Tensile deformation of NiTi wires

We examine the structure and properties of cold drawn Ti-50.1 at %, Ni and Ti-50.9 at % Ni shape memory alloy wires. Wires with both compositions possess a strong < 111 > fiber texture in the wire drawing direction, a grain size on the order of micrometers, and a high dislocation density. The more Ni rich wires contain fine second phase precipitates, while the wires with lower Ni content are relatively free of precipitates. The wire stress-strain response depends strongly on composition through operant deformation mechanism, and cannot be explained based solely on measured differences in the transformation temperatures.