Grain boundary glassy phase and abnormal grain growth of silicon nitride ceramics

The microstructure of pressureless sintered Si3N4 with MgO–CeO2 additives has been studied by TEM. The grain boundary glassy phase is observed and confirmed directly by microdiffraction. EDAX analysis suggests that the main function of CeO2 lies in the formation of a glassy phase, which contains hardly any MgO. This cerium silicate glassy phase is good to wet Si3N4. MgO–CeO2 is an excellent sintering aid for Si3N4. Abnormal grain growth of Si3N4 occurred at a sintering temperature of above 1850°C, which leads to microcracks and dislocations and is harmful to mechanical properties.