Freckle Formation and Thermodynamic Assessment for Nb-Bearing Superalloys

IN718, IN625 and IN706 are wildly used Nb-bearing cast-wrought superalloys. With the ever increasing demand for large ingot size to meet new design for aggressive jet engine and industrial land base engine, the solidification macrosegregation, i.e. freckle, becomes more and more concerned in recent years. The freckle is believed to be caused by instable convective flow in the mush zone, and the well-adopted approach to evaluate freckle formation tendency is through the calculation of Rayleigh Number (Ra). However, it is difficult to calculate Ra due to complex solidification behaviors of multi-components superalloys.