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Öğe Dynamical and structural properties of metallic liquid and glass Zr48Cu36Ag8Al8 alloy studied by molecular dynamics simulation(Elsevier, 2021) Celtek, M.; Sengul, S.; Domekeli, U.; Guder, V.The structure and dynamics of the Zr48Cu36Ag8Al8 alloy were investigated by molecular dynamics simulation method using the embedded atom method (EAM) and tight-binding (TB) potentials. Total structure factors and pair distribution functions calculated from both potentials are in good agreement with the reported experimental data. The glass transition temperature was determined more easily by using the Wendt-Abraham parameter, which we modified with small changes. The fraction of 1551-bonded pairs and Zr-, Cu-, Ag- and Al-centered icosahedral-like clusters increased with decreasing temperature. High fractions of Cu-, Ag- and Al-centered perfect icosahedra and Zr-centered icosahedra-like clusters were detected in both supercooled liquids and glasses. The critical temperature was determined to be similar to 760.65 K from mode coupling theory. Although the results for the EAM and TB potentials were largely consistent with the experiment, aggregations were detected in the Ag and Al atoms at low temperatures for the EAM potential.Öğe Effects of Ag or Al addition to CuZr-based metallic alloys on glass formation and structural evolution: A molecular dynamics simulation study(Elsevier Sci Ltd, 2021) Celtek, M.; Domekeli, U.; Sengul, S.; Canan, C.The local environment of Cu47.5Zr47.5M5 (M = Ag and Al) metallic liquids and glasses has been studied in detail using the embedded atom method combined with molecular dynamics simulations. The effects of the addition of Al and Ag separately to CuZr-based alloys on the microstructure have been comprehensively discussed in terms of structural functions, bond angle distributions, coordination numbers and common neighbor analysis. The simulated structure factors and coordination numbers are in good agreement with the experimental results the literature. According to different analysis results, it has been observed that Ag prefers Zr to Cu and Al prefers Cu to Zr as the neighboring atom. Our results show that Al is much more effective than Ag in the development of the icosahedral short range order, although the short range order of both glass-forming liquids and glasses shows a strong dependence on Ag and Al additions. In addition, the atomic radii of Ag and Al atoms are very close to each other, but results have shown that Ag atoms (12 = CN <= 15) tend to form interestingly larger clusters than Al atoms (12 = CN <= 14).Öğe Glass formation and structural properties of Zr50Cu50-xAlx bulk metallic glasses investigated by molecular dynamics simulations(Elsevier Sci Ltd, 2017) Celtek, M.; Sengul, S.; Domekeli, U.Temperature effects on the structural evolution and the glass formation of Zr50Cu50-xAlx (x = 0, 10, 20, 30, 40, and 50) in the liquid and glassy states are studied by classical molecular dynamics simulations. In order to perform a comprehensive comparison and analysis, we consider the Honeycutt-Andersen indices, Voronoi analysis, radial distribution functions, coordination numbers, enthalpy, specific heat, and self-diffusion coefficients in our classical simulations in conjunction with the many body tight binding and embedded atom method potentials. The simulated structural properties were found to be in good agreement with available experimental data for Al poor concentration. We may conclude that the Al is a key element in glass transition and icosahedral ordering in considered systems, Zr-Cu-Al alloys have the best GFA until the concentration of Al in ternary alloy reaches the value of 20% and the parameters of TB model potentials for Al need to improve to explain the aggregation of Al atoms in ternary Zr-Cu-Al alloy. (C) 2017 Elsevier Ltd. All rights reserved.Öğe The melting mechanism in binary Pd0.25Ni0.75 nanoparticles: molecular dynamics simulations(Taylor & Francis Ltd, 2018) Domekeli, U.; Sengul, S.; Celtek, M.; Canan, C.The melting mechanism for Pd0.25Ni0.75 alloy nanoparticles (NPs) was investigated using molecular dynamics (MD) simulations with quantum Sutton-Chen many-body potentials. NPs of six different sizes ranging from 682 to 22,242 atoms were studied to observe the effect of size on the melting point. The melting temperatures of the NPs were estimated by following the changes in both the thermodynamic and structural quantities such as the total energy, heat capacity and Lindemann index. We also used a thermodynamics model to better estimate the melting point and to check the accuracy of MD simulations. We observed that the melting points of the NPs decreased as their sizes decreased. Although the MD simulations for the bulk system yielded higher melting temperatures because of the lack of a seed for the liquid phase, the melting temperatures determined for both the bulk material and the NPs are in good agreement with those predicted from the thermodynamics model. The melting mechanism proceeds in two steps: firstly, a liquid-like shell is formed in the outer regions of the NP with increasing temperature. The thickness of the liquid-like shell increases with increasing temperature until the shell reaches a critical thickness. Then, the entire Pd-Ni NP including core-related solid-like regions melts at once.