Characterization on the Precipitates in the Ti-Ni-Al-Zr Alloy during Heat Treatment

In the present paper, the Ti-15Ni-6Al-2Zr alloy is fabricated and heat treated at different temperatures. Its microstructure and morphology of Ti2Ni phase are investigated by SEM and TEM. The results reveal that the Ti-15Ni-6Al-2Zr alloy is composed of eutectoid and eutectic microstructure, which possesses fine Ti2Ni fiber in eutectoid region and fine α-Ti phase in eutectic region. With the increase of heat treatment temperature, the amount of α-Ti and Ti2Ni phases decrease gradually. When the heat treatment temperature is higher than 900°C, almost no α-Ti phase is left. The transformation temperature of α-Ti phase to β-Ti phase is about 850°C, and the transformation of α-Ti phase promotes the decrease of Ti2Ni phase. During the heat treatment, the Ti2Ni fiber phase experiences the refining, fragmentation, coarsening and granulating.