Contact Fatigue Behaviour of PVD-coated Spur Gears

In this paper the contact fatigue behaviour of gears coated with PVD (Physical Vapor Deposition) thin hard film was studied. Contact fatigue tests (R = 0) were carried out on both coated and uncoated automotive transmission spur gears. The bulk material and the coating analysed throughout the tests were, respectively, case hardened 18NiCrMo5 and CrN. The influence of the coating was both experimentally and numerically evaluated. Several FEM models were developed to assess the stress and strain distributions from tooth flank surface to in-depth layers. The influence of the surface treatments on the bulk material was taken into account with the models and the Coffin-Manson equation was used to predict the number of load cycles necessary for initial fatigue damage to occur. All the tested tooth flanks were observed using optical microscope and SEM.