Modeling the improved hydrogen embrittlement tolerance of twin boundaries in face-centered cubic complex concentrated alloys

AMZ Tan and Z Li and YK Zhao and U Ramamurty and HG Ba, JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, 188, 105657 (2024).

DOI: 10.1016/j.jmps.2024.105657

With increasing interest in hydrogen as an alternative fuel, there is a need to develop structural alloys with improved resistance to hydrogen embrittlement (HE) for application in the new hydrogen economy. Complex concentrated alloys (CCAs), which include high entropy alloys and their derivatives, medium entropy alloys, are a new class of structural materials, some of which have reported improved HE resistance. While some studies have suggested that the improved HE resistance in CCAs with the face -centered cubic (fcc) crystal structure may be due to the high density of nanotwins within them, a detailed mechanistic understanding is yet to be developed. Towards that end, following the approach of Zhou, Tehranchi and Curtin, we employ a density functional theory -informed Griffith-Rice model 2 to predict the ductile or brittle response of a crack tip interacting with twin boundaries (TBs) in a model fcc CCA, CrCoNi, both in the absence of and presence of hydrogen. Both the model and molecular dynamics simulations predict that TBs in fcc alloys are not inherently more susceptible to HE than the bulk matrix, and could in fact improve HE resistance by retarding cracks while promoting dislocation emission along the TB. Thus, designing fcc CCAs with a high density of nanotwins or utilizing gradient nanotwinned structures could be a way forward for realizing alloys with high HE resistance.

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