基于β凝固的新型γ-TiAl合金多向变形行为及协调变形机制研究

γ-TiAl alloys are considered to be most promising light-weight structural materials for high temperature application in aviation and aerospace fields. However, the development of TiAl alloys was hindered by poor hot workability and intrinsic brittleness. Multi-directional forging is a versatile technique for the great grain refinement and improvement of mechanical properties. The novel γ-TiAl alloy based β solidifying exhibits excellent hot workability, which provides an opportunity for the application of multi-directional forging in TiAl alloys. Currently, the related research is rather less. In this project, it is hoped to obtain β solidifying TiAl alloys with fine grains and excellent mechanical properties fabricated by multi-directional forging. Meanwhile the studies will be done to clarify some scientific issues about the multi-directional forging and room temperature deformation mechanisms of β solidifying TiAl alloys. The microstructural evolution law of β solidifying TiAl alloys during the multi-directional forging will be studied. The effect of β phase on the decomposition and dynamic recrystallization of lamellar structure in TiAl alloys will be explained. The compatible deformation mechanisms among γ,α2 and β0 phases during room temperature deformation can be illustrated. The optimum multi-directional forging processes and sequential heat treatment of β solidifying TiAl alloys can be proposed. The research of this project will not only provide theoretic support for multi-directional forging of β solidifying TiAl alloys, but also improve the plastic deformation theoretical system of TiAl alloys .

γ-TiAl合金是一种在航空航天领域极具应用前景的新型轻质高温结构材料。但较低的室温塑性和较差的热加工性能始终阻碍着TiAl合金的发展。多向锻造能有效细化合金的显微组织，改善合金的力学性能。基于β凝固发展的新型γ-TiAl合金具有优异的热加工性能，为多向锻造在TiAl合金中的应用提供了可能。目前尚未有相关的文献报道。本课题提出利用多向锻造技术制备细晶高性能的β凝固TiAl合金，并针对β凝固TiAl合金多向锻造及室温变形的若干科学问题，研究β凝固TiAl合金多向锻造的组织演变规律；阐明β相对TiAl合金片层组织分解及动态再结晶的影响机制；揭示室温变形条件下γ、α2和β0三相的协调变形机制；提出适于β凝固TiAl合金的多向锻造工艺和锻后热处理工艺。通过本课题的研究，将为β凝固TiAl合金的多向锻造提供理论支持，并丰富和完善TiAl合金的塑性变形理论。

γ-TiAl合金具有低密度、高强度、优异耐高温性能和抗蠕变性能等优点，是制备航空发动机叶片的理想备选材料。但传统γ-TiAl合金热加工性能较差，阻碍了其工程应用。通过引入β相，能够显著改善TiAl合金的热加工性能，基于此发展了新型的β凝固TiAl合金。这为实现TiAl合金的多向变形提供了条件。因此，本项目研究了β凝固TiAl合金的多向变形行为。取得的主要创新成果如下： 深入研究了新型β凝固TiAl合金的多向变形行为，在多向变形过程中，γ/α2片层大量分解为等轴γ晶粒和无规则β相；γ相的动态再结晶和β相的动态回复是β凝固TiAl合金多向变形过程中的主要软化机制；软质β相的存在大幅改善了TiAl合金的高温变形能力，使其能够实现无包套多向锻造；确定了β凝固Ti–43Al–2Cr–1.5Mn–0.1Y合金最佳的多向变形工艺：道次变形量30%；道次数为3；每道次的初始变形温度为1250°C，变形速率不低于0.2mm/s；制备了细晶、无裂纹的β凝固TiAl合金锻坯；通过多向锻造，显著改善了TiAl合金的室温拉伸强度和延伸率；无Nb-TiAl合金的韧脆转变温度一般低于750°C；通过调整β稳定元素的种类含量，能够在一定程度上降低β相硬度，从而有利于β凝固TiAl合金在室温下γ和β相的协调变形。研究了适于β凝固TiAl合金的锻后组织热处理工艺。Ti–43Al–2Cr–1.5Mn–0.1Y合金全片层组织的热处理工艺为1320℃/10min/炉冷，其片层晶团直径约为200μm。全片层组织的断裂机制以穿片层及沿片层断裂为主。以上成果将为β凝固TiAl合金的多向锻造提供理论支持，并丰富和完善TiAl合金的塑性变形理论。