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. Unlabelled Image • A new formation mechanism of interfacial twin boundary (ITB) ω -phase has been revealed in metastable β -Ti alloys. • The formation of ITB ω -phase is experimentally ascribed to the reorientation of ω -variants. • The ω -reorientation mechanism is further rationalized in terms of the encountered energy barrier by first-principles calculation. [ABSTRACT FROM AUTHOR]