TiAl具有轻质耐热的特点，是目前公认的新型航空、航天和车辆等结构选材。通过减重和提高工作温度，可促进航空航天等动力系统的高效和低排放。TiAl合金的规则片层取向有利于其本征脆性的改善。但定向凝固复杂形状构件（如涡轮叶片）时，构件截面形状的改变引起温度场、溶质场等能量失稳，会使TiAl原本复杂的包晶凝固（如凝固路径和相选择等）更加趋于复杂化，不但不利于对定向片层取向、形态和含量等的控制，更不利于定向凝固铸件性能的改善，尤其是韧性。因此，如何通过定向凝固来制备变截面形状的TiAl构件，揭示几何形状因素对其定向组织的影响规律，消除变截面区的杂晶，建立控制定向片层结构转变的方法，将具有重要研究价值。本项目拟采用冷坩埚结合惰性陶瓷模壳的复合定向凝固法，研究变结构形状TiAl构件的凝固行为和片层结构演变行为，阐明定向凝固中几何形状因素的影响机理，为优化TiAl基构件组织和性能及工程应用奠定理论基础。

Due to its excellent properties of low density, excellent burning and oxidizing resistance at elevated temperature from 750℃ to 900℃,TiAl-based alloy has been received considerable attention as one of the promising structural materials for application in aviation, aerospace, automobile and power generation industries. The efficient of aerospace and transportation are promoted through weight lossing and operation temperture enhancing. The intrinsic brittleness of TiAl alloys can be improved by directionally solidified microstructures with regularly arranged lamellar microstructures. However, during the directional solidification of complex shaped components (e.g. engine turbine blade), changes of temperature and solute field occurred that they were induced by changes in the areas with shaped cross-section. Nucleation induced by these changes would make the control of directionally solidified microstructure difficult, such as morphology, phase content and lamellar orentation. Then the mechanical properties of the components become unstable, especially decreasing in ductility and toughness. Therefore, the influence of different cross-section shapes, namely geometrical factors, on the solidification process can be obtained by analyzing the microstructure of TiAl alloys with different shape prepared by directional solidification. In the present research, attention is paid on the solidification behavior and lamellar microstructure evolution. Effects of withdraw rate and temperature gradient on the crystal growth of variable cross-section will be clarified during directional solidification of TiAl alloys, and the growth mechanism of stray grains and directional lamellar structure will be analyzed. The theoretical basis will be developed for the materials optimization of TiAl alloy, performance improvement and the prospect engineering application.