A morphological study of nitride formed on Al at low temperature in the presence of Mg

A detailed study was conducted of AlN formed at low temperature on Al with the aid of Mg. The nitride exhibits a bilayer structure comprising a layer forming outward and a layer growing into the Al. In its early stages of formation the outward forming layer consists of fine, randomly aligned AlN crystallites dispersed within an Al matrix. The later forming outer region is primarily composed of fine, columnar hexagonal AlN crystallites aligned in the growth direction, in conjunction with small amounts of fine polycrystalline Al. The inward forming layer comprises nodules, regions or layers of reacted Al, containing a mixture of fine polycrystalline AlN and Al, in conjunction with Al exhibiting the original Al crystal structure. A fine-grained, Mg-containing nitride approximately 150 nm thick was observed at the interface of the outward forming layer with either the underlying Al substrate or the inward forming layer when it is present. A mechanism is proposed for the formation of the nitride and the development of the bilayer structure. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved