Monotonic and Cyclic Deformation-induced Dislocation Substructures in BCC Metals

Abstract

In this investigation, we observed dislocation substructures associated with the mobility difference between edge and screw dislocations in bcc metals at low homologous temperatures and the effects of dislocation source density. Surface oxide films were used to enhance nucleation of high mobility edge dislocations under applied stress. In monotonic deformation of Nb at 77 K, sufficient excess densities of edge dislocations can be generated at the film-substrate interface to support macroscopic strain levels at a greatly reduced flow stress compared to that required for motion of screw dislocations. In cyclic deformation of W at 295 K, the same surface film effects alter the range of stresses over which cyclic saturation hardening occurs at cyclic microstrains and macrostrains.