【摘要】 采用β单相区热处理消除了高铌TiAl合金中的包晶α相(α_p),并从热力学和动力学角度分析了包晶α相与热处理温度、保温时间的相关性。结果表明:铸态高铌TiAl合金呈现出显著的凝固偏析,导致包晶α相的产生,通过在1 520℃保温20 min可消除铸态组织中的包晶α相。上述现象归因于:(1)热力学方面,在1 520℃热处理时,包晶α相为亚稳相,其稳定性显著降低,会发生α_p→β相变;(2)动力学方面,包晶α相的消除与Al、Nb元素的扩散密切相关,在1 520℃保温时,Al、Nb元素在枝晶间和枝晶干相互扩散。随着保温时间的延长,枝晶间Al元素呈指数衰减,当保温时间为20 min时,由Al元素富集造成的包晶α相被完全消除,合金整体以β凝固路径发生相变,获得了均匀细小的近片层组织。更多还原

【Abstract】 In this work, a heat treatment in single β region was utilized to remove the peritectic α phase(α_p) in a high Nb containing TiAl alloy and the relationships among treatment temperature, annealing time and peritectic α phase were analyzed from the aspect of thermodynamics and dynamics. The results showed that the as-cast high Nb containing TiAl alloys exhibited a significant solidification segregation, resulting in the formation of peritectic α phase, and the α_p phase was eliminated by a heat treatment in single β region, i.e., 1 520 ℃ for 20 min. These phenomena were attributed to the instability of peritectic α phase and interdiffusion of Al and Nb elements in local regions. The thermodynamic instability led to the occurrence of α_p→β transformation. The Al concentration in interdendritic regions decreased exponentially with annealing time. After the heat treatment at 1 520 ℃ for 20 min, the peritectic α phase was completely removed.The alloy undergoes a phase transition in the β solidification path, and a uniform and fine near-lamellar structure is obtained.更多还原