Investigating the electronic origins of the repulsion between substitutional and interstitial solutes in hcp Ti

TL;DR

This study uses first-principles calculations to reveal the short-range electronic interactions causing repulsion between substitutional and interstitial solutes in hcp titanium, impacting oxygen solubility and alloy design.

Contribution

It identifies a hybridization mechanism and Coulomb interactions responsible for solute repulsion, providing new insights into alloying effects in titanium.

Findings

Hybridization between substitutional elements and oxygen causes repulsion.

Charge accumulation on solutes leads to Coulombic repulsion.

Repulsive interactions are short-ranged, similar to closed-shell atoms.

Abstract

The high solubility of oxygen in Ti, Zr and Hf makes it difficult to stabilize the 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 substitutional alloying additions to titanium repel interstitial oxygen. Here we use first-principles calculations to show that this repulsion is short ranged and identify a variety of factors that are likely responsible for the repulsive interaction. 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. Calculations of Bader charges also 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.