Tribological behavior of W-DLC coated rubber seals

Tungsten-containing diamond-like carbon (W-DLC) coatings have been deposited on FKM (fluorocarbon) and HNBR (hydrogenated nitrile butadiene) rubbers via unbalanced magnetron reactive sputtering from a WC target in a C2H2/Ar plasma. The surface morphology and fracture cross sections of uncoated and coated rubbers have been characterized with high resolution scanning electron microscopy (SEM). The tribological behavior of uncoated and coated rubbers has been investigated with ball-on-disc tribotest under dry sliding condition against a 100Cr6 ball. The coefficient of friction (CoF) of uncoated rubbers is very high (> 1). Equally a relatively high CoF of W-DLC coated FKM (about 0.6) is observed due to the gradual failure and delamination of the coatings. On the contrary, W-DLC coated HNBR rubber exhibits a superior tribological performance with a very low CoF of 0.2-0.25. The latter is comparable to that of Me-DLC coatings deposited on steel substrates. After 10,000 sliding laps almost no damage of the coatings is observed on the wear tracks. In fact the network of micro-cracks as deposited facilitates the flexibility of the coatings. The different surface roughness and mechanical properties of the rubber substrates explain the differences in the tribological performances of the coated rubbers. (C) 2007 Elsevier B.V. All rights reserved.