【Background】

The properties of polycrystalline metals and ceramics are closely related to the structure and composition of their grain boundaries. Alloys, dopants and impurities are usually present in the grain boundaries at a higher concentration than the interior of the particles, which is called grain boundary segregation or adsorption. Since the alloying elements and impurities are preferentially aggregated at the grain boundaries, the nature of the material sometimes changes materially. The study of twin crystals shows that the regular atomic pattern usually appears due to the solute segregation at the high symmetry boundary, but it is not known whether the superstructure is present at the general grain boundaries in the polycrystal.

【Introduction】

Beijing, October 6, 2017, Science published online at the University of California, Luo Jian, Li Hai University Martin P. Harmer (Common Communications) and others entitled "Segregation-induced ordered superstructures at general grain boundaries in a nickel-bismuth alloy In the bismuth-doped polycrystalline nickel, the team found that ordered segregation-induced grain boundary superstructures occurred at randomly selected general grain boundaries, which were driven by the orientation of the discontinued grain surface, rather than Crystal lattice matching between grains. This finding suggests that the superstructure induced by the adsorbate is not limited to a particular grain boundary but can be present in a variety of general grain boundaries and thus can affect the properties of the polycrystalline alloy. The discovery of Bi segregation-induced superstructures at the general grain boundary enriches the perception of existing studies and can provide new insights into structural-related grain boundary properties such as plasticity, diffusivity and conductivity.

Fig.1 Ultra-structure induced by atom-scale segregation in Ni-Bi system

Fig.2 DFT calculation results of Ni-Bi surface and grain boundary

Figure 3 is the crystal interface of Bi doped with Ni

Figure 4 The distance between the interface and the Bi-Bi at the grain boundary