Extension of cellular/dendritic eutectic growth model to off-monovariant range: Phase selection map of a ternary eutectic alloy

For practical purposes it is necessary to predict the phase selection not only along the monovariant line but also out of the monovariant line for a ternary eutectic system. To do this, the growth model of a cellular/dendritic eutectic has been extended from the monovariant line to an off-monovariant region. A way to estimate an imaginary tie line between the initial composition and the corresponding solid phase or a relative fraction of two solids has been proposed. A method to estimate the solutal undercooling due to cellular or dendritic shape has been proposed with help of the single-phase dendritic growth model for a three-component system. A demonstration of phase selection for Al-Al2Cu-Ag2Al system from a nearly pure Al-Al2Cu region to the three-phase eutectic point has been made. Phase selection maps in three different growth rates were compared with experimental data. A semi-quantitative agreement was obtained at intermediate and high growth rates.