Synthesis and microstructural characterization of NiAl-Al2O3 functionally gradient composites

Reactive Hot Compaction of Ni and Al powders in which one or both of the powders were preoxidized was carried out to fabricate functionally gradient composite (FGC) of NiAl with in -situ Al2O3 reinforcement. The FGC consisted of five layers with a variation of alumina content from less than 4% on one side to about 52% on the other. The gradient in the composition was obtained by stacking different powder mixtures of desired compositions. Individual composites corresponding to the different layers were also synthesized to study the evolution of microstructure during compaction. The alumina was observed to form a continuous network around the NiAl during the synthesis. The effects of powder oxidation and of the heating rate on the process and microstructure have been discussed on the basis of the DTA studies. The results indicate that during the synthesis of NiAl, Al3Ni is the phase that forms first, followed by Al3Ni2 and NiAl. (C) 1998 Elsevier Science Limited. All rights reserved.