Hydrogen Induced Dislocation Core Reconstruction in Bcc Metals

Abstract

Dislocation, playing a crucial role in the plastic deformation of metals, can be significantly affected by introducing solute elements. Hydrogen (H) embrittlement is one such example, while the underlying mechanism for H affected dislocation structural stability and mobility remains unclear and the role of H has been controversial. Here, using first-principles calculations, we demonstrate that the effect of H on screw dislocation in bcc metals is H concentration-dependent, signified by a H-induced transition of SD core structure. At low concentrations of H segregation, dislocation maintains the intrinsic easy-core structure, and H atoms are attached to the "periphery" of dislocation to enhance dislocation motion. In contrast, at high H concentrations, dislocation transforms into a hard-core, metal hydride-like structure, as H atoms become the "body" of dislocation to significantly reduce the dislocation mobility. Further, such local easy-to-hard transition is found to be induced by just one solute of other elements, including helium, carbon, nitrogen and oxygen, independent of solute concentration. Our work sheds new light on the H-dislocation interactions in bcc metals, having broad implications in the interstitial solute-related phenomena.

Keywords: screw dislocation, core structure, dislocation motion, hydrogen and interstitial solutes, bcc metals