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

Abstract 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.