Dislocation processes during the deformation of NiAl-0.2at.%Ta

Macroscopic compression tests and in situ straining experiments in a high-v oltage electron microscope were performed on NiAl-0.2at.%Ta at room tempera ture and at elevated temperatures. At room temperature in soft orientations , dislocations of a[100] Burgers vectors bow out between jogs. In contrast to pure NiAl, the dislocations move in a viscous way between the pinned con figurations. At 475 degrees C in a hard orientation, dislocations with a[11 0] Burgers vectors move in a viscous way in configurations strongly dependi ng on the respective slip plane. Preferred orientations of dislocations are of mixed character, most pronounced as very straight dislocations oriented along [111] directions on {110} planes. These configurations cannot be exp lained on the basis of the existing atomistic theories. The flow stress is interpreted in terms of the back stress of the dislocations bowing out betw een jogs at room temperature, the statistical theory of solid solution hard ening, and the formation of atmospheres containing Ta atoms at elevated tem peratures. (C) 1999 Elsevier Science Ltd. All rights reserved.