关键词: 激光熔覆, 激光扫描速率, NiCr/Cr₃C₂涂层, 组织, 耐磨性

Abstract: NiCr/Cr₃C₂ composite coating was prepared by laser cladding at three laser scanning rates. The microstructure, hardness and friction and wear properties of the coatings were characterized using scanning electron microscope (SEM), X-ray diffractometer (XRD), micro-hardness tester and friction and wear testing machine. The results show that the structure in clad layer transfer from dendrite to equiaxed as the laser scanning rate increases from 2 mm/s to 4 mm/s, and the defects transfer from pores to large gaps and microcracks. When the scanning rate is below 3 mm/s, the melting and decomposition of Cr₃C₂ results in the clad layer mainly containing Cr₇C₃. As the laser scanning rate increases, the melting degree of Cr₃C₂ decreases, and the clad layer is mainly composed of Cr₇C₃ and Cr₃C₂. Therefore, the hardness of the clad layer increases from 400 HV0.3 to 780 HV0.3 when the laser scanning rate rises from 2 mm/s to 4 mm/s. The wear mechanism of the clad layer at different laser scanning rates is mainly abrasive wear, but due to its dense structure and higher hardness, the wear loss of the clad layer at scanning rate of 3 mm/s is the smallest and the wear resistance is the best.

Key words: laser cladding, laser scanning rate, NiCr/Cr₃C₂ coating, microstructure, wear resistance