METAL DISTRIBUTION IN ALUMINA ALUMINIUM COMPOSITES SYNTHESIZED BY DIRECTED METAL OXIDATION/

The directed oxidation of molten aluminium alloys by vapour phase oxid ants can be used to produce Al2O3/Al ceramic matrix composites. The to ughness of these composites is determined by the amount and the nature of metal distribution in the composite. This paper addresses the prob lem of understanding the metal distribution in Al2O3/Al composites and its dependence on growth temperature. Electrical conductivities and m icrostructures of Al2O3/Al composites synthesized by directed oxidatio n of Al-5056 alloy are investigated. The high conductivity of the Al2O 3/Al composite compared to sintered Al2O3-4 wt% MgO is shown as a proo f of the presence of some continuous metal channels in the composite. The activation energy for the diffusion of the dominant charge carrier in the oxide matrix is found to be 1.36 eV from the analysis of the c onductivity data. Both the amount of metal in the composite and the ex tent of interconnection of the metal channels decrease with increasing growth temperature. The observed changes in microstructure with tempe rature can be explained by considering temperature variations of grain boundary energies in alumina and the alumina/aluminium interfacial en ergy. The metal content of the Al2O3/Al composites, prepared by direct ed oxidation of Al-5056 alloys, can be tailored by the choice of the g rowth temperature.