Chapter 7 Flashcards
Resolved Shear Stress in Crystals
Dislocations move on slip planes in slip directions when the shear stress on that plane in that direction exceeds a critical value
Resolved Shear Stress equation
shear stress = stress * cosine(angle between direction of load and the normal to slip plane) * cosine(angle between direction of load and slip direction)
Solid Solution Strengthening
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
Solid Solution Strengthening Cases
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
Strain Hardening
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
Annealing
Low Temperature
<= 0.3 Tm (Melting Temperature in absolute scale)
Annealing
Recrystallization
Temperature
Equivalent to 0.4 Tm
Annealing
Recrystallization
Microstructural Changes
Replacement of old grains with new, nearly dislocation free grains with free orientations and equiaxed shape
Annealing
Recrystallization
Property changes
Large drop in strength
Large increase in ductility and toughness
Loss of cold-work-induced anisotropy
Annealing
High Temperature
> = 0.5Tm
Annealing
Ordering of stages
Lowest temperature to highest temperature for constant time of annealing
Shortest time to longest time for constant annealing temperature
Annealing
Recovery Stage
Microstructural Changes
Slight decrease in # of dislocations
reorganization of dislocations into orderly subgrains
Annealing
Recovery Stage
Property Changes
Elimination of residual stresses
Increase in thermal and electrical conductivity
Reduction of susceptibility to corrosion
Annealing
Grain Growth Stage
Microstructural Changes
A few grains grow by cannibalizing their neighbors
Grain becomes fewer and larger
Annealing
Grain Growth Stage
Property Changes
Slight loss of both strength and ductility at low temperatures