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

Abstract

AbstractDense Si3N4 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 (Y2O3–MgO–Al2O3, Y2O3–MgO–SiO2, Y2O3–MgO–ZrO2) on the phase, microstructure, and mechanical properties of Si3N4 was examined. Only 5 wt.% of Y2O3–MgO–Al2O3 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, Y2O3–MgO–Al2O3 displayed the finest grain diameter (0.54 μm), whereas Y2O3–MgO–ZrO2 produced the largest average grain diameter (∼0.95 μm); the influence was seen on their mechanical properties. The low additive content Si3N4 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 Si3N4 with excellent mechanical properties.