A study on the wire drawing of TiNi shape memory alloys

Drawn wires of TiNi shape memory alloys (SMAs) have been studied systematically using DSC, microhardness, SEM and tensile tests. Severe work hardening during the drawing process is observed and hence interannealing is necessary. Multi-pass drawing around the Ms temperature is recommended. The defects induced by cold drawing depress martensitic transformation but promote the R-phase transformation. Defect recovery and recrystallization during interannealing are responsible for the decrease of drawing stress. At the same time, surface oxide film thickness is another important factor related to drawing stress. A thin surface oxide film can be used as a lubricant during the drawing process, however, thick oxide films tend to exhibit cracks and spalling which decrease the drawing surface quality, shape memory effect and pseudoelasticity of TiNi SMAs. MoS2 is shown to be an effective lubricant for the wire drawing of TiNi SMAs.