The first refined granular microstructure solidified from undercooled Cu₇₀Ni₃₀ melts

The microstructure evolution of Cu₇₀Ni₃₀ alloy melts was systematically investigated in the undercooling range of 21 K to 270 K by using glass fluxing technique combined with cycle superheating and cooling processing in high vacuum. When ΔT < ΔT^*₂(120 K), the first granular crystalline formed gradually from dendrite with increasing undercooling. The analysis of microstructure and composition shows that high-angle boundaries do not coincide with the segregation zone between remelted fragments. It is shown that the grain refinement process consists of the disintegration of dendrite formed in rapid solidification and recrystallization of dendritic fragments.