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![Figure 2. Internal energy of AuCu 3 alloy versus temperature [41].](publication/49854045/figure/fig2/AS:305850251005964@1449931790632/Internal-energy-of-AuCu-3-alloy-versus-temperature-41_Q320.jpg)
We review the studies on the thermophysical properties of undercooled metals and alloys by molecular simulations in recent years. The simulation methods of melting temperature, enthalpy, specific heat, surface tension, diffusion coefficient and viscosity are introduced and the simulated results are summarized. By comparing the experimental results...
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... with the experimental values above the melting temperature, the simulated densities of pure metals generally display a good agreement. Table 4 shows a comparison of the simulated and experimental (above melting temperature) values of some pure liquid metals. The error between the simulations and experiments is less than 5% near the melting temperatures; particularly for liquid titanium, the error is controlled within 1%. ...
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... At first, we analyzed the selfdiffusion coefficients of pristine Cu and found that it possesses a value of 3.70 × 10 − 10 cm 2 /s at 473 K (200 • C) and 7.96 × 10 − 8 cm 2 /s at 1073 K (800 • C), as shown in Fig. 10a. The obtained diffusion coefficients of Cu are in a good agreement with previous reports [54][55][56][57]. This is considered a benchmark to further analyze the diffusion properties of GRCop. ...
Electronic structure calculations with Hubbard U correction are completed to investigate the formation energies, electronic properties and elemental diffusion of Cu–Cr–Nb (GRCop) alloy. GRCop has a higher formation energy (−0.213 eV/atom) compared to Cu (0.031 eV/atom) due to the different atomic radii and locations of Cr and Nb atoms in the Cu matrix. The charge distribution associated with Cr and Nb is more likely to change during the synthesis of GRCop-42 due to the disparity in oxidation state as the composition changes. The temperature-dependent self-diffusion coefficient of Cu is analyzed above 473 K and found to be in the order of 10⁻¹⁰ cm²/s, which is comparable to the earlier reports. Self-diffusion of all the elements in GRCop is calculated to be significantly high, and this indicates that GRCop alloy is suitable for high-temperature applications including electronic packaging, welding electrodes, propulsion components, and heat-exchangers.
... Γ is a factor which characterizes crosscorrelation effects that arise in collective diffusion process, and in many cases Γ≈0.7. 27 As another theoretical approach, molecular dynamics simulation (MD) is can both provide D self and the relationship between D self and the liquid structure. However, reliability of the diffusion coefficients from the classical molecular dynamics simulation (CMD) often depend on the accuracy of potential models which are not so flexible for liquid alloys over the whole range of composition, since they stem from some intermetallic compounds. ...
Through first-principles molecular dynamics simulation, the self-diffusion coefficients of five elements in the four liquid binary M-Si (M=Al,Fe,Mg,Au) alloy systems are obtained under the same overheating temperature. Except for DFe, the self-diffusion coefficient of the other four elements vary significantly with concentration of Si (cSi). The mixing enthalpy between Si and M elements determines the slop of DSi vs cSi curves in Si-rich range. The dominant factor on DSi is the partial coordination number of NSiSi: the larger the NSiSi is, the smaller DSi becomes. The secondary factor on DSi is the medium-range order in liquid alloys: the stronger the medium-range order is, the smaller DSi will be. Complex behavior of coupling or decoupling of self-diffusion coefficients in these liquid binary alloys are observed.
... These methods can be used to predict the value of a T melt for various metals. These include molecular dynamics simulations that are widely used to investigate the coexistence of liquid and solid phases [4,5] and the thermophysical properties of a wide range of materials in general [6]. Notable applications include transition metals [7,8], selected rare-earth elements [9] and binary alloys such as Al-Cu [10,11] or Ni-Zr [12]. ...
The thermophysical properties of metal alloys are often investigated via molecular dynamics (MD) simulations. An exact and reliable estimation of the thermophysical parameters from the MD data requires a properly and carefully elaborated methodology. In this paper, an improved two-phase sandwich method for the determination of the metal melting temperature is proposed, based on the solid-liquid equilibrium theory. The new method was successfully implemented using the LAMMPS software and the C++11 Standard Libraries and then applied to aluminum and copper systems. The results show that the proposed procedure allows more precise calculations of the melting temperature than the widely used onephase boundary methods.
... More importantly, high undercooling is hard to achieve although the contact between melts and container walls has been completely avoided. As an alternative, the molecular dynamics (MD) simulation together with a reasonable potential is considered to be a powerful method to investigate the thermophysical properties of liquid metals [12,13]. It is easier to obtain high undercoolings and to evaluate the thermophysical properties for pure metals and simple alloys, especially for some dilute alloys. ...
The thermophysical properties of undercooled liquid Ni-Zr binary alloys were investigated by molecular dynamics simulation combined with a Finnis-Sinclair (F-S) potential, including melting temperature, density, excess volume and thermal expansion. The melting temperatures were obtained by the evolution of crystal-liquid-crystal sandwich model, where there exist rather low differences of 4.14% for Ni77.8Zr22.2 alloy and 3.98% for Ni50Zr50 alloy when they were compared with the reported values. The calculated densities of liquid Ni-Zr alloys increase with the decrease of temperature, which agree well with the reported experimental values except for the Ni-rich composition alloys. Thus, the reported experimental density of liquid Ni77.8Zr22.2 alloy was employed to re-gauge the current F-S potential and the densities of the Ni-rich composition alloys were recalculated by the re-gauged potential. This binary liquid alloy system shows a negative excess volume, which could be attributed to the strong attractive interactions between Ni and Zr atoms. It is indicated that the Ni-Zr alloy system seriously deviates from the ideal solution, and the accuracy would be very low if the thermophysical properties are estimated by Neumann-Kopp rule. Meanwhile, the thermal expansion coefficients were also derived on the basis of the density data, which increase with the enhancement of temperature except for liquid Ni77.8Zr22.2 alloy.
