Atomic mechanism and prediction of hydrogen embrittlement in iron

J Song and WA Curtin, NATURE MATERIALS, 12, 145-151 (2013).

DOI: 10.1038/NMAT3479

Hydrogen embrittlement in metals has posed a serious obstacle to designing strong and reliable structural materials for many decades, and predictive physical mechanisms still do not exist. Here, a new H embrittlement mechanism operating at the atomic scale in alpha-iron is demonstrated. Direct molecular dynamics simulations reveal a ductile-to- brittle transition caused by the suppression of dislocation emission at the crack tip due to aggregation of H, which then permits brittle- cleavage failure followed by slow crack growth. The atomistic embrittlement mechanism is then connected to material states and loading conditions through a kinetic model for H delivery to the crack-tip region. Parameter-free predictions of embrittlement thresholds in Fe- based steels over a range of H concentrations, mechanical loading rates and H diffusion rates are found to be in excellent agreement with experiments. This work provides a mechanistic, predictive framework for interpreting experiments, designing structural components and guiding the design of embrittlement-resistant materials.

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