Morphological and elemental analysis of wear debris naturally formed in grease lubricated railway axle bearings.

This work characterises wear debris/particles generated naturally in grease-lubricated spherical roller bearings (SRBs) used in urban rolling stock. Morphological examination revealed the most active wear in grease lubricated SRBs is predominantly associated with the rolling/sliding contact and adhesive mechanisms, resulting in chunk, laminar and spherical wear debris found most frequently. Morphological transitions in spherical and chunky wear debris associated with bearings' service life was seen for the first time in railway SRBs. Interestingly, the formation of chunky wear debris was not necessarily governed by rolling contact fatigue and crack propagation mechanisms seen in oil lubricated systems, but rather associated with the collapse of larger spherical wear debris. Additionally, the surface complexity observed on individual debris, associated with rolling-sliding wear is also discussed. The findings add to the sparse knowledge of wear debris formation and their contribution to grease degradation, particularly for railway SRBs. Furthermore, an estimate of the contamination level of the SRBs was obtained by carefully adapting the fluid lubricant standards. The combination of these results will allow for improved wear prediction and the optimisation of bearing maintenance practices. • Seven types of wear debris naturally generated in grease lubricated rolling stock SRBs was identified and studied. • Formation of wear debris in the railway SRBs is mostly associated with rolling/sliding contact mechanism. • Morphological evolution of spherical debris linked with service life was seen for the first time in grease lubricated SRBs. • Chunk wear debris found in grease lubricated SRBs were governed by collapse and/or fracture of large spherical wear debris. [ABSTRACT FROM AUTHOR]