The densification of Si₃N₄ ceramics using different additives via microwave sintering

Abstract

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.