Wear Failure Analysis of Ball Bearings with Artificial Pits for Gas Turbines

The ingression of external contaminants probably causes spalling even severe failure, which may have significant effects on operation reliability of gas turbines. To investigate the evolution and determine the mechanism, artificial pits were made on the outer bearing ring raceway to simulate such failure. Comprehensive investigation into the base materials, macro and micro surface morphologies, service environments including lubricating oil analysis were conducted after disassembly of the engine. Also, during the 3-hours’ operation, vibration and the metal debris monitoring were implemented. Results of this paper have demonstrated that the rolling contact fatigue spalling initiated from the edge of the dent with a distance of approximately 100 millimeters and extended along the balls’ movement trace in the load-carrying area, while in the non-load-carrying area, no visible wear traces were found. The vibration and the metal debris analysis have demonstrated that the protruded edge was formed due to metal accretion around the dent, which later lead to stress concentrations, and it disappeared in the load-carrying area and induced spalling. This paper has discovered the initial failure morphologies and original site of contact fatigue spalling of ball bearings, and specified the mechanism through the simulation caused by foreign substance.