Materials Science Chapter 7

Slip

the permanent plastic deformation of a crystalline material caused by planes of atoms sliding over one another

Edge Dislocation

Formed by the insertion of an extra half-plane of atoms into a crystal lattice. The Burgers vector is perpendicular to the dislocation line.

Screw Dislocation

Formed by applying a shear stress that offsets one part of the crystal relative to another, creating a helical (spiral) ramp of atomic planes. The Burgers vector is parallel to the dislocation line.

Slip System

Combination of slip plane and slip direction

Slip Plane

Usually the plane with the largest inter-planar spacing and highest planar density, making it easiest for planes to glide over one another.

Slip Direction

the direction with the highest linear density (shortest Burgers vector), meaning atoms need to travel the shortest distance during a slip step.

What are strengthening techniques for metals?

grain size reduction

solid solution strengthening

strain hardening (cold working)

Metals having small grains

relatively strong and tough at low temperatures

Metals having large grains

good creep resistance at relatively high temperatures

Grain Growth

occurs as heat treatment continues

Average grain size increases

Small grains shrink (and ultimately disappear)

Large grains continue to grow

Dislocation motion

applying a sheer force & we see that the dislocation is moving in the same direction as the applied sheer force.

Burger Vector

a vector that completes the circuit that is drawn around the dislocation