Solidification microstructure of directionally solidified superalloy under high temperature gradient

The effect of solidification rate on the microstructure development of nickel-based superalloy under the temperature gradient of 500 K.cm(-1) was studied. The results show that, with the increase of directional solidification rate from 50 to 800 mu m.s(-1), both the primary and the secondary dendrite arm spacings of the alloy decrease gradually, and the dendrite morphologies transform from coarse dendrite to superfine dendrite. The sizes of all precipitates in the superalloy decrease gradually. The morphology of gamma' precipitate changes from cube to sphere shape and distributes uniformly in both dendrite core and interdendritic regions. MC carbide morphology changes from coarse block to fine-strip and then to Chinese-script and mainly consists of Ta, W, and Hf elements. The gamma-gamma' eutectic fraction increases firstly and then decreases, and similar regularity is also found for the variation of segregation ratio of elements.