Hydrogen-induced cracking behavior of twin boundary in γ′ phase strengthened Fe-Ni based austenitic alloys

The hydrogen-induced cracking behavior is investigated in two Fe-Ni based austenitic alloys with different amounts of γ′ phase. It is observed that intergranular cracking existed in both alloys, while hydrogen-induced twin boundary cracking only occurred in the alloy with higher amount of γ′ phase. The occurrence of twin boundary cracking is primarily related to the stacking fault energy (SFE) of alloys, which decreases with the increasing amounts of γ′ phase. Enhanced slip planarity and increased difficulty in cutting through twin boundary are observed in the low-SFE alloy. Therefore, twin boundary cracking is induced by cooperative effects of SFE and hydrogen in Fe-Ni based austenitic alloys.