Kink-Helium Interactions in Tungsten: Opposing Effects of Assisted Nucleation and Hindered Migration

TL;DR

This study investigates how helium atoms influence dislocation behavior in tungsten, revealing that helium stabilizes kinks and reduces nucleation energy but also impedes kink migration, with implications for material plasticity.

Contribution

It provides a detailed atomic-scale analysis of helium-dislocation interactions in tungsten, highlighting opposing effects on nucleation and migration of dislocation kinks.

Findings

Helium binding significantly lowers kink nucleation energy.

Helium stabilizes kinks, facilitating nucleation.

Helium presence hinders kink migration at higher concentrations.

Abstract

Point defects such as interstitial atoms are known to be attracted to screw dislocations. Understanding these interaction mechanisms is key to predicting the plasticity of real materials. Using a potential derived from ab initio calculations of helium in tungsten, we find that the binding of a helium atom to dislocation kinks is significantly more favorable than to a straight dislocation. This preference directly translates to a reduction in the kink pair nucleation energy, provided that the mechanism proceeds through a helium-stabilised kink. It is lowered from 1.64 eV (in the pure metal) to 0.51 eV when helium binds to the right kink. However, binding also has a competing effect whereby the kinks are unable to migrate. This hindering aspect becomes more relevant as the helium concentration increases.