The twin grid structure enhances low-angle grain boundaries (LAGBs) in the γ phase, effectively storing and hindering dislocations to improve the high-temperature properties of TiAl alloys. Hf was added to Ti-47Al-6Nb-0.1C-1.6Ta alloy and related mechanisms were studied. The results indicate that the addition of Hf promotes the formation of a Hf-enriched γ phase (with an L₁₀ structure, defined as the γ_Hf phase) in the TiAl alloy. The γ_Hf phase is surrounded by a γ phase containing twin grids (with an L₁₀ structure, defined as the γ_n phase). The γ_Hf and γ_n phases exhibit close orientations with LAGBs at their interfaces. The Hf and Al-rich regions in the α phase preferentially transform into the γ_Hf phase, with α grain boundary migration making γ_Hf either within the α parent phase or at its boundaries. The residual α phase around γ_Hf undergoes multiple twinning on {111} and {100} planes, ultimately resulting in the formation of the γ_n phase with twin grids. The 900℃ tensile strength and elongation of the Hf-added TiAl alloy reach 620.8±23.1 MPa and 7.27±0.6%, respectively. The twin grids in the γ_n phases uniformly accommodate dislocations, while the substantial lattice distortion and strong atomic bonding in γ_Hf impede dislocation activation, resulting in the absence of dislocations within γ_Hf. Consequently, the LAGB between γ_n and γ_Hf effectively hinders dislocations originating from the twin grids, thereby enhancing the alloy's high-temperature strength.

中文翻译：

---

通过孪晶网格强化小角度晶界：提高 TiAl 合金中γ相存储和阻断位错的能力

双网格结构增强了 γ 相中的小角度晶界 （LAGB），有效储存和阻碍位错，从而改善 TiAl 合金的高温性能。将 Hf 添加到 Ti-47Al-6Nb-0.1C-1.6Ta 合金中，并研究了相关机理。结果表明，Hf 的添加促进了 TiAl 合金中富含 Hf 的 γ 相（具有 L ₁₀ 结构，定义为 γ _Hf 相）的形成。γ _Hf 相被一个包含双网格的 γ 相包围（具有 L ₁₀ 结构，定义为 γ _n 相）。γ _{Hf n} 相和 γ 相在其界面处表现出与 LAGB 的紧密取向。α相中的富 Hf 和富 Al 区域优先转变为 γ _Hf 相，α晶界迁移使γ _Hf α母相内或其边界处。γ 周围的残余 α 相在 {111} 和 {100} 平面上 _Hf 经历多次孪晶，最终形成具有双网格的 γ _n 相。添加 Hf 的 TiAl 合金在 900°C 下的拉伸强度和伸长率分别达到 620.8±23.1 MPa 和 7.27±0.6%。γ _n 相中的双网格均匀地容纳位错，而 γ 中的大量晶格畸变和强原子键 _Hf 阻碍了位错激活，导致 γ 内部没有位错 _Hf 。因此，γ _n 和 γ 之间的 LAGB _Hf 有效地阻碍了源自双栅的位错，从而提高了合金的高温强度。