Processing of co-continuous ceramic composites by reactive penetration method: influence of composition of ceramic preforms and infiltrating alloys
The reactive penetration of Al based alloys in massive silica glass and sintered preforms (made of silica, silica plus silicon carbide or silica plus aluminium nitride) was investigated. The reactions occurring during preform sintering and reactive metal penetration were preliminarily studied by Differential Thermal Analysis. Square bars of co-continuous composites were then processed by using this reactive metal penetration (RMP) method. The effect on infiltration rate of temperature, alloying elements added to aluminium (Mg and Si) and preform microstructure (composition and porosity) was assessed. The microstructure of both sintered preforms and final co-continuous composites was investigated by XRD, SEM and mercury intrusion porosimetry. Vickers, Charpy, bending and tensile tests were used to study the mechanical behaviour of composite bars. The addition of magnesium to molten aluminium (used for infiltration) enhances the penetration rate, while the process speed decreases with the preform porosity increase. The addition of silicon to the molten bath decreases the infiltration rate, but this element is needed in order to avoid the detrimental formation of aluminium carbide, otherwise resulting from the reaction between Al and SiC. The thermal expansion and the mechanical features of the composites greatly change when SiC or AlN are mixed to the silica powders used for preform fabrication.