Abstract
Frictional characteristics of polytetrafluoroethylene (PTFE) films deposited by a hot filament chemical vapor deposition (HFCVD) method on glass substrates was investigated. A universal micro-tribotester (UMT) was used in the ball-on-flat configuration to examine the effect of coefficient of friction (COF). The effects of normal force (2.5–15 N), sliding speed (1.4 × 10−3 to 14 mm/s) and film thickness (0.3, 1, 5, 10 μm) on the frictional behavior of the PTFE film were tested. Optical microscopy was used to examine the wear tracks of the PTFE films. In addition, durability of the PTFE films was examined by monitoring the change of COF in ball-on-disk tests. The COF values of the tested PTFE films were found to be in the range 0.03–0.18 depending on the measurement conditions. In particular, PTFE exhibits a low COF at slow speeds and high normal forces compared to a high COF at high speeds and small normal forces. Modified Hertzian contact equations and finite element analysis were used to analyze the indentation process. Comparison with the width of the experimental wear tracks indicates that the PTFE layer has a small contribution in carrying the normal load yet provides good protection against tangential forces.
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