Rapid solidification of Cu-5wt% Ni alloy under supercooling

The variation of grain degree with undercooling temperature is shown. The variation can be presented by a step function. The transformation of the microstructures in the four straight-line portions of the curve of variation are: (1) 63K-T₁. With increasing supercooling, dendritic microstructure begins to transform into spherical grain microstructure. Such microstructural change is accompanied by remelting and disappearance of secondary dendrites. (2) T₁-127K. The microstructure becomes spherical grain. (3) 127K-T₂. Fully developed dendritic microstructure transforms into degenerated primary dendrite trunk and spherical grains distributed among dendrite stems, the average crystallized fraction functions of dendrite trunk is 10%. (4) T₂-292K. The microstructure becomes spherical grain. Experimental results show that directional solidification of Cu-5wt% Ni alloy can be obtained under large growth driving force under certain conditions. These conditions should be artificially created and include: (1) excitation of nucleation of liquid metal within a certain supercooling range; (2) application of a certain temperature gradient.