对Al-15%Y (质量分数)过共晶合金在1~100 μm/s的抽拉速率下进行定向凝固实验, 研究抽拉速率对组织演化及Al₃Y相生长规律的影响. 结果表明, 铸态Al-15%Y合金主要由Al₃Y先析出相和Al₃Y/Al共晶体组成. 在定向凝固过程中, 当抽拉速率为1 μm/s时, Al₃Y相为不规则形状且边界清晰, 为小平面的生长特性. 随着抽拉速率的增加, Al₃Y相的形貌逐渐转变为拉长的六棱柱形态, 其中少量的Al₃Y相具有中空形貌. 当抽拉速率为10和20 μm/s时, Al₃Y相按粗大的六棱柱形态生长. 进一步增加抽拉速率至100 μm/s时, 组织中出现“十”字形貌的Al₃Y相, 为2个六棱柱垂直交叉结构, 类似枝晶的生长形式. 在抽拉速率增加的过程中, 固/液界面前沿逐渐出现领先相, 且凝固速率越大, 领先距离越长.

The intermetallic compound has been widely introduced in alloys as a reinforced phase due to its high strength, high hardness and enhanced heat stability. The size, morphology, distribution and volume fraction of these intermetallic compounds affect the mechanical properties of materials significantly. In this work, the microstructures evolution and growth behoviors of primary intermetallic Al₃Y phase have been investigated in directionally solidified Al-15%Y (mass fraction) hypereutectic alloy at a wide range of pulling rates (1~100 μm/s). The as-cast Al-15%Y alloy is composed of primary intermetallic Al₃Y phase and Al₃Y/Al eutectic structure. At relatively low pulling rates (1~5 μm/s), primary Al₃Y phase exhibits irregular and having a branching structure on the top of the specimens. Primary Al₃Y phase also precipitates in a faceted growth with sharp edges and corners. As the pulling rate increases, the morphologies of Al₃Y phase transit to elongated prism. Al₃Y phase distributes dispersively in the eutectic structure at a higher pulling rate, presenting a crossing shape with two prisms crossed vertically. Further increasing the growth rate to 100 μm/s, the cross morphology such as two six prismatic vertical cross structure of primary Al₃Y appear, similar to the growth in the form of dendrites. During the increase of pulling rates, the leading-phase at solid-liquid interface appear gradually, and the growth distance of primary phase increases with the pulling rates increase.