Constitution of Ni-rich alloys in Ni–AI–Mo–Ta system at 1273 and 1073 K

Abstract

An investigation is reported of the constitution of the Ni rich portion of the Ni–Al–Mo–Ta system at 1273 and 1073 K. Alloys containing 85 and 75 at.-% Ni respectively were used for the investigation, their constitution at 1523 K having been previously determined. Electron probe microanalysis, X-ray diffraction, and light microscopy were the main techniques of examination. In the 85 at.-% Ni section of the system, only the γ and γ′ phases were present in the composition range extending up to 6 at.% Ta. In the 75 at.% Ni section, the following phases were encountered: γ, γ′, δ (based on Ni₃Ta), η (based on Ni₆TaAl), δ ′ (based on NiMo), and ″ (based on Ni₃Mo). For the part of the section having Ta contents greater than about 10 at.-%, the equilibria involving γ γ′η, η and δ changed little from at 1523 K. However, the γ region (based on Ni₇₅Mo₂₅)and the γ+ γ′ regions which existed at 1523 K were replaced by regions representing equilibria involving NiMo and Ni₃Mo. A reaction γ+δ ′⇛ γ′+ δ″ is proposed between 1200 and 1073 K.

MST/90