Formation of deformation twins in a crept lamellar TiAl alloy

Abstract

The substructures of a lamellar TiAl alloy deformed at 760 C with a low applied stress to a large strain (138 MPa, 1.5%), and a high applied stress to a small strain (518 MPa, 0.67%) were examined. During creep, interfacial gliding dislocations are initially retarded by either intrinsic barriers (e.g., ledges in the surface) or extrinsic barriers (i.e., the reaction of lattice dislocation with interface), resulting in a dislocation pile-up configuration. With further deformation, deformation twins are formed, and dislocation emission from interfaces also occurs. A critical local stress is required to initiate deformation twins which are suggested to be formed via a stair-rod cross-slip mechanism. This critical stress can be fulfilled by an interfacial dislocation pile-up.