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Recently, academician Zhang Ze of Zhejiang University and researcher Wang Jiangwei team in Nat. Commun. "The research results entitled "In situ atomistic observation of disconnection-mediated grain boundary migration" were published on the website (NAT.COMMUN.|(2019)10:156). Researchers use PicoFemto in transmission electron microscopy®In situ mechanical-electrical sample rod cleverly designed experiments, successfully prepared and measured a variety of metal nanostructures in situ. The research results provide a strong experimental basis for the establishment of a complete grain boundary deformation theory, and then provide a new idea for improving the mechanical properties of materials.

In-depth study of the grain boundary migration mechanism is of great significance for regulating the mechanical properties of materials. As a common plastic deformation behavior, grain boundary migration has been widely reported and concerned. Among them, the disconnection-dominated grain boundary migration mechanism focuses on the phenomenon of grain boundary migration under the action of shear stress, and this theoretical model has been widely concerned and has been confirmed and perfected in molecular dynamics simulation. However, if we want to have a more systematic understanding and in-depth understanding of the grain boundary mechanism in the process of plastic deformation of materials, we must observe the dynamic evolution process of the atomic structure at the grain boundary under the action of stress in real time.

This paper combines advanced in-situ electron microscopy technology and molecular dynamics simulation to reveal the universal mechanism of reciprocating migration of grain boundaries with different structures under shear stress through disconnection nucleation, slip and interaction. Further studies have found that the trigeminal grain boundary in nanocrystalline materials can be used as an effective position for disconnection nucleation to promote grain boundary migration, and other grain boundary defects (such as dislocations) do not produce obvious pinning effect on the migration, which significantly improves the plastic deformation ability of the material.

PicoFemto®In situ mechanical-electrical sample rod combined with spherical aberration electron microscope and high-speed camera to prepare a variety of metal nanostructures containing different types of grain boundaries with high quality. On the basis of realizing stable in situ shear loading, the dynamic evolution of grain boundary structure during deformation can be captured in real time by high-speed camera. This method can effectively prepare different types of grain boundaries, thus providing an effective means for the study of grain boundary deformation behavior. Even in spherical aberration, PicoFemto®The in-situ mechanical-electrical sample rod also maintains atomic stability, thus ensuring the original resolution of the spherical aberration electron microscope. The product has the control range (XY-2.5 mm,Z-1.5 mm,9 orders of magnitude), high control accuracy (XY-0.4 nm,Z-0.04 nm) and high stability (no jitter, to ensure the original resolution of the electron microscope). In the experiment, both coarse and fine adjustments are all software operations, with friendly interface and strong ease of use.

Figure 1 Observe the grain boundary migration phenomenon caused by two different types of disconnection slip on the Σ 11(113) grain boundary at the atomic scale, it is verified in molecular dynamics simulation that

Figure 2 Σ 11(113) grain boundary realizes reciprocating migration through disconnection mechanism during cyclic loading

Figure 3 Disconnection Trigeminal Grain Boundary Nucleation Mechanism in Plastic Deformation of Complex Grain Boundary Structure