Grain Refinement Effect on Resistance to Hydrogen-assisted Crack Growth in Equiatomic CoCrFeNi High-entropy Alloy with Different H Charging Conditions

抄録

The hydrogen embrittlement (HE) resistance of a fine-grained equiatomic CoCrFeNi high-entropy alloy (HEA) is investigated via tensile testing under electrochemical H charging. The HE behavior is compared with that of HEA specimens charged with 100 MPa of H gas. The fine-grained HEA shows > 40% elongation with a tensile strength of ~800 MPa under electrochemical H charging. Meanwhile, H gas-charged specimens with a uniform distribution of H show deformation twin-related intergranular cracks, whose initiation length decreases owing to grain refinement. Such small cracks, which feature blunted tips, do not significantly affect the fracture of the specimens. The electrochemically H-charged specimens exhibit numerous surface cracks because of their higher surface H content compared with that of the H gas-charged specimens. Nevertheless, similar to the case of the H gas-charged specimens, most of the cracks do not propagate significantly. In conclusion, fine-grained HEA exhibits remarkable resistance to H-related crack growth.