Transmission electron microscopy of boundary-lubricated bearing surfaces. Part I: Mineral oil lubricant

Transmission electron microscopy (TEM) was performed on the near-surface material (depth <500 nm) of tapered roller bearing inner rings (cones) that were tested at two levels of boundary-lubricated conditions in mineral oil with no additives. Site-specific thinning of cross section cone surface sections for TEM analyses was conducted using the focused ion beam (FIB) milling technique. High-resolution structural and compositional characterization of near-surface material and surface layers was performed on an untested cone as well as cones tested at Λ ∼ 1.1 and 0.3. This approach revealed near-surface microstructural distortion and grain size gradients that were attributed to surface finishing operations during manufacture. The characteristics of oxide surface layers and micro-cracks on the tested bearing surfaces were evaluated and found to depend on lubrication conditions.