Study on structure refinement mechanism in rapid solidification of a deeply undercooled Cu60Ni38Co2 alloy

Abstract

Employing molten glass purification and cyclic overheating technologies, a Cu60Ni40 alloy was modified by introducing trace amounts of Co element. Through this process, we aimed to understand how the addition of Co element influences the microstructure morphology of the alloy. By combining the BCT model and metallographic analysis, the intrinsic factors of microstructure transformation in the alloy were studied. In the case of small undercooling, solute diffusion dominates dendritic growth, but the undercooled melt is limited to a narrow range of growth, resulting in the formation of coarse dendritic morphology in Cu–Ni alloy. As the undercooling increases, the growth of dendrites is gradually controlled by both solute diffusion and thermal diffusion, and the remelting effect of dendrites is also gradually enhanced. During rapid solidification with lower undercooling, the dendrites formed by the undercooled melt can be remelted to form numerous crystal seeds. Within a moderate undercooling range, dendrites grow directionally due to thermal diffusion and exhibit specific characteristics. At high undercooling, the dendrites' directional growth, primarily driven by thermal diffusion, undergoes stress fragmentation.