Yield of Inconel 718 by Axial-Torsional Loading at Temperatures up to 649°C

An experimental program has been implemented to determine small offset yield loci for the nickel-base superalloy Inconel 718 (IN718) under axial-torsional loading at elevated temperatures. Initial and subsequent yield loci were determined for solutioned IN718 at 23 and 454°C and foraged (precipitation-hardened) IN718 at 23 and 649°C. The shape of the initial yield loci for solutioned and aged IN718 agrees well with the von Mises prediction. However, in general, the centers of initial yield loci are eccentric to the origin due to a strength-differential (S-D) effect that increases with temperature. Subsequent yield loci exhibit kinematic and distortional hardening, and solutioned IN718 shows a weak cross effect. This work demonstrates that it is possible to determine yield surfaces for metallic materials at temperatures up to at least 649°C using multiple probes of a single specimen. The experimental data are first of their kind for a superalloy at these temperatures and will enable a better understanding of multiaxial material response.