Mechanism of the Koehler dislocation multiplication process

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Abstract
In the Koehler dislocation multiplication process, segments of screw dislocations glide off the primary glide plane onto secondary planes, and then back onto a primary plane parallel to the first plane. This generates 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 cross-gliding. The properties of this process are described. It is similar to a two-dimensional random walk, and this determines the dipole height distribution. The Koehler process is dominant for dislocation multiplication in structural materials, especially at high strain rates. The resulting dipole height distribution is an important factor in determining 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.

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