Phase-Field Modeling of Grain Boundary Premelting
Phase-Field Modeling of Grain Boundary Premelting
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晶界预熔的相场模拟
DOI：
10.1029/2019jb017632
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发表时间：
2019
期刊：
影响因子：
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通讯作者：
Yasuko Takei
中科院分区：
文献类型：
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作者：
池田豊和;永徳はるか;木村康之;Yasuko Takei
在熔化温度附近，晶界无序的增强，称为预熔化，已知是冰，但不是岩石。最近，上地幔可能发生的预熔融已成为一个关注，因为它会导致岩石的固态弱化。这是一个可能的解释地震低速带和弱软流圈没有调用熔融。在本文中，我介绍了一个现有的晶界的热力学模型，并讨论了在二元共晶系统，这是最简单的情况下，这样的多组分系统的预熔化的物理机制。该模型基于相场方法，并捕获预熔化和部分熔化。它预测，即使有非常少量的次要组分，发生预熔化的温度也会从略低于主要组分的熔化温度急剧下降到略低于共晶温度。它还预测，平衡二面角熔体可以是一个部分代理的晶界无序。该模型很好地解释了实验测量的有机多晶体二元低共熔体系（α-Al 2 O3 + 0.3 - 1.7%二苯胺）的机械性能：在少量二苯胺的情况下，α-Al 2 O3-Al 2 O3晶界处的扩散率和剪切应力松弛在低共熔温度以下显著增强，该温度远低于α-Al 2 O3的熔化温度。
The enhancement of grain boundary disorder near the melting temperature, called premelting, has been known for ice, but not for rock. Recently, possible occurrence of premelting in the upper mantle has become a concern because it causes a solid‐state weakening of rock. This is a possible explanation of the seismic low‐velocity zones and weak asthenosphere without invoking melt. In this paper, I introduce an existing thermodynamic model of the grain boundary and discuss the physical mechanism of premelting in a binary eutectic system, which is the simplest case of such a multicomponent system. The model is based on a phase‐field approach and captures both premelting and partial melting. It predicts that even with a very small amount of the secondary component, the temperature at which premelting occurs drastically decreases from just below the melting temperature of the primary component to just below the eutectic temperature. It also predicts that equilibrium dihedral angle of melt can be a partial proxy for the grain boundary disorder. The model explains well the experimentally measured mechanical properties of a binary eutectic system of organic polycrystals (borneol +0.3–1.7% diphenylamine): With a small amount of diphenylamine, diffusivity and shear stress relaxation at the borneol‐borneol grain boundary are significantly enhanced just below the eutectic temperature, which is much lower than the melting temperature of borneol.