LAUSR

The wear rates of tribological polymers are strongly influenced by counterface roughness through competing mechanisms such as polymer abrasion by counterface asperities and mechanical engagement of debris into the features of the rough surface. Previous studies have shown that an ultra-low wear (k ~ 10−7 mm3/Nm) alumina–PTFE solid lubricant loses wear resistance and the ability to form stable transfer films when the counterface roughness exceeds a critical magnitude or aligns with the sliding direction. In this paper, we aimed to test the independent effects of counterface peaks and valleys on polymer wear and transfer using this well-studied alumina–PTFE system. Wear tests were performed against 304 stainless steel counterfaces of systematically varied peak height and valley depth. Interrupted microscopy measurements were used to record the details of debris engagement, migration, aggregation, and removal. Preferential removal of the tallest peaks on the counterface helped stabilize the transfer films and dramatically reduced the transient wear volume of the polymer composite even on very rough surfaces. The results illustrate the independent and competing effects of counterface peaks, plateaus, and valleys on the wear and transfer of this ultra-low wear polymer composite. While increased peak height promoted primary material removal from the polymer composite and inhibited the formation of the transfer film, intersecting valleys and smooth plateaus helped nucleate and stabilize transfer films. On rough surfaces with tall peaks, the composite eventually achieved ultra-low wear by gradually removing the tallest asperities to achieve a more favorable topography for transfer film formation.