The microstructural origin of work hardening stages
The microstructural origin of work hardening stages
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DOI：
10.1016/j.actamat.2018.02.002
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发表时间：
2018-04-15
期刊：
影响因子：
9.4
通讯作者：
Hansen, N.
中科院分区：
文献类型：
--
作者：
Hughes, D. A.;Hansen, N.
利用完全描述的变形微观结构，探讨了第三和第四阶段流变应力和加工硬化速率的应变演变。通过透射电子显微镜的广泛测量显示，晶粒由低角度偶然位错边界（IDBs）和中到高角度几何必要边界（GNBs）分层细分。在0.05-5.5的应变条件下，通过冷轧变形的镍、铜和铝也表现出这种普遍演化。显微组织形态随着应变的增加而演变，通过过渡导致与变形对齐的层状细胞块结构。这种转变是由新的滑移体系的出现和稳定的结构引起的。四个参数描述了微观结构、通过各边界类型的错取向角及其各自的间距。通用标度表征了三个独立参数的归一化分布。一种新的标度规律将两种强度参数：idb的位错密度和gnb间距的应变演化联系起来。这两个参数的强化机制和强度贡献分别表示为经典Taylor和Hall-Petch公式的线性加法。模型预测与流动应力和加工硬化速率在阶段III和阶段IV的实验值非常吻合。变形微观结构的演化阶段和加工硬化速率之间的紧密联系为金属和合金加工硬化的经典问题创造了新的（现代的）基础。这些连接为通过塑性变形生产的超高强度延性金属的未来发展指明了道路。(c) 2018材料学报Elsevier Ltd.出版。版权所有。
The strain evolution of the flow stress and work hardening rate in stages III and IV is explored by utilizing a fully described deformation microstructure. Extensive measurements by transmission electron microscopy reveal a hierarchical subdivision of grains by low angle incidental dislocation boundaries (IDBs) and medium to high angle geometrically necessary boundaries (GNBs). This universal evolution is demonstrated for nickel, copper, and aluminum deformed by cold rolling from strains of 0.05-5.5. Microstructural morphology evolves with increasing strain through a transition resulting in a lamellar cell-block structure aligned with the deformation. This transition is caused by the emergence of new slip systems and a stable texture. Four parameters describe the microstructure, the misorientation angle across each boundary type and their respective spacing. Universal scaling characterizes the normalized distributions of three separate parameters. A new scaling law connects the strain evolution of two strength parameters: the dislocation density of IDBs and the spacing between GNBs. Strengthening mechanisms and strength contributions for those two parameters are expressed respectively as a linear addition of the classical Taylor and Hall-Petch formulations. Model predictions agree closely with experimental values of flow stress and work hardening rate in stages III and IV. Strong connections between the evolutionary stages of the deformation microstructure and work hardening rates create a new (modern) basis for the classic problem of work hardening in metals and alloys. These connections lead the way for the future development of ultra high strength ductile metals produced via plastic deformation.(c) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.