中文摘要：

采用Φ4 mm、Φ7 mm两种Ni-Ni_3Si共晶合金试样,研究试样直径对定向凝固共晶组织失稳的影响。实验结果表明：Ni-Ni_3Si共晶耦合生长的初生相为Ni_3Si相,定向生长的小直径试样更易发生zigzag失稳,形成弯曲的层片组织。分析认为小直径试样的液相温度梯度较大,合金凝固过程中过冷度较低,在生长速率为4μm/s时,即可发生zigzag失稳,这种失稳有利于减小共晶两相扩散生长速率的差异性,缩小两相的宽度差。此外,这种晶内失稳与晶粒的层片取向有关。

英文摘要：

The effect of sample diameters on the instability of eutectic structure was studied by directional solidification experiments on Ni-Ni_3Si alloy with diameters of 4 mm and 7 mm. The results show that the primary phase of coupled eutectic growth is Ni_3Si phase and the zigzag instability of lamellar eutectic is more likely to occur in the sample with a small diameter,which leads to curved lamellar structure. The sample with a smaller diameter gets higher thermal gradient,resulting in the smaller undercooling of the alloy. Furthermore,the zigzag instability of lamellar eutectic happens at larger growth rates,which can help to reduce the difference of diffusion growth rate of the eutectic phase,and thus narrows the width gaps between the two phases. In addition,this instability is related to the grain orientation.