Material removal on lubricated steel gears with W-DLC-coated surfaces

The wear process that occurs in lubricated steel gears with thin, metal-containing diamond-like-carbon (Me-DLC) films deposited on the surface has been characterized using a variety of techniques that include the atomic force microscope and the focused ion beam imaging system. The profile of the tungsten-containing DLC (W-DLC) has been found to duplicate that of the original steel surface with peaks and valleys having amplitude up to 1 μm, superposed on a very thin (50 nm) Cr adhesion layer. Beneath the surface, imperfections are embedded in the steel. Wear occurs through the removal of the peaks by a polishing mechanism, leaving the valleys intact. When the peaks have been fully removed to create a plateau, the RMS roughness is approximately 35 nm. There are still pits corresponding to the original valleys up to 200 nm deep. When the remnant DLC becomes smaller than the amplitude of the peaks on the steel surface, the steel and the Cr adhesion layer become polished, causing the peaks to be eliminated, as well as the imperfections present in the subsurface. The resulting surface has RMS roughness with amplitude 25 nm, as well as small protuberances associated with the carbide particles in the steel.