Dislocation relaxation in single crystals of molybdenum

Abstract

The characteristics of the α dislocation relaxation peak in molybdenum have been examined in three orientations of high purity single crystals deformed in tension at 170, 300 and 450 K. For deformation at 450 K, the α peak is absent in crystals oriented for easy glide and deformed into stage 1 of work hardening. For crystals of the same orientation deformed into stages 2 and 3 and for crystals with [001] and [101] tensile orientations, the peak is observed superimposed on a step-like background; it grows rapidly, sharpens and moves to lower temperatures with increasing amounts of plastic deformation. Crystals with the easy glide orientation deformed at 170 and 300 K exhibit rapid work hardening and display small, broad, asymmetrical α peaks. Mild strain aging at 500 K does not greatly affect the α peak, but drastically reduces the step-like background damping. The overall response of the α peak to changes in dislocation substructure is very similar to that of the Bordoni peak in f.c.c. metals. Three widely divergent models are considered: double kink generation on non-screw dislocations, kink diffusion on screw dislocations, and breakaway of dislocations from immobile pinning points. It is concluded that the major features of both peaks are better explained by the breakaway models. For the α peak, a variation of the Hasiguti trapped kink model seems most appropriate.