通过Bridgman定向凝固技术对Al－12%Ni(质量分数)过共晶合金在1－100 μm/s的生长速率范围内进行恒速定向凝固以及不同初始生长条件和变速比下的跃迁加速定向凝固实验, 获得耦合共晶组织的条件. 研究发现, 生长速率为1 μm/s时, 经过一定距离生长后, 组织中无单独生长的初生相, 获得耦合共晶组织; 而当生长速率为2－100 μm/s时, 初生Al₃Ni相领先生长且呈现典型小平面生长特性. 跃迁加速实验表明, 跃迁加速前的初始组织对最终组织有决定性影响, 只有当跃迁前的组织中无单独生长的初生相时, 跃迁后才可在较高生长速率下获得耦合共晶组织. 同时定向凝固可以有效提高Al－12%Ni合金的强度和塑性, 跃迁加速获得的耦合共晶组织延伸率也得到进一步提高.

The Al－12%Ni (mass fraction) hypereutectic alloy from pure Ni and Al (99.9%) was induction melted and directionally solidified at constant growth rates ranging from 1 μm/s to 100 μm/s and abrupt change of growth rate were carried out in a Bridgman－type furnace. After solidification, the samples were quickly quenched into liquid Ga－In－Sn alloy to preserve the microstructure. The microstructures of the samples were observed using OM and SEM. It was indicated that at a growth rate of 1 μm/s, after experiencing a certain growth distance, the primary Al₃Ni phase disappeared and the coupled growth of eutectic could be obtained. The morphology of Al₃Ni phase was faceted when it was the leading phase at growth rates from 2 μm/s to 100 μm/s. The result of experiments with abrupt change of growth rate indicate that the initial microstructure before abrupt change of growth rate determine the microstructure after abrupt change of growth rate. Only if there existed no coarse primary Al₃Ni phase before abrupt change of growth rate could entirely coupled eutectic structure be obtained at relatively higher growth rates. After abrupt change of growth rate, the growth of primary Al₃Ni phase was suppressed and the coupled eutectic could grow continuously without any coarse primary phases. The strength and plasticity could be improved effectively through directional solidification.Besides, the elongation of Al－12%Ni alloy could be greatly improved by the abrupt change of growth rate during directional solidification.