Study On Properties Of Spark Plasma Sintered AlN/nano-BN Composites Ceramics

The AlN/BN composite ceramics integrates the merits of AlN and BN, such as thermal conductivity, high electrical resistivity, low dielectric constant, resistance high temperature, resistance corrosion and machinability and so on. However, AlN and BN are both covalent compounds, which has technical problem for sintering the single-phase ceramics and the multi-phase ceramics.AlN/nano-BN powder were synthesized via the situ chemical reactions, the composite powder were sintered with the spark plasma sintering (SPS) after adding right amount sintering addition agent. The densification process and the sintering mechanism of prepared AlN/nano-BN ceramics were studied. The microstructure of AlN/nano-BN ceramics was analyzed. Effect of BN content on the mechanical properties and the electrical properties of the AlN/nano-BN ceramics was discussed.Boric acid and urea as the source were used, the AlN/nano-BN composite powder with nano-BN coated AlN were prepared under reacting 12h at 600℃with N₂,The SPS process of AlN/nano-BN ceramics is divided into three stages: 1500 -1600℃is the initial sintering process. The sintering temperature is higher than 1600℃, which is considered as the sintering middle process, the sintering additives Sm₂O₃ and Al₂O₃ are formed the liquid phase, the mass transfer process is accelerated, which leads to rapidly densification. The densification process is ended above 1700℃, which is considered as sintering late process. When the temperature is under 1700℃, it is useful for the densification of AlN/nano-BN ceramics. The relative density of AlN/nano-BN ceramics is higher than 98.5%.Nano-BN of prepared AlN/nano-BN composite powder via the situ synthesized is shown the form of t-BN with swirl-shaped. The t-BN is transformed to the cards stucture h-BN during the sintering process. The microstructure of AlN/nano-BN ceramics is uniform and dense.Due to the nano-BN, the microstructure of AlN/nano-BN ceramic is fine and the AlN/nano-BN ceramic's mechanical strength is improved. The bending strength of AlN/30vol%nano-BN sample(261MPa) and the AlN single phase ceramics is nearly. The bending strength of AlN/10vol%nano-BN sample reach 347Mpa. The elastic modulus and fracture toughness of AlN/nano-BN composite ceramics are decreased with increasing the BN content.The dielectric constant and dielectric loss of AlN/nano-BN composite ceramics are decreased with increasing BN content. AlN/nano-BN composite ceramics shows good insulation, volume resistivity ratio reaches 10¹²-10¹⁴Ω·cm.