| As a new type of metallic material with properties of glass, metal, solid and liquid, metallic glass has excellent mechanical, chemical, physical properties, which make it widely used in many fields. It is well known that the property of the material is determined by microstructure. Therefore, clarifying the relation between microstructure and macro property of metallic glass is the key to understand the property of metallic glass.Compared with the crystalline material, the microstructure of the metallic glass has the characteristics of long-range disorder and short-range order, thus, adoptting appropriate microstructure characterization method is the prerequisite to in-depth understanding of metallic glass' various natrues. For this purpose, in this paper, the Molecular Dynamics (MD) simulation is carried out for the rapid solidification process of metallic silver, both advantages and disadvantages of CTIM and VPIM in characterizing local atomic clusters are concluded by systematically comparing the correlation and differentiation of the local atomic clusters characterized by these two methods respectively.The following analysises are provided in this thesis:(1) MD is simulated in the rapid solidification process of liquid metallic silver. Firstly, the result provided by PDF and energy change with temperature show that the glass-transition temperature at the cooling rates of 5×10I3K/s is 757K and the crystallization temperature at the cooling rates of 5×1011K/s is 726K. Secondly, the details given by a collection of quantive H-A bond-types show that at the cooling rate of 5×1013K/s, the amorphous structure is formed mainly with the 1551?1441and 1431 featuring bond-types; at the cooling rate of 5×101 K/s, the crystal structure is formed mainly with the 1421? 1422 featuring bond-types; at last, the same system's basic clusters are characterized by CTIM and VPIM respectively. The results show that in the amorphous system, the fractions of perfect icosahedrons are both rare by VPIM and CTIM, while the frictions of the defect and deformed icosahedrons are both substantial In the crystal system, the extended CTIM can facilitate to characterize fcc and hcp basic clusters by (12,12/1421) and (12,6/1421, 6/1422), while this two different atomic clusters are classified into one type Voronoi Polyhedron Index<0 12 0 0>. Besides, in these two systems, the clusters' types by CTIM are far more than the ones by VPIM, and this tendency expands in the ascending temperature system. The abundant clusters' may be helpful to the evolution of microstructure, but can go against the statistics on clusters' types and the analysis on atomic clusters' structure.(2) By tracing the atoms'ID, there exists a complicated intersect corelation between the CTIM Clusters and Voronoi Polyhedrons (VPs). Generally, a kind of CTIM cluster with coordination number Z may find several corresponding counterparts of VPs with coordination number (Z+1) or even (Z+2). When approximation to remove tiny faces is adopted on VPIM; the ability to identify the typical atomic clusters is undermining, mistakenly classifying different kinds of VPs into one kind. On condition that atomic configuration and coordination number stay fixed, VPIM adopted by approximation to remove tiny edges is remarkably favorable to enhance the ability of identifying typical cluster.Summarily, CTIM is more favorable in characterizing cluster' configuration in microstructrues with different complicated local atomic clusters, expecially enpolying in crystal with atomic close packed ordering systems of fcc and hcp clusters and identifying five symmetric icosahedrons in amouphous and quasicrystal. But compared with VPIM, excessive and highly dispered types of CTIM clusters may be unfavourable in characterizing large-scale system's micorostructure. |
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