... It is optimal that the experimental evidence can be obtained by performing measurements. The molecular dynamics (MD) simulation, combining with a resonable potential model, has been extensively applied in the calculation of the physical properties of several metals as a powerful approach [21,22], especially in exploring metastable liquids. The embedded atom method (EAM) potential model proposed by Daw and Baskes [23,24] is always employed to study the transition-metals with fcc crystal structure such as Ni, Cu, Ag and Au. ...
The density of normal and metastable undercooled liquid zirconium was predicted by performing molecular dynamics calculation with a system consisting of 4000 atoms and measured by electrostatic levitation experiments. The results show that the density increases linearly with the descending of temperature, including a maximum undercooling of 928 K. The density is 6.00 g cm-3 at the melting temperature, which agrees well with the experimental result of 6.06 g cm-3. Furthermore, the atomic number is increased to 32,000 on the basis of 4000 atoms and there appears only 0.02% difference. Besides, the pair distribution function was applied to display the atomic structure, which indicates the liquid structure change occurs at the first neighbor distance.
... Solid–liquid phase transition in bulk Au–Cu alloy Copper doping has been done on melting temperature of gold–copper Cu x Au 55-x bimetallic nanostructure. Sutton–Chen (SC) (Kart et al. 2005), quantum Sutton– Chen (QSC) many-body (Kart et al. 2005), and EAM (Lv and Chen 2011) potentials have been used for investigation of solid–liquid phase transition of gold– copper bulk alloy previously. For comparison and validation of different potential models, we have chosen semi-empirical potential model for investigation of melting temperature of copper–gold alloy in bulk structure. ...
Molecular dynamics simulation has been implemented for doping effect on melting temperature , heat capacity, self-diffusion coefficient of gold– copper bimetallic nanostructure with 55 total gold and copper atom numbers and its bulk alloy. Trend of melting temperature for gold–copper bimetallic nanocluster is not same as melting temperature copper–gold bulk alloy. Molecular dynamics simulation of our result regarding bulk melting temperature is consistence with available experimental data. Molecular dynamics simulation shows that melting temperature of gold–copper bimetallic nanocluster increases with copper atom fraction. Semi-empirical potential model and quantum Sutton–Chen potential models do not change melting temperature trend with copper doping of gold–copper bimetallic nanoclus-ter. Self-diffusion coefficient of copper atom is greater than gold atom in gold–copper bimetallic nanocluster. Semi-empirical potential within the tight-binding second moment approximation as new application potential model for melting temperature of gold–copper bulk structure shows better result in comparison with EAM, Sutton–Chen potential, and quantum Sutton–Chen potential models.
... A brief synopsis of undercooled liquid sample preparation is also given in Appendix A. Limited MD results for the heat capacity of Ni [17] and Au (in Au-Cu) [18] liquids are available for temperatures above and below T M . A review of atomistic simulations of undercooled liquid alloys is in Ref. [19]. ...
We describe current approaches to thermodynamic modelling of liquids for the CALPHAD method, the use of available experimental methods and results in this type of modelling, and considerations in the use of atomic-scale simulation methods to inform a CALPHAD approach. We begin with an overview of the formalism currently used in CALPHAD to describe the temperature dependence of the liquid Gibbs free energy and outline opportunities for improvement by reviewing the current physical understanding of the liquid. Brief descriptions of experimental methods for extracting high-temperature data on liquids and the preparation of undercooled liquid samples are presented. Properties of a well-determined substance, B2 O3, including the glass transition, are then discussed in detail to emphasize specific modelling requirements for the liquid. We then examine the two-state model proposed for CALPHAD in detail and compare results with experiment and theory, where available. We further examine the contributions of atomic-scale methods to the understanding of liquids and their potential for supplementing available data. We discuss molecular dynamics (MD) and Monte Carlo methods that employ atomic interactions from classical interatomic potentials, as well as contributions from ab initio MD. We conclude with a summary of our findings.
... Thermodynamic properties of solid-liquid interface affect solidification structure and properties of the solidified components [1]. How to obtain accurate thermodynamic properties of metal solidification is crucial for both industry application and fundamental research. ...
... As a consequence, experimentally measured thermodynamic data at solidliquid interface is rather limited. To overcome the experimental difficulties, computer simulations based on atomistic models such as molecular dynamics (MD) simulations have been developed and becoming a powerful tool for gaining fundamental knowledge of materials processes and properties over the past two decades [1,5]. ...
The aim of this study is to identify the best available inter-atomic potentials for molecular dynamics (MD) calculation of solidification of iron and then to use the best potential to calculate thermodynamic properties such as equilibrium melting temperature, enthalpy, heat capacity and solid-liquid interfacial free energy. Our study reveals that embedded atom method (EAM) potential developed by Ackland et al. [2004 J. Phys.: Condens Matter.16 S2629] appears to be the most accurate model for MD simulation of iron solidification. Simulations with the above EAM model predict the equilibrium melting temperature of iron is 1790K, the solid-liquid interfacial energy 214 mJ/m2. The difference with the experimental data is 1.2%, and 4.9% respectively.
