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 Cr₂O₃-forming alloys oxidized at 1000 \(^{\circ }\)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 with 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.

晶界扩散影响多晶选择性氧化过程中形成的成分分布。因此，在选择合金或为耐高温腐蚀性很重要的应用设置可接受的操作条件时，需要考虑晶粒尺寸。本文旨在提供指导，以评估作为晶粒尺寸和氧化条件函数的地下成分变化。我们表明，Ni 基 Cr ₂ O _{3形成合金的孤立晶界周围的耗尽轮廓在 1000} \(^{\circ }\)下氧化 C 可以通过二维扩散模型来描述，其中除了晶界扩散之外，还考虑了合金-尺度界面处的快速扩散。然后，我们与单晶相比，说明了多晶中耗尽剖面的一般特征。最后，我们使用一组涵盖广泛时间、温度和晶粒尺寸的模拟来确定可以使用一维模型的范围，这要么是因为晶界扩散可以忽略，要么是因为它产生了均匀的耗尽前沿。