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The role of grain boundary mobility in diffusional deformation

机译：晶界移动在扩散变形中的作用

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The model of diffusional deformation is revisited by accounting for the dependence of the diffusion potential on grain boundary curvature. The issue is developed through the analysis of two case-studies: the deformation of a lattice of columnar grains in conditions of Coble creep, and the rotation of a grain embedded in a polycrystal in conditions of either Nabarro-Herring creep or Coble creep. The analysis reveals that, unless grain boundary mobility is infinite, grain boundary curvature is dynamically induced by strain rate. A link is established between the curvature distribution and the transfer of diffusion fluxes across grain boundaries. For the two case-studies, the equation expressing the balance of grain boundary motions at steady-state is solved for calculating, within a range of grain boundary mobilities, the grain boundary profiles, the diffu-sion fluxes, and the contributions to power dissipation arising from curvature. The latter con-tributions are found to scale closely as the square of grain size. It follows that the dissipation contribution due to curvature is larger in conditions of Nabarro-Herring creep. In conditions of Coble creep, the dissipation contribution due to curvature translates into a lower bound for the apparent boundary viscosity parameter to be used in numerical simulations. This lower bound is consistent with previous identifications of the parameter in the literature. The classical model assuming flat grain boundaries with transfer of fluxes via triple junctions emerges as a particular case involving the implicit assumption of an infinite grain boundary mobility.
机译：通过算用于晶界曲率的扩散电位的依赖性来重新判断扩散变形模型。该问题是通过对两个病例研究的分析来开发的：在咔哒蠕变条件下柱状晶格的变形，以及在Nabarro - 鲱鱼蠕变或碎屑的条件下嵌入多晶中的谷物的旋转。分析表明，除非晶界移动性是无限的，否则晶界曲率通过应变速率动态诱导。在曲率分布和横跨晶界之间的扩散通量转移之间建立了一个链接。对于两种情况研究，解决了表达稳态下晶界运动平衡的方程，用于计算，在一系列晶界迁移率，晶界谱，散流量，散流度的贡献中，计算曲率引起。后者的核心促进局被认为是粒度的平方束缚。因此，在Nabarro-Herring蠕变的条件下，由于曲率引起的耗散贡献较大。在咔屑蠕变的条件下，由于曲率导致的耗散贡献转化为在数值模拟中使用的表观边界粘度参数的下限。这个下限与文献中的参数的先前标识一致。假设通过三相势态传递扁平晶界的经典模型作为特定情况，涉及无限晶界移动性的隐含假设。

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