Abstract
A large series of dry-sliding pin-on-disk tests was carried out with different wear-resistant surface coatings under consistent conditions of load, sliding speed and air environment. The primary objective of these tests was to provide information which can be used to facilitate the selection process for surface coatings intended for sliding-bearing applications. The coatings were produced using physical vapour deposition (PVD), chemical vapour deposition (CVD) and plasma spray (PS) techniques and were tested in combination with themselves and with an uncoated hardened tool steel. In the latter case, the effect of the coating on the wear of the steel was examined. The relative wear and friction behaviour of the different coatings was compared for the conditions applied in the tests. Some important mechanisms influencing the wear and friction characteristics were identified. With uncoated steel as the counterpart material, an amorphous W-C:H coating (H. Dimigen and H. Huebsch, US Patent 4 525 417, 1985) produced by PVD resulted in particularly low wear of the steel ( K≈0.01×10 −15 m 3 Nm −1) and a low friction coefficient (μ≈0.3). Significantly different wear behaviour was observed for TiN coatings produced by different PVD techniques. This can be partially attributed to friction-induced heating of the contact area which causes oxidation of the free titanium contained within certain PVD TiN coatings. The relatively low wear recorded for a PS WC−12%Co coating may be attributed to a similar effect involving the formation of lubricious cobalt oxide. The coating surface topography was identified as an important factor in the transfer (by trapping) of steel wear debris to the coating surface. This effect greatly influences the friction and wear behaviour. The R a roughness parameter was found to characterize inadequately the coating surface in terms of its tendency to trap wear debris and promote material transfer.
Published Version
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