Lecture 8 Flashcards
What direction is the screw dislocation motion in reference to the shear stress?
Perpendicular
What is a screw dislocation?
Atoms in the lattice are displaced in a spiral manner around a dislocation line
What direction is the Burgers vector in screw dislocations in reference to the dislocation line?
Parallel
What is true for both edge and screw dislocations?
Dislocation line separates the slipped and unslipped portions
What atomic distance is the Burger’s vector normally for both edge and screw dislocation?
The shortest atomic distance
What is the Burgers vector for FCC?
b = a0/2 <110>
What is the Burgers vector for BCC?
b = a0/2 <111>
What is the dislocation motion under shear stress for positive edge?
dislocation moves at the same direction as the shear
What is the dislocation motion under shear stress for negative edge?
moves in the opposite direction as shear
What is the dislocation motion under shear stress for right hand screw?
Burgers vector and dislocation line are in the same direction
What is the dislocation motion under shear stress for left hand screw?
Burgers vector and dislocation line are in the opposite direction
Where does a dislocation end and where does it not end.
It either forms a loop or ends at surface/interface, but it cannot end inside a crystal
What are some common properties for edge and screw dislocations?
- 1D line defect
- forms closed loop inside crystal or emerges at surface
- dislocation line separates slipped and unslipped portions
- difference in amount of slip across the dislocation line is constant
- Burgers vector is typically alone close packed directions
Distinct features of edge dislocations?
- extra half plane
- BV perp L
- moves parallel to BV on slip plane
- unique slip plane (cant change)
Distinct features of screw dislocation?
- no extra half plane
- BV parallel to L
- moves perpendicular to BV on the slip plane
- no unique slip plane (can change)
