The correlation between the flow stress and grain size for severely deformed metals remains undefined because the conventional Hall-Petch relationship ignores the expected contributions from thermally-activated phenomena in nanomaterials and also it fails to explain the reported strain softening of metals having low melting temperatures. In this study, the contribution of thermally-activated creep mechanisms to the room temperature flow stress is evaluated for 31 pure metals processed by high-pressure torsion. The steady-state grain size and the hardness of these metals are first compared to theoretical predictions from high temperature creep mechanisms. It is shown that these mechanisms are not able to predict the flow stress, although the data from metals with low melting temperatures fall close to the theoretical prediction for high-temperature grain boundary sliding suggesting a possible explanation for the unusual softening of these metals. Nevertheless, a detailed analysis demonstrates that a modified model for grain boundary sliding at low temperature provides the capability of correctly predicting the flow stresses for metals having both high and low melting temperatures. The results confirm the significance of thermally-activated phenomena in determining the flow stress of nanomaterials processed by severe plastic deformation.

严重变形金属的流动应力和晶粒尺寸之间的相关性仍未确定，因为传统的 Hall-Petch 关系忽略了纳米材料中热激活现象的预期贡献，也无法解释报道的低熔点金属的应变软化。在这项研究中，评估了 31 种高压扭转处理的纯金属的热激活蠕变机制对室温流动应力的贡献。首先将这些金属的稳态晶粒尺寸和硬度与高温蠕变机制的理论预测进行比较。结果表明，这些机制无法预测流动应力，尽管来自具有低熔化温度的金属的数据接近高温晶界滑动的理论预测，这表明这些金属异常软化的可能解释。然而，详细的分析表明，低温下晶界滑动的修改模型提供了正确预测具有高熔点和低熔点金属的流动应力的能力。结果证实了热激活现象在确定由严重塑性变形加工的纳米材料的流动应力中的重要性。详细分析表明，改进的低温晶界滑动模型能够正确预测具有高熔点和低熔点金属的流动应力。结果证实了热激活现象在确定由严重塑性变形加工的纳米材料的流动应力中的重要性。详细分析表明，改进的低温晶界滑动模型能够正确预测具有高熔点和低熔点金属的流动应力。结果证实了热激活现象在确定由严重塑性变形加工的纳米材料的流动应力中的重要性。