Transmission electron microscopy of boundary-lubricated bearing surfaces. Part II: Mineral oil lubricant with sulfur- and phosphorus-containing gear oil additives

Transmission electron microscopy (TEM) was performed on cross-sectional samples of tapered roller bearing cone surfaces that were tested at two levels of local boundary lubrication severity, Lambda similar to 1.1 and 0.3. Unlike our previously reported work in which a base mineral oil was used, the bearing tests were conducted in mineral oil with sulfur- and phosphorus-containing gear oil additives. Structural and compositional characterization of undetached antiwear surface layers on the base steel (cone raceway) revealed that the films contained crystalline and amorphous regions. A sharp interface (< similar to 10 nm) that separated the surface layer and base steel was imaged. The surface layer for the cone tested at Lambda similar to 1.1 consisted of Fe, O, and P, whereas that for the cone tested at Lambda similar to 0.3 consisted of Fe, O, P C, Ca, and S Various TEM analytical techniques were used to study the segregation of these elements throughout the antiwear surface layer volume.