Microstructure evolution and Competitive Growth during Grain Growth of Directionally Solidified Column Crystal DZ4125 Superalloy

Abstract:

The directionally solidified column crystal DZ4125 superalloy was prepared by means of Bridgman directional solidification. The microstructure evolution and the competitive growth of oriented crystal at a constant withdrawal rate were studied. The results showed that the temperature gradients of solid-liquid interface gradually decreased and the primary dendrite spacing increased, as the growth height increased. At the same time, the sizes of the γ′ precipitates gradually decreased and their morphologies changed from irregular butterfly shape into regular cube and sphere shapes. The contents of γ+γ′ eutectics and carbides, which were mostly distributed in the interdendritic areas, increased gradually. Moreover, due to the competitive growth proceeding, the number of columnar crystals decreased significantly with the increase of growth height. With the convex solid-liquid interface, the crystals diverged towards the furnace wall.

Key words:directional solidification; DZ4125 alloy; microstructure; competitive growth