Near net shape SiC–mullite composites from a powder precursor prepared through an intermediate Al-hydroxyhydrogel

Abstract

SiC–mullite composites with low dimensional changes on sintering were fabricated by partial oxidation of SiC followed by reaction bonding using hydroxyhydrogel derived alumina keeping SiC as dispersed phase in the intermediate gel-like mass as starting material. The sintering-induced shrinkage is compensated by volume expansion caused by the silicon carbide oxidation-induced-volume expansion. This work describes a new processing route to fabricate SiC–mullite composites where in situ formation of mullite takes place that proceeds at much lower temperatures (⩽1600°C) than in normal ceramics processing routes. Specimens containing Al 2O 3⩽40% are not suitable due to the formation of large amount of low eutectic aluminosilicates at processing temperatures. Specimens containing ⩾40% Al 2O 3 yield different aluminosilicates, mainly mullite, which acted as a retarder for oxidation of SiC and at the same time it helped to consolidate SiC compacts. Final phases in fired compact were identified by XRD and different phases present were calculated on the basis of X-ray diffraction results.