Microstructure refinement mechanism upon deeply undercooled solidification of a Ni88Cu6Co6 alloy

Applying molten glass purification and cyclic superheat methods, deep undercooling treatment was performed on a Ni88Cu6Co6 alloy system. The alloy was undercooled to an undercooling as high as 300 K and the corresponding microstructure characteristics were analyzed systematically. Compared with the Ni88Cu12 system, the addition of a minor amount of Co had a pronounced impact on the grain refinement mechanism of Ni88Cu6Co6 system. Grain refinement observed at low undercooling was attributed to the dendritic melting mechanism. On the other hand, in the high undercooling region, the recrystallization process played a dominant role in refining the microstructure. Through the present analysis, the characteristic undercoolings of microstructure evolution had been determined. In addition, BCT model was applied to study the free growth of an undercooled Ni88Cu12 alloy, and by comparing Ni88Cu12 and Ni88Cu6Co6 alloys, we aimed to find the effect of Co on the microstructure refinement mechanisms of deeply undercooled Ni-Cu alloys.