The purpose of the study is to investigate the behavior of WC/C (tungsten carbide/carbon) coated gears lubricated with the special formulated low viscosity oil blend ISO VG 32 identified in the previous investigation. Load-carrying capacity and surface fatigue life tests were performed for coated and un-coated gears on FZG test rig. Tests were conducted at reduced oil level that corresponds to an immersion depth of three times the modulus of the gear. Higher scuffing performance was found for WC/C coated gears lubricated with the special tailored oil in comparison to standard case carburized gears lubricated with the conventional gear oil of the similar viscosity. Approximately 40% lower surface composite roughness was found for coated gears, resulting in about two times higher oil film parameter λ, compared to a standard un-coated gear set. Partial wear of WC/C coated gears appears to be a gradual small-scale material removal that results in tooth gear flanks smoothening. Smoothening of the mating gear flanks also resulted in coated gears pitting durability that exceeds the calculating pitting life grade in accordance with ISO 6336 calculation and durability of case hardened gears lubricated with the conventional oil, as well.
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