Relation between the microstructure and microchemistry in Ni-based superalloy

Ni-based superalloys with biphasic structure (γ + γ') are widely used for high-temperature applications, such as disks and blades of gas turbines and aeronautical engines. For these applications, the stability at high temperature is of the utmost importance, in particular the coarsening and the morphological changes of γ' may be seriously detrimental for in-service components. Evolution of γ' particles strongly depends on the composition difference between disordered matrix and particles. The present work is devoted to the investigation of the γ' morphology and the microchemistry in single crystal CM186LC superalloy in as-received condition and after creep. The study was carried out by SEM and AFM microscopies, standard XPS and Scanning Photoemission Microscopy (SPEM) at the ELETTRA synchrotron facility in Trieste. The difference in the chemical composition of two phases, γ and γ', was revealed from the SPEM images and their spectral analysis. The structural evolution, taking place during creep and leading to rafting, seems to be determined not only by the external applied stress but also by W diffusion from γ to γ’ phase.