Effect of refractory elements on the evolution of the NiAl intermetallic phase in NiCrAl alloys

Abstract

The evolution of the NiAl (β) intermetallic phase in NiCrAl and NiCrAlX (X ≡ Nb, Ta, Mo) alloys after heat treatments has been studied by quantitative metallographic techniques and hardness tests to investigate the effect of different refractory elements. Other phases observed have been γ (nickel-rich solid solution), γ' (Ni3Al) and α (chromium-rich solid solution). The alloys are two phase close to the solidus surface. Refractory elements have a stabilizing effect on β but do not change the types of phase present after heat treatments. Hardness tests show that they strengthen the ternary alloy because (i) they decrease the γ' coarsening rate, and (ii) stabilization prevents a decrease in the volume fraction of the stronger phase, β. © 1990.