添加Ti2AlNb的TiAl基合金电磁搅拌激光增材制造组织控制及增塑机理

TiAl based alloys, lightweight high temperature structural materials, exhibit the greatest potential to replace nickel-based superalloys due to their high specific strength, excellent creep and oxidation resistance. They are believed to have broad application prospects in blades of aero-engine with high thrust-weight ratio, however, low plasticity at room temperature is the main barrier for their applications. It is an important scientific issue to find an effective solution to obtain fine, low segregation TiAl based alloys, fundamentally improve their plasticity at room temperature, and reveal the plasticizing mechanism of the alloys..In this project, the laser melting deposition and electromagnetic stirring will be combined to refine the grains and relieve composition segregation of TiAl based alloys. Additionally, the plasticizing effect and pinning effect for restraining grain growth of Ti2AlNb alloying will also be combined to improve the plasticity of TiAl based alloys at room temperature. The effect of Ti2AlNb alloying on microstructures of TiAl based alloys, grains refining mechanism of the TiAl based alloys prepared by laser melting deposition with electromagnetic stirring, plasticizing mechanism at ambient temperature, optimization of the composition and microstructure of TiAl based alloy, and the evaluation of comprehensive mechanical properties at room and elevated temperature, will be investigated. The project findings will not only provide scientific guidance and theoretical basis for the fabrication of TiAl complex components by laser direct manufacturing, but also supply a new solution for the preparation of homogeneous and fine-grain TiAl billets. Therefore, the project is valuable in science and undoubtedly shows high potential for engineering application.

TiAl基合金具有高比强度、优良的抗蠕变及抗氧化性能等优点，是最有望替代镍基高温合金的轻质高温结构材料，可制作高推重比航空发动机叶片等部件，有广泛应用前景，但室温塑性不足是限制其应用的主要障碍。研究新的途径，获得组织细小、成分近无偏析的TiAl基合金，根本上改善材料的室温塑性，并揭示其增塑机理，是值得研究的科学问题。.本项目提出激光熔化沉积+电磁搅拌的途径，达到显著细化组织、减小偏析的效果，并结合Ti2AlNb合金化的增塑作用及其“钉扎”对晶粒长大的限制作用，提高TiAl合金的室温塑性。拟研究：Ti2AlNb合金化对TiAl合金微观组织的影响；电磁搅拌辅助激光熔化沉积TiAl合金的晶粒细化机理；室温增塑机理；合金成分、组织优化及室高温力学性能评价。项目成果将为激光直接成形制造TiAl复杂构件提供科学依据和理论基础，并为制造均匀细晶的TiAl坯体提供新途径，具有重要科学研究价值和应用前景。

本项目针对TiAl基合金室温塑性低的难点，采用“高温预热+激光熔化沉积+Ti2AlNb合金化”的技术途径，成功制备出了无裂纹、未熔合等缺陷的TiAl基合金，并获得了Ti2AlNb合金化对TiAl基合金LMD成形组织的影响，明确了Ti2AlNb添加量与合金中γ-TiAl相、α2-Ti3Al相含量之间的关系。.利用三相异步电动机旋转原理，设计并建设了一台电磁搅拌装置。采用“高温预热+电磁搅拌+激光熔化沉积+Ti2AlNb合金化”的技术途径，研究了电磁搅拌输入电流对增材制造TiAl基合金组织的影响，揭示了TiAl基合金的晶粒细化机理，并实现了晶粒细化和组织改善，并得到了均匀、细小的等轴晶组织。.通过对激光熔化沉积TiAl基合金室温拉伸性能的测试与分析，获得了Ti2AlNb合金化和电磁搅拌对TiAl基合金室温塑性的影响规律，并揭示了其增塑机理。测得添加Ti2AlNb的沉积态TiAl基合金室温拉伸强度和延伸率分别可达537~892MPa和1.4~3.1%。.在上述基础上，优化确定TiAl基合金中Ti2AlNb最佳添加量为5vl.%。测得该成分的TiAl基合金室温拉伸强度和延伸率分别为433MPa和2.1%；800℃拉伸强度和延伸率分别可达567MPa和4.3%；800℃/160MPa条件下持久寿命可达150h~210h。.本项目通过采用“高温预热+电磁搅拌+激光熔化沉积+Ti2AlNb合金化”的新途径，解决了TiAl基合金的难成形问题，并实现了室温塑性的大幅改善，为增材制造TiAl基合金零件在航空、航天发动机上的应用提供了技术储备；也为TiAl基合金新品铸件缺陷的维修提供了可行的技术途径和解决方法。另外，对于设计所在发动机高温零部件的轻量化设计与制造应用方面提供了更大的灵活性和创新思路。.此外，本项目通过对电磁搅拌辅助激光增材制造TiAl基合金的增塑机理研究，揭示了低塑性合金成形机理和开裂机制，并获得了有效的热裂纹控制方法，对更广阔范围内金属间化合物的增材制造具有借鉴意义。