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.