Orientation of crystalline growth in melt under negative temperature gradient and its control

Evolution pattern of solidification microstructure in the monophase Cu Ni alloy in the range of thermo dynamically supercooling of 63～292 K is investigated, and both the condition of supercooling degree and orientation mechanism and control method of directional crystalline growth in the melt under negative temperature gradient are analyzed. The results show that (1) the process of grain refining is controlled by solute diffusion at the temperature near critical supercooling degree Δ T * (about 106 K) and however, by thermal diffusion near Δ T ** (about 200 K), and (2) the direction of crystalline growth is when the temperature is in the range of 63 to Δ T * K and, however, the direction may be or as well in the range of 127 to Δ T ** .