β to ω transformation strain associated with the precipitation of α phase in a metastable β titanium alloy

It is well known that ω phase has a significant influence on the precipitation of α phase in metastable β titanium alloys. However, the assistance of the transformation strain induced by the formation of ω phase to the nucleation of α phase has not well been addressed. In this work, the precipitation of α phase with the assistance of the β → ω transformation was investigated in terms of the crystallographic orientation relationships and the accommodation of the transformation strains. The analyses of transformation strains indicate that α phase originates from the β phase, but not from the ω phase due to the large strain of the ω → α transformation. This corresponds to the experimental TEM/HRTEM observations in which α phase nucleates nearby the ω/β interfaces and are separated with ω phase by the distorted β matrix. The lattice distortion of β matrix induced by the β → ω transformation can be well accommodated by the precipitation of α phase, and the vicinities of ω/β interfaces are the favorable nucleation sites for α phase. This work provides new information on the ω-assisted nucleation of α phase in metastable β titanium alloys.