Kinetics of Alloy Depletion During Selective Oxidation in Polycrystals

International audience ; Grain boundary diffusion affects composition profiles developed during selective oxidation in polycrystals. It is therefore desirable to consider the grain size when choosing an alloy or setting acceptable operating conditions for an application where high temperature corrosion resistance is important. This paper aims to provide guidelines to evaluate subsurface composition changes as a function of grain size and oxidation conditions. We show that depletion profiles around isolated grain boundaries of Ni-based Cr 2 O 3-forming alloys oxidized at 1000 • C can be described by a 2D diffusion model, where fast diffusion at the alloy-scale interface is considered in addition to grain boundary diffusion. We then illustrate the general features of depletion profiles in polycrystals, in comparison to single crystals. Finally, we use a set of simulations covering a wide range of times, temperatures and grain sizes to identify regimes where a 1D model can be used, either because grain boundary diffusion can be neglected or because it produces a uniform depletion front.