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Effect of Chemical Composition on Atomic Structure and Mechanical Properties of Mg-Zn Glass Alloys Using Molecular Dynamics Simulation
, M.Sc. Thesis Sharif University of Technology ; Tavakoli, Rohollah (Supervisor)
Abstract
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...
Simulation of the Effect of Cooling Rate and Chemical Composition on the Atomic Structure of Bulk Metallic Glass Iron-Phosphorus and Nickel-Phosphorus
, M.Sc. Thesis Sharif University of Technology ; Tavakoli, Rouhollah (Supervisor)
Abstract
bulk metallic glass Unlike metal materials that have a crystalline structure, amorphous glass is an amorphous material with an irregular atomic structure that simultaneously has the same physical properties as metals. Due to the absence of crystal defects such as dislocation and grain boundaries, these materials show unique mechanical properties such as high strength and elastic strain, abrasion resistance and proper corrosion. However, their plastic deformation is heterogeneous, concentrated, and accompanied by sudden failure. Unlike metals, these materials do not have a long-range crystalline order, and their atomic structure includes short-range and mid-range order. The short-range order...
Molecular dynamics study of structural formation in Cu50-Zr50 bulk metallic glass
, Article Journal of Non-Crystalline Solids ; 2015 ; 00223093 (ISSN) ; Tavakoli, R ; Aashuri, H ; Sharif University of Technology
Elsevier
2015
Abstract
In this work, the evolution of the local structure in Cu50-Zr50 bulk metallic glass during glass formation was studied by molecular dynamics simulation. The pair distribution function and Voronoi analysis were adopted to characterize local structures in this alloy. The stability of icosahedral clusters and the role of other local clusters in the formation of icosahedra were evaluated. It was found that the (0,2,8,2) polyhedron is not only the dominant cluster in this alloy, but also the most prone cluster to convert into an icosahedron in the course of cooling. Moreover, it acts as an intermediate state during the icosahedron formation. The onset of stability of icosahedra emerges at the...
Molecular dynamics study of structural formation in Cu50–Zr50 bulk metallic glass
, Article Journal of Non-Crystalline Solids ; Volume 432 , 2016 , Pages 334-341 ; 00223093 (ISSN) ; Tavakoli, R ; Aashuri, H ; Sharif University of Technology
Elsevier B. V
2016
Abstract
In this work, the evolution of the local structure in Cu50–Zr50 bulk metallic glass during glass formation was studied by molecular dynamics simulation. The pair distribution function and Voronoi analysis were adopted to characterize local structures in this alloy. The stability of icosahedral clusters and the role of other local clusters in the formation of icosahedra were evaluated. It was found that the (0,2,8,2) polyhedron is not only the dominant cluster in this alloy, but also the most prone cluster to convert into an icosahedron in the course of cooling. Moreover, it acts as an intermediate state during the icosahedron formation. The onset of stability of icosahedra emerges at the...
Structural modification through pressurized sub-Tg annealing of metallic glasses
, Article Journal of Applied Physics ; Volume 122, Issue 21 , 2017 ; 00218979 (ISSN) ; Ashuri, H ; Tavakoli, R ; Stoica, M ; Ažopu, D ; Eckert, J ; Sharif University of Technology
Abstract
The atomic structure of metallic glasses (MGs) plays an important role in their physical and mechanical properties. Numerous molecular dynamics (MD) simulations have been performed to reveal the structure of MGs at the atomic scale. However, the cooling rates utilized in most of the MD simulations (usually on the order of 109-1012 K/s) are too high to allow the structure to relax into the actual structures. In this study, we performed long-term pressurized sub-Tg annealing for up to 1 μs using MD simulation to systematically study the structure evolution of Cu50Zr50 MG. We find that from relaxation to rejuvenation, structural excitation of MGs and transition during sub-Tg annealing depend on...
Universal correlation between the thermodynamic potentials and some physical quantities of metallic glasses as a function of cooling rate during molecular dynamics simulation
, Article Journal of Non-Crystalline Solids ; Volume 536 , 2020 ; Tavakoli, R ; Sharif University of Technology
Elsevier B.V
2020
Abstract
The existence of universal semi-log linear relation between potential energy and cooling rate during the molecular dynamics simulations of metallic glasses for Cu-Zr system was formerly reported. For this purpose, different classes of metallic glasses are considered and the validity of this correlation is studied. It is shown that it holds for other thermodynamics potentials and some physical quantities like density and Wendt and Abraham parameter, too. This observation enables us to economically construct atomic scale metallic glass structures equivalent to very low cooling rates, more consistent to experimental works, not accessible using classic molecular simulations. © 2020 Elsevier B.V
On the glass-forming ability of (Zr0.5Cu0.5)100−xAlx ternary alloys: A molecular dynamics study
, Article Materials Today Communications ; Volume 31 , 2022 ; 23524928 (ISSN) ; Shabestari, S. G ; Tavakoli, R ; Sharif University of Technology
Elsevier Ltd
2022
Abstract
In this research, the atomic scale local structures in (Zr0.5Cu0.5)100−xAlx (x = 0,2,4,6,8,10,12) bulk metallic glass was studied using molecular dynamics simulation method. The pair distribution function, Voronoi analysis and mean squared displacement (MSD) were adopted for investigation of the local structures. It was found that Cu- and Al-centered full icosahedra possess the most frequency accompanied by the most changes during the glass transition process in the supercooled liquid region temperature. Moreover, it was observed that the Al-centered full icosahedra (Al-FI) and Cu-centered full icosahedra (Cu-FI) clusters with 2.5% and 1.9% increase (relative to total atoms), respectively,...
Effect of chemical composition and affinity on the short- and medium-range order structures and mechanical properties of Zr-Ni-Al metallic glass
, Article Journal of Non-Crystalline Solids ; Volume 456 , 2017 , Pages 68-75 ; 00223093 (ISSN) ; Tavakoli, R ; Koh, J. J ; Aitken, Z. H ; Zhang, Y. W ; Sharif University of Technology
Elsevier B.V
2017
Abstract
Previous studies have shown that a small variation in the chemical composition of metallic glasses (MGs) can drastically alter their strength and ductility. However, the underlying structural origin and atomistic mechanisms remain unclear. Using large-scale molecular dynamics simulations, we studied the effect of chemical composition and affinity on the microstructure and deformation behaviour of Zr50Ni50 − xAlx MG by varying the value of x in the range of 5 ≤ x ≤ 25 (at.%). We show that an increase in x is able to strengthen and embrittle the material. In particular, a ductile (homogeneous deformation) to brittle (shear banding) transition occurs at x ~ 15. To reveal the structural origin,...
Medium range order evolution in pressurized sub-Tg annealing of Cu64Zr36 metallic glass
, Article Journal of Non-Crystalline Solids ; Volume 481 , 2018 , Pages 132-137 ; 00223093 (ISSN) ; Tavakoli, R ; Aashuri, H ; Sharif University of Technology
Elsevier B.V
2018
Abstract
Molecular dynamics (MD) simulations have been widely used to study the structure of metallic glasses (MGs) at atomic scale. However, ultrafast cooling rates in MD simulations create structures that are substantially under-relaxed. In this study, we introduce long-term pressurized annealing up to 1 μs slightly below the glass-transition temperature, Tg, in MD simulation, which effectively relaxes the structure of Cu64Zr36 MG toward experimental conditions. It is found that applying hydrostatic pressure up to 2 GPa relaxes the MG to low-energy states whereas higher pressures retard relaxation events. In the sample annealed at 2 GPa pressure, equivalent cooling rate reaches to 3.7 × 107 K/s,...