Effect of Grain Contiguity on the Thermal Diffusivity of Aluminum Nitride

Thermal diffusivity of AlN‐based ceramics was studied as a function of second‐phase amount and heat‐treatment time. The Y 2 O 3 ·Al 2 O 3 contents varied over the range of 13‐31 vol%. The thermal diffusivity decreased as the amount of second phase increased. After sintering at 1850°C, the AlN ceramics consisted of rounded, largely isolated grains. Heat treatment of these samples for 5‐50 h at 1800°C resulted in microstructures that consisted of largely contiguous AlN grains. There was a substantial increase in the thermal diffusivity after the heat‐treatment step, and the incremental improvement was essentially constant for the three compositions that have been studied. The amount of second phase was unchanged during heat treatment; therefore, the increase in thermal diffusivity is assumed to be a direct result of the enhanced contiguity of AlN grains.