高压凝固下γ-TiAl合金组织演变及热稳定性研究

γ-TiAl alloy is one of the most potential light-weight high temperature structure materials in the field of aerospace engineering. However, γ-TiAl alloy shows low room-temperature ductility and fracture toughness, which contrains its application. Conventional studies focused on improving the ductility by HIP and rapid solidification, the significant influence of high pressure on improving ductility and inhibiting segregation by high pressure solidification has been ignored, which largely restricted the further development of γ-TiAl alloy. For this reason, this current subject will study γ-TiAl alloy solidified under high pressure to clarify the evolution of microstructures and the phase selection mechanism. Further, the process of peritectic reaction and the segregate mechanism will be built by studying the influence of the microstructures. The inter-relationship between the heat treatment and high pressure solidified microstructures will also be built. Therefore, the study of this subject can decrease the segregation and improve the mechanical properties, which will have directive significance for the engineering of γ-TiAl alloy.

在航空航天领域，γ-TiAl合金是目前最具发展潜力的一种轻质高温结构材料，但合金的室温塑性低和断裂韧性差极大的限制了合金的应用。以往的研究局限于通过热等静压、快速凝固方式等方式来提高合金塑性，而忽略了高压对γ-TiAl基合金偏析抑制的重要作用，对γ-TiAl基合金在高压下的相及组织演变规律缺乏基本认识，严重制约了γ-TiAl基合金的进一步发展。对此，本项目以γ-TiAl基合金在高压条件下的凝固行为为对象展开研究，揭示高压对γ-TiAl合金相选择机制、组织演变规律，分析高压下的包晶反应过程及偏析机制，建立热处理工艺和高压凝固组织之间的内在联系，因此本项目的研究对减少TiAl基合金中的偏析，提高TiAl基合金的力学性能，进一步推动TiAl基合金的工程化应用具有指导意义。

本项目以具有包晶转变的TiAl合金为研究对象，成功采用了GPa级高压对钛铝合金进行了制备，系统研究了高压对TiAl合金的通过研究压力对包晶转变合金(Ti-48Al、Ti-48Al-2Cr等)的过冷度、扩散系数、形核及长大过程等热力学及动力学进行理论分析，结果表明，高压的施加一定程度上抑制了包晶转变的发生，能引起凝固初生相的改变，由于高压引起的热力学及动力学原因，导致最终凝固组织中片层组织体积分数发生变化。分析了TiAl合金经高压凝固后热处理时的连续粗化、不连续粗化转变规律，发现高压使得其转变的驱动力增加。同时对高压凝固后的各组织的纳米硬度进行分析，发现高压凝固后的γ相的纳米硬度未见明显变化，片层组织由于其片层间距的下降，纳米硬度逐渐增加。