The influence of ruthenium and rhenium on the local properties of the γ- and γ′-phase in nickel-base superalloys and their consequences for alloy behavior

Abstract

Rhenium and ruthenium are alloyed to modern nickel-base superalloys to gain good high temperature properties combined with acceptable phase stability. Three experimental alloys with varied contents of rhenium and ruthenium were investigated. It was found with transmission electron microscopy (TEM)-based energy dispersive spectroscopy (EDS) that rhenium distributes more homogenously between the γ- and γ′-phase in the presence of ruthenium (reverse partitioning). Other properties of the alloys as the lattice misfit, local hardness of the individual phases and the high temperature evolution of the microstructure were strongly influenced by the partitioning behavior of rhenium and ruthenium. The changes in lattice constants and hardness of the γ- and γ′-phase could be verified by X-ray diffraction and nanoindentation in an atomic force microscope (NI-AFM). The optimum γ′-size with respect to creep properties was found to be dependent on the lattice misfit.