界面各向异性对层状共晶生长形态的影响
Influence of interphase anisotropy on lamellar eutectic growth patterns
摘要：
大量实验表明，结晶学效应对共晶合金凝固过程中两相形态的形成起着重要作用。特别是，在层状复合材料中，经常观察到大片的完全对齐的层状结构。此外，片层的生长方向通常与温度梯度的方向显着不同（片层相对于主生长方向倾斜）。这两种效应都不能用标准理论或现有的共晶生长的数值模型来解释，这些模型都假设界面是各向同性的。我们已经开发了一个相场模型，其中每个界面（固-液和固-固）的各向异性可以单独控制，我们已经调查了界面各向异性的生长动力学的影响。我们已经发现，各向异性的固-固界面相边界自由能显着改变的生长动力学。倾斜片晶是由三重线处修改的平衡条件引起的，与最近提出的理论猜想非常一致。在三维中，相间边界倾向于与最小能量的方向对齐。我们还进行了模拟，其中两个晶粒具有不同的各向异性的竞争。在所有情况下，在瞬态之后选择包含具有最低能量的边界的晶粒。这些结果为共晶凝固生长方式的选择提供了新的思路。
英文摘要：
It is well documented in many experiments that crystallographic effects play an important role in the generation of two-phase patterns during the solidification of eutectic alloys. In particular, in lamellar composites, large patches of perfectly aligned lamellae are frequently observed. Moreover, the growth direction of the lamellae often markedly differs from the direction of the temperature gradient (the lamellae are tilted with respect to the main growth direction). Both of these effects cannot be explained either by the standard theory or the available numerical models of eutectic growth, which all assume the interfaces to be isotropic. We have developed a phase-field model in which the anisotropy of each interface (solid-liquid and solid-solid) can be separately controlled, and we have investigated the effect of interface anisotropy on the growth dynamics. We have found that anisotropy of the solid-solid interphase boundary free energy dramatically alters the growth dynamics. Tilted lamellae result from the modified equilibrium condition at the triple lines, in good agreement with a theoretical conjecture proposed recently. In three dimensions, the interphase boundaries tend to align with directions of minimal energy. We have also performed simulations in which two grains with different anisotropies are in competition. In all cases, the grain containing the boundaries with the lowest energies was selected after a transient. These results shed new light on the selection of growth patterns in eutectic solidification.
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