安定FCC高エントロピー合金の水素による疲労き裂進展加速と進展経路変化

抄録

Hydrogen embrittlement susceptibility of stainless steels has been evaluated by Ni equivalent (Ni_eq), which is an index of FCC phase stability. Relative reduction of area of stainless steels increases with increasing Ni_eq up to 50 mass%. However, when Ni_eq exceeds about 50 mass%, the relative reduction of area decreases. There is a similar tendency for fatigue crack growth behavior. Namely, the hydrogen embrittlement susceptibility cannot be simply evaluated by FCC phase stability. To examine this subject, we investigated an effect of hydrogen on fatigue crack growth behavior in an equiatomic CrMnFeCoNi high-entropy alloy (HEA, Ni_eq = 52.8 mass%), as a stable FCC alloy. The ΔK increasing compact tension tests were performed at room temperature in air after hydrogen charging with 100 MPa-high pressure gas at 270°C for 237.5 h. The fatigue crack growth rate of the hydrogen charged HEA was 2.5–3.7 times higher than that of the uncharged HEA in the ΔK range of 16 MPa·m^1/2–30 MPa·m^1/2. The crack growth path in uncharged HEA was predominantly transgranular, whereas intergranular crack growth became significant in hydrogen charged HEA.