The limit of adhesive debris retention: A case study using ultra-low wear Alumina–PTFE

Abstract

The addition of a small selection of nano-sized fillers (e.g., α-alumina) could cause a 1000 × run-in induced wear rate reduction to the otherwise high wear polytetrafluoroethylene (PTFE). The exceedingly high wear rate reduction is strongly related to the formation of an adherent and protective transfer film at the sliding counterface; whereas certain aspects of its formation mechanisms remain unclear. Regular wear tests, tribofilm surface nanoindentations, single-stroke polymer debris collection experiments and a special ‘stripe test’ were conducted in this study. Results found 1) the run-in induced wear reduction is dominated by the polymer wear surface and accompanied by substantially reduced debris size, increased tribofilm hardness, modulus, roughness and work of adhesion against a silicon probe, 2) after the run-in, the volumetric percentage of loose debris retention on the counterface (the retention ratio) decreased monotonically with increased transfer film roughness. A simple adhesive wear model based on Rabinowicz's theory of loose debris transfer was proposed which predicts the debris retention ratio as a function of the polymer wear surface adhesiveness, hardness, modulus and the equivalent interfacial roughness. The model is supported by a strong linear relation between measured debris retention ratio and interfacial roughness (1/Sq).