2013 Volume 54 Issue 4 Pages 484-492
The effects of solute X (Mo, Nb, V and W) on the phase stability of β-Ti alloys were studied from first-principles calculations. The first-principles calculations yielded solution enthalpies for hexagonal close-packed (hcp)-Ti35X1 and hcp-X35Ti1 and body-centered cubic (bcc)-Ti26X1 and bcc-X26Ti1 solid solution alloys. The enthalpy curves for the α (hcp)- and β (bcc)-phases of Ti–X alloys were described as a function of the X concentration by using the calculated solution enthalpies and sub-regular solution model. While the enthalpies of the α-phases increased with increasing concentrations of Mo, Nb, V and W, the enthalpies of the β-phases decreased with increasing concentrations. This is consistent with the experimental results, showing that Mo, Nb, V and W are β-stabilizers. The β-stabilizing strength of solute elements in Ti alloys is gauged using the experimental critical concentration. We found a good linear correlation between the experimental critical concentration and the theoretical metastable equilibrium concentration at which the enthalpy of the α-phase is equal to that of the β-phase. The metastable equilibrium concentration decreased with the increasing lattice stability of the bcc structure with reference to hcp structure.