Influence of grain size evolution on convective instability
Influence of grain size evolution on convective instability
复制标题
粒度演化对对流不稳定性的影响
DOI：
10.1029/2002gc000308
复制
发表时间：
2003
期刊：
影响因子：
3.7
通讯作者：
E. Parmentier
中科院分区：
文献类型：
--
作者：
C. Hall;E. Parmentier
晶粒尺寸是材料最重要的微观组织性能之一，它在蠕变过程中发生变化，使多晶聚集体的自由能最小化。我们将晶粒尺寸演化模型应用于冷却边界层对流不稳定性的研究。晶粒尺寸演化模型耦合复合流变，其中变形速率为位错蠕变和晶粒尺寸敏感扩散蠕变的总和。对流的开始对晶粒生长速率和初始晶粒尺寸很敏感。由板块运动引起的应力增强了对流不稳定性的形成；因此，小尺度对流更有可能发生在快速移动的板块下方。在有限振幅对流中，在对流应力较低的区域，晶粒尺寸的演变导致高粘度，并可能导致超过一个数量级的粘度差异。这种粘度差异足以影响对流动力学，通常导致与混合良好的对流流体隔离的区域。包含扩散蠕变的复合黏度比位错蠕变具有更低的活化能，降低了黏度的有效温度依赖性。
Grain size, one of the most important microstructural properties of materials, evolves during creep deformation to minimize the free energy of polycrystalline aggregates. We apply a model of grain size evolution to the study of convective instability of cooling boundary layers. The grain size evolution model is coupled to a composite rheology where the deformation rate is the sum of that due to dislocation creep and grain size sensitive diffusion creep. The onset of convection is sensitive to grain growth rates and the initial grain size. The formation of convective instabilities is enhanced by stresses induced by plate motions; therefore small‐scale convection is more likely to occur beneath fast‐moving plates. In finite amplitude convection, grain size evolution leads to high viscosity in regions where convective stresses are low and can induce viscosity contrasts exceeding one order of magnitude. Such viscosity contrasts are sufficient to influence the dynamics of convection, often leading to domains which remain isolated from the well‐mixed convecting fluid. A composite viscosity including diffusion creep, which has a lower activation energy than dislocation creep, reduces the effective temperature dependence of viscosity.