Effect of combined additives of CaF2-Y2O3 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 degrees C. Different contents of CaF2 and Y2O3 were added as sintering 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 CaF2-Y2O3 are pure AlN and BN phases, and the grain boundaries evaporate at high sintering temperature. The dielectric properties of the AlN-BN composites with combined sintering additives Y2O3-CaF2 decrease little, comparing with that of the AlN-BN composites with CaF2 additive. The thermal conductivity is increased with Y2O3 contents increasing in the combined sintering additives of Y2O3-CaF2. When AlN-BN ceramic composites with 3wt%Y2O3-3wt%CaF2 is sintered at 1850 degrees C for 3h, its thermal conductivity of reaches 132.7W.m(-1).K-1.