Sintered Tribofilm Growth as a Function of Steel Substrate Microstructure

Conventional wear lubricants have historically relied on chemical interactions with the surface for robust film formation, typically limiting them to ferrous metal substrates. Dispersed nanoparticles have been explored as a substrate chemistry agnostic alternative. Recent experiments confirmed that zirconia nanoparticles dispersed in oil have the ability to generate robust tribofilms in steel/oil boundary lubrication tests through nanoparticle surface capture followed by particle accumulation and tribological sintering. This film formation, however, is dependent on the material properties of the counterfaces of the tribocontact. Using a 52100 steel substrate heat treated to hardness targets from 200HV to 700HV, a range of film growth uniformity was observed, with patch-like films observed at lower bulk hardness. This film morphology is compared to the underlying steel microstructure to better understand the sensitivity of nanoparticle tribosintering and film formation to grain specific material properties.