Self-competing and Coupled Effect of Laser-Engraved Counterface Groove Depth and Density on Wear of Alumina PTFE

Polymeric solid lubricants rely on the deposition of a debris-formed transfer film on the usually metallic counterface to reduce wear and friction. Debris retention at the sliding surface is determined by the interactions between debris and roughness asperities which are complex functions of debris size and roughness profile. Recent works found pre-existing, sandpaper-lapped counterface roughness grooves perpendicular to the sliding direction could significantly improve debris retention and reduce the wear rate of an alumina PTFE solid lubricant by 70%. In this paper, we aimed to test the independent effects of roughness groove depth and density on debris retention and wear performance of a well-studied alumina PTFE solid lubricant using laser-textured counterfaces with independently varied groove depth and interval. All grooves in this study were engraved perpendicular to the sliding direction. The results suggested both groove depth and interval have self-competing effect on wear due to the in situ grounding and roughness alignment of the counterface topography during sliding and may compete or cooperate with each other in determining solid lubricant wear. A new surface directionality parameter was defined to quantify the in situ counterface roughness alignment which increased proportionally with increased composite wear volume at low-wear transition. A conceptual framework was proposed to illustrate the relations between counterface texture, transient wear volume, surface directionality and counterface abrasion.