Question Bank: Deformation Flashcards
What is meant by linear density?
A measure of how closely packed atoms are in a given direction.
What is meant by planar density?
A measure of how closely atoms are packed on a given crystal plane.
What is the linear density of the [110] direction in FCC system?
This is a close packed direction. The length of the vector is 4R and there are 2 lattice points. LD = 2/(4R) = 1/(2R)
What is the linear density of the [100] direction in the HCP system?
This is a close packed direction. The length of the vector is 2R and there is 1 lattice point. LD = 1/(2R)
What is meant by slip system?
A slip system is a combination of a slip plane and slip direction (within that plane) along which shear can occur.
What is the critical shear stress?
The minimum shear stress on a slip system required to cause slip.
Write, the equation of the Schmid factor, F.
F = Cos(Φ)Cos(Ψ)
What is the maximum value of the Schmid factor?
0.5
Briefly describe an edge dislocation.
An extra half-plane of atoms inserted into a crystal
What happens to the dislocation density when a material is plastically worked?
The dislocation density increases.
State the common methods of strengthening metals.
Work hardening
Dispersion hardening
Solute strengthening
What property of a dispersion of particles must be reduced so as to improve their strengthening effect?
The average interparticle separation
What does “recrystallisation” mean?
The replacement of old, deformed grains by new, undeformed grains at high temperature.
What drives recovery and recrystallisation?
A reduction in dislocation density.
What effect do recovery and recrystallisation have on the mechanical properties of a metal?
A reduction in strength and an increase in ductility.
