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In response to the increasing need for higher operating temperatures in advanced gas turbine engines, new alloying concepts are required to develop novel nickel-base superalloys with enhanced temperature capabilities. Recent studies have shown that polycrystalline Ni-base superalloys containing elevated levels of Nb additions exhibit superior properties at elevated temperatures when compared to existing commercial Ni-base superalloys. In order to design, develop and fully exploit this innovative class of superalloys, an understanding of how alloying elements partition to each phase is essential. Using atom probe tomography (APT), compositions of the constituent phases were measured in four high Nb content γ-γ′ Ni-base superalloys and the results were compared to thermodynamic database models from Thermo-Calc. Results were also used in predicting the solid solution strength behavior of the four alloys. The differences in phase composition predictions from thermodynamic models resulted in dissimilarities between the generated strength behavior curves and those from the experimental work.

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Enhancement of the physical and mechanical properties of polycrystalline Ni-base superalloys may be achieved through control of the grain boundary structure and is dependent on the optimization of the thermal-mechanical processing parameters. Superalloys containing grain boundary networks that are comprised with a sufficiently high fraction of Σ3/twin boundaries have been reported to exhibit enhanced creep and fatigue properties. In this report, the density and length fraction of twin boundaries in annealed samples of powder processed Ni-base superalloy RR1000 were quantified and expressed as a function of the average grain diameter. The results were found to be consistent with classical models relating density and length fraction to grain size. The effects of varying hot deformation parameters on twin density and length fraction were also quantified and modified models were derived to describe the relationships.