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The rolling contact fatigue of WC/C-coated spur gears

The aim of the study was to investigate the resistance to rolling contact fatigue of WC/C-coated gears. The WC/C low-friction coating was deposited using the physical vapour deposition process by reactive sputtering. The investigation of rolling contact fatigue was realised by means of a back-to-back gear test rig using FZG PT C/10/90 method. Four material combinations of gears were tested: uncoated wheel and pinion, coated wheel and pinion, coated wheel and uncoated pinion, as well as uncoated wheel and coated pinion. The tests were performed for mineral gear oil of API GL-5 performance level and 80 W/90 viscosity grade. The test results indicate that the resistance to the pitting wear of coated gears depends not only on coating material but also on which gear is coated. To increase the fatigue life of gears, the coating should be deposited on the gear with the higher number of teeth. The mechanisms by which the fatigue life is extended are discussed.