Multiphase-field and experimental study of solidification behavior in a nickel-based single crystal superalloy

Understanding the solidification behavior in nickel-based single crystal superalloy solidification is essential for determining the following heat treatment process, while the experimental findings have led to contradictory results. On the one hand, the fine γ/γ′ structure in the interdendritic zone suggests a eutectic reaction. On the other hand, the coarse γ′ precipitates indicate a peritectic reaction. In this work, the CALPHAD-based multiphase-field model was used to investigate the superalloy solidification behavior and complex γ/γ′ morphology generation. The fine γ/γ′ and coarse γ′ patterns were reproduced in the γ/γ′ colony, which were compared with the interdendritic microstructure observed by experiments. And the eutectic and peritectic reactions were verified by analyzing the chemical driving force at the phase interfaces. The simulation results suggest that the coarsening of γ′ in the γ/γ′ colony was due to the fast decrease of chemical driving force at the γ/l and γ'/l interfaces. Besides, remelting of the γ dendrite was found near the bulk γ′, which can be mainly ascribe to the increasing of Mo concentration rejected by the growing γ'. The simulated microsegregation patterns of the alloy components were also obtained and the results were in good agreement with the experimental findings.