Aluminium Enriched Diffusion Layers on Nial Alloy

Abstract

Materials based on Ni–Al intermetallics are prospective materials for high temperature applications. They often show good resistance to oxidation and lower specific gravity than nickel based superalloys. High temperature resistance of Ni–Al intermetallics to oxidation can often be improved by aluminium enriched surface layers. Microstructure and chemical composition of aluminium enriched layers on an Al–79 wt-%Ni alloy were investigated using SEM and local elemental analyses. The layers were prepared by diffusion annealing of the Ni–Al alloy in contact with an aluminium plate preferentially at temperatures 480–500°C, for 5 h. In these conditions continuous layers of the Ni₂Al₃ and NiAl₃ phases originate. The region of the aluminium plate in contact with the nickel rich phases transforms into a two phase structure consisting of an aluminium matrix containing < 1 wt-%Ni and two morphological types of NiAl₃ precipitates which have nominal compositions. Solid state diffusion and reactions in the Ni–Al system are also important phenomena in microelectronic devices.