Microstructure and wear properties of laser clad TiN/Co-based composite coating

Co-based composite coatings reinforced by TiN particles were fabricated on Ni-based superalloy substrate by using a 5 kW CO₂ laser. The microstructures and phases constitution of the composite coating were studied by means of optical microscope (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The microhardness and wear resistance of the coating were also examined. The results showed that the composite coating was mainly composed of γ-Co, TiN, TiC, (Cr, W)₂₃C₆ and Co ₃Ti. And different solidification morphologies, such as planar, cellular and dendrite, were obtained. Structural transformations were attributed to the temperature gradient and solidification rate in metal-melting region. It was found that the microhardness of the composite coating was enhanced prominently as compared to the substrate region, which should be due to the undissolved TiN and other new complicated phase. Friction and wear tests without lubrication showed that the addition of TiN particles into Co-based coating can improve its wear resistance significantly without evidently increasing the friction coefficient of coating.