Microstructure evolution of Ti-30Nb-(4Sn) alloys during classical and step-quench aging heat treatments

摘要

Recent studies involving step-quench (SQ) heat treatments have shown that, unlike classical quench-and-aging (QA) heat treatments, SQ route can favour precipitation mechanisms that are strongly dependent on decomposition of the parent beta-phase. In this work, Ti-30Nb and Ti30Nb- 4Sn (wt-%) alloys were subjected to cold-working, recrystallisation and then to either classical or SQ heat treatments at 400 degrees C. Among QA samples,omega-phase is formed in both alloys during the heating ramp. By the SQ route, we found extensive isothermal omega-phase precipitation in Ti-30Nb during aging. On the other hand, a complete suppression of omega-phase in Ti-30Nb4Sn was observed, thus, alpha-phase precipitation could take place improving hardness while still preserving a low elastic modulus.