A preliminary study on the tribological compliance of ball and race materials for application in unlubricated hybrid bearings

Tribological compliance of various steel grades, metal matrix composites, and Si 3 N 4 ceramics against Si 3 N 4 balls of different grain sizes and surface finishes, as well as reference AISI 52100 steel balls, was investigated under reciprocating sliding tests. Both constant and oscillating loads were used to better simulate real operational conditions of hybrid ball bearings. Adhesive wear was the dominant mechanism for both ceramic/ceramic and ceramic/steel contacts. Unpolished nanometer-grain Si 3 N 4 balls exhibited superior adaptability and reduced wear compared to polished ones. Among the various combinations tested, the unpolished Si 3 N 4 ball paired with a metal matrix composite demonstrated the lowest friction coefficient and minimal wear. The formation of a tribofilm at the sliding interface was observed.