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

Abstract

Macroscopic compression tests and in situ straining experiments in a high-voltage electron microscope were performed on NiAl± 0.2at.%Ta at room temperature and at elevated temperatures. At room temperature in soft orientations, dislocations of ah100i Burgers vectors bow out between jogs. In contrast to pure NiAl, the dislocations move in a viscous way between the pinned con®gurations. At 475 C in a hard orientation, dislocations with ah110i Burgers vectors move in a viscous way in con®gurations strongly depending on the respective slip plane. Preferred orientations of dislocations are of mixed character, most pronounced as very straight dislocations oriented along h111i directions on {110} planes. These con®gurations cannot be explained on the basis of the existing atomistic theories. The¯ow stress is interpreted in terms of the back stress of the dislocations bowing out between jogs at room temperature, the statistical theory of solid solution hardening, and the formation of atmospheres containing Ta atoms at elevated temperatures. #

The flow stress anomaly in Fe–43at%Al single crystals

“…The proposed model is basically different from the climb dissociation model [5], which was applied to FeAl in [4], where the dislocations dissociate by climb and have to constrict before they move. The strong alignment of dislocations with h110i Burgers vectors along h111i in NiAl was also observed during dislocation motion in in situ straining experiments [49]. It has been suggested that the decomposition model is also responsible for the motion of straight dislocations in MoSi 2 single crystals at high temperatures [15,50].…”

High‐voltage electron microscope high‐temperature in situ straining experiments to study dislocation dynamics in intermetallics and quasicrystals

“…In the intermetallic alloys NiAl (Messerschmidt et al ., 1997), NiAl‐0.5at%Ta (Messerschmidt et al ., 1999a), Ti‐52at%Al (Häussler et al ., 1999) and MoSi 2 (Guder et al ., 1999), the dislocation dynamics show a number of similarities (Messerschmidt et al ., 1999b). Near room temperature, the dislocation mobility is controlled by thermally activated processes such as overcoming localized obstacles, impeding by jogs or the Peierls mechanism.…”