Abstract In order to understand the role of α2-Ti3Al precipitates during the oxidation of Au-coated γ-48-2-2-TiAl alloys, the γ-TiAl and α2-Ti3Al microstructures resulting from Au diffusion at 900 °C were investigated. The as-obtained coatings were characterized using scanning electron microscopy (SEM), combined energy and wavelength dispersive X-ray spectroscopies (EDS, WDS), electron backscatter diffraction analysis (EBSD), X-ray diffraction (XRD) and isothermal oxidation tests. Results showed that Au-coated-γ-TiAl alloys presented an upper aluminoformer TiAlAu2 layer and a lower non-protective TiAlAu layer, both with narrow homogeneity range, and with thicknesses that could be estimated with the use of the Prasad model. A more complex layer structure is obtained after Au diffusion in α2-Ti3Al alloys, since eight different phases were identified. In the lower layers, two new ternary tetragonal phases (Ti2AlAu and Ti3Al2Au) were found, and a partial diagram for the Al-Au-Ti 900 °C isotherm is proposed. Absence or depletion of Al was found in the upper layers and, in addition, a low oxidation resistance of the Au-coated-α2-Ti3Al alloy was reported.

中文翻译：

---

Au 涂层 (γ + α2) 钛铝化物中 Au 扩散的影响

摘要 为了了解α2-Ti3Al 析出物在Au 涂层γ-48-2-2-TiAl 合金氧化过程中的作用，研究了900 °C 下Au 扩散产生的γ-TiAl 和α2-Ti3Al 显微组织。使用扫描电子显微镜 (SEM)、组合能量和波长色散 X 射线光谱 (EDS、WDS)、电子背散射衍射分析 (EBSD)、X 射线衍射 (XRD) 和等温氧化测试对所获得的涂层进行表征。结果表明，Au 涂层-γ-TiAl 合金呈现上铝成型体 TiAlAu2 层和下层非保护性 TiAlAu 层，两者均具有窄的均匀性范围，并且其厚度可以使用 Prasad 模型进行估算。Au 在 α2-Ti3Al 合金中扩散后获得更复杂的层结构，因为确定了八种不同的相。在下层，发现了两个新的三元四方相（Ti2AlAu 和 Ti3Al2Au），并提出了 Al-Au-Ti 900 °C 等温线的局部图。在上层中发现 Al 缺失或耗尽，此外，据报道 Au 涂层-α2-Ti3Al 合金的抗氧化性低。