Adiabatic remelting of the mushy-zone during rapid solidification

Abstract

In two-step solidification of alloys that form a metastable phase, the first stage of microstructural evolution following solidification 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.

Acknowledgements

The authors would like to thank Daniel Backman for conducting the growth model calculations as part of his undergraduate thesis in Mechanical Engineering at Tufts University. Funding was provided under the LODESTARS flight program by NASA grant NNM04AA31G.