Microstructural Effects on the Thermal Conductivity of Polycrystalline Aluminum Nitride

Polycrystalline AIN bodies were made with a range of porosities from various AIN powders by sintering or hot‐pressing. Thermal conductivity data for material produced without sintering aids showed a gradual, yet definite, porosity dependence with scatter similar to other property‐porosity studies. The thermal conductivity‐porosity data for ALN with sintering aids showed the existence of two distinct regions: (1) a higher‐porosity region (greater than approximately 2%) which was similar to the data for material without sintering aids, and (2) a low‐porosity region where grain boundaries were seen to dominate thermal conductivity. Auger spectroscopy was used to investigate fracture surfaces for dense CaO‐doped materials. Thermal conductivity was observed to correlate to effective grain‐boundary thickness, which was calculated from quantitative analysis of the Auger data. A model consisting of cubic grains in a continuous grain‐boundary phase accurately describes these data.