Chemo-mechanical characterization of phosphorus and sulfur containing ashless tribofilms on hypoid gear teeth. (June 2021) - Roache, David C.
Abstract: Wear reduction is critical in the automotive industry, where efficiency, part life, and environmental factors are of concern. Generation of tribofilms by additive-infused lubricants has been effective in reducing wear, and the continued progress of ashless tribofilms offers a promising solution for better protection. A group phosphorus- and sulfur-containing tribofilms were characterized to assess their chemical and mechanical properties in relation to wear protection. Gears were run through modified L-37 with different additive formulations, and were analyzed by EDS, AFM, and nanoindentation. It was discovered that phosphorus and sulfur were well correlated with wear performance, with higher phosphorus and lower sulfur offering better protection. Mechanical testing revealed that a higher elastic modulus was also strongly correlated to better wear performance. Highlights: Characterization of phosphorus and sulfur containing ashless tribofilms. Hypoid gears run through a stressed L-37 test using fully-formed lubricating oils. Revealed high correlation between phosphorus concentration and wear performance. Higher elastic modulus measured by AFM strongly correlated with wear performance. Nanoindentation showed tribofilm thickness between 50 and 200 nm.