The effects of surface conditioning and gear oil type on friction and wear behavior under sliding condition

Highly additized low viscous lubricants, new coatings, and surface treatments have been employed by original equipment manufacturers in several tribosystems to reduce emission and fuel consumption. In this sense, this work investigates the tribological response of four different advanced fully formulated gear oils and three different materials (coatings and topography) in terms of friction and wear using a ball-on-disc test rig under pure unidirectional sliding condition and boundary lubrication. The tested lubricants had different base oils: mineral, semi-synthetic, and synthetic with different additive packages. The ball's material was AISI 52100 bearing steel and the bulk material of the tested specimens (discs) were SAE 4320 steel with surface as follows: (i) ground; (ii) subjected to ceramic shot peening (CSP) and, (iii) coated with WC/C. Optical and scanning electron microscopy and 3D profilometry were used to evaluate the wear track and tribofilm formation. It was found that the frictional dependence on the surface topography and lubricant type is not significant, whilst the wear mechanisms were highly dependent on material and surface conditioning. The harder and rougher the contact body, the higher the wear produced in the counter body. At the harsher conditions base oil type control wear more effectively than the additive package.