Friction and Wear Performance of Surface Coatings in Brake Applications

To improve the wear performance of contacting components, novel surface coatings have been developed over the past decade. In the present investigation, extended duration pin-on-disk experiments were carried out to determine the relative performance of tungsten disulphide, electroless nickel (MP6 and LP9) and hard chromium coatings for use in a commercial brake valve assembly. In the experiments, 100 μm thick coatings were applied to the disk surface and tests were conducted in both lubricated (transmission fluid with 5% weight boric acid additive) and unlubricated conditions. To establish the overall performance of the coatings, the friction coefficient and disk wear rate values were recorded over a sliding distance of 6280 m. Based on the experiments, it was observed that both the electroless nickel and the chromium coatings had moderate friction and insignificant wear over the sliding distance examined. Self lubricating tungsten disulphide, in contrast, exhibited very low friction, but completed degraded over time making it unsuitable for the application of interest.