交变磁场-机械振动协同激光熔覆制备3D功能涂层的微结构演变特征及凝固动力学机制

Presence of cracks in laser cladding coating is the thorny problem to restrict metal powder laser cladding additive manufacturing (3D printing) process large scale used. In recent years, look for a method to suppress or eliminate the cracks in laser cladding additive manufacturing coating and explore the formation mechanism of crack-free coating is the hot and difficult research in the field of domestic and foreign high-energy beam laser processing and manufacturing. This project based on the early mechanical vibration assisted laser cladding 3D printing new ideas to make a significant reduction cracks in coating, further proposed a complex laser cladding 3D printing technology under the synergistic effect of alternating magnetic field and mechanical vibration. First, according to the coating and base material matching principle, WC, BN, Al2O3 particle reinforced FeCSiB, NiCrBSi, NiCoCrAlY no cracks 3D coatings were designed and prepared on the surface of iron-based alloy. Then the relationship between crack formation and the chemical constitution, stress distribution, microstructure, homogeneity of the 3D coatings were characterized by Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). The crack-free 3D coatings microstructure evolution was discussed. And then, the enhanced phase lattice constants were calculated by means of first-principle, the phase content were analyzed by metallurgical color calibration method and the interface diffusion behavior of elements were investigated by the law of diffusion. Combined with the crystal nucleation, growth characteristics, phases existing forms by the collection data of high-speed photography and wear and corrosion, high temperature oxidation resistance tests results, the solidification kinetics mechanism was revealed. At last, according to the both science problem solved of microstructure evolution and solidification kinetics mechanism, optimization of laser cladding additive manufacturing crack-free 3D coating process. In order to provide a theoretical and practical basis for the practical application of alternating magnetic field-mechanical vibration surface modification new technology.

裂纹存在是制约激光熔覆涂层进一步大面积推广的棘手问题，寻找抑制或消除熔覆涂层中裂纹的方法并探讨其形成机理是近年来国内外高能束加工领域关注的热点。本项目拟在前期研究基础上，提出交变磁场-机械振动协同激光熔覆的涂层制备复合新技术，首先在钢基材料表面制备出WC、BN、Al2O3颗粒增强的FeCSiB、NiCrBSi、NiCoCrAlY无裂纹3D功能涂层；然后利用SEM、TEM、XRD、XPS等手段分析涂层不出现裂纹与其内部物相组成、应力分布、组织类型之间的因果关系，探讨无裂纹涂层的微结构演变规律；再借助第一性原理计算增强相点阵常数和扩散定律分析界面处元素的扩散行为，并结合高速摄影采集的晶体生长特征信息、耐磨、耐蚀和高温抗氧化性能测试结果，揭示无裂纹涂层的凝固动力学机制；最后通过微组织演变规律和凝固动力学机制两个科学问题的解决来优化涂层制备工艺流程，以期为该新技术的工程应用提供理论和实践依据。

项目“交变磁场-机械振动协同激光熔覆制备3D功能涂层的微结构演变特征及凝固动力学机制”针对目前激光熔覆涂层中普遍存在气孔、裂纹缺陷而阻碍激光熔覆技术难以大面积推广这一表面工程、材料科学、凝聚态物理领域共同关注的热点和棘手问题，在课题组前期研究基础上，提出了交变磁场-机械振动协同激光熔覆的功能涂层制备复合改性新技术。采用自行设计和组装的交变磁场-机械振动耦合激光熔覆装置，在钢基材料表面制备出了WC、BN、Al2O3陶瓷颗粒增强的FeCSiB、NiCrBSi、NiCoCrAlY等无气孔无裂纹3D功能涂层。通过SEM、TEM、XRD、XPS等表征手段分析了非平衡快速凝固情况下激光熔覆功能复合3D涂层中不出现气孔、裂纹条件与其内部化学组成、应力分布、结晶特征、微结构演变规律之间的因果关系；借助第一性原理计算增强相点阵常数和Fick扩散定律分析了涂层和基材界面结合处元素的扩散行为，结合高速摄影采集的晶体生长特征信息及涂层的耐磨、耐蚀、高温抗氧化、力学性能测试结果，揭示了无气孔无裂纹3D涂层的凝固动力学机制和凝固机理；根据微结构演变规律和凝固动力学机制两个科学问题的解决优化了交变磁场-机械振动协同激光熔覆制备3D功能涂层工艺流程。该项目研究为改善工程上常用铁基、钛基合金在复杂服役环境下的综合性能、扩大激光熔覆及其复合改性工艺的工业应用范围提供了一条新的技术途径和理论指导。. 项目得出低碳钢、中碳钢、不锈钢、模具钢等常用Fe基合金工程零件表面获得无气孔、无裂纹、表面成形质量良好的交变磁场-机械振动协同激光熔覆功能3D涂层理想工艺为：激光功率3.8 kW、扫描速度400 mm/min、圆形光斑直径6.0 mm、离焦量55 mm、振动频率200 Hz、振幅1.5 mm、交变磁场强度32.0 mT。. 通过该项目的系统研究，发表了相关学术论文15篇，其中包括SCI和EI论文12篇；申请了发明和实用新型专利27件，授权国家发明专利13件，实用新型专利5件；培养了研究生12名，参加相关领域的国际国内学术会议8次。为相关企业解决轧辊和曲轴连杆的表面修复问题提供了技术支持。

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