Unit 2 - Deformation and dislocations Flashcards
How do edge dislocations move?
Edge dislocations move across the slip plane under shear stress, with positive and negative dislocations moving in different directions
How does strain hardening progress in an annealed metal?
In annealed metal, new dislocations must be generated and move via Frank Read sources to produce more strain deformation
What is the correct model for slip in dislocation theory?
Slip starts with pre-existing dislocations in a localised region, progressing over the slip plane and reducing the number of atomic bonds broken at any time
How do screw dislocations move?
Screw dislocations move in the direction of the applied stress, causing slipped and non-slipped regions in the crystal lattice
What is dislocation pile-up?
Dislocation pile-up occurs when the movement of dislocations is stopped by obstacles, causing loops to pile up against each other
How do dislocations interact?
Like signs repel each other causing loop expansion (repulsion), while opposite signs attract and cancel out (annihilate)
How does climb occur in edge dislocations?
Climb in edge dislocations involves movement normal to its plane, occurring by diffusion of vacancies or interstitials, and happens at high temperatures
What initiates strain hardening in metals?
In an annealed metal, strain hardening begins when the yield condition is reached, causing some dislocations to move on favorable planes
What is the Frank-Read Source?
The Frank-Read Source generates new dislocations within a material to accumulate bulk strains, creating loops that expand and slip
What is the significance of the Burgers vector?
It determines the magnitude and direction of dislocation in a crystal lattice.
How does dislocation density affect strain hardening?
As deformation occurs, increasing dislocation density decreases the distance between dislocations, requiring greater stress for further deformation
What factors affect yield stress in metals related to temperature?
Increased temperature makes slip easier by increasing atomic vibrations, thereby decreasing yield stress.
How does grain size affect yield stress in metals?
Generally, as grain size decreases, yield stress increases, as described by the Hall-Petch relationship.
What is the role of the dislocation network in crystals?
In crystals, the dislocation network forms a 3-D structure during solidification, with nodes acting as anchors where dislocation lines end and are stable.
What is plastic deformation in metals and how is it achieved?
Plastic deformation in metals is achieved by breaking and reforming atomic bonds, occurring via slip or movement of a plane of atoms relative to their neighbours.
