DIRECT EXPERIMENTAL EVIDENCE OF DISLOCATIONS

Abstract

When a metal crystal is deformed plastically, the crystal changes its shape by the slipping of atomic planes over one another. In this process the atomic planes do not slip over each other as rigid entities; instead, slip starts at one or more places in the slip plane and then spreads gradually over the remainder of the plane. In general, therefore, there will be a boundary line on the slip plane dividing the area over which slip has already taken place from that over which slip has not yet occurred. This boundary line between the slipped and unslipped parts ot the crystal is a dislocation line. A dislocation is essentially a line defect; in the neighbourhood of the dislocation the atoms are displaced from their positions in the ideally perfect crystal lattice.