Microstructural features of TA15 titanium alloy under different temperature routes in isothermal local loading forming

In this paper, an analogue isothermal local loading experiment was carried out to study the microstructure of TA15 titanium alloy in different temperature routes. The experimental results show that four different types of microstructure are obtained in various temperature routes: Widmanstätten microstructure consisting of α plates in coarsen β grains and continuous grain boundary α layer is produced by β forging in each loading step; bi-modal microstructure composed of equiaxed primary α and β transformed matrix with α plates and residual β phase is obtained by deformation at the same temperature in two-phase region in each loading step; basket-weave microstructure consisting of lamellar α and β transformed matrix can be achieved by β forging in the first loading step followed by near-β forging in the second loading step; tri-modal microstructure with equiaxed primary α, lamellar α and β transformed matrix can be got through near-β forging in the first loading step combined with conventional forging in the second loading step. For a certain microstructure above, the contents of each constituent phase (equiaxed primary α, lamellar α or β transformed matrix) are all close for different loading regions. The lamellar α in basket-weave and tri-modal microstructure present varied morphology and distribution in different loading regions due to various deformation paths.