Influence of low friction coatings on the scuffing load capacity and efficiency of gears

Abstract

The influence of multilayer composite surface coatings on gear scuffing load carrying capacity, gear friction coefficient and gearbox efficiency is discussed in this work. The deposition procedures of molybdenum disulphide/titanium (MoS 2/Ti) and carbon/chromium (C/Cr) composite coatings are described. Tests reported in the literature, such as Rockwell indentations, ball cratering, pin-on-disc and reciprocating wear, confirm the excellent adhesion to the substrate and the tribological performance of these coatings, suggesting they can be applied with success in heavy loaded rolling–sliding contacts, such as those found in gears. FZG gear scuffing tests were performed in order to evaluate the coatings anti-scuffing performance, which both improved very significantly in comparison to uncoated gears. These results in conjunction with the friction power intensity (FPI) scuffing criterion allowed the determination of a friction coefficient factor X SC to include the coating influence on the friction coefficient expression. The composite coatings were also applied to the gears of a transfer gearbox and its efficiency was measured and compared at different input speeds and torques with the uncoated carburized steel gears. Significant efficiency improvement was found with the MoS 2/Ti coating.