Calculation of alloying effect of Ruthenium in Ni-based single-crystal superalloys

A first principles calculation method was used to investigate the site preference of platinum group metals (PGMs) at the γ/γ′ interface in Ni-based single-crystal superalloys. The calculation results show that the addition of PGMs 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 PGMs can stabilize both γ and γ′ phases and have a preference for Ni site at the coherent γ/γ′ interface. The influence of Ruthenium (Ru) on the partitioning behavior of W, Re, Cr and Mo in γ and γ′ phases was studied by Dmol3 calculation as well. It is found that 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. Furthermore, electronic structure analysis of γ/γ′ interface 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.