MECHANISM OF THE KOEHLER DISLOCATION MULTIPLICATION PROCESS

In the Koehler dislocation multiplication process. segments of screw d islocations glide off the primary glide plane onto secondary planes, a nd then back onto a primary plane parallel to the first plane. This ge nerates trailing dipoles for small excursions between the two primary planes, or the pinning points of Frank-Read mills for large excursions . The concern of this paper is the mechanism that causes the lines to cross-glide, and the distribution of dipoles heights that results. It is proposed that self-excited oscillations of moving dislocation lines , induced by thermally induced shear-strain fluctuations, cause the cr oss-gliding The properties of this process are described. It is simila r to a two-dimensional random walk, and this determines the dipole hei ght distribution. The Koehler process is dominant for dislocation mult iplication in structural materials, especially at high strain rates. T he resulting dipole height distribution is an important factor in dete rmining various properties of the cold-worked state. Some of these are specific heat, the thermal conductivity, fatigue degradation, strain hardening, Bordoni internal friction and corrosion resistance.