Excellent Hydrogen Embrittlement Resistance of CoCrFeMnNi high-entropy Alloy Compared with 304 and IN718 Alloys

The hydrogen embrittlement (HE) behavior of the CoCrFeMnNi high-entropy alloy (HEA), 304 stainless steel (304SS) and IN718 alloy were studied via slow strain rate tensile tests, and fracture surface analysis before and after electrochemical hydrogen pre-charging. An equiatomic CoCrFeMnNi ingot was prepared by using magnetic levitation melting technology. Pure metals (>99.9 wt.%) were used during this process. The results demonstrate that the HEA exhibited the greatest HE-resistance, followed by 304SS and then IN718 alloy, when the alloys were charged at 1.79 mA cm-2 for 24 h and 48 h, and 179 mA cm-2 for 2 h. Hydrogen-induced reduction in ductility was observed for 304SS and IN718 alloys, whereas the hydrogen-affected fracture strain of the HEA was dependent on the hydrogen charging time. The short hydrogen changing time 24h showed an improvement in the resistance to HE while it reduced at the 48h charging time. This is attributed to the competing mechanisms between hydrogen-enhanced twin formation and HEDE (hydrogen-enhanced decohesion). The number of nano twins (2.71) and the width of SF bundles (5.77 nm) in the hydrogen-assisted brittle zone is greater than in uncharged samples (2.57 and 5.02 nm). It clearly demonstrates that the presence of hydrogen promotes the formation of stacking faults and twins in CoCrFeMnNi alloy.