Rolling contact fatigue of bearing components coated with carbon nitride thin films

• The presence of CNx coating on roller prevents run-in effects during rolling.
• Coating debris prevent metal contact and facilitate shearing between counterparts.New run-in effects due to steel-to-steel contact during rolling are prevented.
• Probability for premature fatigue and excessive wear are significantly reduced.
• Effective thickness of W interlayer, for avoiding roller fatigue, is ~15 nm.

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.