Öğe Melting properties of tin nanoparticles by molecular dynamics simulation(Natl Inst Optoelectronics, 2009) Dalgic, S. S.; Domekeli, U.Molecular dynamics calculations have been performed to study the melting properties of tin (Sn) nanoparticles with different number of atoms. The modified analytic embedded atom method (MAEAM) interatomic potentials are used to describe the interaction between Sn atoms. The temperature dependent of atomic diffusion in nanoparticles and the heat of fusion as a function of reciprocal of nanoparticle diameter have obtained. The structural properties such as radial distribution functions and static structure factors have computed at different temperatures. Both particle size dependent melting temperature and latent heat of fusion have been determined. It has been shown that the melting point of tin nanoparticles depends nonlinearly on the particle radius. Dynamical properties of tin nanoparticles such as the diffusion coefficient (D), mean square displacement (MSD) and velocity autocorrelation function (VACF) have also calculated.Öğe Molecular dynamics simulation studies on melting of Sn nanowires(Natl Inst Optoelectronics, 2011) Dalgic, S. Senturk; Domekeli, U.The melting process of Sn nanowires has been simulated by using molecular dynamics with the modified analytic embedded atom method (MAEAM) interatomic potentials. The wires studied here are chosen approximately cylindrical in cross-section. The periodic boundary conditions has been applied along their length; the atoms were arranged initially in a crystal structure of beta-Sn block which belongs to tetragonal group with the [0 0 1] direction parallel to the long axis of the wire. The size effects of the nanowires on the melting temperatures have been investigated. In order to characterize melting transition, we have interested in some structural, energetic and dynamical quantities of Sn nanowires. We find that for the nanoscale regime, the melting temperatures of Sn nanowires are much lower than that of the bulk. It has been resulted that melting point of Sn nanowires shifts to higher temperatures when the diameter of nanowires increased. There is in a good agreement between the results obtained from MD simulations and other theoretical and experimental data. When a nanowire is heated up above the melting temperature, the neck of the nanowire begins to arise and the diameter of neck decreases rapidly with the equilibrated running time. Finally, the breaking of nanowire arises, which leads to the formation of the spherical nanoparticles.Öğe Molecular dynamics simulations of glass formation and atomic structures in Zr60Cu20Fe20 ternary bulk metallic alloy(Pergamon-Elsevier Science Ltd, 2017) Sengul, S.; Celtek, M.; Domekeli, U.In this study, the atomic structures and the glass formation process of Zr60Cu20Fe20 ternary bulk metallic alloy were studied by molecular dynamics simulation using the many body tight-binding potentials. In order to investigate glass transition, the specific heat, enthalpy, radial distribution functions, and coordination number were used. The local atomic order in the ternary Zr60Cu20Fe20 was been analyzed using Honeycutt-Andersen pair analysis technique, the distribution of bond-angles and Voronoi analysis. The results show that Zr60Cu20Fe20 alloy begins to transform into a glass, the temperature decreased rapidly to -1000K, and Cu and Fe atoms play important role in the formation of icosahedra environment in alloy. (C) 2016 Elsevier Ltd. All rights reserved.Öğe Molecular dynamics simulations of glass formation, structural evolution and diffusivity of the Pd-Si alloys during the rapid solidification process(Elsevier, 2023) Celtek, M.; Sengul, S.; Domekeli, U.; Guder, V.The atomic structure, glass formation process and diffusion mechanism of Pd100-xSix (x = 10, 20, 30, 40 and 50) alloys during rapid solidification have been investigated by molecular dynamics simulations using embedded atom method potentials. The structure factors, total (or Pd90Si10) and partial pair distri-bution functions calculated for Pd80Si20 bulk metallic glass are in good agreement with the experimental/ other data. Bond angle distribution function, Honeycutt-Andersen index and Voronoi tessellation analysis have revealed that the increasing Si amount caused a decrease in the number of icosahedral-like clusters and an increase in the number of crystal-like clusters. The majority of icosahedral-like clusters in the sys-tems are mostly composed of Pd-centered clusters, suggesting that Pd has an effective role in the glass formation process in Pd-Si systems. It has been observed that the mobility of Si atoms decreases in envi-ronments with more Pd atoms. The critical temperature and T0 temperature for Pd-Si liquids have been determined from the self-diffusion coefficients using the mode-coupling theory and the Vogel-Fulcher-Tammann law, respectively. The present findings show us that the Pd70Si30 compound has a critical importance in terms of the glass formation process, which is consistent with experimental observations. We hope that the results will contribute to understanding the Si effect on the atomic local structure of Pd -Si systems and will encourage research on many properties of these systems, such as their mechanical properties.