Tribological studies of high surface finish ceramic coatings for low friction and adhesive wear resistant applications

Abstract

Adhesive wear is a significant material loss mechanism that leads to wide scale surface degradation of functional components especially in engineering industries like wind turbine roller bearings. This paper deals with improving the tribological properties of surfaces where adhesive wear is prominent. Adhesive wear is a common problem in gears, bearings, cutting tools, fittings, valves and earth moving equipment. For instance in a planetary gear arrangement, worn out debris from gears cause adhesive wear on the surface of roller bearings. Ceramic coatings are significant for protecting components and to improve the performance of surfaces subjected to adhesive wear over longer periods. Most of the ceramic coatings have high surface roughness owing to which they contribute to further adhesive wear of fine surfaces. In this paper, focus is on studying the performance of ion plated titanium nitride (TiN) and titanium carbide (TiC) PVD coatings against adhesive wear on EN 31 steel (substrate). Surfaces of samples coated with TiN, TiC and uncoated substrate of EN 31 steel are comparatively studied for adhesive wear behavior using wear tests as per ASTM standards. EN 31 steel is composed of 95% Fe, 0.9–1.1% C, 0.35% Mn, and 0.2% Si. Surface morphology and compositional analysis is inferred from Electron Microscopy (SEM and EDS) and surface roughness is estimated using 3-D confocal microscopy and surface profile measurement. The bond strength of coating is analysed from nanoscratch test; the coefficient of friction, material removal rate and hardness of surface is obtained from nano indentation Test. On experimental investigation, it is found that TiN and TiC ceramic coatings have excellent wear resistance, a low coefficient of friction and fine surface finish which are suitable for adhesive wear resistant applications.