Influence of lubricant formulation on rolling contact fatigue of gears – interaction of lubricant additives with fatigue cracks
Résumé
The influence of lubricant additives on rolling contact fatigue crack propagation and the mechanisms responsible for the resulting micro-scale damage, was studied via experiments conducted on complete transmissions in a test cell. Bench-scale tribological tests and the exposure of steel surfaces to two different formulated lubricants were also carried out. Scanning and Transmission Electronic Microscopy observations, Electron Dispersive Energy and X-ray Photoelectron Spectroscopy analyses indicated that the sulphur present in the extreme pressure (EP) additives has a positive impact on limiting damage propagation. Thanks to TEM observations of cracks, it was demonstrated that a sulphur rich film is formed at the crack tip. This film can act as both a barrier film towards hydrogen permeation within the metal and / or as an inhibitor of oil decomposition. The latter is associated with the nascent surface's ability to limit hydrogen generation. Without such hydrogen embrittlement, crack propagation is slowed down. © 2017
Mots clés
Crack propagation
Crack tips
Cracks
Electron microscopy
Fatigue crack propagation
Fatigue damage
Fatigue of materials
Friction
Gears
Hydrogen
Hydrogen embrittlement
Hydrogen production
Lubricants
Steel
Sulfur
Damage propagation
Extreme pressure additives
Hydrogen generations
Hydrogen permeation
Lubricant additives
Rolling contact fatigue
Rolling contact fatigue cracks
Transmission electronic microscopies
X ray photoelectron spectroscopy