Effect of Combined Additives of CaF_2-Y_2O_3 on Microstructrue and Thermal Conductivity of AlN-BN Composite Ceramics

AlN (Aluminum nitride)-BN (Boron nitride) ceramic composites were prepared by hot- pressing in nitrogen atmosphere at 1850℃.Different contents of CaF_2 and Y_2O_3 were added as sinter- ing additives.The effects of sintering additives and soaking time on crystalline phase,microstructure, and thermal conductivity of AlN-BN composite were explored.The experimental results show that the AlN-BN composites with combined sintering additives CaF_2-Y_2O_3 are pure AlN and BN phases,and the grain boundaries evaporate at high sintering temperature.The dielectric properties of the AlN-BN com- posites with combined sintering additives Y_2O_3-CaF2 decrease little,comparing with that of the AlN-BN composites with CaF_2 additive.The thermal conductivity is increased with Y_2O_3 contents increasing in the combined sintering additives of Y_2O_3-CaF_2.When AlN-BN ceramic composites with 3wt%Y_2O_3- 3wt%CaF_2 is sintered at 1850℃for 3h,its thermal conductivity of reaches 132.7W·m~(-1)·K~(-1).