Papers by Author: Fei Sun

Abstract: A first principles calculation method was used to investigate the site preference of Ruthenium (Ru) at the γ/γ′ interface in Ni-based single-crystal superalloys. The calculation results show that the addition of Ru can decrease the total energy and the binding energy of γ/γ′ interface, which may result in an improved microstructure stability of Ni-based single-crystal superalloys. Moreover, by calculation, it is also found that Ru can stabilize both γ and γ′ phases and have a preference for Ni site at the coherent γ/γ′ interface. When Ru substitutes the central Ni at the γ/γ′ interface, a reverse partitioning of W, Re and Cr occurs; while the partitioning behavior of Mo is not affected. The influence of Ru on the partitioning behavior of W, Re and Cr in γ′-Ni3Al was studied by Dmol3 calculation as well. The calculation results show that W, Re and Cr have a preference for Ni site in γ′- Ni3Al with Ru alloying. When Ru substitutes the central Ni atom, the site preference of W, Re and Cr varies accordingly. Furthermore, electronic structure analysis of γ/γ′ interface and γ′-Ni3Al in terms of Mulliken population and partial density of states (PDOS) was performed to understand the alloying mechanism of Ru in Ni-based single-crystal superalloys. The results show that the strengthening effect of Ru alloying is mainly due to the reduction in binding energy of Ru as well as a p-orbital hybridization between Ru and the host atoms.

Abstract: The addition of refractory elements is effective in improving the comprehensive performance of Ni-based superalloys, and meanwhile, the precipitation trend of TCP phases increases with the elements content due to the segregation of refractory elements during high temperature service. The precipitation of TCP phases obviously decreased the creep properties and creep rupture life of superalloys. The toughness and plastic of superalloys also dramatically deteriorated. The addition of Ruthenium (Ru) is shown to suppress the formation of TCP phases in Ni-based superalloys, resulting in much improved the creep resistance and the microstructural stability. The studies on TCP phases in Ni-based superalloys including crystallography and precipitation of TCP phases and the effect of alloy composition on TCP phases are reviewed.

Abstract: Addition of Ru in Ni-base single crystal superalloys had been used to improve the elevated temperature strength and other multiple properties. Significant decreases in stacking fault energy of the γ phase and the volume fraction of γ′ phase are observed with the addition of Ru. As well as serving as an effective solid-solution strengthening element in high refractory content Ni-base single crystal superalloys, Ru additions are able to effectively strengthen both the γ and γ′ phases and suppress the formation of TCP phases. Due to the changes in the partitioning behavior of elements and the slight decrease in the supersaturation of refractory elements in γ phase associated with Ru additions, high temperature creep resistance and the microstructural stability of the alloy are improved remarkable. The influence of Ru on the microstructure of Ni-base single crystal superalloys is reviewed.