Effect of appropriate vibration frequency on microstructure and properties of laser cladding Co-based self-lubricating composite coatings

Abstract

CrS/NbC reinforced Co-based self-lubricating composite coatings were successfully prepared on the surface of Cr12MoV steel by high-frequency micro-vibration (HFMV) assisted laser cladding technology. The microstructure, phase composition, microhardness, and wear resistance of the composite coatings were studied by means of X-ray diffractometer (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), microhardness tester, and friction-wear tester. The results show that there were excellent metallurgical bonding and free of pores and cracks in the CrS/NbC Co-based self-lubricating composite coating with 10% WS₂ prepared by laser cladding at 552 Hz vibration frequency. The appropriate vibration frequency could cause strong convection in the molten pool and refine the microstructure, which made NbC hard particulates and CrS lubricants to be evenly distributed in the composite coating. In particular, the refined CrS and NbC in the upper area of the coating were combined with each other to form a dense network microstructure. Moreover, the hardness of the coating prepared at the vibration frequency of 552 Hz was significantly improved due to its excellent microstructure compared with the without vibration and 985 Hz vibration frequencies and the maximum hardness reached 652.8 HV_0.5. Its wear resistance was also significantly improved, and the friction coefficient of the coating was reduced to 0.451. Only abrasive wear and slight adhesive wear were observed on the coatings surface, and the tearing layer and wear loss of grinding defects were significantly reduced.