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Effect of Chemical Composition on Atomic Structure and Mechanical Properties of Mg-Zn Glass Alloys Using Molecular Dynamics Simulation

Asl Roosta, Pouneh | 2020

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 53197 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Tavakoli, Rohollah
  7. Abstract:
  8. In this research, Mg-Zn bulk metallic glasses have been investigated using molecular dynamics simulation. In order to study the structure of this alloy, coordination number, short and medium order of chemical range, Voronoi analysis, glass conversion temperature and atomic pair distribution function have been used. According to the results, the full icosahedral structure with IS connection type in comparison with other structures has an essential role in the stability of the system during cooling and creating medium-scale areas. The results show that the ability to form glass depends on the chemical composition and cooling rate. In this research, the cooling rate is considered to be 1011 K/s and 5×1010 K/s and in order to study the chemical composition, the range of 10 to 50% of the atomic element Zn is considered. At lower cooling rates, the ability to form glass structures increases as the chance of atoms being placed in the system increases. In this particular alloy, in the range of 25 to 50% of the atomic element Zn, due to the increase in the full icosahedral structure, the ability to form a glass structure also increases. Due to the fact that in the molecular dynamics method, the cooling rate is inherently high, in this study, by maintaining the isotherm below and near the glass transition temperature, and by reducing the potential energy of the structural relaxation process occurs. Also, by comparing the coordination number before and after isothermal maintenance, it is found that the coordination number 12, which represents a full and distorted icosahedral, has increased, and this type of structure is more compact and stable than other structures, which indicates the occurrence of Structural relaxation is in the sample. During isothermal maintenance over time, an increase in the frequency of icosahedron and a decrease in free volume also indicate the emergence of structural relaxation in the system
  9. Keywords:
  10. Magnesium Alloy ; Cooling Rate ; Structural Relaxation ; Molecular Dynamic Simulation ; Bulk Metallic Glass ; Chemical Compounds

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