An in-situ transmission electron microscopy study of pyramidal slip in Ti₃Al: II. Fine structure of dislocations and dislocation loops

Abstract

An in-situ transmission electron microscopy investigation has been conducted of the dynamic behaviour of dislocations in the type I pyramidal (π₁) slip plane of Ti₃Al single crystals which operates when specimens are strained in tension along the c-axis. Superpartial dislocations are split asymmetrically into two unlike partials. The high-energy complex stacking fault involved is thought to relax by short-range diffusion and this can account for the very strong disordering, the glide softening, and the nucleation of loops reported in part I. Three loop families have been identified, all vacancy type. Mechanisms are proposed to explain the formation of loops, their interactions with mobile dislocations, and their alignment along a c + a/2 direction which is different from the Burgers vector direction of the gliding dislocations. It is concluded that the critical resolved shear stress of pyramidal slip is determined by the nucleation process of loops.