Clear evidence for element partitioning effects in a Ti-6Al-4V alloy by the first-principles phase field method.

Ti-6 wt% Al-4 wt% V (Ti64) is an alpha + beta titanium alloy, in which the alloying components strongly affect the mechanical properties. In this report, element partitioning effects in Ti64 are investigated by using the first-principles phase field (FPPF) method, which has recently been proposed by our group. In the FPPF method, the local free energy is calculated using a cluster expansion method in combination with density functional theory and the temperature effect is incorporated using potential renormalization theory. We have succeeded in identifying enrichment of Al (V) in the alpha (beta) phase, i.e., the clear evidence for the element partitioning effects of Al and V, without using any thermodynamical parameter. The transformation of the beta phase and the alpha phase in microstructure is investigated by varying the V and Al concentrations by a small amount. Our results are in excellent agreement with the recent experimental results, showing the validity of the FPPF method for ternary alloys.