Intrinsic Nano-Diffusion-Couple for Studying High Temperature Diffusion in Compositionally Complex Superalloys

We present a new approach for the quantitative study of high-temperature diffusion in compositionally complex superalloys on the nano-scale. As key element, the approach utilizes the γ/γ'-microstructure itself as intrinsic nano-diffusion-couple. By establishing equilibrium at one temperature followed by annealing at a different temperature, well-defined transient states are generated which are studied using analytical transmission electron microscopy (TEM). We demonstrate this approach for a high-performance multi-component superalloy. The temporal evolution of element concentrations is consistently revealed for γ- and γ'-forming elements and is compared to multi-component diffusion simulations. Excellent agreement is obtained for Ni, Co, and Cr whereas diffusion of Al and, in particular, Re lacks behind in the experiment. Finally, it is demonstrated that transient states can also be captured by in-situ TEM using chip-based heating devices. The nano-diffusion-couple approach offers great opportunities for diffusion studies in compositionally complex superalloys and might be extended to other two-phase multicomponent systems.