Tribological behavior of the bronze–steel pair for worm gearing

The wear damage mechanisms occurring in the tribological pair bronze (CuSn12)-quenched and tempered steel (42CrMo4V) frequently used as reference materials for worm gearing power transmissions were investigated. Lubricated rolling sliding tests in the disk-on-disk configuration were performed. Different radial loads were applied in order to reach in the contact region Hertzian pressures close to the allowable design limit for bronze. The relative sliding speed was set to a level typical of screw-worm wheel transmissions. The tests were conducted up to a sliding distance of about 1800 km and periodically interrupted for measuring the specimen's weight loss and for inspecting the surface modifications. At the end of the test, the wear curves (specific weight loss vs. sliding distance) were built up and the surface damage was analyzed by means of optical and scanning electron microscopy. Different damage phenomena as scoring, pitting, spalling were identified, whose severity depends on the applied load. Microstructural features, i.e. the interdendritic phase, strongly dictate the subsurface crack path and crack branching.