J Fail. Anal and Preven.(2011)11: 158-16 Table 1 Chemical composition of the bearing inner-ring material (wt %) C Mn 0.963 0.582 1064 0.017 0.008 Specified 0.95-105 0.40-0.6 0.95-1.20 1.30-1.65 corrosion, and was just resulted from wear due to poo lubrication Eichler et al. [15] stated that a bearing running under a well-lubricated condition benefits from a lubricant film which could completely separates the two counterfaces Namely, there was hydrodynamic lubrication between the asperities and the betula g. However, if there is, or is likely to be contact between asperities, then the bearing is said to be running in the boundary lubrication regime. From the analysis in the Characterizations of the Lubricating Grease"section, it is 100pm inferred that the chemical compositions of used grease were changed due to thermo-oxidation degradation, which led to a loss of lubricating capacity during the bearing operation. Consequently, the lubricant film in the roller raceway contact was not formed effectively, and thus could not contribute to an effective separation of the contacting surfaces. Whenever two curved surfaces were in contact under load, the contact began to occur along a very small circular or elliptical area and resulted in the rolling contact fatigue with continued bearing operation Due to the damage of used grease structure, MoS2 parti cles were aggregated in"sludge"on the damaged raceway surface or in the pits. Figure 8a shows the SEM micrograph 5 AgoE(q) of partial pits contained black particles, and Fig &b shows its EDS result. It can be seen that the composition of particle in the pits was mainly molybdenum and sulfur, while the 1200 presence of iron and chromium was mainly resulted from metallic wear debris from the matrix material of the bearing e formation of contact fatigue pits were accompanied by the occurrence of the wear debris. The bearing steel debris oxidized and formed the distinct red powder [ 16], which can in return cause abrasive wear. Figure 9a shows 600 the SEM micrograph of the red-brown discolored zone on the outer perimeter of the inner ring of the bearing, and 300 Fig. 9b shows the EDS results of the particles on the sur- face. As shown in Fig. 9a, there were large amounts of particulates on the discolored surface of the raceway with the parallel bands pattern. EDS analysis shows that the chemical composition of particulates was mainly iron and Fig. 7 SEMand EDS of wear pits of outerperimeter of bearing inner ring. oxygen(see Fig 9b, namely, iron oxides Fe2O3(red-brown a)Iregular pits. (b)magnified image of a single pit, and(e) EDS of pit particulates). The bands show the position where the bearing surface was subjected to sliding and thus wear. chromium(see Fig. 7c), which was consistent with that of These particulates further acted as stress concentration sites the bearing materials itself. It is further illustrated that and accelerated the initiation of surface cracks. Under formation of the pits had nothing to do with any kinds of rolling and rolling-sliding contact fatigue, flaking occurredchromium (see Fig. 7c), which was consistent with that of the bearing materials itself. It is further illustrated that formation of the pits had nothing to do with any kinds of corrosion, and was just resulted from wear due to poor lubrication. Eichler et al. [15] stated that a bearing running under a well-lubricated condition benefits from a lubricant film which could completely separates the two counterfaces. Namely, there was no contact operating under elasto￾hydrodynamic lubrication between the asperities and the bearing. However, if there is, or is likely to be contact between asperities, then the bearing is said to be running in the boundary lubrication regime. From the analysis in the “Characterizations of the Lubricating Grease” section, it is inferred that the chemical compositions of used grease were changed due to thermo-oxidation degradation, which led to a loss of lubricating capacity during the bearing operation. Consequently, the lubricant film in the roller/ raceway contact was not formed effectively, and thus could not contribute to an effective separation of the contacting surfaces. Whenever two curved surfaces were in contact under load, the contact began to occur along a very small circular or elliptical area and resulted in the rolling contact fatigue with continued bearing operation. Due to the damage of used grease structure, MoS2 parti￾cles were aggregated in “sludge” on the damaged raceway surface or in the pits. Figure 8a shows the SEM micrograph of partial pits contained black particles, and Fig. 8b shows its EDS result. It can be seen that the composition of particle in the pits was mainly molybdenum and sulfur, while the presence of iron and chromium was mainly resulted from metallic wear debris from the matrix material of the bearing. The formation of contact fatigue pits were accompanied by the occurrence of the wear debris. The bearing steel debris oxidized and formed the distinct red powder [16], which can in return cause abrasive wear. Figure 9a shows the SEM micrograph of the red-brown discolored zone on the outer perimeter of the inner ring of the bearing, and Fig. 9b shows the EDS results of the particles on the sur￾face. As shown in Fig. 9a, there were large amounts of particulates on the discolored surface of the raceway with the parallel bands pattern. EDS analysis shows that the chemical composition of particulates was mainly iron and oxygen (see Fig. 9b, namely, iron oxides Fe2O3 (red-brown particulates). The bands show the position where the bearing surface was subjected to sliding and thus wear. These particulates further acted as stress concentration sites and accelerated the initiation of surface cracks. Under rolling and rolling-sliding contact fatigue, flaking occurred Table 1 Chemical composition of the bearing inner-ring material (wt.%) C Si Mn P S Cr 0.963 0.582 1.064 0.017 0.008 1.464 Specified 0.95–1.05 0.40–0.65 0.95–1.20 ≤0.027 ≤0.02 1.30–1.65 Fig. 7 SEM and EDS of wear pits of outer perimeter of bearinginner ring. (a) Irregular pits, (b) magnified image of a single pit, and (c) EDS of pit 164 J Fail. Anal. and Preven. (2011) 11:158–166 123