Effect of W Addition on the Martensitic Transformation and Shape Memory Behaviour of the TiNi-Base Alloys

Department of Mechanical and System Engineering, Ryukoku University, Seta, Ohecho, Otsu City 520-21, Japan

Abstract

The effect of W addition on the martensitic transformation (MT) and SM effect, especially reversible shape memory(two way shape memory) effect of the TiNi base alloys was investigated. It was found that addition of W in the TiNi and TiNi-Cu SM alloys does not affect essentially MT itself. Transformation temperatures slightly decrease with increasing W content (3 to 5K/at%W) and transformation hysteresis does not widen. By measuring change in bending strain above and below Af and Ms of the specimen of W added alloys showed that quite clear RSM effect is obtained even in the specimen slightly deformed by simple bending with bending strain 0.05 below Ms. It was found that W is less soluble in the TiNi matrix and makes fine particles with the size around 20 microns by EPMA analysis. It is expected that fine and hard W precipitates would make the origin of strain field for MT during the 2nd and further heating and cooling cycle. It is thus quite hopeful to develope TiNi alloys with good RSM effect by using these W added alloys.