Reducing stress corrosion cracking sensitivity of Inconel 625 alloy at different Cl− concentration by tailoring annealing twin boundaries

Annealing twin boundaries (ATBs) are low-energy grain boundaries (GBs) that play a key role in markedly enhancing the mechanical properties and stress corrosion resistance of Inconel 625 seamless tube. Here, the effect of ATBs on the stress corrosion sensitivity and mechanical properties of Inconel 625 alloy in Cl − -containing corrosion environment was investigated by slow strain rate tensile (SSRT) tests. The results show that compared with air media, Cl − -containing media improves the stress corrosion sensitivity of Inconel 625 alloy. Specifically, as the Cl − concentration rises, the alloy's stress corrosion cracking (SCC) sensitivity increases, while its fracture elongation decreases. Meanwhile, at the same Cl − concentration, the CR-AT1120 sample with a higher ATBs fraction exhibits higher fracture elongation and lower SCC sensitivity, which is mainly attributed to the fact that ATBs, as a special GB, can effectively inhibit crack initiation and propagation along the GBs, as well as Cl − corrosion at the GBs. In addition, the stress corrosion failure mechanism of Inconel 625 alloy in Cl − environments involves two critical effects. One is the high-temperature oxidation-induced crack propagation inhibition mechanism, where oxygen regulates crack growth by promoting oxide layer formation. The other is the localized corrosion mechanism triggered by Cl − adsorption at crack tips, which accelerates material degradation. This indicates that tailoring ATBs fraction at the same grain size level could be an effective approach to improve the SCC resistances of Ni-based superalloys.