Modification of Frictional Surfaces of Bearings by Addition of Nanoparticle Compositions to Lubricants

The results of a study of the effect of additives to lubricating oils on changes in the structure of the friction surface and, as a consequence, the tribological characteristics of the "steel to steel" friction pair are presented. The experiments were conducted using a standard "disk-disk" scheme on a friction machine with double cycles of step loading. The material of the disks was bearing steel ШХ-15 with a hardness of 61-63 HRC. Changes in the surface structure were monitored using a binocular microscope. A detailed study of the friction surfaces was carried out using a scanning electron microscope. The microhardness of the friction surfaces was also measured before and after loading. Quantitative changes in the surface relief were determined using a profilometer. The study of the friction surface, conducted using X-ray fluorescence analysis, revealed changes in the composition of the surface layer, which can be explained by the formation of a surface servovite film, which includes elements from the used additive to lubricant (silicon, magnesium, manganese, aluminum, sulfur). The increase in the microhardness of the friction surface when working with the additive from 4.1 GPa to 6.6 GPa, which has a positive effect on the tribological characteristics, is also explained by the formation of a servovite film, which can significantly improve the friction conditions, as well as reduce damage and wear of surfaces. Using scanning electron microscopy, surface waviness oriented at large angles (close to the normal) to the direction of deformation during friction was revealed. It was assumed that the reason for the formation of such a surface relief is microplastic deformation under the action of bias stresses arising in the surface layers of the friction pair. The structural changes observed during friction with the use of a lubricant additive support the assumption of the formation of a ceramic (servovite) film, which has a significantly greater reserve of plasticity compared to a surface with an oxide film, usually present on the surface during friction with a lubricant without an additive.