Mechanical Properties and Hydrogen Embrittlement Resistance of the High-Entropy Alloy CrFeMnNiCo and Its Subsystems

The effects of hydrogen on the mechanical properties of CrNiCo and CrFeNiCo medium-entropy alloys (MEAs) and CrFeMnNiCo high-entropy alloys (HEAs) are investigated. Although their total elongation is less than that of the commonly used stainless steel (SS) 316L (SS316L), the tensile strengths of HEAs and MEAs are 150-350 MPa higher than that of SS316L. Hydrogen charging up to 1400 appm (nominal concentration) does not affect the tensile strength of SS316L; however, it decreases the elongation by less than 20%. In contrast, hydrogen increases the tensile strength of MEAs and HEA, but has little effect on elongation. Among the MEAs and HEAs, CrNiCo exhibits the highest tensile strength and total elongation. No brittle fracture due to hydrogen is observed on the fracture surfaces of the H-charged samples. However, nanotwin structures are more common in H-charged MEAs and HEAs than in H-uncharged MEAs and HEA. Additionally, the calculation results based on the first-principles reveal for the first time that single vacancies or tiny vacancy clusters do not trap H in MEAs compared to HEAs, such that cracks due to H are unlikely to occur. Thus, the hydrogen embrittlement resistance of MEAs may be improved.