The formation of the α-Al₂O₃ scale on reactive element (RE)-doped FeCrAl alloys is commonly believed to be primarily caused by inward oxygen transport along grain boundaries. However, this study suggests that metal ion outward diffusion also plays a role in the development of the oxide scales and their microstructural characteristics. The study examines the oxidation behavior and grain boundary outward diffusion of iron-chromium alloys containing ~ 10 at% aluminum and ~ 22 at% chromium, doped with an over-critical concentration of REs, i.e., Zr and Hf. All samples were investigated after thermal exposure at 1100 °C by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atom probe tomography (APT). As a result of the overdoping, a considerable increase in oxide growth, an increase in the depth of internal oxidation, and RE-oxide formation near and at oxide grain boundaries (GBs) were observed as a consequence of increased inward and outward diffusion. The effect of overdoping manifests itself differently depending on the RE type and amount due to different solubility, ionic size, and electronic structure of alumina. The sample with Zr retained the adhesion of alumina to the alloy after the first and second thermal exposure, while Hf overdoping resulted in severe spallation after the second thermal exposure.

_{通常认为，活性元素（RE）掺杂的 FeCrAl 合金上 α-Al 2} O ₃氧化皮的形成主要是由沿晶界的向内氧传输引起的。然而，这项研究表明金属离子向外扩散也在氧化皮的形成及其微观结构特征中发挥作用。该研究检查了铁铬合金的氧化行为和晶界向外扩散，铁铬合金含有约 10 at% 的铝和约 22 at% 的铬，并掺杂了超临界浓度的 RE（即 Zr 和 Hf）。所有样品在 1100 °C 热暴露后均通过扫描电子显微镜 (SEM)、透射电子显微镜 (TEM) 和原子探针断层扫描 (APT) 进行研究。由于过度掺杂，由于向内和向外扩散增加，观察到氧化物生长显着增加，内部氧化深度增加，并且在氧化物晶界（GB）附近和处形成稀土氧化物。由于氧化铝的溶解度、离子大小和电子结构不同，过量掺杂的效果根据稀土类型和用量的不同而表现不同。在第一次和第二次热暴露后，含有 Zr 的样品保留了氧化铝对合金的粘附力，而 Hf 过度掺杂导致在第二次热暴露后严重剥落。