Octahedral cross-slip in Ni₃(Al, Ti) deformed at −196°C

Abstract

A single crystal of L1₂ long-range-ordered Ni₃(Al, Ti) has been deformed in compression at −196°C. The dislocation structure in the (111) planes is predominated by edge superlattice dislocations which are arranged in dipoles and bundles of dipoles. The density of screw superlattice dislocations is low. They are mainly dissociated on octahedral (1ī1) and (111) planes. This provides strong evidence for octahedral (1ī1) cross-slip. Cube (010) cross-slip was only observed locally presumably assisted by the help of localized internal stresses. It is assumed that, at very low temperatures, cross-slip of screw dislocation from octahedral (111) to cube (010) planes cannot be thermally activated.

Altogether the results are consistent with the fact that the increase in the flow stress is strongly correlated to cross-slip of screw superlattice dislocations from (111) to (010) planes.