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Hydrogen can significantly influence the plastic deformation behaviour of high entropy alloys (HEAs) by altering the dominant deformation mechanisms. In this work, the tensile deformation of a face-centred cubic (FCC) Al0.35CoCrFeNi alloy was investigated using acoustic emission (AE) analysis before and after hydrogen charging, with a focus on statistical evaluation of deformation mechanisms. The mechanical response shows only minor changes after hydrogen charging, with a slight increase in yield strength (Rp0.2 from 214 ± 2 MPa to 228 ± 3 MPa) and ultimate tensile strength (Rm from 576 ± 3 MPa to 587 ± 5 MPa), while ductility remains nearly unchanged (elongation ~65%). Despite these small differences, the AE response reveals a pronounced transition in deformation behaviour. Hydrogen charging under tensile loading leads to a significant increase in AE activity and promotes a transition from twinning-dominated to dislocation-controlled plasticity. This transition is accompanied by a higher occurrence of high-energy AE events, indicating more intense and localized deformation processes. Statistical analysis confirms that these changes are highly significant and that hydrogen markedly increases the likelihood of dislocation-related AE events. The observed behaviour is consistent with Hydrogen Enhanced Localized Plasticity (HELP), suggesting that hydrogen under tensile loading enhances localized dislocation movement while suppressing competing mechanisms such as twinning. These results demonstrate that acoustic emission combined with statistical analysis provides a sensitive and reliable tool for identifying hydrogen-induced changes in deformation mechanisms, even when conventional mechanical properties remain largely unaffected.
Keywords: high entropy alloy, acoustic emission technique, tensile deformation, statistical analysis, Hydrogen Enhanced Localized Plasticity.© This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.