γ′-Rafting mechanisms under complex mechanical stress state in Ni-based single crystalline superalloys

The morphological evolution of the gamma' precipitates has been studied in a second generation nickel-based single crystal superalloy during isothermal creep straining at 1093 degrees under multiaxial stress state. For this purpose, a specific V-shaped specimen has been designed to induce an evolving multiaxial stress state along its thickness. These stress conditions are quantified by the stress triaxiality obtained using viscoplastic finite element simulations. gamma channel width and gamma' rafting orientation have been analyzed along the thickness for several triaxiality values, using Rose diagrams and specifically developed image processing tools. The gamma' rafting process is shown to be highly sensitive to the sign and magnitude of the stress triaxiality. Finally, it is shown that the gamma/gamma' topological inversion development is faster under compression.