Using NiTi20Hf As A High-Temperature Shape Memory Alloy – Review Of Physical Properties

NiTi20Hf is one of several ternary shape memory alloys with elevated transformation temperatures. One motivation of their development is a demand for actuators unaffected by ambient conditions, practically meaning that A_s temperature should be above 70°C. Although several high-temperature ternary alloys were investigated in the last two decades, currently NiTi20Hf provides the best combination of mechanical properties and price.

However, designing an SMA-based actuator cannot rely on transformation temperature and yield strength only. It must take into consideration various physical properties such as density, latent heat, specific heat and thermal conductivity, as well as electrical conductivity (for actuators heated by current). These properties, measured in samples of NiTi20Hf rod and sheet, will be presented in comparison to the binary NiTi alloy. Possible limitations due to the physical properties will be discussed.