Effect of β-stabilizer elements on stacking faults energies and ductility of α-titanium using first-principles calculations

The effect of W, Mo, V, Ta, and Nb, five common beta-stabilizing substitutional elements, on alpha-Ti stacking fault energy has been studied using first principle calculations. The generalized stacking fault energy (GSFE) curves have been determined for different concentrations of beta-stabilizers at the fault plane using supercells with up to 360 atoms. Both basal and prismatic slip systems with the stable (gamma(SF)) and unstable (gamma(USF)) stacking faults and twinning fault energies were determined. All the alloying elements reduce the stacking fault energy for Ti for both basal and prismatic slip. At higher concentration of 25 at.% of V, Ta, and Nb at the slip plane, the basal slip becomes more favorable than the prismatic slip in Ti. Ti-Mo and Ti-W systems also show a significant shift in the GSFE curve towards a higher shear deformation strain along < 01 (1) over bar0 > due to the change in bond character between Ti and those two elements. Using Rice criterion, which employs gamma(S)/gamma(USF) ratio to estimate ductility, we show that all the alloying elements likely improve the ductility of alpha-Ti with Ti-25 at.% Nb exhibiting the most ductile behavior. However, according to the Tadmor and Bernstein model, all the alloying elements considered here do not improve the partial dislocation emission or the twinning propensity in spite of decreasing the stacking fault energies for alpha-Ti and. Hence, a better empirical model that incorporates changes in the character of directional bonding upon alloying is needed to estimate how alloying influences ductility in hcp metals. Published by AIP Publishing.