Two-way shape memory effect in a Ti–Zr–Nb–Ta high-temperature shape memory alloy

The two-way shape memory effect in a Ti–18.5Zr–10Nb–3.5Ta high-temperature shape memory alloy was investigated. X-ray diffraction measurement shows that the alloy is composed of orthorhombic α″-martensite. ω phase is not found in Ti–18.5Zr–10Nb–3.5Ta alloy due to the suppressing effect of Ta element. The α″-martensite laths are found in the transmission electron microscope observation; after the bending deformation, there appear a lot of dislocations. The alloy exhibits a shape memory strain of 3.8% and a high reverse martensite transformation start temperature of 464 K. The maximum two-way shape memory strain of 1.2% is obtained in the alloy with the pre-bending training strain of 10%. The mechanism can be ascribed to the effect of internal stress field caused by dislocations.