Chapter 7

Question 1

Resolved Shear Stress in Crystals

Answer 1

Dislocations move on slip planes in slip directions when the shear stress on that plane in that direction exceeds a critical value

Question 2

Resolved Shear Stress equation

Answer 2

shear stress = stress * cosine(angle between direction of load and the normal to slip plane) * cosine(angle between direction of load and slip direction)

Question 3

Solid Solution Strengthening

Answer 3

Point defects such as substitutionals and interstitials either repel dislocations or else attract and then anchor dislocations, depending on the stress fields of the dislocation and point defect

Question 4

Solid Solution Strengthening Cases

Answer 4

1) Where the stress fields are both tensile or both compressive, there is repulsion
2) Where one stress field is tensile and the other is compressive, there is attraction and anchoring

In both cases these point deflects make motion of dislocations harder, thus requiring larger stress for plastic deformation

Question 5

Strain Hardening

Answer 5

As plastic deformation proceeds, more and more dislocations are generated from dislocation sources.

These dislocations repel siblings on the same slip plane and also interfere with the motion of dislocations on other slip planes, thereby increasing the stress necessary for further plastic deformation

Question 6

Annealing

Low Temperature

Answer 6

<= 0.3 Tm (Melting Temperature in absolute scale)

Question 7

Annealing

Recrystallization
Temperature

Answer 7

Equivalent to 0.4 Tm

Question 8

Annealing

Recrystallization
Microstructural Changes

Answer 8

Replacement of old grains with new, nearly dislocation free grains with free orientations and equiaxed shape

Question 9

Annealing

Recrystallization
Property changes

Answer 9

Large drop in strength

Large increase in ductility and toughness

Loss of cold-work-induced anisotropy

Question 10

Annealing

High Temperature

Answer 10

> = 0.5Tm

Question 11

Annealing

Ordering of stages

Answer 11

Lowest temperature to highest temperature for constant time of annealing

Shortest time to longest time for constant annealing temperature

Question 12

Annealing

Recovery Stage
Microstructural Changes

Answer 12

Slight decrease in # of dislocations

reorganization of dislocations into orderly subgrains

Question 13

Annealing

Recovery Stage
Property Changes

Answer 13

Elimination of residual stresses

Increase in thermal and electrical conductivity

Reduction of susceptibility to corrosion

Question 14

Annealing

Grain Growth Stage
Microstructural Changes

Answer 14

A few grains grow by cannibalizing their neighbors

Grain becomes fewer and larger

Question 15

Annealing

Grain Growth Stage
Property Changes

Answer 15

Slight loss of both strength and ductility at low temperatures

Question 16

Effect of annealing on Weld Heat Affect Zone

Answer 16

If a cold-worked material is welded, the region of material near a weld which is raised to annealing temperatures will incur a loss of strength

Question 17

Ways to minimize undesirable effects if Weld Heat Affect Zone

Answer 17

Minimize the amount of energy deposited in the material during welding

Make the welding process as narrow in extent and short in duration as possible