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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。
The influence of sample diameter on the instability of directional solidification eutectic structure was studied by using two kinds of Ni-Ni_3Si eutectic samples of Φ4 mm and Φ7 mm. The experimental results show that the Ni_3Si phase is the primary phase of the Ni-Ni_3Si eutectic coupling growth, and the smaller diameter of the directional growth is more prone to zigzag instability, forming a curved lamellar structure. It is considered that the liquidus temperature gradient of the small diameter sample is larger and the degree of undercooling during the solidification of the alloy is lower. When the growth rate is 4μm / s, zigzag instability can occur, which is beneficial to reduce the eutectic Two-phase diffusion growth rate of the difference, narrow the two-phase width difference. In addition, this intragranular instability is related to the grain orientation of the grains.