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|Title:||Atomic structure and composition-structure-properties correlations in metallic glasses||Authors:||SHA ZHENDONG||Keywords:||molecular dynamics simulation, LAMMPS, Cu-Zr metallic glasses, Atomic-level structure, Polyhedral clusters, Structure-properties correlations||Issue Date:||17-Aug-2010||Citation:||SHA ZHENDONG (2010-08-17). Atomic structure and composition-structure-properties correlations in metallic glasses. ScholarBank@NUS Repository.||Abstract:||We have performed molecular dynamics (MD) simulation based on the embedded atom method (EAM) potential using the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) code, in order to investigate the atomic-level structures and the composition-structure-properties correlations in Cu-Zr metallic glasses (MGs). From the viewpoint of atomic-level structure, the chemical short-ranger order, topological short-range order, and short-to-medium-range order of the Cu-Zr binary system were investigated, respectively. Then these atomic-level structures are related to composition-structure-properties correlations. Two aspects of physical properties were taken into account, i.e. the glass-forming ability (GFA) and mechanical behavior. It was found that the quantitative composition-structure-GFA correlation could be established based on the full icosahedra. Weak yet significant peaks in fraction of Cu-centered <0,0,12,0> full icosahedra (fico) obtained from a statistical analysis over a broad compositional range with high resolution were observed at certain compositions, which coincide with the GFA enhancement. This correlation implies that the change in fico is a fundamental structural factor in determining the ease of glass formation. Besides, it was found that the composition-structure-GFA correlation could also be established based on the average number of the basic clusters. Certain peaks showed up at certain compositions, which indicate good glass formers. These optimum compositions with enhanced GFA are consistent with the previously reported experimental and simulation results. The liquid behaviors of Cu61.8Zr38.2, Cu64.5Zr35.5, and Cu66Zr34 amorphous alloys including their pair distribution functions, distributions of Voronoi clusters with different coordination numbers, and mean square displacements of Cu and Zr atoms were investigated. Compared to Cu61.8Zr38.2 and Cu66Zr34, high concentrations of distorted icosahedra with indices of <0, 2, 8, 2> and <0, 4, 4, 4>, high numbers of Cu-centered Cu8Zr5 and Cu9Zr4 clusters, and reduced atomic diffusivity of Cu and Zr atoms were found in molten Cu64.5Zr35.5 alloy. These effects would make the liquid more viscous, and thus benefit glass formation in Cu64.5Zr35.5 alloy. Short- and medium-range orders in the Cu64Zr36 metallic glass have been investigated from the first to the sixth coordination shell up to 15.3 ? length scale. In the first three coordination shells, the total number of atoms within the nth coordination shell N is 13, 61, and 169. And the number of atoms on the nth coordination shell is 12n2. Besides, we recognized that the basic atomic structure could be obtained from a central icosahedron surrounded by a shell of 12n2 atoms. From the fourth coordination shell on, the total number of atoms within the nth coordination shell N is 307, 561, and 924 with the characteristics of an icosahedral shell structure. Our study indicates that in good glass former, an icosahedral shell structure prevails in both short and medium range in the Cu-Zr binary system. Our findings have implications for understanding the atomic structure, GFA and mechanical properties of MGs.||URI:||http://scholarbank.nus.edu.sg/handle/10635/22863|
|Appears in Collections:||Ph.D Theses (Open)|
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