Microstructure and Composition of Alumina/Aluminum Composites Made by Directed Oxidation of Aluminum

Two Al2O3/Al composites, grown by the directed oxidation of molten Al alloys at 1400 and 1600 K, were investigated by X‐ray diffraction, optical microscopy, scanning electron microscopy, transmission electron microscopy, and wet chemical analysis. The materials were found to contain a continuous network of Al2O3, which was predominantly free of grain‐boundary phases and was made up of nanometer‐ to micrometer‐sized crystallites, a continuous network of Al alloy, and isolated inclusions of Al alloy. No crystallographic orientation was observed in the metallic phase, whereas the Al2O3 was oriented with its c axis parallel to the growth direction. The higher process temperature yielded a lower metal content and less connectivity of the metallic consituent.