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 degreesC. 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 pm. 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.% nanocornposite. (C) 2002 Elsevier Science Ltd. All rights reserved.