包晶相变使传统钛铝合金在铸造过程中极易出现成分偏析、显微组织粗大等现象，导致塑性较差且各向异 性明显，显著影响了钛铝合金的使役性能。为深入理解包晶相变过程并进一步合理调控微观组织，本文建立了适用于可 描述钛铝合金包晶相变的多相场模型，基于定量化多相自由能输入、多相界面处理、考虑反溶质截流及相界面处虚拟相 成分的简化计算策略，针对Ti-45Al(原子分数)合金的包晶相变过程，主要研究了过冷度对包晶相变时微观组织演变的 影响规律。研究发现，发生包晶反应(β+L→α)时，α相沿着β/L界面快速增长。考虑到α向L与β相的生长速度存在差 异，使得α相片层生长时表现出非对称性。包晶转变过程由扩散控制，α/L、α/β相界面的迁移满足xij =Aij t1/2规律。随着过 冷度增大，两种相界面迁移速率均增大，且α/L界面迁移速率的增幅较为显著；较低过冷度下，在α片层前端可见β相 的重熔现象。 增大过冷度后，其重熔现象逐渐消失，但L/β/α三相区的形状保持不变。 三相交界区域形状主要由界面能 (界面张力)之间的平衡决定，而与界面迁移速率的差异无关。

The peritectic phase transition in traditional TiAl alloys during the casting process often leads to issues such as composition segregation and coarse microstructures, resulting in poor plasticity and significant anisotropy, which significantly affects the performance of TiAl alloys. To gain a deeper understanding of the peritectic phase transition process and further control the microstructure, a multiphase-field model was developed to describe the peritectic phase transition in TiAl alloys. By incorporating quantitative input of multiphase free energy, effectively handling multiphase interfaces, considering anti-trapping current, and a simplified calculation strategy for the virtual phase composition at phase interfaces, the peritectic phase transition process of Ti-45Al (at. %) alloy has been investigated. The focus is on studying the influence of undercooling on microstructural evolution during peritectic phase transition. Research has shown that during the peritectic reaction process, α grows rapidly along the β/L interface. Considering the difference in the growth rates of the α phase towards the L and β phases, asymmetry is observed in the growth of the α plate. Moreover, the peritectic transformation process occurs under diffusion control, and the migration of the α/L and α/β interfaces follows the law of xij =Aij t1/2. As the degree of undercooling increases, the migration rates of both phase interfaces increase, especially the migration rate of the α/L interface, which significantly increases. At lower degrees of undercooling, phenomena such as remelting of the β phase can be observed at the front end of the α layer. After increasing the degree of undercooling, this remelting phenomenon gradually disappears, but the shape of the L/β/α triple-phase region remains unchanged. The shape of the triple-phase region is mainly determined by the balance between the interface energies (interfacial tension) and is independent of the differences in the interface migration rates.