Wear resistant solid lubricant coating made from PTFE and epoxy

Abstract

A composite coating of polytetrafluoroethylene and epoxy shows 100 · improvements in wear resistance as compared to either of its constituents alone and reduced friction coefficient 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 1-3 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 ¼ 10 )3 mm 3 /Nm and friction coefficients around l ¼ 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 ¼ 10 )6 mm 3 /Nm and friction coefficients around l ¼ 0.15. The neat epoxy films showed significant scatter in the tribological measurements with wear-rates on the order of K ¼ 10 )4 mm 3 /Nm and friction coefficients around l ¼ 0.40. The enhanced tribological behavior of these composites is believed to stem from the coatings ability to draw thin PTFE transfer films into the contact from the nodes of PTFE, which act like reservoirs. Nanoindentation mapping of the coatings and the transfer films supports this hypothesis, and accompanies scanning electron microscopy observations of the worn and unworn coatings.

A Review of Transfer Films and Their Role in Ultra-Low-Wear Sliding of Polymers

“…They found transfer films in the lowest wear system were~30% harder and stiffer than either counterpart material and suggested that this was the result of mechanical alloying. McCook et al [56] conducted similar measurements on the wear surface of a PTFE-epoxy composite. Whereas the composite contained clear regions of high and low hardness from the epoxy and PTFE, respectively, the wear surface exhibited uniformly low hardness, suggesting that a running film of PTFE was preferentially drawn over the entire surface; these PTFE running films were thought to substantially decrease friction and wear by preventing adhesion between the epoxy phase and the counterbody.…”

Cryogenic Friction Behavior of PTFE based Solid Lubricant Composites

“…composite was machined from a sample that was prepared via a powder blending and compression molding procedure described in [6], and the ePTFE/epoxy coatings were prepared as described in [7]. The PTFE/PEEK composite was 50 wt% PEEK and the ePTFE/epoxy composite was 46 wt% epoxy.…”

“…There were two objectives for this research effort. This first objective was to collect data on PTFE, a PTFE/PEEK composite [6], and an expanded PTFE/ epoxy coating (table 2) [7] from ambient temperatures to cryogenic temperatures in an inert gaseous environment of high purity nitrogen (<5PPM O 2 and H 2 O). The second objective was to link the frictional behavior at cryogenic temperature to the existing data and models for the frictional behavior at ambient temperatures and above.…”

Effect of simulation conditions on friction in polytetrafluoroethylene (PTFE)

“…This makes it particularly challenging to develop tribological coatings that work equally well in terrestrial and space environments. Multifunctional materials are being explored for use in such coatings; nanostructured polymer composites have been shown to be particularly good candidates, especially those that include polytetrafluoroethylene (PTFE) [1][2][3]. The C-F bond in PTFE provides both thermal and oxidative stability, and confers resistance to almost all solvents [4].…”