Rolling Contact Fatigue of Bearing Components Coated with Carbon Nitride Thin Films
Bearing rollers were coated with CNx films using high power impulse magnetron sputtering deposition in order to reduce their rolling-contact fatigue as investigated using a Micro-Pitting Rig tribometer under poly-alpha-olefin lubricated conditions. Coated rollers with a ~15 nm thick W adhesion layer to the substrate, exhibit the best performance, presenting mild wear and no fatigue after 700 kcycles. The steady-state friction coefficient was ~0.05 for both uncoated and coated rollers. Uncoated rollers show run-in friction in the first 50 kcycles, because of steel-to-steel contact, which is absent for coated rollers. Analytical transmission electron microscopy and X-ray photoelectron spectroscopy show that the presence of a CNx coating prevents steel-to-steel contact of the counterparts, prior to the elastohydrodynamic lubrication, reducing their wear and increasing the lifetime expectancy.
Keywords: Coating, Pitting, Rolling, Lubrication