fig8

Figure 8. The proposed pitting corrosion mechanisms of the precipitants. (A) When secondary phases are enriched in chromium or molybdenum, a surrounding depleted zone is formed. The passive film at the depleted zone is weak or absent. Pitting corrosion occurred at the Cr-depleted zone. This theory is applicable to σ phase, χ phase and CrN. (Reproduced with permission^[87]. Copyright 2014, Elsevier). (B) Cathodic Cr-enriched secondary phases surround anodic Cr-depleted phases. The micro-galvanic corrosion induces pitting corrosion in the Cr-depleted phase. This theory has been recently proposed and is applicable to α and α’ phases. (Reproduced with permission^[94]. Copyright 2022, Elsevier). (C) A large strain field is generated around the square precipitate, which promotes the initiation of pitting corrosion preferentially at this location. (Reproduced with permission^[96]. Copyright 2020, Elsevier). This opinion has been proposed to interpret the pitting corrosion around the G phase, which is still under discussion.