Critical assessment of hydrogen effects on the slip transmission across grain boundaries in {\alpha}-Fe

TL;DR

This study investigates how hydrogen influences dislocation interactions at grain boundaries in alpha-iron, revealing that hydrogen increases slip transmission barriers and may promote intergranular fracture, with effects dependent on grain boundary energy.

Contribution

It provides a systematic simulation-based analysis of hydrogen's impact on dislocation-grain boundary interactions in alpha-iron, highlighting the correlation with grain boundary energy and fracture mode transition.

Findings

Hydrogen increases the energy barrier for slip transmission across grain boundaries.

Lower energy grain boundaries have higher barriers for slip transmission.

Hydrogen presence may lead to a transition from transgranular to intergranular fracture.

Abstract

Grain boundaries (GBs) play a fundamental role in the strengthening mechanism of crystalline structures by acting as an impediment to dislocation motion. However, the presence of an aggressive environment such as hydrogen increases the susceptibility to intergranular fracture. Further, there is a lack of systematic investigations exploring the role of hydrogen on the dislocation-grain-boundary (DGB) interactions. Thus, in this work, the effect of hydrogen on the interactions between a screw dislocation and <111> tilt GBs in {\alpha}-Fe were examined. Our simulations reveal that the outcome of the DGB interaction strongly depends on the underlying GB dislocation network. Further, there exists a strong correlation between the GB energy and the energy barrier for slip transmission. In other words, GBs with lower interfacial energy demonstrate a higher barrier for slip transmission. The introduction of hydrogen along the GB causes the energy barrier for slip transmission to increase consistently for all of the GBs examined. The energy balance for a crack initiation in the presence of hydrogen was examined with the help of our observations and previous findings. It was found that the presence of hydrogen increases the strain energy stored within the GB which could lead to a transgranular-to-intergranular fracture mode transition.