脉冲电流辅助金属层状复合材料超声波增材制造关键科学问题

In order to improve the forming capacity and expand the applicable field of the current metal Ultrasonic Additive Manufacturing (UAM) technology, and enable this advanced manufacturing method to be available in consolidation and fabrication of the high strength metal foils with relatively larger thickness, a novel technique of UAM assisted by pulse current for fabricating metal laminate composite and structure is proposed for the first time in this proposal. The basic principle is to utilize the electroplastic effect of the pulse current for promoting the atom diffusion and dislocation motion, reducing the deformation resistance and increasing the plastic deformation capacity of the metals. UAM technique can be therefore used to fabricate metal laminate composite and structure using metal foils with high strength and large thickness. To figure out some fundamental scientific issues associated with the novel UAM assisted by pulse current, the theoretical analysis, experimental observation and numerical simulation will be employed to deeply and systematically explore the mechanisms and influence factors of metal atom diffusion, plastic deformation and interface consolidation solid physical metallurgical natures under the conditions of the UAM combined with pulse current, and also to study the relationship between the microstructures and mechanical properties of the interface. The results achieved in this study can provide a theoretical foundation for establishing an advanced multi-energy fields coupled manufacturing technology with independent intellectual property rights that is used for fabricating metal laminate composite and for developing manufacturing science, high-tech equipments and technology of UAM assisted by pulse current.

为了提升现有金属超声波固结成形与增材制造装备的加工能力、拓宽其工艺适用范围，本项目首次提出了脉冲电流辅助金属层状复合材料与结构超声波固结成形制造技术。即利用脉冲电流的电致塑性效应，促进金属原子扩散和位错运动、降低金属变形抗力、提高金属塑性变形能力，实现高强度、大厚度金属箔材超声波快速固结成形与制造。针对脉冲电流辅助金属层状复合材料与结构超声波固结成形制造技术中的若干基础科学问题，本项目拟采用理论分析、实验研究与计算机模拟相结合的方法，深入系统地研究脉冲电流与超声波能场耦合作用下金属原子扩散机制、塑性变形及其机理、金属界面成形固态物理冶金机制及影响因素、界面微结构与力学行为的关系等若干关键科学问题。本项目的研究成果将为形成具有自主知识产权的原创性多能场耦合金属层状复合材料先进制造技术，发展脉冲电流辅助超声波能场快速固结成形与增材制造科学、制造装备、工艺技术提供理论基础。

为了提升现有金属超声波固结成形与增材制造装备的加工能力、拓宽其工艺适用范围，本项目采用多能场耦合的制造方式，对同种、异种金属脉冲电流辅助超声波固结增材制造进行了系统性的研究。脉冲电流辅助超声波固结的主要工艺参数包括：超声波振幅、正压力、焊头滚动速度、脉冲电流密度、脉冲频率等，通过控制变量方式最终获得脉冲电流辅助超声波固结金属箔材的最优工艺窗口。选用剥离实验、线焊接密度测量、显微硬度、纳米压入等实验进行固结质量的评定，通过SEM、EDX、XRD、EBSD、TEM和原子探针等测试手段对脉冲电流辅助超声波固结试样的界面形貌、原子扩散半径、界面微区塑性变形及再结晶组织织构演变等进行表征与分析。实验结果表明，脉冲电场与超声能场耦合作用下能够带来更好的固结质量，对于高强金属的结合，能够瞬时在近室温状态下降低金属材料变形抗力，增加界面结合过程中的塑性流动，降低残余应力并使内部应力分布更均匀等，解决了传统持续基板加热带来的种种问题。同时与单超声能场相比，脉冲电流协同制造的层状复合材料，固结界面处动态再结晶更为充分，纳米晶富集带来更优良的界面结合强度与更高的线焊接密度。同时，脉冲电流的微裂纹愈合能力在超声波叠层固结过程中，动态修复材料内部微区缺陷，提高材料整体焊接密度。通过脉冲电流辅助超声波固结技术的研究，降低了传统单超声能场固结下的工艺门槛，为大范围的工业化生产应用提供了先决条件。可以预见，未来脉冲电流辅助超声波固结技术将被应用于更多领域，包括：复合层状梯度材料的制备、传感器嵌入智能材料，以及复杂结构功能材料等。