Antagonist softening and hardening effects of hydrogen investigated using nanoindentation on cyclically pre-strained nickel single crystal

Since hydrogen-plasticity interaction is a key feature in the study of hydrogen embrittlement, series nanoindentation tests were carried out to evaluate possible impact on dislocation structures formed during cyclic pre-straining nickel single crystal. Ex-situ and in-situ electrochemical performed cyclically pre-strained crystal nickel-hydrogen systems characterise change reduced modulus hardness. Although was less affected by conditions explored, hardness highlights competition between hardening softening processes associated with hydrogen. When pre-charged before tests, microstructures softer than those induced hydrogen-free metals. In contrast, when performed, ingress strained microstructure. This effect due pinning solute dislocations. The these discussed terms vacancy concentrations.