Effect of Free Surface, Oxide, and Coating Layers on Rafting in \(\upgamma -\upgamma '\) Superalloys

Complex microstructureMicrostructure evolution has been observed in both bare and coated Ni-based single crystalSingle crystal superalloysSingle crystal superalloy. RaftingRafting and \(\upgamma '\) depletionDepletion are investigated in this study through a brief experimental analysis and a detailed phase fieldPhase field model to account for mechanical-diffusionDiffusion coupling. The proposed model has been implemented in a finite element code. As the main result, it is shown that raftingRafting, \(\upgamma '\) depletionDepletion close to free surface/oxide layer or \(\upgamma '\) coalescenceCoalescence close to coatingCoating layer, and mechanical behavior are strongly coupled. The local additional flux of Al explains this coupling to a large extent. Finally, a discussion of strain localization and local flux of Al paves the way for clarification of these cases that degrade the performance of superalloys.