Nanoindentation and XRD investigations of single crystalline Ni-Ge brazed nickel-base superalloys PWA 1483 and René N5

Abstract

Two single crystal nickel-base superalloys of the first and second generation (PWA 1483 and René N5) were diffusion brazed with two different Germanium containing brazing materials which were optimised for each alloy. The two-phase microstructure of the single crystalline brazing joint consists of a γ’ precipitate phase embedded in a γ matrix. The local mechanical properties of the γ- and γ’-phases and the lattice misfit of single crystalline nickel-base superalloy brazing joints were measured over the joint region and the surrounding base material. The results for both systems show strong differences in the properties with respect to local chemical composition, hardness and lattice constants. The γ-phase in the joint center and the base material has almost the same hardness, whereas a large difference was found for the γ’-phases respectively. In both alloys the hardness of the γ’-phase in the base material was about 15 % higher than in the joint. The lattice misfit at room temperature was negative in both base materials. In case of the brazing joint of René N5 a positive lattice misfit was measured, while the PWA 1483 joint shows a negative misfit in the former gap center. Accordingly the microstructural evolution of each brazing joint shows significant differences during creep.