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Unformatted text preview: Tribology Transactions, 51: 247-253, 2008 Copyright C Society of Tribologists and Lubrication Engineers ISSN: 1040-2004 print / 1547-357X online DOI: 10.1080/10402000701730494 Effect of Particle Size on the Wear Resistance of Alumina-Filled PTFE Micro- and Nanocomposites STEVEN E. McELWAIN, THIERRY A. BLANCHET and LINDA S. SCHADLER Rensselaer Polytechnic Institute Troy, NY 12180, USA and W. GREGORY SAWYER University of Florida Gainesville, FL 32611, USA It was long supposed that the ability of hard particle fillers to reduce the wear rate of unfilled PTFE (typically 10 3 mm 3 /Nm) by an order of magnitude or more was limited to fillers of microscale or greater, as nano-fillers would likely be encapsulated within the large microscale PTFE wear debris rather than disrupting the wear mechanism. Recent studies have demonstrated that nano-fillers can be more effective than mi- croscale fillers in reducing wear rate while maintaining a low coefficient of friction. This study attempts to further elucidate the mechanisms leading to improved wear resistance via a thorough study of the effects of particle size. When filled to a 5% mass frac- tion, 40- and 80-nm alumina particles reduced the PTFE wear rate to a 10 7 mm 3 /Nm level, two orders of magnitude better than the 10 5 mm 3 /Nm level with alumina micro-fillers at sizes ranging from 0.5 to 20 m. Composites with alumina filler in the form of nanoparticles were less abrasive to the mating steel (stainless 304) countersurfaces than those with microparticles, despite the filler being of the same material. In PTFE contain- ing a mixture of both nano- and micro-fillers, the higher wear rate microcomposite behavior predominated, likely the result of the continued presence of micro-fillers and their abrasion of the countersurface as well as any overlying beneficial trans- fer films. Despite demonstrating such a large effect on the wear rate, the variation of alumina filler size did not demonstrate any significant effect on the friction coefficient, with values for all composites tested additionally falling near the = 0.18 mea- sured for unfilled PTFE at this studys 0.01 m/s sliding speed. KEY WORDS PTFE; Nano-Composites; Wear; Friction; Self Lubrication; Nanotribology; Self-Lubricating Composites Presented at the STLE Annual Meeting in Calgary, Alberta, Canada, May 7-11 2006 Manuscript received June 9, 2007 Final Manuscript approved October 9, 2007 Review led by Yeau-Ren Jeng INTRODUCTION Polytetrafluoroethylene (PTFE) polymer is well known for the low friction it can provide in dry sliding. The hypothesis for the low friction coefficient is the presence of a thin, highly oriented transfer film as well as orientation in the wearing body. Unfortu- nately, if not reinforced, PTFE can additionally form very large lump- or plate-like wear debris (Makinson and Tabor (1) ; Bahadur and Tabor (2) ), via a delamination process with thicknesses on the order of 10 m and dimensions in the plane of the plate of sev-...
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