Fretting Friction and Wear Characteristics and Damage Behaviors of Si₃N₄ Ceramic Balls Sliding against Bearing Steel

Si₃N₄ ceramic balls are widely used in high speed and high precision bearings as the rolling bodies, because of their excellent performances, such as high bearing capacity, light weight, vibration and noise reduction, and stable chemical properties. As the rotating rolling bodies in service process, Si₃N₄ ceramic balls greatly reduce the friction behaviors in bearings, but there are still complex fretting friction and wear phenomena between the rolling bodies and ball tracks. The surface damage of Si₃N₄ ceramic balls caused by fretting wear, impact and fatigue may greatly increase the friction resistance, energy loss and loss of bearing accuracy. Meanwhile, that will accelerate the surface damage of themself, ball tracks and bearing retainer, thereby accelerating the bearing failure, or causing major mechanical accidents. Sintering additives are the essential parts of Si₃N₄ ceramics, which must have certain influence on the tribological properties of Si₃N₄ ceramic balls. In consideration of the fretting friction and wear behaviors between the bearing balls and ball tracks, the fretting friction and wear experiments of the Si₃N₄ ceramic balls with various sintering aids sintered under different processes were carried out by sliding against bearing steel, to analyze and compare the effects of sintering aids and sintering processes on the friction state and damage degree, by proposing a method for detecting surface damage degree of bearing balls. Results showed that the Si₃N₄ ceramic balls with 5AlEr and 3AlY aids exhibited more stable friction state and lower wear degree under non-lubricated conditions. Increasing sintering temperature of GPS process can alleviate the fretting damage behaviors and reduce the damage degree. The introduction of HIP technology could further alleviate the wear behaviors, but generally weakened the wear resistance of Si₃N₄ ceramic balls. The results provided a basis for the optimization of the formulas and preparation processes of Si₃N₄ ceramic balls as bearing rolling bodies. Meanwhile, the microstructures, morphologies and chemical composition of worn surfaces of Si₃N₄ ceramic balls and wear debris were characterized and analyzed by 3D profilometer, scanning electron microscope, elemental energy spectrometer and Raman spectrometer. And then the damage characteristics of friction damage, micro exfoliation and fatigue cracks of Si₃N₄ ceramic balls combined with the damage mechanisms consisting of abrasive wear, adhesive wear, fatigue damage and tribochemical reactions were further revealed.