Formation and Characterization of Ni-P-WS 2 and Ni-P-CNT Electroless Composite Coatings One of the promising methods of developing solid lubricant coatings is the incorporation of particles as reinforcement in a coating in order to produce a composite with dispersed solid lubricant particles. Electroless coatings can be used as matrix material for solid lubricant particles. Solid lubricant particles are suspended in electroless bath and are embedded in the layer to improve the coating properties. In this study, the effect of incorporation of tungsten disulfide solid lubricant particles in electroless coatings and its effect on tribological properties are investigated. Furthermore, the tribological properties of Ni-P-CNT composite coating have been compared and contrasted with the former. Coating procedure was carried out in a laboratory electroless bath. Process parameters included pretreatment of steel substrate by grinding and polishing to reach an appropriate roughness, surface activation by degreasing and acid-cleaning and preparation of WS2 and CNT powder before its addition to the electroless bath. The concentration of particles in plating bath was varied from 1 to 5 gr/lit for WS 2 and from 1 to 3 gr/lit for CNT. Characterization of the surface and interface was achieved by scanning electron microscopy (SEM), microhardness measurements, X-ray diffraction and energy dispersive microanalysis to identify the chemical composition and phases in the composite coatings. X-ray diffraction showed that the as-plated composite coatings had amorphous structure and formed crystalline structure after heat treatment. The SEM results illustrated that the thicknesses of both coatings were about 20 µm and the deposited coatings had nodular features with a typical cauliflower-like morphology. Considering Ni-P-WS 2 coatings, nodular features and surface roughness were higher compared to Ni-P-CNT coating. By increasing particle concentration in the bath, the concentration of particles in the coatings increased to a maximum value and then decreased. The maximum concentration of WS 2 particles were achieved in 4 gr/lit and this value for Ni-P-carbon nanotube coatings was 2 gr/lit. Microhardness measurement featured that maximum hardness for both coatings were achieved after heat treatment, because of the formation of crystalline nickel and semicoherent Ni 3 P phases, however, the hardness of Ni-P-CNT coatings was more than that of Ni-P-WS 2 due to excellent load bearing of CNT particles. Wear and friction investigation of coatings proved that Ni-P-WS 2 coatings reduced friction coefficient and created good lubrication in comparison with conventional
