电子束选区熔化高温TiAl合金相变及强韧化机理研究

TiAl合金具有低密度、高比强、高模量、高蠕变抗力等优异性能，比镍基高温合金减重约50%。影响TiAl合金大规模工业应用的主要障碍表现在两方面：本征脆性和加工成形难度大，高温组织稳定性和高温抗氧化性不足，目前TiAl合金只能应用在航空发动机650-750°C的部件。本基金以高Nb-TiAl合金为母合金，通过研究EBM凝固和相变机制，提出针对EBM技术的合金设计和组织调控原理；结合EBM的特点提出纳米陶瓷颗粒强化和金属颗粒韧化的概念，即利用陶瓷纳米颗粒提高高温蠕变性能，提升其服役温度，用高熔点金属纳米颗粒提高室温塑性和韧性，揭示EBM高Nb-TiAl合金的强韧化机理。该研究工作不但发挥EBM近净成形的特点，更重要的是进一步提升高Nb-TiAl合金的综合力学性能，解决其难加工成形问题，开发出高温高性能适合EBM的新型TiAl合金,这将丰富TiAl合金设计理论,为TiAl合金的广泛应用奠定基础。

Titanium aluminides possess low density, high specific strength/modulus, excellent creep resistance at high temperatue, which have only half the specific weight of superalloys. Two major barriers against a large scale industrial application of TiAl alloys are: 1) the intrinsic brittleness of the alloy and manufacturing difficulty; 2) a lack of long term microstructure stability and oxidization resistance. Therefore, the service temperature for engine components ranges from 650 to 750°C. This project proposes a novel alloy design and microstructure control principles aiming at EBM technique by studying the mechanisms of solidification and phase transformation during EBM based on the previous work for high temperature high Nb-TiAl alloys as raw materials. This project will explore the strengthening/toughening mechanism for high temperature TiAl alloys by ceramic nanoparticle strengthening/ high melting nanoparticles toughening taking full advantages of EBM technique, i.e. with thermodynamically stable ceramic nanoparticles, the high temperature creep resistance, long durability, and service temperature of TiAl can be significantly enhanced; high melting metal nanoparticles can also be used to improve the mechanical property greatly, especially ambient plasticity and toughness. The completion of the current project is to take the advantages of nearly net forming not only, but also to further enhance the balanced mechanical properties of high Nb-TiAl alloy; to develop new type of TiAl alloys for EBM with high temperature high performance, which can enrich TiAl alloy design theory and lay the foundation of wide application.