采用熔融玻璃净化法使大体积Co85Cu15亚包晶合金的最大过冷度达到351K（0.21TL），实验测得其超过冷临界过冷度为379K.随着过冷度的增大，显微组织由树枝晶转变为等轴晶，并显著细化；溶质截留效应增强，显微偏析程度减小,Co的同素异构转变受到抑制，凝固组织中Co主要是亚稳的过饱和α-Co固溶体,ε-Co含量极少.对初生相形核率进行了理论计算，发现在过冷度为351K时合金熔体仍然发生异质形核.依据LKT／BCT枝晶生长理论对初生相生长速度和枝晶顶端半径进行了理论计算
Co85Cu15 hypoperitectic alloy melt was undercooled by 351 K (0.21TL ) with glass fluxing technique. The hypercooling limit of this alloy was determined to be 379 K. With increasing undercooling temperature, the microstructure transformed from dendrites into equiaxed grains and was refined drastically. Significant solute trapping has taken place during the rapid solidification of highly undercooled Co85Cu15 alloy, and it resulted in the remarkable extension of solubility of Cu in Co phase and much weaker intragranular segregation. It was also revealed by X-ray diffraction that the microstructures were comprised mainly by metastable supersaturated α-Co and Cu solid solutions together with a small amount of ε-Co phase. In addition,the theoretical calculation for nucleation rate indicates that heterogeneous nucleation has still taken place at an undercooling of 351 K. Calculations of dendrite growth velocity, solubility of Cu in α-Co, partial undercoolings, and dendrite tip radius were also performed on the basis of LKT/BCT theory.
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