when the atoms have similar electro negativities

24. Which ONE of the following statements is correct?

1. Diffusion coefficient for interstitial diffusion is very low compared to diffusion coefficient for substitution diffusion
2. Diffusion coefficient for substitution diffusion is very high compared to diffusion coefficient for interstitial diffusion
3. Diffusion coefficient for substitution diffusion increases at a higher rate compared to diffusion coefficient for interstitial diffusion with increasing temperatures
4. Diffusion coefficient for substitution diffusion is generally larger compared to diffusion coefficient for interstitial diffusion

25. The ceramic structures are governed by which of the two parameters?

1. Relative size of cations and anions and the requirement of charge neutrality
2. Relative size of cations and anions and the vacancies in lattices
3. The requirement of charge neutrality and the vacancies in lattices
4. The distance between adjoining atoms and the charges on them

26. Which one of the following does NOT contribute to the strengthening of metals?

1. Formation of precipitates.
2. Addition of impurity metals
3. Reduction of vacancies
4. Cold working

27. Cold working results in higher strength of metals because:

1. It results in reduced grain sizes which obstruct movement of dislocation
2. It increases the number of dislocations
3. It generates precipitates which obstruct movement of dislocation
4. It results in larger grain sizes which obstruct movement of dislocation

28. The anions in ceramics are generally                    in size than the cations.

1. smaller
2. similar
3. bigger

29. Frankel defects are presence of one interstitial ion accompanied by a nearby vacancy so that the net charge in the vicinity is zero. Such defects for ANIONS do not occur in ionic ceramics in large numbers. Why not?

1. It is difficult to accommodate the large anions in the interstitial spaces
2. The anion charge cannot be balanced by vacancy
3. The anions cannot occupy interstitial spaces due to kinematic constraints

30. In ceramics, point defects occur in pairs so that

1. mass conservation is maintained

2. charge neutrality is maintained
3. movement of ions is facilitated

31. There are                stable ceramic structures based upon the cation anion radius ratio r_C/r_A:

1. Three
2. Four
3. Five

d More than 10

32. The compressive strength of ceramics is typically                         times the tensile strength.

1. Two
2. Five
3. Ten
4. Hundred

33. The hardest materials is

1. Alumina
2. Diamond
3. Tungsten Carbide
4. Quartz

34. Which ONE of the following is not a ceramic category?

1. Glass
2. Refractories
3. Cements
4. Dry woods

35. When clay pottery is dried and fired, it becomes strong due to:

1. Local formation of glassy regions
2. Formation of additional primary bonds within clay particle
3. Settling of clay particles into lower energy states
4. Generation of dislocations which get entangled with each other