Zhou Xin, Li Xiuyan, Lu K
Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, China.
School of Materials Science and Engineering, University of Science and Technology of China, Hefei 230026, China.
Phys Rev Lett. 2019 Mar 29;122(12):126101. doi: 10.1103/PhysRevLett.122.126101.
The greatly increased grain boundary (GB) mobility in nanograined metals under mechanical loading is distinguished from that in their coarse-grained counterparts. The feature leads to softening of nanograined materials and deviation of strength from the classical Hall-Petch relationship. In this Letter, grain size dependences of GB migration in nanograined Ag, Cu, and Ni under tension were investigated quantitatively in a wide size range. As grain size decreases from submicron, GB migration intensifies and then diminishes below a critical grain size. The GB migration peaks at about 80, 75, and 38 nm in Ag, Cu, and Ni, respectively. The suppression of GB migration below a critical size can be attributed to GB relaxation during sample processing or by postthermal annealing. With relaxed GBs the governing deformation mechanism of nanograins shifts from GB migration to formation of through-grain twins or stacking faults. GB relaxation, analogous to GB segregation, offers a novel approach to stabilizing nanograined materials under mechanical loading.
纳米晶金属在机械加载下晶界（GB）迁移率的大幅提高，与粗晶金属的晶界迁移率有所不同。这一特性导致纳米晶材料软化，强度偏离经典的霍尔-佩奇关系。在本快报中，对拉伸状态下纳米晶银、铜和镍在较宽尺寸范围内的晶界迁移的晶粒尺寸依赖性进行了定量研究。随着晶粒尺寸从亚微米减小，晶界迁移加剧，然后在低于临界晶粒尺寸时减弱。银、铜和镍的晶界迁移分别在约80、75和38纳米处达到峰值。低于临界尺寸时晶界迁移的抑制可归因于样品加工过程中或热退火后的晶界弛豫。晶界弛豫后，纳米晶粒的主要变形机制从晶界迁移转变为穿晶孪晶或堆垛层错的形成。晶界弛豫类似于晶界偏析，为在机械加载下稳定纳米晶材料提供了一种新方法。
