The effect of temperature and orientation on dislocation microstructures in b2-type coti single crystals

Abstract

B2-type CoTi single crystals with the yield strength anomaly were deformed at various temperatures and on various compressive orientations. The Burgers vectors and the morphological feature of the activated dislocations were then investigated by means of transmission electron microscopy. At low temperatures of 77 and 293 K, relatively straight dislocations with the <001>-type Burgers vector were observed. They consisted of the mixed components of edge and screw, and tended to form dipoles. At intermediate temperatures where the yield stress increases with increasing temperatures, the screw components of dislocations with the <001>-type Burgers vector were dominant and showed peculiar morphology revealing the pinning or cross-slip. At high temperatures above the peak temperature, the Burgers vectors of activated dislocations depended upon the compressive orientations; the <001>-type for orientation axes close to [011] and , whereas the <110>-type for orientation axis close to [001]. These dislocation microstructures were discussed in correlation with the yield strength anomaly observed in this compound.