Research In Microstructure And Performance Of In Situ Synthesis Of AlN Reinforced BN Composites

The aluminum nitride (AIN), which has many excellent properties like high thermal conductivity, high electrical resistivity, low dielectric constant and low dielectric loss, is potential material in microelectronic industry. h-BN has good thermal shock resistance and machinability with high electrical resistivity and low dielectric constant. But both h-BN and AIN have their own defects. They are hard to sinter, and AIN ceramic has a high hardness and low fracture toughness, whereas the strength of BN is very low. Therefore, the application of monophase material is limited due to their defects.Al and h-BN were used as raw materials in this paper. In situ reaction method was undertaken to synthesize AIN powder. Factors including temperature, heat preservation time, and the ratio of Al to BN were investigated in this system. The production analysis showed that the content of AIN increaseed with the increasing temperature and soaking time and the ratio of of Al to BN. According to the results of the reaction and the nitridation temperature of AIB2, optimum parameters were decided to be temperature 950 ℃ and 2 h for soaking time.HP and SPS were employed to fabricate in situ synthesis AIN reinforced BN composites. The sintering processes were studied under different sintering temperature and ratio of Al to BN. The analysis of microstructure showed that temperature increasing promoted the densification of AIN reinforced BN composites and the microstructure changed from sparse to dense. The temperature increase continually promoted the growth of grains. The density of sintered samples increased with the sintering temperature increasing whereas decreased with the ratio of Al to BN decreased. The performances of sintered samples were also studied in this paper. Thermal expansion coefficient of sintered samples decreased with sintering temperature increasing. The values of hardness and bending strength and fracture toughness and thermal conductivity increased with sintering temperature increasing. At the same time, the dielectric property was improved with temperature increasing,due to the further growth of grains. The values of hardness and bending strength and fracture toughness and thermal conductivity decreased with the ratio of Al to BN decreasing..The value of thermal conductivity of sample sintered by HP under the sintering temperature of 1800 °C and A1/BN=1 and the soaking time of 2 h was 69.4 w/m-k, while the value of dielectric constant was 15.12. When the ratio of Al to BN was 0.6, the value of dielectric constant decreased to 10.35. The value of thermal conductivity of sample sintered by SPS under the sintering temperature of 1700 "C and A1/BN=1 and the soaking time of 10 min was 75 w/mk, while the value of dielectric constant was 9.76. When the ratio of Al to BN was 0.6, the value of dielectric constant decreased to 6.91. The results showed that thermal conductivity and dielectric property of samples fabricated by SPS were prior to those fabricated by HP.