界面能各向异性体系中Eurone-colony形成的相场研究
Eutectic colony formation in systems with interfacial energy anisotropy: A phase field study
摘要：
由于三元杂质的排斥，二元共晶凝固前沿对形态扰动的不稳定性导致共晶团的形成。然而，各向同性系统的不稳定动力学和由此产生的微观结构特征是相当好理解的，一些实验观察指出在具有各向异性界面的系统中存在菌落。在这项研究中，我们将共晶团的理解扩展到各向异性系统，其中只有固-液或固-固界面的某些取向是热稳定的。通过2D和3D相场模拟，我们系统地探讨了作为拉速和平衡界面相对取向与外加温度梯度的函数的菌落形成动力学和由此产生的微观结构。我们发现，在2D中，稳定的手指间距被选择与引入的各向异性的大小增加，无论是在固-液或固-固界面。的手指有一个明确的取向的情况下，各向异性的固-液界面，没有固定的取向的lamenum构成的殖民地。对于各向异性存在于固-固界面的情况，层流倾向于沿着施加的温度梯度的方向定向，而固-液界面从水平方向倾斜。三维模拟揭示了共晶螺旋的存在，它可能会成为倾斜下的平衡界面的某些取向。我们的模拟能够解释我们在Ni-Al-Zr合金凝固实验研究中观察到的几个关键特征。
英文摘要：
Instability of a binary eutectic solidification front to morphological perturbations due to rejection of a ternary impurity leads to the formation of eutectic colonies. Whereas, the instability dynamics and the resultant mi- crostructural features are reasonably well understood for isotropic systems, several experimental observations point to the existence of colonies in systems with anisotropic interfaces. In this study, we extend the un- derstanding of eutectic colonies to anisotropic systems, where only certain orientations of the solid-liquid or solid-solid interfaces are thermodynamically stable. Through phase field simulations in 2D and 3D, we have systematically probed the colony formation dynamics and the resulting microstructures, as functions of the pulling velocity and the relative orientation of the equilibrium interfaces with that of the imposed tempera- ture gradient. We find that in 2D, stabler finger spacings are selected with an increase in the magnitude of anisotropy introduced, either in the solid-liquid or in the solid-solid interface. The fingers have a well-defined orientation for the case of anisotropy in the solid-liquid interface, with no fixed orientations for the lamellae constituting the colony. For the case where anisotropy exists in the solid-solid interface, the lamellae tend to orient themselves along the direction of the imposed temperature gradient, with tilted solid-liquid interfaces from the horizontal. The 3D simulations reveal existence of eutectic spirals which might become tilted under certain orientations of the equilibrium interfaces. Our simulations are able to explain several key features observed in our experimantal studies of solidification in Ni-Al-Zr alloy.
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