New insights into formation mechanism of interfacial twin boundary ω-phase in metastable β-Ti alloys

The ω-phase transformation in metastable β-titanium (Ti) alloys has attracted great attention in the past decade due to its intrinsic complexity and modifying mechanical properties. Interfacial twin boundary (ITB) ω-phase was reported to appear along {332}_β or {112}_β twin boundaries in metastable β-Ti alloys. The formation of such ITB ω-phase was proposed to arise from the reverse α″ to β martensitic transformation and subsequent stress relaxation along the twin boundaries. In this study, a new formation mechanism is revealed in Ti-10wt.%Cr alloy containing ω-precipitates in the initial microstructure. It is experimentally found that the formation of ITB ω-phase is closely correlated with the favored pre-existing one ω-variant at the expense of the other three-siblings, i.e., reorientation of ω-variants. The ω-reorientation mechanism is further rationalized by first-principles calculation in terms of the energy barrier of transformation pathway between ω-variants. These findings advance our fundamental understanding to the ω-phase transformation and further plastic deformation behavior of Ti alloys.