INTERMETALLIC NIAL-TA ALLOYS WITH STRENGTHENING LAVES PHASE FOR HIGH-TEMPERATURE APPLICATIONS .1. BASIC PROPERTIES

Various Ta-containing NiAl-base alloys with the Laves phase TaNiAl, wi th C14 structure, as strengthening second phase were prepared by ingot metallurgy. They were studied with respect to the deformation behavio ur at ambient and high temperatures - including elastic deformation an d 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 boundar ies, whereas the Laves phase covers the grain boundaries completely to form a continuous skeleton for higher Ta contents. The observed stren gthening of NiAl by Ta is a result of both solid-solution strengthenin g and second-phase strengthening. The latter effect increases with inc reasing fraction of Laves phase and is accompanied by an increasing br ittle-to-ductile transition temperature. The oxidation behaviour was c hecked. These alloys are promising for applications at temperatures ab ove those of the Ni-base superalloys. (C) 1997 Elsevier Science Limite d.