posted on 2023-11-27, 16:12authored byDongwei Li, Zhanxin Wang, Yufeng Zhao, Weijing Zeng, Zihao Zhang, Shuai Li, Huibin Lian, Chengpeng Yang, Yan Ma, Libo Fu, Yizhong Guo, Ze Zhang, Yadi Zhai, Shengcheng Mao, Lihua Wang, Xiaodong Han
Permanent
structural changes in pure metals that are caused by
plastic activity are normally irreparable after unloading. Because
of the lack of experimental evidence, it is unclear whether the plastic
activity can be repaired as the size of the pure metals decreases
to several nanometers; it is also unclear how the metals accommodate
the plastic deformation. In this study, the in situ atomic-scale loading and unloading of ∼2 nm Ag nanocrystals
was investigated, and three modes of plastic deformation were observed:
(i) the phase transition from the face-centered cubic (fcc) phase
to the hexagonal close-packed (hcp) phase, (ii) stacking faults, and
(iii) deformation twin nucleation. We show that all three modes resulted
in structural changes that were reparable, and their generation and
restoration during loading and unloading were observed in
situ. We discovered that the deformation modes of nanosized
metals can be predicted from the ratio of the energy barriers of the
fcc–hcp phase transition (ΔγH) and the
deformation twin nucleation (ΔγT), which differ
from those of the theoretical modes of relatively large-sized metals.
The proposed ΔγH/ΔγT criterion provides insights into the deformation mechanism of nanometals.