试样直径对Ni-Ni3Si定向凝固共晶组织失稳的影响

Effect of sample diameter on the instability of lamellar eutectic in directional solidification of Ni-Ni3Si alloy

摘要:

采用Φ4 mm、Φ7 mm两种Ni-Ni3Si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-Ni3Si共晶耦合生长的初生相为Ni3Si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。

Abstract:

In order to study the effect of different sample diameters on the instability of eutectic structure, directional solidification experiment was carried out on Ni-Ni3Si alloy with sample diameters of 4 mm and 7 mm.The results show that the primary phase of coupled eutectic growth is Ni3Si phase and the instability of lamellar eutectic is more likely to occur on the sample with small diameter. The form of instability is a zigzag instability which leads to curved lamellar structure. The sample with smaller diameter gets higher thermal gradient, leading to the smaller undercooling of the alloy. Further, the instability of lamellar eutectic will happened at larger growth rates, and which can help to reduce the difference of diffusion growth of the eutectic phase, thus narrowing the width gaps between the two phases. In addition, this instability is related to the grain orientation.