Phase Transformation and Shape Memory Effect of Ti–Pd–Pt–Zr High-Temperature Shape Memory Alloys

To understand the potential of high-temperature shape memory alloys, we have investigated the phase transformation and shape memory effect of Ti–(50 − x)Pt–xPd–5Zr alloys (x = 0, 5, and 15 at.%), which present the B2 structure in the austenite phase and B19 structure in the martensite phase. Their phase transformation temperatures are very high; A_f and M_f of Ti–50Pt are 1066 and 1012 °C, respectively. By adding Zr and Pd, the phase transition temperatures decrease, ranging between 804 and 994 °C for A_f and 590 and 865 °C for M_f. Even at the high phase transformation temperature, a maximum recovery ratio of 70% was obtained for one cycle in a thermal cyclic test. A work output of 1.2 J/cm³ was also obtained. The recovery ratio obtained by the thermal cyclic test was less than 70% because the recovery strain was < 1% and a large irrecoverable strain was obtained. The shape recovery was explained by the austenite strength. The training effect was also investigated.