Abstract:  Aiming at the problems that the components had high crack sensitivity due to the intense temperature field changes accompanied by stress and strain evolution in laser cladding processes. The evolution of residual stresses under different laser scanning paths and processing parameters was studied. Fe-based multilayer coatings were prepared by laser cladding on Q345 steels. The residual stress distribution along the coating depth was measured by X-ray diffraction method combined with electrochemical corrosion stripping method. The effects of laser scanning path, power and scanning speed on the microstructure and stress distribution of the coatings were investigated. The results show that the residual compressive stress occurs on the surface and inside of the coatings, the residual stresses changes at the coating-substrate fusion line, and the heat-affected zones are of the residual tensile stress. Laser cladding processes have significant influences on the size and distribution of residual stresses for coatings. When laser scanning path is contour bias, power is as 1.8 kW and scanning speed is as 0.02 m/s, the coatings have the best residual stress distribution and forming quality. The residual stress is mainly related to the impacts of laser beams on the molten pool and the non-equilibrium solidification characteristics of the cladding layers.

Key words: laser cladding, Fe-based coating, residual stress, microstructure, microhardness

摘要： 针对激光熔覆过程中剧烈的温度场变化伴随着应力、应变演化，进而导致零件具有高裂纹敏感性的问题，对不同激光扫描路径及工艺参数下残余应力演变规律进行研究。采用激光熔覆在Q345钢上制备了Fe基双层多道涂层，并以X射线衍射法结合电化学腐蚀剥层法测量沿涂层深度方向的残余应力分布，探究激光扫描路径、功率以及扫描速度对涂层显微组织和应力分布的影响。结果表明：涂层表面和内部为残余压应力，在涂层基体熔合线处残余应力发生突变，热影响区表现为残余拉应力；激光熔覆工艺对涂层残余应力的大小和分布规律有显著影响，当激光扫描路径为轮廓偏置式、激光功率为1.8 kW、扫描速度为0.02 m/s时，涂层具有最优的残余应力分布和成形质量；残余应力的产生主要与激光束对熔池的冲击作用以及熔覆层的非平衡凝固特性有关。

关键词: 激光熔覆, 铁基涂层, 残余应力, 微观组织, 显微硬度