Quantification of primary dendritic and secondary eutectic undercoolings of rapidly solidified Al-Cu droplets

Abstract : Rapid solidification undercooling of alloys results in microstructures with reduced microsegregation. Indeed, the metastable extension of solute solubility yields materials with relatively low fraction of eutectic structure. This paper reports on the quantification of primary and eutectic undercoolings resulting from rapid solidification of Al-Cu droplets of different sizes and compositions obtained by Impulse Atomization. Previous work by some of the authors of this study showed that different combinations of estimated primary and eutectic undercoolings can lead to the same eutectic fraction. The aim of the present study is to use the eutectic fraction values measured by Neutron Diffraction to determine the right combination of the corresponding primary and eutectic undercoolings and validated using a microsegregation model. Thermo-Calc is used for the metastable extension of solute solubility in Al-Cu system. Measurement of heat evolved during the period of recalescence by a microsegregation model showed evidence of heat loss during phase transformation.