Microstructure and tribological behavior of tungsten-containing diamondlike carbon coated rubbers

Abstract

Tungsten-containing diamondlike carbon (W-DLC) coatings have been deposited on FKM (fluorocarbon), ACM (acrylate), and HNBR (hydrogenated nitrile butadiene) rubbers via unbalanced magnetron reactive sputtering from a WC target in C2H2/Ar plasma. The surface morphology and fracture cross sections of coated rubbers have been scrutinized by high resolution scanning electron microscopy (SEM). The random crack networks formed due to the large difference in the coefficients of thermal expansion break down the W-DLC coatings into segments of a couple of hundred micrometers in size, facilitating good flexibility if the interfacial adhesion between the coating and a rubber substrate is strong enough. The size and density of growth defects in the W-DLC coatings strongly depend on the surface roughness of the rubber sheets. The tribological behavior of uncoated and coated rubbers has been investigated with ball-on-disk tribotest under dry sliding condition against a 6 mm 100Cr6 ball. Uncoated rubbers exhibited a very high coefficient of friction (>0.9). W-DLC coated FKM did not considerably reduce the friction because the coating was damaged due to poor adhesion. W-DLC coated HNBR and ACM exhibited excellent tribological performance, and very low coefficients of friction (<0.24) were achieved even at high normal load of 5 N. After tribotests, the W-DLC coatings on HNBR and ACM were intact and no serious damage was observed on the wear tracks.