Processing of Al2O3/SiC nanocomposites—part 2: green body formation and sintering

Pressure filtration was used to form green compacts from aqueous slurries of alumina with 5 vol.% silicon carbide. Green densities of 64%TD were achieved for slurries containing a 50 vol.% solids loading. Lower green densities were obtained for a very fine alumina due to the practical limits on maximum slurry solids loading when using finer powders. The samples were dried in a purposely built humidity cabinet to limit sample cracking. It was found that a higher consolidated layer permeability gave a higher initial drying rate. Near fully dense (99% TD) nanocomposites were produced, via pressureless sintering at 1900 °C. Poor sintered densities were obtained in the case of the fine alumina because of localised sintering of these low green density compacts. The required intra/inter-granular nanocomposite microstructures have been obtained for several different systems, with an average grain size of approximately 5 μm. Abnormal grain growth was noted for samples containing the larger particle size silicon carbide. This shows that a maximum particle size limit exists when selecting the powders for a 5 vol.% nanocomposite.