Influence of local chemical segregation on the γ′ directional coarsening behavior in single crystal superalloy CMSX-4

The influence of local chemical segregation on the directional coarsening behavior of γ′ phase has been investigated in a nickel-base single crystal superalloy during load-free thermal exposure. It is found that the γ′ phase was preferentially oriented with the direction perpendicular to the dendrite arm growth axis. The chemical gradients caused by local chemical heterogeneities were carefully measured on the scale of a dendrite. It showed that the directions of the γ′ rafting and the chemical gradients are consistent and the magnitude of the chemical gradients affects the rafting rates to some extent. It is suggested that the internal chemical gradients can orientate the development of the γ′ rafts by leading to anisotropy in their growth kinetics during Ostwald ripening. Furthermore, influence of the local chemical segregation on the mechanical properties is also discussed.