Effect of Carbon Coating on Scuffing of Steel Surfaces during Oil Lubrication

A failure mode in engine components that undermines engine reliability is scuffing; defined as sudden catastrophic failure of sliding surfaces. Usually accompanied by a rapid rise in friction and temperature, occurrence of scuffing marks the end of the component's useful life. At Argonne National Laboratory, we recently developed low-friction amorphous carbon coatings with exceptional tribological properties. The present study evaluates the scuffing performance of three variations of the carbon coating deposited on H-13 steel surfaces and lubricated with base-stock and fully formulated synthetic Poly-alfa-olefin (PAO) lubricants. Using a ball-on-flat contact configuration in reciprocating sliding, we found that although the coatings reduced friction slightly, they increased scuffing resistance significantly when one of the sliding surfaces was coated when compared to uncoated steel-on-steel contact. Improvement in scuffing resistance was more pronounced in the tests conducted with the base-stock oil because of the absence of extreme pressure (EP) additive in the lubricant.