Solidification of undercooled molten Cu30Ni70

Recently, it was demonstrated that grain refinement in undercooled Cu30Ni70 is brought about by a remelting of those initially formed dendrites (termed novel dendrites) which are unstable against melting. Also, it was found that in the same transition regime, there is a sharp drop in the specific volume of the undercooled specimens. Before entering into the transition regime, the novel dendrites found in an undercooled specimen are arranged in a regular pattern and the microstructures consist of large dendrites. Voids are found mainly at the dendritic spacings of the large dendrites. On the other hand, near the upper end of the transition regime, the microstructures consist of equiaxed refined grains. Furthermore, each of these grains contains a novel dendrite. Voids have moved to the interdendritic or grain boundaries. Based on these observations, a solidification mechanism of undercooled molten Cu30Ni70 is proposed.