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

Abstract The microstructure of pressureless sintered Si 3 N 4 with MgO–CeO 2 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 CeO 2 lies in the formation of a glassy phase, which contains hardly any MgO. This cerium silicate glassy phase is good to wet Si 3 N 4 . MgO–CeO 2 is an excellent sintering aid for Si 3 N 4. Abnormal grain growth of Si 3 N 4 occurred at a sintering temperature of above 1850°C, which leads to microcracks and dislocations and is harmful to mechanical properties.