Effect of a new nonoxide additive, Y ₃ Si ₂ C ₂ , on the thermal conductivity and mechanical properties of Si ₃ N ₄ ceramics

Enhancement of the thermal conductivity of silicon nitride is usually achieved by sacrificing its mechanical properties (bending strength). In this study, β‐Si 3 N 4 ceramics were prepared using self‐synthesized Y 3 Si 2 C 2 and MgO as sintering additives. It was found that the thermal conductivity of the Si 3 N 4 ceramics was remarkably improved without sacrificing their mechanical properties. The microstructure and properties of the Si 3 N 4 ceramics were analyzed and compared with those of the Y 2 O 3 ‐MgO additives. The addition of Y 3 Si 2 C 2 eliminated the inherent SiO 2 and introduced nitrogen to increase the N/O ratio of the grain‐boundary phase, inducing Si 3 N 4 grain growth, increasing Si 3 N 4 grain contiguity, and reducing lattice oxygen content in Si 3 N 4 . Therefore, by replacing Y 2 O 3 with Y 3 Si 2 C 2 , the thermal conductivity of the Si 3 N 4 ceramics was significantly increased by 31.5% from 85 to 111.8Wm −1 K −1 , but the bending strength only slightly decreased from 704 ± 63MPa to 669 ± 33MPa.