Frictional properties and wear of a molybdenum coating and a bronze (Cu-10%Sn) with friction modifier fillers

A new manufacturing process and a new family of composite materials (bronze matrix + friction modifiers) for lubricated tribological systems, such as synchronizer rings in manual gear boxes, has been developed. The research has provided a better understanding of lubricating oil film formation and how to stabilize it by a suitable surface chemistry and morphology, as well as the ability to produce such a surface by means of non flat powder-metallurgical (P/M) composite coatings. Commonly used synchronizers are of two types: forged brass and sintered steel with molybdenum coating. Brass synchronizers work very well when new but degrade with use. Molybdenum coatings are produced by a high cost plasma spraying. The new bronze based friction materials have reached the performance level of molybdenum coating in tribometer measurements. The tribological behaviour of the Mo and bronze ring types was characterized in lubricated conditions (temperature: - 10°C to 120°C). XPS and SEM/EDX analysis allowed to verify tribochemical reactions taking place during the working process.