【摘要】 通过改变试样质量和冷却规范,研究了过冷Cu-30%Ni(原子分数)单相合金在不同凝固时间下的组织转变规律.在实验所选择的几秒到数分的凝固时间内,均于较低的过冷度范围和高过冷度下观察到了粗大树枝晶向细小等轴晶的转变.延长凝固时间,晶粒发生细化的两个过冷度区间扩大.对低过冷度下细化组织进行的考察表明,快速凝固刚结束时,细化晶粒仍具有树枝晶的特征,随缓凝阶段持续时间的延长,晶粒逐步蜕化为球状晶和蠕虫状晶,与此同时,晶粒度以幂函数规律重新增大.过冷熔体快速凝固使初生固相含有过饱和的低熔点组元以及较多的晶体缺陷,最终导致快速凝固结束后形成的细小晶粒在缓凝阶段的重新粗化速度明显快于正常凝固过程中晶体的粗化速度.更多还原

【Abstract】 The solidification structure evolution of undercooled Cu30%Ni alloy with solidification time was investigated by varying the weight of sample and the cooling condition. The structure transition from coarse dendrites to fine equiaxed crystals, occurred at a certain range of low undercoolings and above a critical undercooling respectively, was all found in the experimental solidification time changing from several seconds to several minutes. The two undercooling ranges where the grain refinement occurred are enlarged with the increasing solidification time. The observation of the crystals refined at low undercoolings indicates that they are dendritic at the end of rapid solidification, and as the duration of the subsequent slow solidification extends, they degenerate gradually into spheric or vermiculate morphology. Meanwhile, the grain size powerlaw increases. The combination of supersaturated lowmelting point component and lattice defects into the primary solid during the rapid solidification of the undercooled melt accelerates the recoarsening of the refined crystals.更多还原