Extensive mechanical property assessments spanning a wide range of compositions have clearly illustrated that Ni-base superalloys containing ruthenium additions exhibit properties superior to those containing only additions of rhenium. Although a wide range of beneficial effects have been associated with ruthenium additions, explanations regarding the dominant underlying mechanism(s) by which ruthenium additions are beneficial are still being debated. Subtle changes in bulk alloy composition were observed to drastically suppress the precipitation of Topologically-Close-Packed (TCP) phases and enhance the structural integrity of single crystal Ni-base superalloys at elevated temperatures. Identifying the characteristic interfacial partitioning tendencies at the TCP and γ - γ□ interfaces should provide an improved understanding of the elemental interactions present in these complex systems and enable engineering of the alloy for optimized properties. Atom probe tomography has been used to investigate interfacial and solute partitioning between the various phases in novel single crystal superalloys. A dual beam scanning electron microscope/focus ion beam (FIB) miller was used to fabricate atom probe specimens from site specific regions from a series of nominally identical alloys with and without additions of ruthenium. The results of a systematic local electrode atom probe investigation that focused on identifying the compositional variations in the TCP phases and characterizing the differences in interfacial partitioning that occurs between the TCP, γ and γ□ phases will be presented.
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