Hydrogen Effects on Hall–Petch Coefficient and Fracture Strength in Pure Ni and Ni-20Cr Alloy: A Macroscopic Insight of the Hydrogen Embrittlement Mechanism

The effects of Cr and H on the yield and fracture strengths in pure Ni and Ni-20Cr alloy were investigated based on the Hall–Petch relationship. The Hall–Petch coefficient, which depends on the dislocation pile-up length and slip transfer resistance at the grain boundaries, drastically increased by 20 pct Cr addition and unchanged by gaseous hydrogen charging at 80 MPa. These results indicate that Cr increased the intergranular stress concentration associated with dislocation pile-up, whereas H did not.