Kinetic effects during the plane-front and dendritic solidification of multicomponent alloys

Abstract

A generalized model for the kinetics of a dendrite tip with a non-equilibrium interface is presented for multicomponent alloys. The model includes full coupling with thermodynamic databases to account for non-dilute non-ideal solutions, in addition to a full diffusion matrix in the liquid. The consequences of the computed non-equilibrium phase diagram boundaries on the dendrite tip kinetics are considered, and substantial deviations from existing theories are observed, especially in the case of zero solute drag. The model is applied to the rapid solidification of Inconel 718 (a nickel-based superalloy) and 316L (a stainless steel), which contain seven and five solute species, respectively. From the model, the phase diagram properties (i.e., partition coefficients and liquidus slopes) are able to be directly visualized as a function of velocity and observed to vary non-linearly and, in some cases, non-monotonically due to the combination of non-linear phase diagrams and kinetic effects. Finally, recent reports in the literature on the competition between the growth of ferrite and austenite from the melt in 316L are revisited with these new developments.