REN Yipeng ¹, LI Jianbao ¹, YU Hui ², LUO Lijie ¹, LIU Longyang ¹, HOU Xue ¹, CHEN Yongjun ¹

(1. School of Materials Science and Engineering, Hainan University, Haikou 570228, Hainan, China; 2. School of Materials and Chemical Engineering, Pingxiang University, Pingxiang 337055, Jiangxi, China)

Abstract: Si₃N₄/BN composite ceramics with different BN contents were prepared by using hot pressing sintering. Phase composition, microstructure and thermal conductivity of the Si₃N₄/BN composite ceramics were characterized by using X-ray diffractometer (XRD), scanning electron microscope (SEM) and laser thermal conductivity analyzer. It was found that the composite ceramics mainly consisted of β-Si₃N₄ and h-BN. The ceramic grains are oriented perpendicularly to the direction of the hot pressing, while the grain size gradually decreases with increasing content of BN. At a high content of 30% c-BN, the thermal conductivity still maintains at a high level of 75.1 W·K^-1·m^-1, which is very close to that of pure Si₃N₄ (76.9 W·K^-1·m^-1). Moreover, the thermal conductivity perpendicular and parallel to the direction of the hot pressing both decrease and then increase with increasing content of BN. Meanwhile, finite element method was used to simulate the thermal conductivity of the composite ceramics with different BN grain sizes in the anisotropic system. It was found that thermal conductivity of the Si₃N₄/BN composite ceramics decreases with decreasing BN grain size in both directions. The increase in thermal conductivity perpendicular to the hot pressing direction is attributed to the higher thermal conductivity of h-BN along c axis as compared with that of Si₃N₄, whereas the gradual increase in the thermal conductivity parallel to the direction of hot pressing could be ascribed to the refinement of the grains leading to the weakening of the alignment.
Key words: silicon nitride; boron nitride; thermal conductivity; finite element analysis; grain size