High-Temperature SMAs for Actuator Applications

Compositions and production processes have been developed for making NiTi-based shape-memory alloys (SMAs) that can be tailored for use as actuator materials at temperatures exceeding those of conventional alloys. Whereas conventional shape-memory alloys are limited to use at temperatures well below 100 °C due to low transformation temperatures, these high-temperature shape-memory alloys (HTSMAs) have transformation temperatures exceeding 300 °C while maintaining many of the other attributes associated with NiTi alloys, most importantly high work output (see Figure 1). Other attractive properties of this family of NiTiPt HTSMAs include usefully high values of tensile ductility, relatively narrow hysteresis, good oxidation resistance up to 600 °C, and excellent thermal and dimensional stability. Just as important, these alloys can be readily processed into various structural forms such as thin rod and fine-diameter wire by conventional processes (see Figure 2). These materials hold promise for expanding the variety of applications in which SMAbased actuators could be used.