Enhancing thermal and mechanical performance in Si ₃ N ₄ ceramics via Y ₂ O ₃ /MgO ratio and contents regulation

Abstract This study systematically investigates the effects of Y 2 O 3 /MgO ratio, sintering aid content, and sintering schedule on the microstructure and properties of Si 3 N 4 ceramics fabricated via gas‐pressure sintering. The results demonstrate that increasing the Y 2 O 3 /MgO ratio substantially enhances grain growth in Si 3 N 4 ceramics, leading to improved thermal conductivity. A balanced Y 2 O 3 /MgO ratio promotes grain boundary strengthening, achieving optimal flexural strength. Higher MgO content enhances densification in pre‐sintering, but excessive volatilization at elevated temperatures introduces defects, degrading performance. Post‐sintering heat treatment at 1600°C further improves properties by crystallizing intergranular phases and optimizing liquid phase distribution. Both deficient and excessive sintering aid concentrations result in refined microstructures with weakened grain boundaries, adversely affecting either mechanical strength or thermal diffusion properties. The fabrication of high‐performance Si 3 N 4 ceramics necessitates both adequate sintering aid content to offset liquid phase volatilization losses and an optimized Y 2 O 3 /MgO ratio, as these factors critically govern the development of superior thermal and mechanical properties. The SN‐5Y2M sample, sintered at 1920°C for 12 h, exhibited excellent comprehensive properties, achieving a thermal conductivity of 129.5 W·m −1 ·K −1 , flexural strength of 635 ± 27 MPa, and fracture toughness of 9.9 ± 0.3 MPa·m 1/2 .