EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The hexagonal system of AlN leads to its anisotropy in the a/b-axis and c-axis directions. The thermal conductivity is different in a/b axis and c axis due to the phonon propagation velocity is obviously different in the a/b axis and c axis direction of AlN. Besides, AlN has different elastic modulus and thermal expansion coefficients in the a/b axis and c axis directions, which results in different mechanical properties. The fabrication of oriented AlN bulk ceramics was explored by slip casting under 3T, 6T and 9T vertical magnetic field, coupled with pressureless sintering in the nitrogen atmosphere at 1800℃ for 24 hours. The texture degrees of AlN ceramics samples were controlled by the viscosity of the slurry and the grain growth during sintering. The influences of magnetic field intensity on the texture and microstructure of the sample were researched by XRD and ESBD. The density, thermal conductivity and mechanical properties of the sintered AlN ceramics were tested by Archimedes drainage method, laser thermal conductivity analyzer and Vickers hardness tester. The experimental results show that the a/b axis of the AlN grains is aligned parallel to the magnetic field, and the degree of the texture of the ceramic increases with the increase of the magnetic field intensity. The thermal conductivity, residual stress and hardness of the textured AlN ceramic are closely related to the orientation of the AlN grains and the degree of the ceramic texture. When the added magnetic field strength is 9T, the texture of AlN ceramic is 73%, the thermal conductivity is 170 W/(m·K), and the hardness under a load of 500g is 850 kgf/mm$^2$.