Investigating The Electronic Origins Of The Repulsion Between Substitutional And Interstitial Solutes In Hcp Ti

The high solubility of oxygen in Ti, Zr, and Hf makes it difficult to stabilize protective oxide scales on their surfaces as the subsurface regions can serve as boundless sinks that continuously dissolve oxygen. Alloying elements are crucial to reduce the oxygen solubility and diffusivity within early transition metals. Past studies have shown that most substitutional alloying additions to titanium repel interstitial oxygen. Here we use firstprinciples calculations to show that this repulsion is short ranged and explore several factors that are likely responsible for the repulsive interaction. Calculations of Bader charges suggest the existence of short-range Coulomb interactions due to the accumulation of charge on the substitutional solute and interstitial oxygen that is drawn from the Ti host. Misfit strains due to differences in the atomic radii of the solutes and Ti are also found to play a role. We identify a unique hybridization phenomenon between dissolved substitutional elements and interstitial oxygen within hcp Ti that leads to a repulsive interaction at short distances, similar to that between closed-shell atoms, which is especially pronounced for Al and Si solutes.