3.1 Surface defect analysis
During the preparation process, due to abrasive friction, insufficient purity of raw materials and sintering temperature, the surface of Si3N4 ceramic bearing is prone to defects, such as pit, snowflake, wear and crack defects. On account of the formation of volatile substance CO, pores are left on the surface of ceramics. As the oxidation temperature increases to 1100°C, grains with dendritic shapes begin to form and grow, and the growth process of dendritic grains will fill the pores and heal the crack defects formed during the heating process [12]. Si3N4 ceramics are subjected to extrusive external forces during grinding and polishing processes. The grinding disc is directly squeezed and abrasive grains are pressed into the ceramic under the action of the grinding disc, forming pit defects[13]. Ceramic materials are brittle, and wear defects remain on the surface of ceramic materials due to severe abrasive wheel wear [14]. In the polishing process of Si3N4 ceramics, the material removal process mainly includes plastic deformation, brittle fracture and powdering of the surface material. The plastic deformation and powdering of surface materials lead to the generation of snow defects[15].