STRUCTURE OF ALUMINUM NITRIDE ALUMINUM AND ALUMINUM-OXIDE ALUMINUM COMPOSITES PRODUCED BY THE DIRECTED OXIDATION OF ALUMINUM

Unreinforced AlN/Al ceramic/metal composites were produced by the directed oxidation of molten Al alloys in nitrogen. The microstructures of these composites were compared with those of previously studied Al2O3/Al composites. In both composite systems the ceramic phase was interconnected and oriented in a columnar structure. The metallic phase showed no significant crystallographic orientation and appeared as both interconnected channels and isolated inclusions. The columns in the nitride system were found to be of micrometer size and to contain subgrains weakly defined by lattice defects, unlike the oxide system, where the columnar structure was shown to be of millimeter size and to contain well-defined micrometer-sized subgrains. Finer structures were obtained in both systems via the addition of Ni to the parent alloy.