Predicting freckle formation in single crystal Ni-base superalloys

Freckle formation has been investigated in thirty-two distinct experimental single crystal Ni-base superalloys with large compositional variations. In addition to variations in alloy chemistry, the components studied in this investigation consisted of cylindrical bars with different diameters and solid blade-shaped components unidirectionally solidified in industrial casting trials. The occurrence of freckles was statistically assessed in over four hundred and seventy single crystal components. Detailed analyses of the microstructures, segregation behavior and phase transformation temperatures are presented and utilized to develop regression models capable of predicting the occurrence of freckle formation during solidification. The significance of the physical parameters incorporated with the model, and the implication of the model on the approach for alloy design are discussed.