The effect of dimples geometry in the sliding surface on the tribological properties under starved lubrication conditions

• Coefficient of friction depends on geometry of the dimples on the sliding surface.
• Decrease in friction coefficient was found for suitably chosen depth and width of the dimple.
• Dimples in the surface prevent the mating sliding pair from the boundary friction regime.
• Shallow dimples were superior than deeper to obtain low friction at low sliding velocities.

Surface topography should be constructed adequately according to the operating condition of the tribological system. Although there are many sophisticated lubrication systems that deliver the lubricant to the sliding elements, in exploitational conditions, co-acting elements operate in starved lubrication, as well. For example, while starting and stopping the machine, certain parts are exposed to wear or failure. In the article, the results of examinations of sliding pairs in material matching of steel–steel are presented. The tests were conducted with application of the tribology tester pin-on-disc with the modified sliding pair geometry. The ball surface was subjected to grinding to obtain uniform contact of approximately 10 mm2 with a co-acting disc. The disc surface was subjected to burnishing technology to produce dimples in various dimensions. The values of the friction coefficient were measured and compared to all examined elements with pits and without depressions. It was established that the presence of dimples improved the tribological characteristics under starved lubrication conditions at low sliding speeds. The positive effect of the dimple presence was more significant at a lower load. The dimensions of the depressions in the surface had an influence on the tribological characteristics. The decrease of the friction coefficient values was substantial where dimples were shallow and where the area density of oil pockets was thus small.