Ti-Al-Nb-Mo-B-Hf体系相图热力学数据库建立及 γ-TiAl 合金凝固过程中硼化物结构与形貌控制

B是 γ-TiAl 合金中普遍采用的晶粒细化元素。随合金体系和冷却速度不同,硼化物具有复杂多变的结构和不同的形貌。如何控制硼化物结构与形貌是提高铸造γ-TiAl合金叶片性能需要解决的关键科学问题。第一原理计算是理解硼化物复杂多变结构的基础，相图是理解γ-TiAl合金中硼化物形貌的关键。Hf是γ-TiAl合金重要合金元素，HfB2 熔点为3378℃，比TiB2高178℃，因此在含硼的γ-TiAl合金中加Hf，可以扩大硼化物初晶区，提高硼化物形核率，减少粗大和弯曲长条状硼化物的形成，提高合金的室温塑性。本项目以如何控制硼化物的结构与形貌为出发点，开展硼化物自由能的第一原理计算，测量与优化部分含Hf体系的相图，构建Ti-Al-Nb-Mo-B-Hf体系相图热力学数据库，计算γ-TiAl合金凝固过程中的凝固通道与相反应，揭示Hf对硼化物结构与形貌的影响，为提高γ-TiAl合金叶片的性能打基础。

B is a common grain refiner of γ-TiAl alloy. The crystal structure and morphology of titanium borides vary with the alloy composition and cooling rate, which will impact the properties of the casting TiAl blades. How to control the structure and morphology of the borides is a key problem for improving the properties of casting γ-TiAl blade. First principle calculation is an useful tool for understanding the structure of borides. Phase diagram is a key to understand the morphology of borides. Hf is an important alloying element for γ-TiAl intermetallics. The melting points of HfB2 is 3378℃, which is 178℃ higher than that of TiB2. Thus, addition of Hf into the B containing γ-TiAl alloy will enlarge the primary phase field, increase the nucleation rate, reduce big borides and boride ribbons, and increase the plasticity of the casting TiAl alloy at room temperature. The scope of this project is calculating the Gibbs energy of borides with first principle method, determining and optimizing the phase diagram of some Hf containing systems, constructing the thermodynamic database of the Ti-Al-Nb-Mo-B-Hf system, predicting the solidification path and phase reactions during solidification of the γ-TiAl alloys, and exploring the influence of Hf to the structure and morphology of the boride, so as to build a sound scientific bases for improving of the properties of the casting TiAl alloy blade.