Table of Contents

Materials and Structure




Dislocations and Slip

Dislocations are one-dimensional defects that occur in real crystalline solids and control their plastic deformation. The presence of dislocations permits atomic planes to slip "one atomic row at a time." Dislocations interact with the microstructure of the material and these interactions are responsible for their yield, work-hardening, ductility, and other plastic properties. Dislocation motion in a crystal is analogous to moving a rug over a floor by introducing a ruck on one edge. Pushing the ruck to the other edge moves the carpet by the width of the ruck. This process may be repeated many times to achieve the desired shear displacement between the rug and the floor with less work than sliding the carpet in one go.

For a crystal, the size of the "ruck" is the distance between the atom planes, about 0.4 nm. The macroscopic shear is produced by the motion of many dislocations newly created by the applied stress. This process will tend to occur on planes for which the resolved shear stress is the largest. The right hand diagram and photograph illustrate this for a Zinc single crystal

From: Guy, "Introduction to Materials Science, "McGraw Hill (1972)