Coupling effect of undercooling and cooling on Ti–Al–V alloy solidification

Rapid solidification is one of the most significant studies for titanium alloys. In this paper, we investigated the rapid solidification of Ti–Al–V alloy micro-droplets by a drop tube. The generally ignored coupling effect of undercooling and cooling on the solidification was explored, which associated with inherent solute contents. According to the results of thermal analysis, as well as the calculation of undercooling and cooling rate, a valid model was proposed to discuss the β → α phase transition. It suggested that the microstructures of supersaturated Ti–Al–V alloys hardly preserved primary β phase in the rapid solidification. Moreover, the formation energy calculated from first principle complementally indicated that excess addition of vanadium was against to the stability of β phase. Accordingly, the rapid solidification paths and microstructure evolutions were summarized, which was explained by the calculation results. The final microstructures were all composed of α phase with various grain configurations, including lamellar and dendritic crystals, evolving with the decrease of droplet diameter. The excess solutes changed the way of dendrite growth from the regular dendrite to worm-like dendrite. Note that the competitive nucleation behavior between β phase and α phase was clarified in the rapid solidification. In addition, the mechanical properties of master alloys and solidified droplets were also studied.