Relative strength of β phase stabilization by transition metals in titanium alloys: The Mo equivalent from a first principles study

During the past decades, the use of Mo equivalent calculation has become a common method on titanium alloy designing due to the convenient and relatively accurate prediction of alloy phase composition as well as some mechanical properties. However, due to experimental limitation and difficulties, the current Mo equivalent empirical equation only includes a few transition elements with limited explanation for their effects on phase stability. In order to further study the role of all transition metals in stabilizing the titanium β phase and uncover the underlying mechanism, the relative strength of β phase stabilization by transition metals were calculated via the density functional theory in this study. The strength of β phase stabilizers was quantified based on the energy difference between the transition metal doped β phase titanium and ω phase titanium, which providing an excellent explanation for the classical Mo equivalent empirical equation obtained from the experimental measurement. The study found that d6 transition metal, such as Fe, have the strongest effect on β phase stabilization and the results provide a solid guideline for developing of new titanium alloys in the future.