A STUDY ON THE WIRE DRAWING OF TINI SHAPE-MEMORY ALLOYS

Drawn wires of TiNi shape memory alloys (SMAs) have been studied syste matically using DSC, microhardness, SEM and tensile tests. Severe work hardening during the drawing process is observed and hence interannea ling is necessary. Multi-pass drawing around the Ms temperature is rec ommended. The defects induced by cold drawing depress martensitic tran sformation but promote the R-phase transformation. Defect recovery and recrystallization during interannealing are responsible for the decre ase 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, howe ver, thick oxide films tend to exhibit cracks and spalling which decre ase the drawing surface quality, shape memory effect and pseudoelastic ity of TiNi SMAs. MoS2 is shown to be an effective lubricant for the w ire drawing of TiNi SMAs.