An Analytical Model for Irregular Eutectic Growth

摘要

In this paper a modification of the present theory of irregular eutectic growth is proposed. The proposed analytical model relaxes the assumption of an isothermal interface and accounts for density differences between the liquid and solid phases. Validation of this model is presented against experimental lamellar spacing and undercooling measurements available in the literature for both regular and irregular eutectics. Based on the proposed model two separate mechanisms are identified as spacing selection criterion in the irregular Al-Si eutectic system. First, the minimum spacing selection in Al-Si is dictated by the condition of an isothermal interface, that is the spacing at which the undercoolings of the two phases a and β are identical. However, the proposed theory predicts a unique value for minimum spacing, without invoking the extremum condition, as opposed to the classical Jackson and Hunt approach. Second, it will be shown that the average spacing selected by irregular eutectic systems is dictated by the minimum undercooling of the faceted phase.