Anisotropic rheology during grain boundary diffusion creep and its relation to grain rotation, grain boundary sliding and superplasticity
Anisotropic rheology during grain boundary diffusion creep and its relation to grain rotation, grain boundary sliding and superplasticity
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DOI：
10.1080/14786431003636097
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发表时间：
2010-05
影响因子：
1.6
通讯作者：
John Wheeler
中科院分区：
文献类型：
--
作者：
John Wheeler
周期性微结构对变形的响应可以进行严格的分析，这为理解更复杂的微结构提供了指导。当变形的扩散蠕变伴随着滑动，不规则六边形被证明是各向异性的流变。解析解推导出粮食旋转是一个关键方面的变形。如果晶界不能支持剪切应力，则多晶粘度是极端各向异性的。存在两个正交的零强度方向：滑动和旋转协作以允许在没有任何溶解或电镀的情况下实现平行于这些方向的应变。当引入线速度/剪切应力关系的晶界，各向异性是不极端的，但仍然存在两个弱方向，沿着多晶强度仅由晶界的“粘度”控制。不规则六边形由四个参数表征。由两个参数定义的六边形的一个特定子集，包括正六边形以及一些细长形状，显示出奇异行为。接近子集的晶粒形状可能表现出大的晶粒旋转速率，并且没有明确定义的流变学，除非存在有限的晶界粘度。这种新的分析解释了为什么基于不规则但近等轴晶粒的微观结构在扩散蠕变期间显示出高旋转速率，并且它为理解扩散蠕变期间的强度各向异性提供了框架。
The response of periodic microstructures to deformation can be analysed rigorously and this provides guidance in understanding more complex microstructures. When deforming by diffusion creep accompanied by sliding, irregular hexagons are shown to be anisotropic in their rheology. Analytic solutions are derived in which grain rotation is a key aspect of the deformation. If grain boundaries cannot support shear stress, the polycrystal viscosity is extremely anisotropic. There are two orthogonal directions of zero strength: sliding and rotation cooperate to allow strain parallel to these directions to be accomplished without any dissolution or plating. When a linear velocity/shear stress relationship is introduced for grain boundaries, the anisotropy is less extreme, but two weak directions still exist along which polycrystal strength is controlled only by the grain boundary “viscosity”. Irregular hexagons are characterised by four parameters. A particular subset of hexagons defined by two parameters, which includes regular hexagons as well as some elongate shapes, shows singular behaviour. Grain shapes that are close to that of the subset may exhibit large grain rotation rates and have no well-defined rheology unless there is a finite grain boundary viscosity. This new analysis explains why microstructures based on irregular but near equiaxed grains show high rotation rates during diffusion creep and it provides a framework for understanding strength anisotropy during diffusion creep.