Effect of Quenching and Reheating on Isothermal Phase Transformation in Ti-15Nb-10Zr Alloy

Isothermal phase transformation in Ti-15Nb-10Zr (at%) alloys has been examined by mainly means of transmission electron microscopy. Specimens solution-treated at 1000 degrees C in beta phase field were directly held at temperatures between 350 and 450 degrees C for 1 8-86.4ks, which are called "DH (direct holding)-specimen". On the other hand, some specimens solution-treated at 1000 degrees C were quenched into iced brine and then aged at temperatures between 350 and 450 C, which are called "QA(quench arid aging)-specimen" In the DH-specimen held at 400 degrees C a phase formed in beta matrix. Microstructure evolution of OA-specimen aged at 400 degrees C, on the other hand, is as follows. omega phase formed in beta matrix after aging for 1.8ks and further aging led to growth of w phase. After prolonged aging, alpha phase started to form in beta matrix. These experimental results indicate that process of the quenching and reheating promotes the formation of omega phase. Specimen quenched into iced brine after solution treatment exhibited alpha" phase formation. The alpha '' phase in the quenched specimen would transform into beta phase during reheating to the aging temperature. Reversion process of a" ---> 13 phase could promote the formation of omega phase in beta. Microstructure formation in the DH- and OA-specimens at 350 and 450 degrees C will also be explained