Grain boundary depletion and migration during selective oxidation of Cr in a Ni–5Cr binary alloy exposed to high-temperature hydrogenated water

High-resolution microscopy of a high-purity Ni–5Cr alloy exposed to 360 °C hydrogenated water reveals intergranular selective oxidation of Cr accompanied by local Cr depletion and diffusion-induced grain boundary migration (DIGM). The corrosion-product oxide consists of a porous, interconnected network of Cr2O3 platelets, with no further O ingress into the metal ahead. Extensive grain boundary depletion of Cr (to <0.05 at.%), typically 20–100 nm wide, is observed as a result of DIGM, and reaches depths of many micrometers beyond the oxidation front.

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