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].