Interpreting the softening of nanomaterials through gradient plasticity
Interpreting the softening of nanomaterials through gradient plasticity
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DOI：
10.1557/jmr.2011.123
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发表时间：
2011-06
影响因子：
2.7
通讯作者：
Xu Zhang;K. Aifantis
中科院分区：
文献类型：
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作者：
Xu Zhang;K. Aifantis
实验和模拟研究表明，将纳米材料的晶粒尺寸减小到某一临界值以下，纳米材料的屈服应力和流动应力都会软化而不是硬化。在这项工作中，提出了一个梯度塑性框架，它可以通过将晶界视为有限厚度的单独相来捕捉这种软化行为。得到的屈服应力随晶粒度变化的理论表达式可以捕捉到大量的实验数据，这些实验数据显示了这种“正常”到“反常”的Hall-Petch转变，并得到了一个可以预测发生这种转变的晶粒度的解析式。此外，还得到了纳米材料中流动应力的解析表达式，并与纳米晶铜的原子模拟结果进行了精确的比较，结果表明，在临界晶粒度以下，流动应力与临界晶粒度成正比。
Experimental and simulation studies have shown that decreasing the grain size below a critical value results in softening rather than hardening in both the yield stress and flow stress of nanomaterials. In this work, a gradient plasticity framework is presented that can capture this softening behavior by treating grain boundaries as a separate phase with a finite thickness. The theoretical expression obtained for the yield stress as a function of the grain size can capture numerous experimental data that exhibit this “normal” to “abnormal” Hall–Petch transition, and an analytical equation is obtained that can predict the grain size at which this transition occurs. Furthermore, analytical expressions are obtained for the flow stress in nanomaterials, and they are in precise agreement with atomistic simulations on nanocrystalline Cu, which predict that below a critical grain size the flow stress decreases proportional to it.