Influence of forging deformation and heat treatment on microstructure of Ti–xNb–3Zr–2Ta alloys

Ti–xNb–3Zr–2Ta alloys (x = 33, 31, 29, 27, 25) (wt.%) were fabricated by vacuum non-consumable arc melting and hot forging. The hot-forging specimens were solid solution treated at 1053 K for 1.8 ks followed by water quenching (WQ) and air cooling (AC) respectively. The microstructure of hot-forging specimens with different deformation rate and solid solution treated at different temperatures was investigated. The result showed that a large amount of α" martensite appeared in the WQ group while only a little amount of α" phase could be found in the AC group. Moreover, for the WQ group, less niobium resulted in more diffraction peaks of α" phase in XRD profiles. This result suggested that the stability of β phase decreased with the decrease of Nb content. The microhardness of Ti–xNb–3Zr–2Ta (wt.%) alloys was improved significantly with the decreasing Nb content in both WQ group and AC group. Increasing deformation ratio could effectively refine β grains for Ti–25N–3Zr–2Ta (wt.%). Both acicular martensite and lath martensite were found in the transmission electron microscope observation of Ti–25Nb–3Zr–2Ta (wt.%) alloy. Martensitic internal twins were identified as well.