J Fail. Anal and Preven.(2012)12: 427-437 The face material of the bearing with 18 rolling-elements side of the raceway of the detached failed bearing, turned was GCrl5 bearing steel. The out to become agglomerated, semisolid, and heavy machined brass cage (MA/C3). The lubrication Meanwhile, the outer ring of the bearing presented the was molybdenum disulfide(MoS2)lithium grease. During fracture failure. Hence, in order to confirm the actual its operation, the bearing suddenly failed when its opera- causes of this failure, a variety of characterization methods tional temperature exceeded the warning limit of 70C. were successively conducted according to our previous Afterward, the lubricating grease, which was found on the experiences [8]. Photoelectric direct reading spectrometer, metallographic microscope, and Rockwell hardness(HRC) tester were employed to inspect, respectively, the chemical compositions, the metallographic structures, and the hard- ness of the matrix materials of the failed roller bearing Meanwhile, scanning electron microscope (SEM) and energy dispersive spectroscope(EDS)were used to analyze the microscopic morphologies along with the micro-area compositions of the fracture surface and the contact surface of the bearings outer ring. Furthermore, Fourier transform outer r infrared spectroscopy(FTIR), Raman spectroscopy(RS thermogravimetric analysis (TGA), and x-ray diffraction (XRD)were utilized to characterize the degradation extent of the greases applied within the roller bearing. Based on conclu Isions were put forward hypothesizing that this fracture failure was brought about Fig. 1 3D schematic diagram of a cylindrical roller bearing by both the unqualified matrix materials and the degraded fracture position (c) (d) comer Fig. 2 External appearances of the fracture on the failed roller bearing:(a) total morphology, (b) magnification of front face, (c)magnification of side face, and(d) fractographThe face material of the bearing with 18 rolling-elements was GCr15 bearing steel. The cage was a combined machined brass cage (MA/C3). The lubrication medium was molybdenum disulfide (MoS2) lithium grease. During its operation, the bearing suddenly failed when its opera￾tional temperature exceeded the warning limit of 70C. Afterward, the lubricating grease, which was found on the side of the raceway of the detached failed bearing, turned out to become agglomerated, semisolid, and heavy. Meanwhile, the outer ring of the bearing presented the fracture failure. Hence, in order to confirm the actual causes of this failure, a variety of characterization methods were successively conducted according to our previous experiences [8]. Photoelectric direct reading spectrometer, metallographic microscope, and Rockwell hardness (HRC) tester were employed to inspect, respectively, the chemical compositions, the metallographic structures, and the hard￾ness of the matrix materials of the failed roller bearing. Meanwhile, scanning electron microscope (SEM) and energy dispersive spectroscope (EDS) were used to analyze the microscopic morphologies along with the micro-area compositions of the fracture surface and the contact surface of the bearing’s outer ring. Furthermore, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy (RS), thermogravimetric analysis (TGA), and x-ray diffraction (XRD) were utilized to characterize the degradation extent of the greases applied within the roller bearing. Based on these analytic results, conclusions were put forward hypothesizing that this fracture failure was brought about Fig. 1 3D schematic diagram of a cylindrical roller bearing by both the unqualified matrix materials and the degraded Fig. 2 External appearances of the fracture on the failed roller bearing: (a) total morphology, (b) magnification of front face, (c) magnification of side face, and (d) fractograph 428 J Fail. Anal. and Preven. (2012) 12:427–437 123