The densification of Si3N4 ceramics using different additives via microwave sintering

Silicon nitride ceramics were fabricated via 2.45 GHz microwave sintering at different systems which included Si3N4–Y2O3–Al2O3 system, Si3N4–Y2O3–Al2O3–ZrO2 system and Si3N4–Y2O3–Al2O3–ZrO2–Li2CO3 system. The system of Si3N4–Y2O3–Al2O3–ZrO2–Li2CO3 exhibited preferable properties which had completely phase transformation, Vickers hardness of 12 GPa and the flexure strength of 400 MPa at a lower temperature of 1550°C. The results also showed that ZrO2 had good ability in absorbing microwave and Li2CO3 could promote the densification. Scanning microscopy micrographs revealed the phenomenon of crack deflection, debonding and pull-out of β-Si3N4 grains.