激光熔覆-机械振动耦合场作用下颗粒增强功能复合涂层的凝固机理及其组织演变

Pores and cracks are the key problems to obstacle the further wide application of laser cladding coating. Therefore, the preparation without pores and crack laser cladding coating has been the focus of attention in the field of Surface Engineering and Materials Science. This project uses the mechanical vibration coupling laser cladding modification new technology to fabricate ceramic particles reinforced composite coating on Fe-based alloy surface. The non-equilibrium rapid solidification crystallization behavior, microstructure evolution and stress control in laser molten pool are acted as the research object. Firstly, the ceramic particles reinforced composite coating without pores and cracks were fabricated on Fe-based alloy surface. Secondly, the wear and corrosion properties, high temperature oxidation resistance,fatigue performance and stress control of the ceramic particles reinforced functional composite coatings were characterized. The phase composition, interface behavior between cladding coating and Fe base alloy substrate and microstructure evolution were analized. Thirdly, the thermodynamic and kinetic mechanisms in the laser molten pool were clarified, then according to the thermodynamic and kinetic mechanisms and the influence of microstructure evolution in laser molten pool on coating performance and residual stress to establish the physical model of coating quality control and alloy-particles phase diagram model under mechanical vibration and laser cladding conditions. Last but not least, the solidification mechanism of the ceramic particles reinforced functional composite coating was revealed, thus further regulate and control the coating microstructure, optimize the preparation process. This project proposed without pores and cracks ceramic particle reinforced composite coating modification process under mechanical vibration and laser cladding coupling field conditions, in order to provide a new technical approach and theoretical guidance for improving the Fe-based alloy comprehensive performance and broadening its applications range in the industrial field.

气孔和裂纹缺陷是阻碍激光熔覆涂层难以广泛推广的关键问题。因此，制备无气孔无裂纹熔覆涂层一直是表面工程和材料科学领域共同关注的热点。本项目采用激光熔覆耦合机械振动改性新技术，以非平衡快速凝固条件下熔池中的结晶行为、组织演变和应力调控为研究对象，首先在铁基合金表面制备出陶瓷颗粒增强无气孔无裂纹的功能涂层；然后测试涂层的耐磨耐蚀、抗氧化抗疲劳性能和残余应力，分析耦合场下涂层的物相组成、界面行为及组织演变特征，阐明熔池中的热力学与反应动力学机制；再以该机制和组织演变对涂层性能及应力的影响规律为基础，建立耦合场下控制涂层成形质量的物理模型和合金-颗粒相复合相图模型，揭示耦合场下无气孔无裂纹功能涂层的凝固机理；进而进一步调控涂层微结构，优化工艺流程。项目提出激光熔覆与机械振动耦合场制备颗粒增强无气孔无裂纹功能涂层改性工艺，以期为改善铁基合金综合性能并扩大激光熔覆工业应用范围提供新的技术途径和理论指导。

项目“激光熔覆-机械振动耦合场作用下颗粒增强功能复合涂层的凝固机理及其组织演变”针对激光熔覆涂层中存在气孔和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和材料科学领域共同关注的热点问题，提出激光熔覆耦合机械振动复合改性新技术，采用自行设计和组装的机械振动耦合激光熔覆装置，在工程上常用的45钢和低碳钢等Fe基合金表面制备了无气孔和裂纹的陶瓷颗粒增强激光熔覆复合涂层。分析了非平衡快速凝固条件下涂层的物相组成、结晶特征、组织演变规律和界面处元素的扩散行为；测试了涂层的耐磨耐蚀、残余应力、抗氧化抗疲劳和力学性能；阐明了熔池中的热力学和反应动力学机制；建立了耦合场作用下控制激光熔覆涂层成形质量的物理模型；揭示了耦合场作用下无气孔、无裂纹功能复合涂层的凝固机理；根据表面成形质量良好和无气孔无裂纹涂层产生的条件，寻找出了高能激光束和机械振动耦合作用下，粉末粒度、大小、成分配比、处理状态和熔覆涂层中结晶形态、存在形式、颗粒相尺寸、均匀性、分布规律、应力大小、成分偏析、温度和浓度梯度分布等因素随激光能量密度和激振能变化之间的对应关系，调控了机械振动耦合激光熔覆复合涂层的微观组织结构，优化了无气孔和裂纹涂层的工艺流程。该项目的研究为改善铁基合金综合性能并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、模具钢等Fe基合金工程零件表面获得无气孔和裂纹、表面成形质量良好的机械振动辅助激光熔覆功能复合涂层理想工艺为：激光功率3.8kW、扫描速度400mm/min、圆形光斑直径6.0mm、离焦量55mm、振动频率200Hz、振幅1.5mm。. 通过该项目的系统研究，发表了学术论文18篇，其中SCI和EI收录论文16篇（包括SCI一区论文3篇）；申请了国家发明和实用新型专利22件，授权国家发明专利2件，实用新型专利9件；培养了博士研究生3名，硕士研究生9名。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。