Interactions between Oxygen Interstitial and <a>-Type Screw Dislocations in alpha-Titanium

TL;DR

This study uses density-functional-theory calculations to analyze how oxygen interstitials interact with <a>-type screw dislocations in alpha-titanium, revealing short-range, directional repulsive interactions that influence dislocation behavior and material strengthening.

Contribution

It provides detailed insights into the atomic-scale interactions between oxygen interstitials and screw dislocations in alpha-titanium, highlighting the short-range, directional repulsive forces and their impact on dislocation dynamics.

Findings

Oxygen interstitials exhibit large repulsive interactions with dislocation cores.

Interaction is short-ranged (~5 Å) and mainly on the prismatic plane.

Repulsive interactions can cause oxygen atoms to shift to new interstitial sites.

Abstract

We employ density-functional-theory calculations to analyze the interactions between oxygen interstitial atoms and <a>-type screw dislocations (<a> = a<11-20>/3 ) in alpha-titanium, based on investigations of generalized stacking fault (GSF) energies, dislocation core structures and the strain field of an oxygen interstitial. Compared with the substitutional atoms such as Al, there is a large repulsive interaction between oxygen interstitials at the octahedral site and an <a>-type screw dislocation core, since the volume for the interstitial atom between Ti lattice sites is largely reduced in the core. Differential displacement maps and distributions of interstitial volume surrounding the dislocation core show that the interaction with an oxygen interstitial is very short ranged (~ 5 Angstrom) and directional, mainly located on the prismatic plane where the majority of lattice displacements in the <a> screw dislocation core occurs. At long distances the interactions mediated by the strain from the interstitial oxygen and the dislocation vanish. We show that the large repulsive interaction at short range can push an oxygen atom from its original interstitial site to a new interstitial site on the basal plane in the dislocation core. The strong repulsive interaction and the mechanical shuffle of oxygen interstitials can be expected to have a large impact on dislocation dynamics, and can be used to explain the strong strengthening effects of oxygen impurities in alpha-titanium observed experimentally.