Recent development of TiNi-based shape memory alloys in Taiwan

TiNi-based alloys are considered to be the most important shape memory alloys (SMAs) because of their salient shape memory effect (SME), pseudoelasticity (PE) and high damping capacity (HDC). Recent investigations focus on their transformation behaviors, thermal-mechanical treatments, manufacturing processes, and industrial applications based on the characteristics of SME, PE and HDC. The two-stage martensitic transformations of B2↔R-phase↔B19′ and B2↔B19↔B19′ have been clarified for both TiNi binary and ternary alloys. The deformation behaviors have been investigated by cold-rolling, hot-rolling and wire drawing. Both SME and PE can be improved by thermal-mechanical treatments, and the damping characteristics of TiNi and TiNiX SMAs have been systematically studied. Both B19′/B19 martensite and R-phase have high damping capacities due to the easy stress-induced movement of twin boundaries. The high temperature SMAs, Ti–Ni–X with X=Au, Pd and Zr alloys, have also been intensively studied. The ion nitriding technique has been used to improve the wear and corrosion resistance of TiNi and TiNiX SMAs. TiNi thin films have been successfully fabricated using the sputter-deposition technique. These investigations on the TiNi-based SMAs have attracted much attention and their important characteristics will be applied widely in the near future.