Effect of Er ₂ O ₃ /MgO ratio on mechanical and thermal properties of Si ₃ N ₄ ceramics

Abstract Si ₃ N ₄ ceramics with high mechanical properties and thermal conductivity, exhibiting fine and bimodal microstructure, were prepared by adjusting the Er ₂ O ₃ /MgO ratio and hot‐pressing sintering at 1800°C for 4 h. The microstructure, grain distribution, lattice oxygen content, mechanical properties, and crack propagation process of the sintered bulk samples were systematically investigated. It was found that a low Er ₂ O ₃ /MgO ratio contributed to the densification of Si ₃ N ₄ ceramics, whereas a high Er ₂ O ₃ /MgO ratio favored the grain growth of Si ₃ N ₄ ceramics. In this research, the grain size distribution and average diameters as well as their impact on mechanical properties were examined. When the ratio of Er ₂ O ₃ /MgO was 3:1, Si ₃ N ₄ had a larger average diameter and higher thermal conductivity, but the mechanical properties were somewhat reduced. When the ratio of Er ₂ O ₃ /MgO was 2:2, the sample displayed enhanced mechanical performance, which can be explained by the formation of a bimodal structure. The research indicates that it is feasible to control the microstructure and optimize the mechanical properties of Si ₃ N ₄ ceramics by tailoring the sintering additives.