Competitive growth of different phases in eutectic alloys under directional solidification

By comparisons of interface growth temperatures of different phases in eutectic systems, competitive growth between the primary phase, halo structure and coupled eutectic has been discussed. The compositions for the formation of coupled eutectic have been discussed at the coexisting with the primary phase in eutectic under directional solidification. Solidification conditions, such as growth rate and composition required for the formation of the primary phase, halo structure and coupled eutectic have been proposed. Numerical calculation results show that no halo structure formed in directionally solidified Sn−Pb eutectic, but in Al−Si eutectic, competitive growth structures of the primary β-Si phase, α-Al halo structure and coupled eutectic (α+β) may exist at the hypereutectic composition between 12.6% and 25% Si. The calculated results of Al−Si eutectic fit in with the reported experiment results.