Microstructure and tribological properties of Co-Ti₃SiC₂ self-lubricating composite coatings on 304 stainless steel by laser cladding

The self lubricating wear-resistant coatings were prepared on the surface of 304 stainless steel successfully using laser cladding synchronous powder feeding method, the ratio of cladding powder was pure Co, Co-2%Ti3SiC2(mass fraction, the same below) and Co-8%Ti3SiC2. The microstructure of the cladding coating was characterized by scanning electron microscope(SEM), energy spectrum analyzer(EDS) and X-ray diffractometer(XRD). The tribological performance and related mechanisms of 304 substrate and coatings at RT/600℃ were systematically investigated. The results show that the average microhardness of the N1, N2 and N3 coatings are 285.7HV0.5, 356.3HV0.5 and 463.8HV0.5, which are all much higher than that of the matrix(240.3HV0.5). Co-Ti3SiC2 composite coatings are composed of continuous matrix γ-Co solid solution, hard phase (Fe2C, Cr7C3 and TiC) and lubricating phase Ti3SiC2. At room temperature, the friction coefficients of the matrix and the N1, N2 and N3 coatings are 0.56, 0.62, 0.68 and 0.42, the wear rates of the N1, N2, N3 coatings are 9.15×10-5, 7.81×10-5, 4.66×10-5 mm3/(N·m), which are lower than that of the matrix (66.42×10-5 mm3/(N·m)); at high temperature, the friction coefficients of the matrix and the N1, N2 and N3 coatings are 0.66, 0.54, 0.52 and 0.46, the wear rates of the N1, N2, N3 coatings are 37.79×10-5, 35.6×10-5, 18.83×10-5 mm3/(N·m), which are lower than that of the matrix (41.3×10-5 mm3/(N·m)).At room temperature and 600℃, compared with the 304 stainless substrate, the coatings have the obvious higher microhardness, and the Co-8%Ti3SiC2 coating exhibits the best self-lubricating wear resistance.