Abrasive wear behaviour of Si3N4/TiO2 nanocomposite coatings fabricated by plasma electrolytic oxidation

Si3N4/TiO2 nanocomposite coatings were fabricated by plasma electrolytic oxidation of commercially pure titanium samples in a suspension of fine Si3N4 nanoparticles and the effects of time, current density, frequency and duty cycle of the pulsed current were investigated on the nanostructure of coatings and their wear mass loss rates. Layer by layer X-ray diffraction (XRD) was used for detection of nanostructure and phase characteristics of the nanocomposite layers for different levels of coatings from the top surface toward the substrate. Surface nanostructures of the fabricated layers were evaluated by scanning electron microscopy (SEM) and roughness checker. Abrasive wear rig under modified ASTM G105 was used for evaluation of abrasive wear properties. Relations between the roughness values of coatings and the effective parameters of coating process were also studied. Roughness values of the coated samples were found to be in direct relation with the distribution of nanoparticles in titania based matrix. It was concluded that the studied effective factors not only control the nanostructure of coatings but also affect the distribution of embedded nanoparticles in the layer. The optimum conditions were discussed with respect to each factor. The effects of nanostructure and preparation conditions of nanocomposite coatings on abrasive wear mechanism and mass loss rate of coatings were investigated.