Parameter-free test of alloy dendrite-growth theory

In rapid alloy solidification the dendrite-growth velocity depends sensitively on the deviations from local interfacial equilibrium manifested by kinetic effects such as solute trapping. The dendrite tip velocity-undercooling function was measured in dilute Ni(Zr) over the range 1--25 m/s and 50--255 K using electromagnetic levitation techniques and compared to theoretical predictions of the model of Trivedi and colleagues for dendritic growth with deviations from local interfacial equilibrium. The input parameter to which the model predictions are most sensitive, the diffusive speed VD characterizing solute trapping, was not used as a free parameter but was measured independently by pulsed laser melting techniques, as was another input parameter, the liquid diffusivity DL. Best-fit values from the pulsed laser melting experiment are VD=26 m/s and DL=2.7×10^-9 m²/s. Inserting these values into the dendrite growth model results in excellent agreement with experiment with no adjustable parameters.