(c) 2022 Elsevier B.V. All rights reserved.Öğe Pressure dependent evolution of microstructures in Pd80Si20 bulk metallic glass(Elsevier, 2022) Guder, V; Sengul, S.; Celtek, M.; Domekeli, U.The effect of the pressure on the local microstructure in the amorphous Pd80Si20 alloy was investigated by coordination analyses and structural calculations using molecular dynamics simulations. We observed that the glass transition temperature increases monotonically as the pressure increases. Also, it was seen that the Pd atoms composing the face centered cubic (fcc)- and icosahedral-like order are the origin of the complexity of the local structure while the short-range order around Si atoms is characterized by a tri-capped trigonal prism. We found that the topological structure and local environment of the system which consists of icosahedral-, hexagonal- and fcc-like structural units, change significantly with the effect of pressure. We revealed that the short-range order of the system develops with pressure due to the increase of icosahedral and some defected icosahedral polyhedra, and Pd atoms are responsible for the formation of the amorphous state of the system.Öğe Static and dynamic structure of liquid GaSb using the modified embedded atom method (MAEAM) potentials(Natl Inst Optoelectronics, 2007) Dalgic, S. Senturk; Domekeli, U.Using the effective potentials derived from the modified analytic Embedded Atom Method (MAEAM) in conjunction with the Variational Hypenetted Chain (VMHNC) liquid state theory, we have investigated the structure and atomic dynamics of liquid GaSb alloy near and above the melting point. The effective pair potentials have constructed from the MAEAM potential functions which are parameterized by fitting to both solid and liquid state properties of pure metals. The calculated partial pair correlation functions and static structure factors of liquid GaSb alloy near its melting have compared with experiment and the results of MD studies. The total structure factors of molten GaSb have computed at three different temperatures. The overall agreement has been found in reported works. The dynamical properties evaluated within the framework of the mode-coupling theory, using a self-consistent scheme have been also presented. The single-particle dynamics of the system has been analyzed by computing the mean square displacement (MSD) and velocity autocorrelation function (VACF). Temperature dependence of self diffusion coefficient and shear viscosity have also been shown. The collectiveÖğe Static structure of liquid K-Sb alloys using the MAEAM potentials(Natl Inst Optoelectronics, 2007) Dalgic, S. Senturk; Domekeli, U.The structure of K-Sb liquid alloys at different compositions of Sb have been obtained using the modified analytic EAM (MAEAM) based effective pair potentials in conjunction with the Variational Hypernetted Chain (VMHNC) liquid state theory. The effective pair potentials are constructed from the MAEAM potential functions which are parameterized with fitting to both solid and liquid state properties of pure metals. The partial pair correlation functions and total static structure factor in liquid KSb alloys are computed and than compared with experiments and the results of MD studies. The overall agreement has been found in reported works.Öğe The structural evolution and abnormal bonding ways of the Zr80Pt20 metallic liquid during rapid solidification under high pressure(Elsevier, 2020) Sengul, S.; Celtek, M.; Domekeli, U.The structural evolutions and abnormal bonding ways of the Zr80Pt20 binary alloy during rapid solidification under different pressures from 0 to 120 GPa have been investigated by classical molecular dynamics simulations in conjunction with the embedding atom method. The pair distribution function, the coordination number, the Warren-Cowley parameter, the bond length and the pair analysis technique are used to reveal the structural evolution of the Zr80Pt20 solidified under normal and high pressures. Persuasive evidence indicates that the applied pressure strongly affects the vitrification (for 0 <= P <= 20 and 90 <= P <= 120 GPa) and crystallization (for 30 <= P <= 80 GPa) processes of the metallic liquid and causes significant changes in the microstructure of the system. Interestingly, we have observed that the crystallization for the Zr80Pt20 system is associated with volume expansion between 50 and 80 GPa, in contrast to the volume contraction observed under 30 and 40 GPa. The results of the atomic structure analysis show that there is an unexpected shortening of Zr-Zr bonds under high pressures, which is related to the change of the atomic packing in the Zr80Pt20 alloy from loose to dense with increasing pressure. The results of the analysis show that the bonds between Zr-Zr and Pt-Pt pairs can be shortened more easily than the bonds between Zr-Pt pairs at high pressures and also the clustering behaviors of Zr-Zr or Pt-Pt bonds reveals the presence of composition segregation. This study presents encouraging findings for the experimental investigation of glass transition and crystallization processes in Zr-Pt metallic liquids during rapid cooling and under high pressure.
