Intermetallic NiAlTa alloys with strengthening Laves phase for high-temperature applications. I. Basic properties

Abstract

Various Ta-containing NiAl-base alloys with the Laves phase TaNiAl, with C14 structure, as strengthening second phase were prepared by ingot metallurgy. They were studied with respect to the deformation behaviour at ambient and high temperatures — including elastic deformation and creep — as a function of alloy composition and microstructure. NiAl dissolves up to 0.2 at% Ta in solid solution. NiAl with up to 3 at% Ta forms precipitate particles of Laves phase primarily on grain boundaries, whereas the Laves phase covers the grain boundaries completely to form a continuous skeleton for higher Ta contents. The observed strengthening of NiAl by Ta is a result of both solid-solution strengthening and second-phase strengthening. The latter effect increases with increasing fraction of Laves phase and is accompanied by an increasing brittle-to-ductile transition temperature. The oxidation behaviour was checked. These alloys are promising for applications at temperatures above those of the Ni-base superalloys.