High-temperature strength of nickel alloys based on γ′-phase

Abstract

An investigation has been made of the influence of tantalum, hafnium, and carbon on the strength of Ni₃Al (γ′). Ternary and quaternary alloys have been studied, based on the Ni-Al-Ta and Ni-Al-Hf systems, with aluminium contents in the range ∼20–25 at.-%, tantalum or hafnium contents up to 5 at.-%, and carbon up to 1·4 at.-%. These alloys consisted wholly or predominantly of γ′, with compositions on the (Al + Ta, Hf)-rich side of γ′-stoichiometry. Also, a multicomponent alloy (Ni-Al-Ta-Hf-W-Cr-Co-Zr-B-C) on the nickel-rich side of stoichiometry has been studied. Structural observations have been made, together with measurements of yield stress and of secondary-creep rates at temperatures up to ∼1000°C. Tantalum and hafnium conferred substantial solid-solution strengthening on γ′; however, with carbon additions, carbide formation significantly reduced the matrix strength as a result of solute depletion. The strength and creep resistance of the multicomponent alloy consisting of γ + γ′ + carbide were improved by heat treatment.