Role of precipitates-decorated Σ3 twin boundaries on hydrogen-induced crack initiation and propagation in Ni-based superalloy 718

The role of ∑3 twin boundaries (∑3s) on hydrogen embrittlement behavior of Ni-based superalloy 718 was investigated by uniaxial tensile tests. The hydrogen resistance is improved with the fraction of ∑3s increasing after grain boundary engineering treatment. A high fraction of ∑3s can effectively reduce the nucleation sites of cracks and suppress the further propagation. ∑3s also act as potential sites for hydrogen-induced crack initiation. A distinct morphology of γ′′/γ′ co-precipitates and γ′ precipitates with one-to-one correspondence along the ∑3s is observed. The mechanism of hydrogen-induced ∑3s cracking is extensively discussed in terms of precipitates and hydrogen distribution.