Effect of Texturing on Friction Properties of CNx Coating Layer under Oil Lubrication with Imitation Wear Debris

Abstract

Frequent contacts between bearing balls or needles and its guide generate friction heat, and it is not demanded because oil viscosity becomes low, then oil film thickness decreases. In such case, direct contact between mating surfaces occurs in the real contact area. To prevent wear by direct contacts, high wear proof and low friction coefficient of hard carbon coating is demanded. However, in the case of wear particles which are generated from hard carbon coating, the particles become wear promotion elements of bearing surfaces. Therefore, a surface shape modification is important to eliminate wear particles from contact area. In this paper, we prepared CNx (Carbon Nitride) coating deposited on surface with texturing to reduce friction coefficient by wear particles which were lied between mating surfaces. Friction tests were carried out at mixed and boundary lubrication condition with VG100 oil. We applied glass beads as imitation wear particles. In the boundary lubrication condition, the CNx coated surface showed friction coefficient of 0.058 in only VG100 lubrication. On the other hand, the friction coefficient was approximately 0.12 without CNx coating in VG100 lubrication. In the case of friction test with glass beads, it was clarified that 40 μm width and 20 μm depth texturing with 32 lines showed lowest friction coefficient when the specimen slid against counter material.