Solidification velocity of undercooled Ni-Cu alloys

The solidification velocity of Ni-Cu alloys was measured as a function of bulk undercooling using high-speed thermal imaging of electromagnetically levitated samples. Two departures from power law growth (approximating plateaus) in the velocity versus undercooling data were observed: the first occurred at intermediate undercoolings and is attributed to copper solute. while the second occurred at high undercoolings and is hypothesized to be an effect of oxygen. The lvantsov solution with marginal stability arguments (IMS model) is a widely used model that relates dendrite growth velocity to total undercooling for dilute alloy systems. However, the model does not predict a plateau at intermediate undercoolings for alloys with a large equilibrium partition coefficient, k(E) Satisfactory agreement between the model and experimental results can be obtained by using a value of k(E) that is smaller than the alloy's actual value, but this is physically unreasonable and causes disagreement with currently accepted kinetic models. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.