Molten glass purification and cycle superheating technologies were used to make Ni65Cu35, Ni65Cu33Co2 and Ni65Cu31Co4 alloys obtain maximum undercoolings of 320 K, 292 K and 300 K respectively. In order to analyze the relationship between morphological characteristics of solidification front and undercooling change during migration of solid–liquid interface, a high-speed camera was used to capture pictures of the recalescence process. Observing the microstructure of the undercooled alloys using metallographic microscope, the characteristics and evolution of microstructure during rapid solidification process of undercooled liquids were analyzed. It was found that grain refinement mechanisms of highly undercooled Ni–Cu–Co alloys was the same as those of the Ni–Cu alloys. Dendrite remelting leads to the grain refinement at low undercooling, while the dominant factor of grain refinement at high undercooling is recrystallization process induced by stress. The internal driving force can be divided into two parts: one is the thermal stress generated by the releasing of solidification latent heat during recalescence process, and the other is the stress and strain accumulated by interaction of liquid flow and primary dendrite during rapid solidification. We also found that addition of third element Co not only played an important role in solidification rate and recalescence effect, but also significantly improved the average hardness of grain refined microstructure, which was about 80% higher than that of as cast alloy. The addition of trace Co was also conducive to the formation of non-segregation solidification microstructure.

采用熔融玻璃净化和循环过热技术，使Ni65Cu35、Ni65Cu33Co2和Ni65Cu31Co4合金分别获得了320 K、292 K和300 K的最大过冷度。为了分析固液界面迁移过程中凝固前沿的形态特征与过冷度变化之间的关系，使用高速相机拍摄了再辉光过程的照片。利用金相显微镜观察过冷合金的显微组织，分析了过冷液体快速凝固过程中显微组织的特征和演变。结果发现，高过冷 Ni-Cu-Co 合金的晶粒细化机制与 Ni-Cu 合金相同。枝晶重熔导致低过冷度下的晶粒细化，而高过冷度下晶粒细化的主导因素是应力诱导的再结晶过程。内部驱动力可分为两部分：一是再炽过程中凝固潜热释放产生的热应力，二是快速凝固过程中液体流动与初生枝晶相互作用积累的应力应变。我们还发现，添加第三元素 Co 不仅对凝固速率和再辉光效应起重要作用，而且显着提高晶粒细化显微组织的平均硬度，比铸造合金高约 80%。微量Co的加入也有利于非偏析凝固组织的形成。