Influence of a WC/a-C:H tribological coating on micropitting wear of bearing steel

• Micropitting depended upon hardness of counter face asperities.
• WC/a-C:H mitigates micropitting damage if applied to a smoother surface.
• WC/a-C:H on a rougher surface abrasively wears the counter face.
• Wear dominated when the slide to roll ratio was +10%.
• Micropitting dominated when the slide-to-roll ratio was −10%.

The focus of this work was to evaluate the use of a WC/a-C:H coating, specifically designed to withstand rolling contact fatigue, to mitigate micropitting damage on through-hardened AISI 52100 bearing steel. This was accomplished by conducting experiments with various combinations of coated discs and rollers using a three-disc-on-roller rolling contact fatigue machine. In addition to testing coated and uncoated contacts, discs and rollers with three hardness levels and different surface roughness values were also evaluated. Upon the completion of this work, it was observed that the onset of micropitting damage was affected by the hardness of the asperities on the mated roller and disc samples. It was also observed that the coated surface can cause abrasive wear damage on an uncoated surface if the coating is applied to a surface that has a roughness Rq≥0.5 μm. If the coating is applied to a smoother roller surface (Rq≤0.26 μm), the coating is able to mitigate micropitting damage on the roller surface without causing high abrasive wear rates on the disc surfaces.