The development of new transmissions and gearboxes is characterized by increasing levels of torque and power, improved efficiency, increased life expectancy, prolonged service intervals, reduced amount of lubricant, and more stringent noise and environmental requirements. The environment, as a new factor in the design process, increases the focus on product improvements that are designed to avoid environmental problems before they occur. Surface coating is one of the future technologies for improving performance of case-hardened gears. A main limiting factor in extending the use of hard coatings to machine component application is the lack of knowledge about how these inert coatings perform under lubricated conditions using today's lubricants, which were originally designed for steel/steel contact situations. The influence of ester-based lubricant on the scuffing capacity of WC-containing DLC coated spur gears was evaluated in a non-standard FZG test procedure. The properties of the formulated ester-based lubricant were investigated in comparison with conventional mineral gear oil. The results show that under present conditions, W-DLC coated gears could provide satisfactory wear resistance for moderate loads.
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