Effect of Zr Addition on Phase Constitution and Heat Treatment Behavior of Ti-25mass%Nb Alloys
In an attempt to optimize the shape recovery temperature, the effect of Zr addition on phase constitution and heat treatment behavior is investigated by electrical resistivity and Vickers hardness (HV) measurements, X-ray diffractometry (XRD) and shape recovery tests. Ti-25mass%Nb-0, 2, 7 and 12mass%Zr alloys (abbreviated as 0Zr, 2Zr, 7Zr and 12Zr, respectively) were prepared using an arc-furnace. Specimens were solution-treated at 1273 K for 3.6 ks and then quenched by iced water (STQ). STQed specimens were isochronally heat-treated. In 0Zr and 2Zr, only the orthorhombic martensite phase a” was identified by XRD, while the two-phase alloys a” and b were identified in 7Zr and 12Zr. In 7Zr, resistivity at liquid nitrogen and room temperature (rLN and rRT, respectively) and resistivity ratio (rLN/rRT) drastically increased at 523 K because of the reverse-transformation of a” into b phase. Thereafter, resistivity and resistivity ratio decreased with increasing heat treatment temperature due to isothermal w precipitation. Starting temperature of shape recovery is 623 K in 7Zr and 523 K in 12Zr. In 7Zr, shape recovery ratio is about 80% at 723 K, which is the maximum obtained in this study.
Z.Y. Zhong, H. Saka, T.H. Kim, E.A. Holm, Y.F. Han and X.S. Xie
M. Ikeda et al., "Effect of Zr Addition on Phase Constitution and Heat Treatment Behavior of Ti-25mass%Nb Alloys", Materials Science Forum, Vols. 475-479, pp. 2337-2342, 2005