Modulating dislocation reactions through preferential hydrogen segregation in bcc metals

TL;DR

This study uses atomistic simulations to reveal how hydrogen segregation influences dislocation reactions in bcc metals, leading to stable <001> dislocation formations that contribute to structural damage during deformation.

Contribution

It uncovers a novel hydrogen-facilitated dislocation reaction mechanism and the formation of vacancy-type dislocation loops in bcc metals, advancing understanding of hydrogen-induced damage.

Findings

Hydrogen enables <111>/2 screw dislocations to form <001> edge dislocation junctions.

Hydrogen segregation stabilizes <001> dislocations and promotes vacancy loop formation.

Dislocation loops serve as precursors for structural damage like cracking.

Abstract

The interaction between dislocations is fundamental to plastic deformation, work hardening, and defect accumulation. While extensive research has focused on the impact of solutes on individual dislocations, how solutes affect dislocation-dislocation reactions remains largely unexplored. Here, using atomistic simulations of iron as a model bcc system, we demonstrate that hydrogen solutes enable two <111>/2 screw dislocations to react and form a <001> edge dislocation junction, a process that is otherwise unfavorable in hydrogen-free environments. This phenomenon arises from the preferential segregation of hydrogen around the <001> dislocation, which reduces the energy of the reaction product. The resulting <001> dislocation demonstrates remarkable stability and transforms into a <001> vacancy-type dislocation loop under strain. These vacancy-type dislocation loops can accumulate during continuous deformation and dislocation reactions, serving as precursors for the initiation of structural damage, such as cracking and blistering. Our findings highlight the pivotal role of hydrogen in dislocation reactions, uncover a novel defect accumulation mechanism crucial for interpreting recent experimental observations, and represent a significant advance in understanding hydrogen-induced damage in bcc metals.