Microstructures of Ti–Ni–Fe wire after severe cold-drawing and annealing

The microstructures and mechanical properties of Ti–47 at% Ni–3 at% Fe shape memory alloy wire under the condition of severe cold-drawing at room temperature and different postdeformation annealing processes were intensively investigated using transmission electron microscope (TEM), X-ray diffraction (XRD), Vickers microhardness tester and electron tensile tester. It is indicated that the structure of the alloy evolves into a predominant amorphous structure with a trace of nanocrystalline B2 phase after the cold-drawing of 76 % areal reduction. Postdeformation annealing process exerted significant influence on the microstructure and mechanical properties. Crystallization occurs when the cold-drawn wire was annealed at 300 °C for 30 min. The ultimate tensile strength and ductility as well as the superelasticity of the wire are improved significantly by cold-drawing plus postdeformation annealing.