In polycrystalline metal materials, plastic deformation is accompanied by lattice rotation caused by dislocation slip. In three-dimensional space, these lattice rotations require non-destructive methods to characterize. So far, existing characterization methods are limited to grain sizes at the micrometer scale.
Today, Qiongyao He, Guilin Wu, Xiaoxu Huang, and others from Chongqing University published a paper in Science, tracking the lattice rotation of individual grains in nanocrystalline nickel using three-dimensional orientation mapping in transmission electron microscopy before and after in-situ nanomechanical testing.
Many larger grain sizes experienced unexpected lattice rotation, attributed to the reversal of lattice rotation during the unloading process. This inherent reversible rotation originates from the reverse stress-induced dislocation slip process, which is more active for larger grains. This provides insights into the fundamental deformation mechanisms of nanocrystalline metals and will help guide strategies for material design and engineering applications.
Figure 1. Transmission electron microscopy three-dimensional orientation imaging technique for deformation induced structural changes in nanocrystalline nickel metal. Orientation mapping in a transmission electron microscope, 3D-OMiTEM characterization
Figure 2. Quantification of deformation induced crystal rotation in nanocrystalline nickel metal.
Figure 4. Deformation mechanism of nanocrystalline nickel metal.
Accurately determining how materials deform is the key to better engineering and design. This study utilizes three-dimensional microscopy technology to track the grains in polycrystalline nickel based on deformation cycling. Research has found that these grains not only rotate in two directions, but sometimes also undergo internal lattice rotation. This unexpected lattice rotation occurs more frequently in larger grains and is due to a phenomenon called back stress, which drives the generation of rotational dislocation slip. This discovery represents an important and unique mechanism for adapting to deformation, and may lead to better material designs.
Editor: Sichuan Jinzhongde Science and Technology Research Institute
Source: Today's New Materials
