Crystallographic mechanisms of fracture in a textured polycrystalline TiNi shape memory alloy

Abstract

The crystallographic mechanisms of the crack initiation and propagation in a textured polycrystalline TiNi shape memory alloy were studied using scanning electron microscope and ex situ electron backscattered diffraction techniques. The results indicated that stress-induced martensitic transformation was triggered and formed a sandwich structure at the front of the crack tip prior to the crack initiation in the polycrystalline TiNi alloy. The crack propagated intragranularly and occasionally across the grain boundaries. The closed packed planes of the B2 parent phase such as {110} and {100} were revealed to favor the crack propagation. The stress-induced B2+B19′ sandwich structure determined the crack propagated by a microscopic sawtooth pattern and therefore a ductile feature in this textured polycrystalline TiNi sheet specimen.