Growth models of two-phase eutectic cell in a ternary eutectic system: a phase selection map

To predict phase selection in a ternary eutectic system, approximate growth models of eutectic cells are proposed. Two models are proposed. The first assumes that the growth adjustment should be governed by elimination and branching of the two solid phases and assumes the extreme condition and uses the Burden-Hunt model to estimate the solutal undercooling due to the needle shape. The second assumes that the growth should be governed by "array stability," and uses the Hunt-Lu model to estimate the solutal undercooling due to "cellular" or "dendritic" shape. In this model, the distinction between "cellular-eutectic" and "dendritic-eutectic" can be made. After calculation, the difference of the growth temperature of eutectic cells between the two models is small; therefore, it is found that direct experiments to examine the growth adjustment mechanism are needed. By using the three-phase planar eutectic growth model and the two-phase planar eutectic growth model together, a phase selection map along the eutectic groove can be made.