Control of R-Phase Transformation Temperature in a Ti-50.8 at.Ni Shape Memory Alloy

摘要

It is well known that the thermoelastic R-phase transformation in NiTi shape memory alloys (SMA) can also show shape memory effect (SME) and superelasticity (SE) [1]. The transformation strain associated with B2<->R transformation is relatively small (< 1%), but it shows a narrow hysteresis and high fatigue resistance [2,3]- Based on these attractive features, the B2<->R transformation is promising for engineering applications. The R-phase transformation can be induced by various thermomechanical treatment [4], e.g., post-deformation annealing treatment, ageing after solution treatment, thermal cycling. The mechanism of R-phase transformation has been well established [4].' However, there has been little discussion on how to control the R-phase transformation temperatures. Although some researchers reported the evolution of R-phase transformation with respect to aging time [5] and aging temperatures [6], the intrinsic multi-stage martensitic transformation in their study may limit the practical applications.