Processing of mullite-based long-fibre composites via slurry routes and by oxidation of an Al-Si alloy powder

A novel technique to synthesize mullite by the oxidation of Al-Si alloy powder was used for the manufacture of Al2O3 long-fibre reinforced mullite composites. It included (1) slurry infiltration/fibre winding of continuous Al2O3 yarns (ALMAX) and (2) slurry infiltration/slip casting of sapphire fibres (Saphikon). The nonaqueous slurry used consisted of an Al-Si alloy, mullite and additives. During reaction-bonding of green matrices, the Al-Si alloy oxidized and was fully converted to mullite after 1 h at 1430 degrees C in air. The oxidation caused an internal volume expansion, resulting in reduced fibre/matrix shrinkage stresses during reaction-bonding of composites, which minimized the sensitivity to crack formations. For the ALMAX-based composites, the fracture was non-catastrophic. Regarding the sapphire-based composites, an interfacial space between the fibres and the matrix gave the desired fibre pull-out.