脉冲电磁场辅助SLM成形钛铝合金微裂纹抑制与各向异性调控机理研究

TiAl alloys show great potential in aerospace field due to their advantages such as low density, excellent high temperature strength; Selective Laser Melting (SLM) can manufacture complex TiAl parts. However, the defects of micro-cracks and anisotropic properties are easily produced in the TiAl parts during the SLM process, which seriously restricts their practical application. To this end, the project innovatively introduces the pulsed electromagnetic field into the SLM processing of TiAl alloys: firstly, reduces stress by pulsed electromagnetic heating; secondly, intensifies the melt flow in micro-molten pools to weaken directional crystallization by pulsed electromagnetic stirring; finally, achieves the ultimate goal of inhibiting micro-cracks and improving anisotropy of TiAl alloys during the SLM process. The project combines theory and experimental methods: reveals the regulation law of the temperature field with the interaction of pulsed electromagnetic field, laser and TiAl alloys; clarifies the mechanism of micro-cracks inhibition and microstructure regulation with the interaction of pulsed electromagnetic field, laser and TiAl alloys; reveals the regulation law of electromagnetic field-laser process on the properties anisotropy of the SLM-fabricated TiAl alloys, establishes the quantitative influence mode between the pulsed electromagnetic field, laser and properties of SLM-fabricated TiAl parts. The research findings of this project are expected to provide scientific guidance and technical support for the regulation mechanisms of the micro-cracks and anisotropy in TiAl alloys during the SLM process, which shows significant theoretical and engineering values.

钛铝合金密度低、高温性能优良，在航空航天等领域具有广泛应用前景；激光选区熔化（SLM）可成形复杂结构钛铝合金零件。但是，在SLM过程中钛铝合金极易产生微裂纹，同时由于逐层堆积导致钛铝合金性能产生各向异性，严重制约了SLM成形钛铝合金的实际应用。为此，本项目提出在钛铝合金SLM过程中引入脉冲电磁场，通过脉冲电磁加热降低应力，并借助脉冲电磁搅拌加剧微熔池熔体流动阻碍方向性结晶，最终实现抑制微裂纹和改善各向异性的目标。项目结合理论和试验方法：揭示脉冲电磁场-激光-钛铝合金交互作用下温度场调控规律，阐明脉冲电磁场辅助下SLM成形钛铝合金微裂纹抑制机理与微观组织调控机制，揭示电磁场-激光复合工艺对SLM成形钛铝合金微宏观性能各向异性调控规律，建立脉冲电磁场-激光-钛铝合金零件性能的定量影响关系。项目有望为SLM成形钛铝合金微裂纹抑制与各向异性调控提供科学指导及技术支持，具有重要的理论意义与工程价值。

钛铝合金具有低的密度和高比强度，在航空航天等领域有极大的应用潜力，激光选区熔化（SLM）可成形复杂结构钛铝合金零件。但是，由于钛铝合金的本征脆性，导致在SLM成形过程中极易产生微裂纹。为此，本项目结合激光选区熔化自身特点，将同步磁场应用于钛铝合金的SLM成形，研发了一种有效的调控微裂纹及凝固组织的新方法。同时，本项目还拓展研究了铝合金和铜合金的SLM成形工艺。具体研究结果如下：（1）研究了钛铝合金的微裂纹磁场强度的关联关系，发现随着磁场强度增加，钛铝合金微裂纹密度逐渐减小，（2）揭示了钛铝合金微观组织随磁场强度的演变规律，发现随着磁场强度的增加，钛铝合的且晶粒取向由(10-11)、(11-21)转变为(0001)；、织构由{10-10}<11-20>取向的棱形织构逐渐转变为{10-10}<11-20>的棱形织构、{0001}<11-20>取向的基体织构和{10-11}<11-20>取向的锥形织构；（3）建立了磁场工艺参数和钛铝合金SLM成形工艺参数、微裂纹与微观组织结构之间的内在影响关系，揭示其相互作用规律与内在机制。（4）研究了在不同磁场下，SLM成形AlSi7Mg试样的学性能的演变规律，揭示了电磁力对AlSi7Mg熔池凝固以及晶粒细和等轴化的影响机制。发现在磁场强度为0.3 T时，SLM成形AlSi7Mg表现出优异的强度和塑性组合，分别为：382.00±2.45 MPa和11.78%±0.20%；（5）研究了SLM成形Cu-15Ni-8Sn合金的微观形貌和组织特点，发现了SLM快熔快凝的加工特点，诱导产生了柱状粗晶和等轴超细晶的逐层周期性分布，分析了周期性微观组织对合金Cu-15Ni-8Sn力学性能的影响规律，SLM成形Cu-15Ni-8Sn的屈服强度和断裂延伸率分别为474.04±2.88 MPa和14.29±1.78%，相比铸造工艺，SLM成形Cu-15Ni-8Sn合金的屈服强度提升了12%，断裂延伸率提升了286%。研究成果在国内外本领域主流期刊如Additive Manufacturing等发表论文7篇，其中SCI论文5篇；申请专利1项，出版专著1本，国内外大会报告3次，协助培养研究生6名。项目在磁场-激光复合作用下的SLM冶金机理及其性能特征方面获得较好成果，为改善SLM零件的性能提供新途径，具有重要的理论意义和工程应用价值。