Influence of Steel Type on the Propensity for Tribochemical Wear in Boundary Lubrication with a Wind Turbine Gear Oil
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Tribochemical wear may occur at the interface between a surface and a lubricant as a result of chemical and mechanical interactions in a tribological contact. Understanding the onset of tribochemical wear damage on component surfaces requires the use of high resolution techniques such as transmission electron microscopy (TEM). In this study, two steel types, case carburized AISI 3310 and through-hardened AISI 52100, were wear tested using a ball-on-disk rolling/sliding contact tribometer in fully formulated commercial wind turbine gearbox oil under boundary lubrication conditions with 10% slip. With the exception of steel type, all other test conditions were held constant. Conventional tribofilm analysis in the wear tracks was performed using X-ray photoelectron spectroscopy, and no significant composition differences were detected in the tribofilms for the different steel disk types. However, TEM analysis revealed significant tribochemical wear differences between the two steel types at multiple length scales, from the near-surface material microstructure (depth < 500 nm) to the tribofilm nanostructure. Nanometer-scale interfacial cracking and surface particle detachment was observed for the AISI 52100 case, whereas the tribofilm/substrate interface was abrupt and undamaged for the AISI 3310 case. Differences in tribofilm structure, including the location and orientation of MoS2 single sheet inclusions, were observed as a function of steel type as well. It is suggested that the tribochemical wear modes observed in these experiments may be origins of macroscopic surface-initiated damage such as micropitting in bearings and gears.
KeywordsAntiwear additives Extreme pressure additives Additive interaction Additive decomposition Power generation Boundary lubrication wear Rolling element bearings: general Ferrous alloys: steel Tapered roller bearings TEM Wear mechanisms
The Timken Company is acknowledged for support of this work and permission to publish. D. W. Coffey from Oak Ridge National Laboratory is acknowledged for FIB sample preparation. G. A. Richter from The Timken Company is thanked for tribology test lab assistance and for performing the rig tests. P. J. Shiller and R. L. Aubrey from Timken are also acknowledged for lubricant characterization. W. Jennings from Case Western Reserve University is thanked for X-ray photoelectron spectroscopy assistance. Microscopy research at Oak Ridge National Laboratory’s SHaRE User Facility was supported by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.
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