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 dire cted 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 interc onnected and oriented in a columnar structure. The metallic phase show ed no significant crystallographic orientation and appeared as both in terconnected channels and isolated inclusions. The columns in the nitr ide system were found to be of micrometer size and to contain subgrain s weakly defined by lattice defects, unlike the oxide system, where th e columnar structure was shown to be of millimeter size and to contain well-defined micrometer-sized subgrains. Finer structures were obtain ed in both systems via the addition of Ni to the parent alloy.