Nucleation Undercooling Measurement and Corresponding Solidification Structure Investigation of Three Single Crystal Superalloys

The undercooling behavior of three single crystal （SC）superalloys DD5, DD6 and WZ30 was investigated under the industrial process condition by the pendant pellet method. During isothermal heating and cooling processes, the liquidus temperature TL and the critical nucleation temperature TN of the alloys were measured. As the average critical nucleation undercooling ΔTN =TL-TN is determined to be 33, 36 and 42 °C for the three alloys. In the samples of alloy DD5 and DD6 with relatively low ΔTN value, very fine dendritic microstructure forms during isothermal cooling processes. In the sample of alloy WZ30 with relatively high nucleation undercooling, the solidification structure becomes a mixture of SC dendrite frame and grain clusters with random orientations. It appears that, the most random oriented grains are equiaxed crystal formed directly from the interdendritic residual melt, instead of dendrite arm fragment owing to remelting. © 2022 Rare Metals Materials and Engineering Press. All rights reserved.