Effect of High Pressure Annealing on Microstructure and Thermal Conductivity of Aluminum Nitride Ceramics

The thermal annealing is an effective means of structural adjustment and performance improvement for AlN ceramics. AlN ceramics prepared at high pressure with Y2O3 as sintering additive, were annealed at high-pressure (5.0GPa) in a chinese cubic anvil ultra high-pressure and hightemperature device. The effects of high pressure annealing on microstructure and thermal conductivity of aluminum nitride ceramics were studied. The results show that the grain size of the AlN ceramics annealed at 5.0GPa and 970℃ for 2h is significantly increased, the actual crystal morphology is realistic and the second phases are almost present at the grain boundaries or triple pockets compared with the samples before annealing at high pressure. Its thermal conductivity reaches 173.2W/(m·K), which is 2.2 times of the samples without heat annealing at high pressure. However, while the annealing time is extended to the 4h, the pore size of AlN ceramics is increased with anti -densification. And the thermal conductivity of AlN ceramics annealed at 5.0GPa and 970℃ for 4h is reduced to 80.9W/(m·K).