The influence of antiwear additive concentration on the tribological behaviour of a-C:H:W/steel tribosystem

Abstract

The effect of antiwear (AW) commercial additive concentration on the load-carrying capacity (scuffing resistance) of a-C:H:W/steel tribo-system intended for heavy-loaded machine parts was investigated. For comparison, steel/steel contacts were also investigated. The scuffing resistance has been measured as the limiting pressure of seizure ( p oz ) using the four-ball apparatus. The method with continuously increasing load was applied. The tribo-systems were lubricated with poly-alpha-olefin as base oil mixed with a commercial zinc dialkyldithiophosphates type of AW additive. The AW concentration was varied in the range of 0.1–5.0 wt%. The results of the tribological experiments performed in sliding contact have shown that, by the application of the a-C:H:W coating, the tribological properties of the system were significantly improved compared with the steel friction pairs. It has also been found that it is possible to reduce the concentration of commercial AW additive below 1.0 wt%. The surface topography of the rubbed surface was investigated with optical microscopy and atomic force microscopy; the elemental chemical nature of the AW film generated on the steel counter-surface (a-C:H:W/steel tribosystem) was investigated with energy dispersive spectrometry, glow discharge optical emission spectrometry, and X-ray photoelectron spectroscopy.