Vlassov Sergei, Mets Magnus, Polyakov Boris, Bian Jianjun, Dorogin Leonid, Zadin Vahur
Institute of Physics, University of Tartu, W. Ostwaldi Str. 1, 50412, Tartu, Estonia.
ITMO University, Kronverskiy pr., 49, 197101 Saint-Petersburg, Russia.
Beilstein J Nanotechnol. 2019 Dec 12;10:2468-2476. doi: 10.3762/bjnano.10.237. eCollection 2019.
In this study, pentagonal Ag and Au nanowires (NWs) were bent in cantilever beam configuration inside a scanning electron microscope. We demonstrated an unusual, abrupt elastic-to-plastic transition, observed as a sudden change of the NW profile from smooth arc-shaped to angled knee-like during the bending in the narrow range of bending angles. In contrast to the behavior of NWs in the tensile and three-point bending tests, where extensive elastic deformation was followed by brittle fracture, in our case, after the abrupt plastic event, the NW was still far from fracture and enabled further bending without breaking. A possible explanation is that the five-fold twinned structure prevents propagation of critical defects, leading to dislocation pile up that may lead to sudden stress release, which is observed as an abrupt plastic event. Moreover, we found that if the NWs are coated with alumina, the abrupt plastic event is not observed and the NWs can withstand severe deformation in the elastic regime without fracture. The coating may possibly prevent formation of dislocations. Mechanical durability under high and inhomogeneous strain fields is an important aspect of exploiting Ag and Au NWs in applications like waveguiding or conductive networks in flexible polymer composite materials.
在本研究中，五角形的银和金纳米线（NWs）在扫描电子显微镜内以悬臂梁结构进行弯曲。我们展示了一种不寻常的、突然的弹性到塑性转变，在狭窄的弯曲角度范围内弯曲时，观察到纳米线轮廓从光滑的弧形突然变为有角度的膝盖状。与纳米线在拉伸和三点弯曲试验中的行为不同，在拉伸和三点弯曲试验中，先是广泛的弹性变形，然后是脆性断裂，而在我们的案例中，在突然的塑性事件之后，纳米线仍远未断裂，并且能够进一步弯曲而不折断。一种可能的解释是，五次孪晶结构阻止了临界缺陷的扩展，导致位错堆积，这可能导致突然的应力释放，这被观察为突然的塑性事件。此外，我们发现，如果纳米线涂有氧化铝，则不会观察到突然的塑性事件，并且纳米线可以在弹性范围内承受严重变形而不发生断裂。涂层可能会阻止位错的形成。在高应变和不均匀应变场下的机械耐久性是在诸如柔性聚合物复合材料中的波导或导电网络等应用中利用银和金纳米线的一个重要方面。
