The influences of Ta and Sn on phase constitution and aging behavior of Ti-Ta-Sn system alloys quenched from a temperature within beta single phase region.

Using Ti-Ta binary and Ti-50Ta-Sn ternary system alloys, the influences of Ta and Sn content 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 1173K for 3.6ks and then quenched into ice water (STQ). STQed specimens were isochronally aging up to 1173K in Ti-Ta alloys and 1323K in Ti-50Ta-Sn alloys, respectively. Shape recovery test was also performed by U shaped Ti-50Ta and Ti-50Ta-4Sn alloy specimens. In the solution treated and quenched state, only reflections of hexagonal martensite, (alpha' were obsereved by XRD in Ti-5Ta to 30Ta alloys, whereas only orthorhombic martensite, alpha", was identified by XRD in Ti-40Ta, 50Ta and 50Ta-4Sn alloys. In Ti-50Ta-8Sn alloy, only beta phase identified. In Ti-50Ta and 50Ta-4Sn alloys, reistivity at liquid nitrogen temperature and resistivity ratio increased with isochronal aging up to a certain temperature, because alpha" reversely transformation to metastable beta phase. Shape recovery was confirmed in both alloys.