Interface dynamics and solute trapping in alloy solidification with density change.

We present a phase-field model for the solidification of a binary alloy, which incorporates hydrodynamic effects due to the different densities of the solid and liquid phases. We start from a generalized thermodynamic potential with squared gradient terms for the associated fields; the condition of local positive entropy production is then utilized to derive a set of equations that drive the system towards equilibrium. The model has been numerically solved in one dimension, to investigate the effects of the flow field on the interface dynamics. We observed that solute trapping is almost unaffected by the fluid advection, while the interface mobility is strongly reduced as the fluid velocity increases. This reflects on the dependence of the interface temperature T 1 on the growth rate υ 1 : the region of the unstable (ascending) branch is reduced, and the maximum of the T1(υ 1 ) curve is shifted towards lower velocities.