Effect of post-coating technique on microstructure, microhardness and the mixed lubrication regime parameters of thermally-sprayed NiCrBSi coatings

Abstract The purpose of this paper is to understand and to quantify the effect of the re-melting technique on the microstructure and tribological behaviour of oxy-fuel (OF) thermally sprayed NiCrBSi coatings in the mixed lubrication regime. Two different re-melting techniques have been used: Surface Flame Melting (SFM) and laser re-melting processes. The microstructure of the obtained coatings was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Deposited coatings demonstrated similar phases but manifested notable differences in their morphology, size, distribution and relative proportions of the observable phases. These differences in microstructure may explain the differences in coating properties. Tribological experiments were carried out using a pin-on-disc approach at different sliding speeds and contact pressures. Wear and indentation tests have also been conducted. Laser re-melted coatings achieve higher hardness, less friction and lower accumulated wear volume in lubricated conditions. Test data were fitted with regression models. The fitted equations allow a robust assessment of the effect of the re-melting technique and working conditions on the friction coefficient in components that operate in the mixed lubrication regime. Therefore, these equations may help to select the adequate coating and tribological parameters for specific applications.