大电流-磁场协同作用下激光熔覆高硬合金涂层组织性能调控及机理研究

Laser cladding technology is widely used in aerospace, equipment manufacturing, petrochemical and other fields. But the problems such as cracks, pores, inclusions, nonuniform distribution of solute elements and surface undulation have severely restricted the application of laser cladding. Improving the quality of coating, especially reduce the cracks in the high-hardness alloy coatings have great implications for the development of laser additive manufacturing and remanufacturing. Applicants proposed "alternating large current-steady magnetic field coupling" technology to reduce the cracks, adjust the microstructure and properties of coatings. The objects of this project are: taking Ni60 alloy as the research object, to find out the regulation of crack number, grain nucleation and growth, hard phase distribution and residual stress under the different electromagnetic assist condition; to analyze the coatings cracking behavior by means of residual stress measurement; to prepare a crack-free, non-porous, uniform solidified high-quality high-hardness alloy coating; to develop a three dimensional numerical model which consisting of electric field-magnetic field-temperature field-flow field by finite element method; to reveal the change regulation of temperature field and flow field in melt pool under electro-magnetic coupling field; to clarify the intrinsic mechanism of influence of complex multi-field coupling on laser cladding layer. Laying a theoretical and experimental foundation for solving the problem of high-hardness materials laser cladding cracks and improve the quality of laser cladding layer.

激光熔覆技术广泛应用于航空航天、装备制造、石油化工等领域，但熔覆层裂纹、气孔和夹杂、溶质元素分布不均及表面形貌波动等问题严重制约了其应用，提高熔覆层质量，特别是减少高硬材料熔覆层裂纹，对发展激光增材制造和再制造具有重要意义。申请者提出“交变大电流-稳态磁场耦合”技术来减少硬质合金涂层的裂纹，调控涂层的组织与性能。以Ni60合金为研究对象，详细考察不同电磁辅助条件下熔覆层裂纹数量、晶粒形核和长大、硬质相分布、以及快速凝固组织残余应力的变化规律，利用残余应力测量技术分析熔覆层开裂行为，制备出无裂纹、无气孔，凝固组织均匀致密的高质量高硬合金涂层。采用有限元法构建电场-磁场-温度场-流场多场耦合的三维数学模型，揭示电-磁复合场对激光熔覆熔池温度场和流场的影响规律，阐明复杂多场耦合对激光熔覆层组织性能影响的内在机理，为解决高硬材料激光熔覆裂纹问题、提高激光熔覆层质量奠定理论和实验基础。

激光熔覆技术广泛应用于航空航天、装备制造、石油化工等领域，但熔覆层裂纹、气孔和夹杂、溶质元素分布不均及表面形貌波动等问题严重制约了其应用，提高熔覆层质量，特别是减少高硬材料熔覆层裂纹，对发展激光增材制造和再制造具有重要意义。我们提出“交变大电流-稳态磁场耦合”技术来减少硬质合金涂层的裂纹，调控涂层的组织与性能。以Ni60合金为研究对象，详细考察了不同电磁辅助条件下熔覆层裂纹数量、晶粒形核和长大、硬质相分布、以及快速凝固组织残余应力的变化规律，利用残余应力测量技术分析熔覆层开裂行为，制备出无裂纹、无气孔，凝固组织均匀致密的高质量高硬合金涂层。采用有限元法构建了电场-磁场-温度场-流场多场耦合的三维数学模型，揭示了电-磁复合场对激光熔覆熔池温度场和流场的影响规律，阐明了复杂多场耦合对激光熔覆层组织性能影响的内在机理，为解决高硬材料激光熔覆裂纹问题、提高激光熔覆层质量奠定理论和实验基础。 . 单一交变电流、单一稳态磁场以及电-磁复合场这三种外场作用下，基体相γ-Ni的固溶度均有所增加，涂层表面裂纹数量显著减少，平均显微硬度提高。在三种外场作用下，涂层平均显微硬度的最大增幅分别为4.1%、8.6%和13.6%。电磁复合场可以提高涂层耐磨性、降低涂层残余应力。综合涂层凝固组织、表面裂纹、显微硬度、耐磨性、残余应力的变化来看，单一交变电流、单一稳态磁场以及电-磁复合场的最佳参数分别为2100 A、0.2 T和0.2 T+1200 A，且电-磁复合场对涂层凝固组织和性能的影响最为显著。采用电-磁复合的辅助方式能够以较小的电流强度发挥更大的作用效果，进而获得性能更佳的激光熔覆涂层。在实际生产中，减小电流强度不仅可以节约成本，还能降低安全隐患，因此电-磁复合场辅助激光熔覆工艺更具有可行性及现实意义。