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Due to a series of exceptional properties, titanium and titanium alloys have received extensive attention in recent years. Different from other alloy systems, there are two allotropes and a sequence of metastable phases in titanium alloys. By summarizing the recent investigations, the phase transformation processes corresponding to the common phases and also some less reported phases are reviewed. For the phase transformation only involving α and β phases, it can be divided into β → α transformation and a reverse transformation. The former one has been demonstrated from the orientation relationship between α and β phases and the regulation of α morphology. For the latter transformation, the role of the stress has been discussed. In terms of the metastable phases, the mechanisms of phase formation and their effects on microstructure and mechanical properties have been discussed. Finally, some suggestions about the development of titanium alloys have been proposed.
Liu et al. (Tue,) studied this question.