Composition optimization of inconel 718 via cluster formula and experimental verification

Superalloys feature multi-elements and complex elemental ranges, which makes the proper composition selection difficult. In fact, more strict composition standards generally apply in practical productions. The objective of this paper is to understand and eventually to renew the composition standard via example of the most common grade Inconel 718. We have recently shown that t he alloy chemistry originates from a nearest-neighbor cluster [center-shell] plus a few next-neighbor glue atoms, or expressed in cluster for-mula [center-shell] (glue atoms). By grouping the elements into Ni = (Ni, Co, Cu, Fe), Cr = (Cr, Mn, Si, Mo), and Nb = (Nb, Al, Ti), it is found that the reported alloys fall within a narrow composition zone Ni11.0-13.0-Cr3.5-4.5-Nb1 confined by cluster formulas of 16 and 18 atoms. This composition zone is also expressed in terms of 288-atom supercluster formulas, Ni198-208-Cr63-72-Nb16-18, which leads to coordi-nated elemental variations in wt.%: 69.0 <= Ni + Co + Cu + Fe <= 72.7; 19.8 <= Cr + Mn + 1.7 Si + 0.6 Mo <= 22.8; 8.7 <= Nb + 3.2 Al + 1.9 Ti <= 9.8. Within this composition zone, Ni206-Cr65.5-Nb16.5 is further pinpointed and validated by our own experiments to possess the optimal match of strength and plasticity both at room and at 923 K.(c) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Automated summary

Superalloys with complex compositions make it difficult to select the proper composition. This paper aims to understand and update the composition standard using the example of the common grade Inconel 718. The study reveals that the alloy chemistry can be expressed using cluster formulas and supercluster formulas, and identifies a specific composition zone.