Characterization Study Of Local Atomic Structure Of Metallic Glasses

With excellent mechanics, magnetism, electrochemistry and other unique properties, metallic glasses attracted much attention in the field of basic science and practical application. However, the structure of the material determines its performance. The atomic arrangement characteristic of disordered long-range and ordered short-range of metallic glasses determines its properties, especially its ordered short-range atomic structure. However, since there is no specific and precise understanding of this unique structure, some mechanism of metallic glasses is still not very clear during the related research, for example, the glass formation mechanism, the deformation mechanism and the glass transition mechanism, et. al.. Moreover, the breakthroughs of the study bottlenecks of metallic glasses need people to resolve its structure, for example, the breakthrough of preparation dimensions and room temperature brittleness. Therefore, a systematic understanding of its structures(such as the atomic arrangement and coordination situation) with the viewpoints of the atomic scale is extremely necessary.On the basis of other scientist’s previous studies, the paper focused on exploring the local atomic structure of simple metallic glasses’ s structure, so that we can lay the foundation for the subsequent more complex research. And we mainly use the binary Ni-Nb system and ternary CoSiB metallic glasses as the object of study, prepared the relevant metallic glass samples, and then through selected area electron diffraction(SAED) and high-energy synchrotron radiation XRD, combined with radial distribution function(RDF) method and the reverse Monte Carlo(RMC) simulation methods to characterize the local atomic structure of metallic glasses. In the paper’s work, we especially use the principle of maximum entropy calculated radial distribution function, optimized the method, and prepared the relevant procedures. The main conclusions are as follows:(1) Ni60+xNb40-x(x = 0, 1, 2, 3, 4) series binary metallic glass strips and Co65B24.4Si10.6 ternary metallic glass strips were prepared by copper mold casting and single roller strip method. The microstructure were characterized by high-energy synchrotron radiation XRD or SAED experiments, which shows that the prepared samples are amorphous structure.(2) SAED method to calculate the radial distribution function, reverse Monte Carlo computer simulation method and the maximum entropy principle method were studied and mastered. RDF principle of maximum entropy calculation method is optimized and a relevant calculation program was wrote. These all provide technical and methodological conditions for subsequent experiments.(3) Short-range atomic structure of the Ni60+xNb40-x(x = 0, 1, 2, 3, 4) metallic glasses was studied, which shows that the trend of structure factors i(s) of the samples are similar. This means that they contain the similar short-range atomic structure information. Through analysis and calculating, we find that the atom numbers of the first coordination sphere of the central atom is 6.22, which is consistent with the actual experimental results.(4) Short-range atomic structure of Co65B24.4Si10.6 ternary metallic glass was studied through SAED method, and we find that the structure of the prepared samples was stable. In addition, the RDF of the samples calculated with the program shows that the nearest neighbor distance of Co-Co atom pairs is about 2.53 ? and Co-B is 2.34 ?, which is similar with the experimental values. The results shows that the program is able to reflect the objective reality truly.(5) Through the diffraction experiment of some Ni62Nb38 metallic glasses samples, we got i(s) and RDF, and found that different batches of Ni62Nb38 metallic glasses samples have good repeatability, which proves that the composition has good glass forming ability and stable structure.(6) Through RMC computer simulation, we made the three-dimensional structure model of Ni62Nb38 and Co65B24.4Si10.6 metallic glasses and through the analysis of the model, we find that the nearest neighbor distance of Ni-Ni, Ni-Nb and Nb-Nb are 2.74 ?,2.80 ? and 2.82 ?, which are agree with the experiment results. Through screening, we find around the central atom Ni with 4 Ni atoms and 2 Nb atoms, which similar with the center atom Nb, the first coordination sphere is 6, namely 4 Nb and 2 Nb; there are Co8B3 clusters and attached three ovtahedral prism Co9 B structure in Co65B24.4Si10.6 metallic glass.