Tailoring hydrogen embrittlement resistance of pure Ni by grain boundary engineering

•Grain boundary engineering used to modify hydrogen embrittlement resistance in Ni•Increasing grain boundary curviness benefits for preventing hydrogen embrittlement By using thermo-mechanical processing, 99.996 wt.% pure Ni with different grain boundary characteristics were fabricated (Sample #1, 700 ℃ × 10 h + cold rolling reduction 50%+ 650 ℃ × 2 h; Sample #2, 700 ℃ × 10 h + cold rolling reduction 50%+ 900 ℃ × 5 min). Hydrogen embrittlement sensitivity of the two samples was determined by using high-pressure hydrogen charging, low strain rate tensile test and SEM fractography. Compared with Sample #1, hydrogen embrittlement index of Sample #2 increased from 0.52 to 0.71. The effects of grain size, grain boundary type and grain boundary curviness on hydrogen embrittlement of pure Ni were discussed. The results indicate that: 1) special grain boundaries including twin grain boundaries may have a marginal effect on tailoring hydrogen embrittlement resistance in pure Ni; 2) increasing grain boundary curviness is an effective way to improve hydrogen embrittlement resistance of Ni.