激光扫描速率对NiCr/Cr_(3)C_(2)涂层微结构与耐磨性的影响

Effect of laser scanning rate on microstructure and wear resistance of NiCr/Cr_(3)C_(2)coating

采用激光熔覆技术在3种扫描速率下制备了NiCr/Cr_(3)C_(2)复合涂层,分别采用扫描电镜(SEM)、X射线衍射仪(XRD)、显微维氏硬度计、摩擦磨损试验机表征了熔覆层的组织形貌、硬度与摩擦磨损性能。结果表明,激光扫描速率从2 mm/s升至4 mm/s时,熔覆层组织从以树枝晶为主转变为以等轴晶为主,缺陷由气孔转变为大尺寸间隙与裂纹。扫描速率低于3 mm/s时,Cr_(3)C_(2)熔化分解导致熔覆层主要含有Cr_(7)C_(3),随着激光扫描速率增加,Cr_(3)C_(2)熔化程度降低,熔覆层以Cr_(7)C_(3)与Cr_(3)C_(2)为主。因此,随着激光扫描速率从2 mm/s升高至4 mm/s,熔覆层硬度从400 HV0.3提升至780 HV0.3。不同激光扫描速率下熔覆层磨损均以磨粒磨损为主,但是由于结构致密和硬度较高,3 mm/s涂层磨损量最小,耐磨性最好。

NiCr/Cr_(3)C_(2)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 Cr_(3)C_(2)results in the clad layer mainly containing Cr_(7)C_(3).As the laser scanning rate increases,the melting degree of Cr_(3)C_(2)decreases,and the clad layer is mainly composed of Cr_(7)C_(3)and Cr_(3)C_(2).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.