Processing and Functional Stability of Ti-Ta High Temperature Shape Memory AlloysThursday (29.09.2016) 11:45 - 12:00 Part of:
Due to their high martensite start temperature and excellent workability, Ti-Ta shape memory alloys (SMAs) are very attractive for applications as high temperature SMAs. We provide results on processing and functional stability of Ti-Ta SMAs. We show how Ti-Ta alloys can be produced through arc melting and subsequent thermal and thermomechanical treatments. Most importantly, sufficient mixing of Ti and Ta during melting and decomposition during solidification are important factors that affect the quality of ingots. After melting, it is necessary to anneal Ti-Ta to remove Ta concentration gradients. The functional stability of Ti-Ta was evaluated through thermal cycling using differential scanning calorimetry (DSC). It was found that binary Ti-Ta only exhibits a relatively poor stability due to the formation of omega phase at relatively low temperatures. Therefore, slow heating/cooling rates, as well as holding steps at elevated temperatures during thermal cycling strongly affect cyclic stability, as they allow for omega phase nucleation. In the present work we present time temperature transformation diagrams for Ti-30Ta and Ti-30Ta-3Al. We show that Al alloy additions slow down the kinetics of omega phase precipitation and thus provide a more stable transformation behavior.