Fabrication of highly dense Si3N4 via record low‐content additive system for low‐temperature pressureless sintering

Abstract Dense Si 3 N 4 ceramics were fabricated by pressureless sintering at a low temperature of 1650°C with a short holding period of 1 h under a nitrogen atmosphere. The role of ternary oxide additives (Y 2 O 3 –MgO–Al 2 O 3 , Y 2 O 3 –MgO–SiO 2 , Y 2 O 3 –MgO–ZrO 2 ) on the phase, microstructure, and mechanical properties of Si 3 N 4 was examined. Only 5 wt.% of Y 2 O 3 –MgO–Al 2 O 3 additive was sufficient to achieve >98% of theoretical density with remarkably high biaxial strength (∼1200 MPa) and prominent hardness (∼15.5 GPa). Among the three additives used, Y 2 O 3 –MgO–Al 2 O 3 displayed the finest grain diameter (0.54 μm), whereas Y 2 O 3 –MgO–ZrO 2 produced the largest average grain diameter (∼0.95 μm); the influence was seen on their mechanical properties. The low additive content Si 3 N 4 system is expected to have superior high‐temperature properties compared to the system with high additive content. This study shows a cost‐effective fabrication of highly dense Si 3 N 4 with excellent mechanical properties.