Phase equilibria in the Ni- Ta-AI system

Abstract

An investigation has been made of the constitution of the Ni-Ta-AI system in the composition range ∼ 50–100 at.-% nickel; in this range isothermal sections of the ternary phase diagram have been determined for temperatures of 1523 and 1273 K. The main technique has been the determination of tie-line and tie-triangle data by electron microprobe analysis; microscopy and X-ray diffraction have also been used. The part of the system studied contained nickel-rich solid solution γ intermediate phases based on the following binary compounds: γ′(Ni₃AI), β(NiAI), Ni₈Ta, δ(Ni₃Ta), Ni₂Ta, μ(NiTa); and also three ternary intermediate phases η(Ni₆TaAI), H(Ni₂TaAI), and NiTaAl. Lattice parameter data for some of these phases have been determined. The phase Ni₆TaAI has been found to show a substantial range of solubility for nickel and to enter into equilibria with the following phases γ, γ′, β, δ and Ni₈Ta. Evidence has been obtained of the occurrence of a peritectoid reaction β + → H + NiTaAl.