Effects of Sn and Zr additions on phase constitution and aging behavior of Ti-50mass% Ta alloys quenched from β single phase region

Abstract

Using Ti-50Ta, Ti-50Ta-Sn and Ti-50Ta-Zr alloys, the effects of Sn and Zr additions on phase constitution in the solution treated and quenched state and aging behavior were studied by electrical resistivity and Vickers hardness measurements and X-ray diffactometry. All alloys were solution treated at 1173 K for 3.6 ks and then quenched into ice water (STQ). STQed specimens were isochronally aged at temperatures up to 1323 K in Ti-50Ta-Sn alloys and 1173 K in Ti-50Ta-Zr alloys. Shape recovery test was also performed in bent Ti-50Ta, Ti-50Ta-Sn and Ti-50Ta-Zr alloy specimens. In the STQed state, only reflections of orthorhombic α″ martensite were observed by XRD in Ti-50Ta and Ti-50Ta-4Sn alloys. In STQed Ti-50Ta-10Zr alloy, coexistence of α″ and β (bcc) phases were found by XRD. In STQed Ti-50Ta-8Sn and Ti-50Ta-20Zr alloys, only β phase was identified. In Ti-50Ta, Ti-50Ta-4Sn and Ti-50Ta-10Zr alloys, resistivity at liquid nitrogen temperature and resistivity ratio increased with isochronal aging up to a certain temperature. It is considered that these increases are due to reverse-transformation of α″ into metastable β phase. Shape-recovery test confirmed the shape memory effect of Ti-50Ta, 50Ta-4Sn and 50Ta-10Zr alloys.