Effect of annealing temperature on microstructure and superelastic properties of a Ti-18Zr-4.5Nb-3Sn-2Mo alloy

In this study a new superelastic Ti-18Zr-4.5Nb-3Sn-2Mo alloy was prepared by adding 2 at% of Mo as a substitute for Nb to the Ti-18Zr-11Nb-3Sn alloy, and heat treatment at different temperatures was conducted. The temperature dependence of superelasticity and annealing texture was investigated. Texture showed a dependence of annealing temperature: the specimen annealed at 923 K for 0.3 Its exhibited {113}(beta) 4 (7) over bar1(beta) type texture which was similar to the deformation texture, while specimens annealed at 973, 1073 K, and 1173 K showed {001}(beta) < 110 > (beta) type recrystallization texture which was preferable for recovery strain. The largest recovery strain of 6.2%, which is the same level as that of the Ti-18Zr-11Nb-3Sn alloy, was obtained in the specimen annealed at 1173 K for 0.3 ks due to the well-developed {001}beta < 110 > (beta) type recrystallization texture. The Ti-18Zr-3Nb-3Sn-2Mo alloy presented a higher tensile strength compared with the Ti-18Zr-11Nb-3Sn alloy when heat treated at 1173 K for 0.3 ks, which was due to the solid solution strengthening effect of Mo. Annealing at 923 K for 0.3 ks was effective in obtaining a good combination of a high strength as 865 MPa and a large recovery strain as 5.6%. The high recovery strain was due to the high stress at which the maximum recovery stain was obtained which was attributed to the small grain size formed at low annealing temperature.