Self-twinning in solid-state decomposition

Abstract

Twinning in face-centered cubic materials has received increasing attention owing to its favorable contributions to materials properties. While the models designed to account for twin nucleation have been mainly concerned with deformation twinning under external stress, addressing autocatalytic nucleation of twin (self-twinning) remains a challenge. Here, we report experimental evidences and a dislocation-based model demonstrating that a new source for twinning (self-twinning) operatives during solid-state decomposition. The initial stage of self-twinning is a stress relaxation process to relieve the local stress concentration caused by pile-up of interfacial dislocations at the precipitate-matrix interface. Dynamical two-beam analyses on dislocations configurations showed that three types of partial dislocations were involved in self-twinning: two Shockley partials, 16[112] on primary (111¯) plane and 16[112¯] on conjugate (111) plane; a stair-rod dislocation of 16[110] connecting primary and conjugate planes. We further show that the thermally-activated cross-slip of Shockley partials with aid of stair-rod dislocation plays a crucial role in self-twinning process.