A study of kinetically limited dendritic growth at high undercooling using phase-field techniques

Abstract

A phase-field model has been used to study the evolution of growth velocity, V, and tip radius, R, as a function of undercooling during the dendritic solidification of pure metals at high undercooling. We find that at sufficiently high undercooling the tip radius passes through a local minimum, beyond which the tip radius increases with undercooling. This local minimum in R is related to a change in the rate limiting process from diffusive transport to interface kinetics. Growth velocity continues to increase with undercooling above the transition undercooling, so that an undercooling regime exists where both V and R increase with undercooling. Clearly under these condition the R 2 V ≈constant scaling law normally applied to dendritic growth can no longer hold. On the basis of a limited number of data points in the region where both V and R increase with undercooling alternative scaling laws are suggested.