TiAl基微叠层复合材料选区激光熔化增材制造机理和方法研究

TiAl alloy has very low density and exellent mechanical properties, and has broad application prospects in the aerospace, ship and automotive fields instead of nickel-base super alloy at the temperature range of 600-850℃. However, its development and application have been strictly restricted by its low room-temperature ductility. TiAl-based composite with plasticity and toughness materials is an effective way to improve the room-temperature ductility. TiAl-based micro-laminated composites has excellent comprehensive mechanical properties. In practice, preparation of TiAl-based micro-laminate composites is even more difficult, and there are not method to produce workpieces with complex shape. This project proposed a method with Selective Laser Melting (SLM) additive manufacturing of heterogeneous material to fabricate TiAl micro-laminate composite material. The proposal will reveal the mechanism that causes the residual stress, the metallurgical imperfection and the microstructure evolution in the TiAl based micro-laminate composite produced by SLM, research the controlling of shape and performance, realize the integration of preparation and manufacturing for complicated structural component made of TiAl based micro-laminate composite, then break the bottleneck of application of TiAl alloy. The proposal is of great significance to realization of the preparation of metal composites and development of new materials.

TiAl合金具有低密度和优异的高温力学性能，可在600-850℃的使用温度范围内取代镍基高温合金，实现高温结构件轻量化，在航空航天、车船动力等领域具有巨大的应用潜力。然而，TiAl合金的室温脆性严重制约了其发展和应用。利用塑韧性材料增韧的TiAl基复合材料是改善塑性的有效途径，其中TiAl基微叠层复合材料具有优异的综合力学性能。但是，传统方法制备TiAl基微叠层复合材料难度大，且无法实现复杂结构件制造。因此，本项目提出了通过异质材料选区激光熔化增材制造方法实现TiAl合金与塑韧性材料（TC4等）逐层交替堆积的微叠层材料成形方法。揭示选区激光熔化TiAl基微叠层复合材料内应力、冶金缺陷和组织演化机理，对复杂构件的控形控性进行研究，实现TiAl基微叠层复合材料复杂结构件的“材料制备-零件制造”一体化，突破TiAl合金应用瓶颈。该研究对实现复杂金属复合材料的制备、高性能新材料的研制具有重要意义。

TiAl合金具有密度低、比强度高、耐氧化和高温抗蠕变性能好等优点，可实现高温结构件减重30-40%，在航空航天、汽车等领域具有广阔的应用前景。然而，由于TiAl合金的室温塑性低和热加工难度大而严重制约了其发展和应用。为改善其塑性，人们发展了具有仿生结构的TiAl基微叠层复合材料，通过塑韧合金（Ti、Nb合金）微叠层增韧，可解决TiAl室温脆性的局限性，呈现出良好的综合力学性能。然而TiAl基微叠层复合材料制备难度更大，目前只停滞在材料制备研究方面，尚无法实现零件制造。激光选区熔化（Selective Laser Melting, SLM）技术是增材制造领域的重要发展方向，与传统加工相比，具有可直接成形任意复杂形状金属零件的优势。该方法基于逐层堆积的原理，可逐层控制材料体系，为实现TiAl微叠层复合材料—零件制备成形一体化制造提供了可能性。为此，本文设计了用于微叠层复合材料制备的异质材料激光选区熔化设备，并选择TC4合金作为增塑韧性材料，研究了通过异质材料激光选区熔化实现TiAl合金与TC4合金逐层交替堆积的微叠层复合材料制备方法。其中，重点研究了TiAl/TC4微叠层复合材料激光选区熔化成形特性。探索了不同层厚和层厚比对微叠层试样的形貌、成分和性能的影响。结果表明，层厚比一定时，TiAl叠层厚度越小，成形件的裂纹缺陷越少；当TiAl层厚降至200μm时，优化微叠层复合材料的层厚比、TC4层厚等关键参数，实现了致密、无裂纹微叠层复合材料的制备。同时发现，TiAl/TC4层厚比越小，增韧相TC4所占的比例越大，叠层试样的室温强度和塑性越好，但叠层复合材料的密度也相应增大。当TiAl层厚为200μm，TC4层厚为400μm时，获得了较高性能的微叠层试样。