Synergistic improvement of thermal conductivity and flexural strength of AlN ceramics with Si3N4–C additives

Si 3 N 4 whiskers and nanocarbon powder were added to AlN–Y 2 O 3 –YF 3 ceramics, and the microstructure, thermal conductivity and flexural strength of the samples were studied. Instead of working as one-dimensional reinforcement in AlN ceramics, the Si 3 N 4 whiskers formed a β-Sialon phase that significantly strengthened the grain boundaries, thereby increasing the flexural strength of AlN sample. The added carbon powder formed a transition layer at the grain boundaries and further strengthened them. The fracture mode of the samples changed from intergranular to transgranular, and their flexural strength was increased. Moreover, carbon powder reduced the concentration of aluminum vacancy and improved the thermal conductivity of the samples. Therefore, the flexural strength and thermal conductivity of AlN ceramics with carbon powder and Si 3 N 4 whisker additives were synergistically increased to 366.4 ± 16.4 MPa and 203.5 ± 3.16 W m −1  K −1 , respectively.