Enhanced resistance to hydrogen embrittlement in a CrCoNi-based medium-entropy alloy via grain-boundary decoration of boron

We found boron doping can substantially reduce the ductility-loss in the CrCoNi medium-entropy alloy after gas-hydrogen charging, from similar to 71% to similar to 46%, while the fracture mode transfers from predominantly intergranular to ductile transgranular dominated. The two alloys have no difference in phase-structures (single face-center-cubic), grain sizes, and grain-boundary (GB) characters. However, atom probe tomography identified apparent GB decoration of boron up to 1.5 at.% and nanometer-scaled scattered borides in boron-doped CrCoNi. Such local chemical difference leads to enhanced GB cohesion and reduced hydrogen diffusivity along GBs, resulting in improved immunity against hydrogen-embrittlement and suppressed mechanical degradation in the boron-doped CrCoNi alloy. IMPACT STATEMENT We found grain-boundary decoration of boron can substantially enhanced resistance to hydrogen embrittlement in a CrCoNi-based medium-entropy alloy when exposing to high-pressure gas-hydrogen charging.