Constitution of Ni rich alloys in Ni-Al-Mo-Ta system at 1523 K

Abstract

An investigation has been made of the constitution of the Ni rich portion of the Ni-Al-Mo-Ta system using alloys lying in the 85 and 75 at.-%Ni sections of the system. Observations are reported of alloys in the as-cast condition and also after annealing at 1523 K; the results of electron probe microanalysis, X-ray diffraction, and microscopical examination of the annealed alloys are presented as isothermal sections. The phases encountered in equilibrium in the composition range studied are as follows: the Ni based solid solution γ and intermetallic compounds based on Ni₃Al(γ′), Ni₃Ta(δ), and Ni₆TaAI(η). The 85 at.-%Ni section is predominantly single phase γ at 1523 K. In the 75 at.-%Ni section, γ enters into equilibrium with γ′ and δ;γ′ enters into equilibrium with γ, η, and δ to form γ + γ′ + δ and γ′ + η + δ phase regions. In the two phase γ + γ′ region, lattice parameter mismatch values lie in the range 0.56–0.81%. In the as-cast condition, some alloys show regions which are interpreted as containing one or more intermetallic compounds based on the Ni-Mo system.