TTePTFE2005 - Wear resistant solid lubricant coating made...

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Unformatted text preview: Wear resistant solid lubricant coating made from PTFE and epoxy N.L. McCook a , D.L. Burris a , G.R. Bourne a , J. Steffens a , J.R. Hanrahan b and W.G. Sawyer a, * a Department of Mechanical Engineering, University of Florida, Gainesville, FL 32611 b W.L. Gore & Associates, Elkton, MD 21922 Received 5 April 2004; accepted 15 August 2004 A composite coating of polytetrauoroethylene and epoxy shows 100 improvements in wear resistance as compared to either of its constituents alone and reduced friction coecient under testing on a pin-on-disk tribometer. This coating is made by impregnating an expanded PTFE film with epoxy, which provides three unique functions: (1) the epoxy compartmentalizes the PTFE nodes, which is believed to reduce the wear of the PTFE, (2) the epoxy increases the mechanical properties such as elastic modulus and hardness, and (3) the epoxy provides a ready interface to bond the films onto a wide variety of substrates easily and securely. The experimental matrix had normal loads of 13 N, sliding speeds from 0.25 to 2.5 m/s, and used a 2.4 mm radius low carbon steel pin in a rotating pin-on-disk tribometer. The skived PTFE films had wear rates on the order of K 10 ) 3 mm 3 /Nm and friction coecients around l 0.2. Both the high density films (70 wt%PTFE) and low density films (50 wt% PTFE) had wear rates on the order of K 10 ) 6 mm 3 /Nm and friction coecients around l 0.15. The neat epoxy films showed significant scatter in the tribological measurements with wear-rates on the order of K 10 ) 4 mm 3 /Nm and friction coecients around l 0.40. The enhanced tribological behavior of these composites is believed to stem from the coatings abil- ity to draw thin PTFE transfer films into the contact from the nodes of PTFE, which act like reservoirs. Nanoindentation map- ping of the coatings and the transfer films supports this hypothesis, and accompanies scanning electron microscopy observations of the worn and unworn coatings. KEY WORDS: solid lubricants, coatings, composites, PTFE 1. Introduction There is great enthusiasm for wear-resistant, inert, environmentally insensitive, low friction, polymeric tri- bological coatings. Polytetrauoroethylene is an excep- tional low friction polymeric material that is used in many bearing applications as a solid lubricant. Unfor- tunately, PTFE suffers from poor wear resistance, and is thus the subject of many tribological research pro- jects in the area of composites [1]. Such research often incorporates hard filler particles into the PTFE matrix such as glass fibers [2], copper [3], ceramics [4], carbon fibers [5], chopped carbon fibers [6] and nano particles [7,8] in an effort to enhance the wear resistance. Other research groups incorporate fillers that may act as additional solid lubricants such as bronze [9,10], graphite [3], carbon nanotubes [11], molybdenum and tungsten disulfide [12], lead [1315], and boric-oxide [16] to improve wear resistance while retaining low...
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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.

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TTePTFE2005 - Wear resistant solid lubricant coating made...

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