J Fail. Anal. and Preven. (2011)11: 158-166 0透以起 003.004005006.007008009.00 Fig8 SEM and EDS of partial pits contained black particles (a)Pits Fig.9 SEM and EDS of red-brown discolored zone on the outer ontained black particles and(b) EDS of black particles perimeter of bearing inner ring(a)particulates and bands(b) EDS of as a progression of the pits [3], and led to the formation of large, irregular-shaped pits which caused rapid failure of resulted in direct friction between the two counterfaces and oc AO e of surface contact fatigue damage 3. Due to damage of the grease structure, MoS2 particu- Conclusions and Remedial Measures lates under rolling and rolling-sliding contact were aggregated by"sludge"on the raceways. The wear 1. The generation of cracks at or near the contact surface debris and pits acted as stress concentration sites. These and presence of flaky wear particles and geometric inhomogeneities led to highly localized shaped pits provided conclusive evidences fo stresses, rapid crack ion. and the formation of contact fatigue. This evidence was found contact fatigue pits continued operation, the detailed electron microscopic investigations of the atigue progress cau flaking. This resulte damaged surface of the inner ring of the bearing. The the formation of large, irregular pits and the accumu- dominant mode of the bearing failure was surface lation of debris which cause rapid deterioration and contact fatigue between the rollers and the rac failure of the bearing. 2. During operation of the bearing, the lubricatin 4. To extend the lifetime of the bearing, probably the best suffered heavily thermo-oxidation degradation due countermeasure is to replace the lubricating greases and temperature. The chemical compositions of greases were hoose temperature resistant, antioxidant lubricating changed, which led to a loss of lubricating capacity and grease such as RD-l, which is a high-temperature failure of the greases. The lubricating film in the roller/ mposite grease. In addition, shortening the cycle of raceway contact cannot be effectively formed, which lubricant replenishment in the track of the bearing is Springas a progression of the pits [3], and led to the formation of large, irregular-shaped pits which caused rapid failure of the bearing. Conclusions and Remedial Measures 1. The generation of cracks at or near the contact surface and presence of flaky wear particles and irregular￾shaped pits provided conclusive evidences for surface contact fatigue. This evidence was found through detailed electron microscopic investigations of the damaged surface of the inner ring of the bearing. The dominant mode of the bearing failure was surface contact fatigue between the rollers and the raceways. 2. During operation of the bearing, the lubricating greases suffered heavily thermo-oxidation degradation due to high temperature. The chemical compositions of greases were changed, which led to a loss of lubricating capacity and failure of the greases. The lubricating film in the roller/ raceway contact cannot be effectively formed, which resulted in direct contact friction between the two counterfaces and occurrence of surface contact fatigue damage. 3. Due to damage of the grease structure, MoS2 particu￾lates under rolling and rolling-sliding contact were aggregated by “sludge” on the raceways. The wear debris and pits acted as stress concentration sites. These geometric inhomogeneities led to highly localized stresses, rapid crack initiation, and the formation of contact fatigue pits. Under continued operation, the pitting/fatigue progress caused flaking. This resulted in the formation of large, irregular pits and the accumu￾lation of debris which cause rapid deterioration and failure of the bearing. 4. To extend the lifetime of the bearing, probably the best countermeasure is to replace the lubricating greases and choose temperature resistant, antioxidant lubricating grease such as RD-1, which is a high-temperature composite grease. In addition, shortening the cycle of lubricant replenishment in the track of the bearing is Fig. 8 SEM and EDS of partial pits contained black particles. (a) Pits contained black particles and (b) EDS of black particles Fig. 9 SEM and EDS of red-brown discolored zone on the outer perimeter of bearing inner ring (a) particulates and bands (b) EDS of particulates J Fail. Anal. and Preven. (2011) 11:158–166 165 123