Adiabatic remelting of the mushy-zone during rapid solidification

摘要

In two-step solidification of alloys that form a metastable phase, the first stage of microstructural evolution following solidi. cation of the primary (metastable) phase involves growth of the stable phase into the mushy-zone. The growth rate of the stable phase can be predicted using a simple dendrite growth model if the heat balance is modified to include isothermal melting of the pre-existing solid. This adiabatic remelting model successfully predicts the growth rates for the stable phase as measured experimentally in the Fe-Cr-Ni alloy system. The growth rate of the stable phase depends strongly on composition, but this dependence is countered by a reduction in the heat absorbed through melting of the metastable solid. Due to the small variation in thermophysical properties over a wide range of compositions, the net result of these two competing effects is a heat flux, which is proportional to the thermodynamic driving force.