Abstract The microstructure in a lamellar γ-based Ti-45Al-8.5Nb alloy has been investigated by transmission electron microscopy (TEM). The results show that there exists a nano-scale modulated structure with tweed contrast within α2 laths and the orthorhombic phase as a constituent of the modulated structure has the O1 structure with a random occupancy of Ti and Nb atoms on the Wyckoff sites 8 g and 4c2. The orthorhombic phase has a thin plate-like morphology with orientation relationships of {001}O//{0001}α2 and O// 11 2 ¯ 0 >α2. The habit plane for orthorhombic phase variants lies at {350}O//{ 13 4 ¯ 0 }α2, and the O1/α2 interface is not atomic flat. The results further exhibit an enrichment of Nb in the orthorhombic phase in comparison with the α2 parent phase. Based on the TEM evidences, the formation of the orthorhombic phase arises from a phase separation reaction in the α2 parent phase, which is dominated by a diffusion mechanism.

中文翻译：

---

高含Nb层状γ-TiAl合金调制结构的高分辨率电子显微镜表征

摘要 用透射电子显微镜 (TEM) 研究了层状 γ 基 Ti-45Al-8.5Nb 合金的显微组织。结果表明，α2 板条内存在具有粗花呢对比度的纳米级调制结构，作为调制结构组成部分的正交相具有 O1 结构，在 Wyckoff 位点 8 g 和 4c2 上随机占据 Ti 和 Nb 原子. 正交相具有薄板状形态，取向关系为{001}O//{0001}α2 和O// 11 2 ¯ 0 >α2。正交相变体的习性平面位于 {350}O//{ 13 4 ¯ 0 }α2，并且 O1/α2 界面不是原子平面。结果进一步表明，与 α2 母相相比，斜方晶相中 Nb 富集。根据 TEM 证据，