Research on the Microstructure and Properties of CL60 Steel Surface Laser Cladding with Medium Entropy Alloy CoCrNi

为提升城轨车轮用钢CL60的表面硬度耐蚀性，采用激光熔覆技术在CL60钢表面制备了CoCrNi中熵合金熔覆层，通过正交实验法研究不同激光熔覆工艺参数对制备CoCrNi中熵合金涂层，分析激光功率、扫描速度、送粉率对涂层微观组织的影响，并对涂层的显微硬度、熔覆层的耐腐蚀性能进行讨论。并研究了熔覆层的相组成、元素分布和耐腐蚀性能。结果表明，CoCrNi中熵合金熔覆层与基体形成了良好的冶金结合，无裂纹、气孔等缺陷；熔覆层由单一FCC相组成，熔覆层顶部主要为等轴晶，上部为蜂巢状的胞状晶，中部主要为柱状晶组织，底部为细小的平面晶。Cr富集在晶界处，晶内主要为Co、Cr、Ni、Fe。CoCrNi中熵合金熔覆层的电荷转移电阻(19470 Ω·cm2)高于CL60钢基体的极化电阻(760 Ω·cm2)，耐蚀性明显高于CL60钢基体。To enhance the surface hardness and corrosion resistance of CL60 steel used in urban rail wheels, a CoCrNi medium entropy alloy cladding layer was fabricated on the surface of CL60 steel by laser cladding technology. The effects of different laser cladding process parameters on the preparation of CoCrNi medium entropy alloy coating were investigated by orthogonal experiments. The influences of laser power, scanning speed and powder feeding rate on the microstructure of the coating were analyzed, and the microhardness and corrosion resistance of the coating were discussed. The phase composition, element distribution and corrosion resistance of the cladding layer were also studied. The results show that the CoCrNi medium entropy alloy cladding layer forms a good metallurgical bond with the substrate, without cracks, pores and other defects. The cladding layer is composed of a single FCC phase, with equiaxed grains at the top, honeycomb-like cellular grains in the upper part, columnar grains in the middle and fine planar grains at the bottom. Cr is enriched at the grain boundaries, while Co, Cr, Ni and Fe are mainly distributed in the grains. The charge transfer resistance of the CoCrNi medium entropy alloy cladding layer (19470 Ω·cm²) is higher than the polarization resistance of the CL60 steel substrate (760 Ω·cm²), and its corrosion resistance is significantly higher than that of the CL60 steel substrate.