Deformation Microstructures in B2-Type CoTi Single Crystals

Abstract

ABSTRACTB2-type CoTi single crystals which exhibit the yield strength anomaly were deformed at various temperatures and on various compression axis in order to investigate the deformation microstructures. The morphological feature and Burgers vectors of the activated dislocations were investigated by means of transmission electron microscopy. At a low temperature of 300 K, relatively straight dislocations with the <001>-type Burgers vector were observed. They consisted of the mixed components of edge and screw, and strongly tended to form the dipoles. At a temperature of 773 K where the yield stress increases with increasing temperature, the screw components of dislocations with a <001>-type Burgers vector were dominant and showed peculiar morphology revealing the pinning or cross slip. However, the examination using the weak-beam method could not show the evidence of any dissociation. At a high temperature of 973 K above the peak temperature, the Burgers vectors of activated dislocations were determined to be a <001>- type for compressive orientation axes close to [111] and [011] whereas a <110>-type for orientation axis close to [001]. These dislocation microstructures were discussed in correlation with the yield strength anomaly observed in these intermetallics.