Tribological Sensitivity of PTFE/Alumina Nanocomposites to a Range of Traditional Surface Finishes

Wear tests were performed with polytetrafluoroethylene (PTFE) + Al2O3 nanocomposites on various manufactured surfaces to determine whether or not the wear resistance of these nanocomposites is a strong function of surface preparation. Four different surface finishes of grade 304 stainless steel counterfaces were used: electropolished (Rq = 88 nm), lapped (Rq = 161 nm), wet-sanded (Rq = 390 nm), and dry-sanded (Rq = 578 nm). PTFE + Al2O3 nanocomposites made from powders of roughly 2-20μm PTFE (matrix) and∼44 nm Al2O3 (filler) were prepared at filler weight percentages of 0, 1, 5, and 10% and tested on each surface finish. Additionally, 5 wt% 44-nm nanocomposites were compared to identically prepared 5 wt% 80and 500-nm Al2O3 filled PTFE composites on each surface. Friction coefficients were between 0.12 and 0.19 and wear rates decreased from K = 810 × 10−6 mm3/(Nm) for the 5 wt% 500-nm alumina-filled PTFE on the dry-sanded surface to K = 0.8 × 10−6 mm3/(Nm) for the 5 wt% 80-nm filled composite on the lapped surface. It was found that the minimum wear rate occurred on the lapped counterface for every composite, and the wear rate is a strong function of the transfer film thickness and morphology.