Correlation between nitriding process and microstructure of reaction bonded aluminium nitride ceramics

Abstract Aluminium nitride samples were produced by a reaction bonding process using AlN and Al powders with flake-like and equiaxed morphologies as starting materials. Changing the particle sizes and morphologies of the aluminium starting powders led to changes in degree of reaction and microstructure of the resulting reaction bonded aluminium nitride ceramics. At 25 wt-%Al, the degree of reaction showed a maximum, decreasing at higher aluminium concentrations. The degree of reaction was increased by increasing nitrogen gas flowrate or nitriding temperature. It was also found to be increased by reducing the average particle size of the Al starting powder, the green bulk density, or the sample thickness, and also by choosing flakelike morphology. SEM and optical micrographs of reaction bonded aluminium nitride samples revealed the pore structure and morphology of primary and secondary aluminium nitride.