Quantitative tests revealing hydrogen-enhanced dislocation motion in α-iron

LC Huang and DK Chen and DG Xie and SZ Li and Y Zhang and T Zhu and D Raabe and E Ma and J Li and ZW Shan, NATURE MATERIALS, 22, 710-+ (2023).

DOI: 10.1038/s41563-023-01537-w

Hydrogen embrittlement jeopardizes the use of high-strength steels in critical load-bearing applications. However, uncertainty regarding how hydrogen affects dislocation motion, owing to the lack of quantitative experimental evidence, hinders our understanding of hydrogen embrittlement. Here, by studying the well-controlled, cyclic, bow-out motions of individual screw dislocations in alpha-iron, we find that the critical stress for initiating dislocation motion in a 2 Pa electron- beam-excited H-2 atmosphere is 27-43% lower than that in a vacuum environment, proving that hydrogen enhances screw dislocation motion. Moreover, we find that aside from vacuum degassing, cyclic loading and unloading facilitates the de-trapping of hydrogen, allowing the dislocation to regain its hydrogen-free behaviour. These findings at the individual dislocation level can inform hydrogen embrittlement modelling and guide the design of hydrogen-resistant steels. Screw dislocations in alpha-iron move more easily in the presence of hydrogen, as evidenced by real-time imaging using quantitative transmission electron microscopy.

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