微叠层TiBw-TiAl复合材料板材设计制备与强韧化机理研究

In order to solve the bottleneck problem of titanium aluminide intermetallic compounds sheet forming and the inverse relationship between strength and toughness/ductility of Metal matrix composites (MMCs), this project proposes a method for the production of TiAl matrix composite sheets with novel nacre-like structure: TiBw/Ti matrix composite foils and pure Al foils are selected as raw materials and stacked to obtain the (TiBw/Ti)-Al laminates, and subsequently reaction annealing and hot pressing sintering are employed to fabricate unique micro-laminated TiBw-TiAl composite sheet, which consists of alternating fully lamellar (α2-Ti3Al/γ-TiAl) layer, equiaxed γ-TiAl layer and TiBw-rich layer. TiBw-rich layer is actually TiAl matrix composite layer containing high contents of TiB whiskers. Effect of heat treatment parameters, thicknesses of TiBw/Ti and Al foils and volume fractions of TiBw reinforcements on micro-laminated microstructure evolution and mechanical properties of TiBw-TiAl composite sheets are systematically investigated. The relationship of constituent layer thicknesses, the refinement of microstructure, the volume fractions of reinforcements and mechanical properties is clarified. Finally, strengthening-toughening mechanism and fracture mechanism of novel micro-laminated TiAl matrix composites are revealed. This project will lay the theoretical foundation for improving the strength and toughness of titanium aluminide intermetallic compounds by microstructural design, and also provide a new approach for the sheet forming of lightweight high-strength titanium aluminide intermetallic compounds.

针对钛铝金属间化合物板材难于成形的瓶颈问题以及金属基复合材料强度—韧性（塑性）倒置问题，本项目提出一种具有仿生贝壳层状结构的TiAl基复合材料板材成形方法：以TiBw/Ti复合材料箔和纯Al箔为原料，通过热处理使Ti和Al发生化学反应结合真空热压烧结技术，设计并制备出全层片(α2-Ti3Al/γ-TiAl)层、等轴γ-TiAl层与TiBw-rich层三层交替排列结构的新型微叠层TiBw-TiAl复合材料板。研究热处理参数、原料箔材层厚以及增强相含量对TiBw-TiAl复合材料的层状组织演变与力学性能的影响规律，阐明组元层厚、层内组织细化和增强相含量与复合材料宏观力学性能的关系，揭示微叠层复合材料的强韧化机制与断裂机理。本项目将从结构设计上为实现钛铝金属间化合物的强韧化奠定理论基础，为轻质耐热高强金属间化合物板材制备提供新途径。

TiAl基合金具有优TiAl基合金具有优异的性能，能够满足未来超音速飞行器对结构减重与高温强度的双重要求。然而目前通过传统工艺路径（先制备后成形：铸造/冶金锭-锻造-包套热轧）制备TiAl基合金薄板类零件非常困难，针对这一瓶颈问题以及金属基复合材料强度—韧性（塑性）倒置问题，本项目突破传统思路限制，创新性地提出“先成形后合成”的研究路线：以纯Al箔和自制的TiB/Ti复合材料箔为原料，并将两种箔材交替堆垛后进行热压烧结获得(TiB/Ti)-Al叠层，随后先对此塑性良好的叠层材料进行变形到预定形状，然后再进行反应热处理，成功开发出一种TiAl曲面类薄板零件的制备成形一体化技术。同时受自然界中强度/韧性达到最佳匹配的贝壳微纳叠层结构启迪，本项目设计了TiAl基复合材料的微观结构，最终优化制备出由全片层 (α2-Ti3Al/γ-TiAl)层、等轴γ-TiAl层与TiB-rich层等三层交替排列构成的新型微叠层TiBw-TiAl复合材料。优化了制备工艺参数，阐明了TiBw-TiAl复合材料微叠层结构的形成机理与调控机理，评价了微叠层TiBw-TiAl复合材料的力学性能，建立了微叠层TiBw-TiAl复合材料的基本断裂模型，并揭示了其强韧化机制。研究表明：通过调节反应退火参数、Al箔与TiB/Ti复合材料箔的厚度以及增强相TiB晶须含量可以调控TiBw-TiAl复合材料的微叠层结构与宏观力学性能，最终制备出的TiBw-TiAl复合材料微观组织细小（α2/γ团簇约100μm，等轴γ-TiAl晶粒约20μm），高温性能优良（750oC拉伸屈服强度＞340MPa），同时表现出较好的断裂韧性（＞15MPa·m1/2），即微叠层TiBw-TiAl复合材料表现出良好的综合力学性能，其主要原因在于其形成了独特的微叠层结构以及TiB晶须自身的强化作用所致。本项目开发的微叠层TiAl基复合材料板材制备成形一体化技术，可能为航空航天曲面类薄板零件的制备提供一种可行的近净成形方法，同时与目前传统镍基高温合金相比，减重约50%。此外，本项目的完成也为从构型设计角度实现金属基复合材料的强韧化提供理论与实验基础。