Scuffing Protection of ZDDP Tribofilm Under Oil-Starved Conditions

Lubricated gears and bearings are increasingly operating in starved conditions due to downsized units, low-viscosity lubricants and increased speeds and loads. Under such conditions where a full hydrodynamic film is not formed, scuffing becomes increasingly prevalent as a critical failure mode. This study investigates how oil film thickness and ZDDP tribofilm development influence scuffing resistance when lubricant supply is limited. Step-sliding speed tests in a ball-on-disk tribometer are used to evaluate scuffing protection of base oils and ZDDP solution under controlled oil volumes. The results show that reduced oil volume accelerates scuffing, particularly for high-viscosity oils, due to rapid transition from EHL to mixed and boundary lubrication. ZDDP significantly improves scuffing protection by forming tribofilms under oil-starved conditions. Its effectiveness depends on additive concentration and chemical reactivity. Higher ZDDP concentrations and reactive structures enable rapid tribofilm growth before critical sliding speeds are reached where scuffing would occur, preventing scuffing. The findings provide insights into the design of lubricant formulation for mechanical systems under oil-starved conditions.