Phase-field modeling of dendritic evolution in undercooled melts

We discuss the results of three-dimensional phase-field simulations of dendritic growth in pure undercooled metallic melts at both high and low undercoolings, At high undercooling, our main finding is that steady-state growth of the dendrite tip is destroyed by the amplification of thermal fluctuations above a critical undercooling that is theoretically estimated. This finding is related to a universally observed break in the velocity-undercooling curve as well as to experimental observations of the macroscopic envelope of the solidification front by Flemings and Matson using thermal surface profiles imaged during recalescence in electromagnetically levitated samples of pure Ni. At low undercooling, we find that the anisotropic deviation of the dendrite tip morphology from an Ivantsov paraboloid is ostensibly independent of anisotropy strength. Both the amplitude and form of this shape deviation are found to be in good agreement with existing microgravity data.