β型γ-TiAl合金β→α相变行为及其与片层结构相关性研究

β→α固态相变作为β型γ-TiAl合金的重要相变之一，决定了α相的结构特征，从而引起（α2+γ）片层结构的变化。但该相变发生于高温阶段、合金后续固态相变复杂、相变序列对成分敏感，给β型γ-TiAl合金β→α相变行为的研究造成了困难，使得α相及片层结构的调控缺乏深入的理论指导。本项目采用高温激光共聚焦显微镜与可控热处理-淬火相结合的方法对β→α相变进行原位研究，研究冷却速率、硼含量对α相形核生长方式的影响，分析硼化物与β相以及α相之间的位相关系，阐明不同条件下α相的形核生长机制及变体选择行为，揭示β→α相变动力学机制，建立连续冷却转变曲线；在精确控制α相微观结构的基础上，探索具有不同初始组织特征的α相与片层结构的相关性，建立片层结构调控的新方法。本研究不仅对于深入理解β型γ-TiAl合金α相演化规律具有理论意义，而且对实现该类合金的组织-性能调控、促进其应用也具有重要的工程价值。

β-solidifying TiAl alloys regarded as the most promising candidates to fulfill the required thermal and mechanical specifications have attracted significant attentions, and their mechanical properties is affected by the lamellar structures. The microstructural characteristics of lamellar structures are determined by the α phase which originate from the β→α solid transformation. Therefore, it is of great importance to investigate the β→α transformation behavior and its relationship with the lamellar structures. In this research project，an in-situ observation by high-temperature laser-scanning confocal microscopy (HTLSCM) combined with controlled heat treatment-quenching method will be utilized to investigate the β→α transformation. Firstly, the nucleation and growth behavior of α phase is studied by the in-situ observation under different conditions, i.e., cooling rates and boron content, and according to the data recorded by HTLSCM, the CCT curves can be established. Secondly, α phase can be retained by the quenching experiments and the microstructural characteristics of α phase, the orientation relationships among boride, β phase and α phase will be investigated. Based on the above experimental results, the nucleation and growth mechanism of α phase, the variational selection effect and the kinetics of the β→α transformation will be analyzed and discussed. Thirdly, the correlation between α phase and lamellar structures is definitely revealed according to the low temperature aging results. The research work is very important and valuable not only for further understanding the microstructure evolution, but also supply a theoretical basis for optimizing the lamellar structures and mechanical properties of β-solidifying TiAl alloys.