Yield of inconel 718 by axial-torsional loading at temperatures up to 649 degrees C

An experimental program has been implemented to determine small offset yiel d loci for the nickel-base superalloy Inconel 718 (IN718) under axial-torsi onal loading at elevated temperatures. Initial and subsequent yield loci we re determined for solutioned IN718 at 23 and 454 degrees C and for aged (pr ecipitation-hardened) IN718 at 23 and 649 degrees C. The shape of the initi al yield loci fbr solutioned and aged IN718 agrees well with the von Mises prediction. However, in general, the centers of initial yield loci are ecce ntric to the origin due to a strength-differential (S-D) effect that increa ses with temperature. Subsequent yield loci exhibit kinematic and distortio nal hardening, and solutioned IN718 shows a weak cross effect. This work de monstrates that it is possible to determine yield surfaces for metallic mat erials at temperatures up to at least 649 degrees C using multiple probes o f a single specimen. The experimental data are first of their kind for a su peralloy at these temperatures and will enable a better understanding of mu ltiaxial material response.