The transition from the dendritic to the seaweed growth morphology during the solidification of deeply undercooled metallic melts

The results of a phase-field model for the solidification of deeply undercooled pure melts are presented. This shows that as the undercooling is increased a morphological transition takes place with dendrite tip-splitting (doublon formation) resulting in the normal dendrite morphology being replaced by the dendritic ‘seaweed’ morphology. It is argued that remelting of this seaweed morphology gives rise to spontaneous grain refinement in deeply undercooled melts. Experimental evidence from a high purity Cu sample undercooled by 280 K is presented which appears to show the seaweed morphology.