9. Strengthening of Crystals Flashcards
____ occurs when the resolved shears tress τR on a favorable slip plane exceeds a critical value τcrss
Slip
Why to grain boundaries impede motion?
- Dislocations must change directions due to grain misorientation
- Atomic disorder at grain boundary causes discontinuity of slip planes
What is the effect of grain size on dislocation movement?
Decreased grain size results in increase in grain boundary area, which increases the impediment to dislocation motion
Define solid solution
a solid which contains at least two different types of atoms
what are the two kinds of solute in a solid solution?
- substitutional solute
2. interstitial solute
define substitutional solute
alloy atom has similar size as host atom, and replaces them in the crystal structure
define interstitial solute
alloy atom is smaller than host atom, and fits into spaces (interstices) between host atoms
How do susbtitutional atoms impede dislocation motion (ie slip)
they impose lattice strain
Smaller substitutional atoms induce ___ stresses in the lattice
tensile
larger substitutional atoms induce ____ stress in the lattice
Compressive
Alloy atoms ____ to a location to reduce strain imposed by dislocation
diffuse
what is another name for work hardening?
cold hardening
What are the three methods that hinder dislocation movement and therefore increase yield strength, ultimate tensile strength, and hardness
- grain size reduction
- solid solution hardening (add solute to induce strain)
- work hardening
what are three dislocation formation sites
- existing dislocation sites
- internal defects
- surface defects
The number and density of dislocations ___ with plastic deformation
increase
