2002 Volume 43 Issue 12 Pages 2984-2990
Using Ti–Ta alloy to which Ta was added systematically, i.e. Ti–5 mass%Ta, 10 mass%Ta, 20 mass%Ta, 30 mass%Ta, 40 mass%Ta and 50 mass%Ta alloys, the effect of Ta concentration on phase constitution in the solution treated and quenched state and aging behavior is 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 heat treated from 323 to 1173 K . STQed specimens of Ti–50 mass%Ta alloy were isothermally aging at five different temperatures, 573 K, 623 K, 673 K, 723 K and 773 K. In the solution treated and quenched state, only reflections of hexagonal martensite, α′ were obserevd by XRD in Ti–5Ta to 30Ta alloys, whereas only orthorhombic martensite, α′′, was identified by XRD in Ti–40Ta and 50Ta alloys. α′′ in Ti–50Ta alloy is reversely transformed into β upon isochronal heat treatment: the starting temperature is situated at a temperature between 623 K and 673 K . Isothermal aging of this alloy shows that α′′ directly decomposes to α and β phases without reverse transformation of α′′ at 573 K and 623 K aging. On isothermal aging above 673 K, α′′ reversely transforms into β and then isothermal ω phase precipitates in the reversed β.
