Tribological behavior of plastic composites and stainless steel in seawater

The tribological behaviors of poly(tetrafluoroethylene) (PTFE) against 9Cr18Mo, PTFE against glass fiber–epoxy resin (GFER), 316L against PTFE and polyamide 66 (PA66) against PTFE in natural seawater were evaluated in this study by using an MMU-5G friction and wear tester. The tribological test results show that the friction coefficients, seawater temperature and wear rates of the four friction pairs decrease in the following order: PTFE–9Cr18Mo > 316L–PTFE > PTFE–GFER > PA66–PTFE. The images from a confocal laser scanning microscope reveal the wear mechanisms of the four friction pairs during seawater lubrication. The results indicate that the worn surface of 9Cr18Mo exhibits corrosion together with scattered pitting, but the worn surface of 316L is smooth and uncorroded. The worn surface of PTFE for the friction pair of PTFE–GFER is smoother than the original surface. The counterface (GFER) is covered with several PTFE transfer films that help to decrease the friction coefficient and wear rate. During sliding, the friction pair of PA66–PTFE shows excellent wear behavior because the worn surface of PA66 is covered by the PTFE film. The PTFE wear rate significantly increases when the PTFE sliding against 9Cr18Mo occurs in seawater given the serious plastic deformation of PTFE when the surface temperature is increased.