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 degrees 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 0 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. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.