Dislocation-type evolution in quasi-statically compressed polycrystalline nickel
Dislocation-type evolution in quasi-statically compressed polycrystalline nickel
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DOI：
10.1016/j.actamat.2018.05.022
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发表时间：
2018-08
期刊：
影响因子：
9.4
通讯作者：
Chaoyi Zhu;Tyler J. Harrington;G. Gray;K. Vecchio
中科院分区：
文献类型：
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作者：
Chaoyi Zhu;Tyler J. Harrington;G. Gray;K. Vecchio
在室温下，实验研究了准静态压缩多晶纯镍中位错产生的性质与外加塑性应变的关系。首先，为了确保与非均匀塑性变形相关的几何必要位错密度(EBSDGND)的代表性数据集，使用基于ρ的EBSD法在大范围(几毫米见方)上进行了测量。此外，基于泰勒硬化模型，根据测量的流动应力估算了导致整体加工硬化的总位错密度(ρT)。然后，从总的位错密度中减去统计存储位错密度，得到统计存储位错密度(ρ)。结果表明，在准静态变形镍中：i)测量到的GND密度在0.05~0.46范围内与塑性应变呈线性关系；虽然Ashby模型预测GND密度在整个应变范围内呈线性变化，但本研究没有涵盖0.05以下的应变；ii)SSD密度的增长速度远远快于GND密度的增长速度；iii)当塑性应变大于0.09时，SSD密度超过GND密度。I)和II)都与Ashby的预测一致，而GND密度(III)的大小与Ashby的模型预测不同，特别是在大应变情况下。总体而言，这项研究能够定量地收集GND和SSD在镍硬化过程中的相互作用。这项研究表明，在加工硬化的早期阶段，GND对多晶金属的强度更重要，而SSD在较大应变时对强度的贡献更大。在本研究的应变范围内，加工硬化主要是通过SSD的快速增殖来实现的；而GND密度最初高于SSD密度(0.05)，这可能是由于GND在低应变(<；0.05)下的非线性演化，这将是未来研究的主题。
The nature of dislocation generation as a function of applied plastic strain in quasi-statically compressed polycrystalline pure nickel has been studied experimentally at ambient temperature. First, to ensure representative datasets of the geometrically-necessary dislocation densities (ρGND) associated with non-uniform plastic deformation, measurements over large (several millimeter square) areas were made using Hough-based EBSD methods. In addition, the total dislocation density (ρT) responsible for the overall work hardening is estimated from the measured flow stress based on Taylor's hardening model. Next, the statistically stored dislocation (SSD) density (ρSSD) is calculated by subtracting the GND density from the total dislocation density. The results demonstrate that in quasi-statically deformed nickel: i) the measured GND density varies linearly as a function of plastic strain in the range between 0.05 and 0.46; although Ashby's model predicts linearity for GND density evolution over entire range of strains, this study does not cover strains below 0.05; ii) the SSD density increases at a rate much faster than GND density; and iii) the SSD density exceeds the GND density at above 0.09 plastic strain. Both i) and ii) are in agreement with Ashby's prediction, while the magnitudes of GND density (iii) differ from Ashby's model prediction, particularly at large applied strains. Overall, this study enables the interplay of GNDs and SSDs in the hardening of nickel to be gleaned in a quantitative sense. This study illustrates that GNDs are the more important for the strength of polycrystalline metals in the early stages of work hardening, whereas SSDs contribute more to the strength at larger strains. Over the range of strain in this study, work hardening is predominantly through rapid multiplication of SSDs; whereas the GND density is initially higher than SSD density at 0.05 probably due to non-linear evolution of GNDs at low strains (<0.05), which will be the subject of future investigation.