Influence of aluminum powder particle size and morphology on microstructure and properties of porous reaction bonded aluminum nitride

摘要

In the present study, porous AlN samples have been produced by reaction bonding using AlN and Al powders with different particle size distributions and morphologies as starting materials. Different AlN/Al ratios were mixed in non-aqueous media. The mixtures were dried, isostatically pressed and nitrided in a tube furnace. Between 1 5..25 Al mass % the degree of reaction shows a maximum and decreases at higher concentrations. This is due to the decreasing open porosity during cold isostatic densification, which prevents nitrogen to reach the reaction front. Changing the particle size and morphology of the aluminum starting powder leads to changes in the degree of reaction and in the microstructure of the nitrided samples. Reaction bonded aluminum nitride (RBAN) shows a residual total porosity of 30 to 35 vol %. SEM micrographs of RBAN indicate the pore structure and the grain morphology of primary and secondary aluminum nitride. Four-point bending strength increases after nitridation with increasing aluminum content in the starting powder. The oxidation behavior of RBAN depends on the pore structure, the Al content, particle size distribution and it's morphology. The mass gain during oxidation in the temperature range of 1000...1200℃ follows a parabolic diffusion law.