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Unformatted text preview: Downloaded By: [University of Florida] At: 18:20 27 February 2008 Tribology Transactions, 48: 147-153, 2005 Copyright C circlecopyrt Society of Tribologists and Lubrication Engineers ISSN: 0569-8197 print / 1547-397X online DOI: 10.1080/05698190590923842 Tribological Sensitivity of PTFE/Alumina Nanocomposites to a Range of Traditional Surface Finishes DAVID L. BURRIS and W. GREGORY SAWYER Department of Mechanical and Aerospace Engineering University of Florida Gainesville, Florida 32611, USA Wear tests were performed with polytetrafluoroethylene (PTFE) + Al 2 O 3 nanocomposites on various manufactured surfaces to determine whether or not the wear resistance of these nanocomposites is a strong function of surface prepara- tion. Four different surface finishes of grade 304 stainless steel counterfaces were used: electropolished ( R q = 88 nm), lapped ( R q = 161 nm), wet-sanded ( R q = 390 nm), and dry-sanded ( R q = 578 nm). PTFE + Al 2 O 3 nanocomposites made from powdersofroughly2-20 mPTFE(matrix)and 44nmAl 2 O 3 (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% 80- and 500-nm Al 2 O 3 filled PTFE composites on each surface. Friction coefficients were between 0.12 and 0.19 and wear rates decreased from K = 810 10 6 mm 3 /(Nm) for the 5 wt% 500-nm alumina-filled PTFE on the dry-sanded surface to K = 0.8 10 6 mm 3 /(Nm) for the 5 wt% 80-nm filled com- posite on the lapped surface. It was found that the minimum wear rate occurred on the lapped counterface for every com- posite, and the wear rate is a strong function of the transfer film thickness and morphology. KEY WORDS Solid Lubricants; Nanocomposites; Friction and Wear; Surface Roughness INTRODUCTION Polytetrafluoroethylene (PTFE) exhibits many desirable tribo- logical characteristics, including low friction, high melting temper- ature, and chemical inertness; it receives much attention for use as a solid lubricant. Although it offers a low friction coefficient in most conditions, PTFE wears rapidly compared to other polymers, precluding its use as a bearing material in many cases. Presented at the ASME/STLE Tribology Conference in Long Beach, California October 24-27, 2004 Manuscript approved October 13, 2004 Review led by Robert Fusaro Significant amounts of research have been done to improve the wear resistance of PTFE without sacrificing its low friction ca- pability. Just about everything put into PTFE generally improves the wear resistance at the expense of friction coefficient, includ- ing nanoparticles. Although there are many theories for the role of filler particles and fibers in tribological composites, there was a general speculation that nanofillers could not prevent large- scale destruction of the banded structure of PTFE and would be transferred with the PTFE onto the counterface (Tanaka and Kawakami (1) ). The qualitative models suggest that the asper-)....
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This note was uploaded on 08/22/2011 for the course EGM 4313 taught by Professor Mei during the Spring '08 term at University of Florida.
- Spring '08