Abstract: Pitting is one of the critical inducements of stress corrosion cracking (SCC) of corrosion-resistant Ni-base alloys. To reduce SCC damage, the corrosion resistance and tensile property should both be guaranteed for Ni-base alloys. However, the majority of the existing alloying approaches failed to realize the harmony between corrosion resistance and tensile property. In the present work, we proved the significant effect of N-alloying on reducing SCC susceptibility. With N addition, the percentage loss of elongation in a corrosive environment decreased from 36.38 % ± 9.61 % to 23.91 % ± 0.80 %, indicating the remarkably reduced SCC susceptibility of Ni-base alloy. The tensile tests in air and electrochemical tests showed that the mechanical property and pitting corrosion resistance of Ni-base alloy were both improved by N-alloying. To suppress the initiation of SCC from pitting, the improvement in the quality of passive film was one of the key contributing factors, with the oxides and Cr contents evidently increased. The calculation results by the self-developed “dissolution-diffusion-deposition” model demonstrated that N atoms anodically dissolved into NH₃ and consumed H⁺, thereby suppressing the acidification of the solution. NH₃ would then hydrolyze into NH₄⁺ and further combine with H⁺. Additionally, CrN on the interface layer between passive film and matrix also accelerated the repassivation process, and inhibited the metastable pitting from developing into a stable one.

Key words: Ni-base alloy, Modelling studies, Passive films, Pitting corrosion, Stress corrosion cracking