Processing of Al2O3/SiC ceramic cake preforms and their liquid Al metal infiltration

In order to prepare ceramic preforms, chemical processes were used rather than using mixing of ceramic powders to obtain porous Al₂O₃/SiC ceramic foams. A slurry was prepared by mixing aluminium sulphate and ammonium sulphate in the water, and silicon carbide powder was added into the slurry so that a uniform mixture of Al₂O₃/SiC cake could be produced. The resulting product was (NH₄)₂SO₄·Al₂(SO₄)₃·24H₂O plus silicon carbide particles (SiC_p) after dissolving chemicals in the water. This product was heated up in a ceramic crucible in the furnace. With the effect of heat it foamed and Al₂O₃/SiC cake was obtained. Resulting Al₂O₃ grains were arranged in a 3D honeycomb structure and the SiC particles were surrounded by the alumina grains. Consequently, homogeneous powder mixing and porosity distribution were obtained within the cake. The morphology of the powder connections was networking with flake like particles. These alumina particles resulted in large amounts of porosity which was desired for ceramic preforms to allow liquid metal flow during infiltration. The resulting high porous ceramic cake (preform) was placed in a sealed die and liquid aluminium was infiltrated by Ar pressure. The infiltration was achieved successfully and microstructures of the composites were examined.