基于电子束选区熔融技术的3D打印铜合金增强增塑机制研究

3D printing, which enables high design and manufacturing flexibility, has been recently attracted increasing attention, and employed to fabricate easily weldable metallic materials such as titanium alloys, nickel alloys and stainless steels. However, it is still a significant challenge to print hard-to-weld alloys (such as aluminum and copper based alloys), because the melting and solidification dynamics during the printing process results in undesirable microstructures with large columnar grains and periodic cracks. Particularly, the specular reflection of laser irradiation from the surface of Cu-based printing parts results in detrimental microstructures with voids, further damaging the mechanical properties of alloys. Herein, a strategy of using electron beam selective melting (EBSM) with the mixed-granularity filler is proposed in this project. Dynamics of beam flow, mixed particle sizes, line scanning speeds and filling spacing is systematically studied; and the principle of EBSM processing is explored to rapidly print high density and high strength-plasticity copper-based alloys. The project will establish a relational model for investigating effects of printing parameters, mixed particle size parameters and temperature field distributions on the microstructure and strength-plasticity of alloys by 3D printing. Meanwhile, mechanisms of the exceptional combination of strength and plasticity promoted by the strong dislocation-stacking fault interaction, as well as mechanisms of strain-induced martensitic transformation based on the stress field and stacking fault nucleation will also be clarified. This project could provide the theoretical basis for overcoming shortcomings of 3D-printed copper alloys, as well as for process designs and optimization of hard-to-weld alloys with exceptional strength-ductility synergy under the high-energy density.

3D打印技术具备极高的设计与制造灵活性，近年来被广泛研究并应用于打印易焊接材料，如钛、镍合金，不锈钢等。而基于熔化和凝固动力学，打印难焊接材料时（如铝、铜合金），打印件组织易出现粗大柱状晶与周期性裂纹；尤其铜合金材料对激光反射率高，成型件易产生随机孔洞，进一步损害合金力学性能。项目提出采用电子束选区熔融技术并结合混合粒度填充料方法，深入研究束流、混合粒径、线扫速度、填充间距有关的动力学问题，探索快速成型高密度、高强高塑铜合金原理。通过性能测试、理论分析和参数优化方法，建立高能量密度场下打印参数、混合粒度、温度场分布等工艺参数对合金组织结构和力学性能影响的关系模型；揭示位错-堆垛层错强交互作用促进高强高塑性能机制；提出基于应力场与层错形核作用下，应变诱导马氏体相变机制，为克服3D打印高性能铜合金的难题并建立高能量密度场下制备先进高强-高塑难焊接合金材料的工艺设计与优化提供理论依据。

增材制造技术具备极高的设计与制造灵活性，近年来被广泛研究并应用于打印易焊接材料，如钛合金、镍合金，不锈钢等。而基于熔化和凝固动力学，打印难焊接材料时（如铝、铜合金），打印件组织易出现粗大柱状晶与周期性裂纹；尤其铜合金材料对激光吸收率低，成型件易产生随机孔洞，进一步损害合金力学性能。项目采用电子束选区熔融技术并结合混合粒度填充料方法，研究了束流、混合粒径、线扫速度、填充间距对铜合金成形性的影响，获得了快速成形高密度、高强高塑铜合金工艺方法，增材制造铜合金的强度提高同时，拉伸率达到35%。通过力学性能测试、理论分析和参数优化方法，建立了高能量密度场下打印参数、混合粒度、温度场分布等工艺参数对合金组织结构和力学性能影响的关联关系；提出了增材制造铜合金内部位错-堆垛层错强交互作用促进高强高塑性能的影响机制；揭示了基于应力场与层错形核作用下，应变诱导马氏体相变机制，为克服增材制造高性能铜合金的难题并建立高能量密度场下制备先进高强-高塑难焊接合金材料的工艺路线提供了可行方案。项目揭示了增材制造铜合金的微观结构（包括纳米析出相、位错、层错）与合金强度与塑性的关联关系，提出了合金在拉伸变形过程中马氏体形核与相变对合金强度与塑性的作用机理，进而为增材制造高强度与高塑性合金部件提供理论基础。同时，本项目研究为增材制造技术应用于深海远洋工程领域提供了理论方案与技术支撑。