Temperature-dependent slip line length in copper single crystals

Abstract

An essential feature of any theory of strain hardening is a mechanism by which slip lines are blocked. In a recent paper on temperature-dependent plastic flow in strain-hardened metals (Alden 1972), it was suggested that expanding dislocation loops, and thus slip lines, are blocked by a co-operative process involving point-like obstacles (namely attractive forest dislocations), rather than by specific linear obstacles which surround the source, as in current theory (Seeker 1957, Hirsch and Mitchell 1967). A unique prediction of the new theory is that the slip line length should increase with decreasing temperature and increasing stress at constant structure; this occurs because increasing numbers of forest dislocations become penetrable at the higher stress.

The purpose of these experiments was to test this prediction in copper single crystals. A series of crystals was identically restrained at 673°K, polished and incrementally strained to produce characteristic slip lines at several lower temperatures down to 4·2°K. Between 573°K and 4·2°K, the average slip line length increases by at least a factor of 3, confirming qualitatively the theoretical prediction.