Abstract
Classical molecular dynamics simulations, employing a modified embedded atom model (MEAM) parametrization recently developed by Trybula, have been performed and combined with thermodynamics-based modelling for weakly interacting compound-forming molten alloys, to investigate the structure and chemistry of liquid Al–Cu alloys over a broad Cu concentration range. The compound-forming model (CFM) based on experimental thermodynamic data revealed the importance of the Al2Cu “associate” in the determination of transport properties such as diffusion and viscosity as well as confirmation of the compound formation ability with regard to the available experimental data. Adequately to this fact, molecular dynamics simulation results showed strong evidence of deviation from regular metallic solution resulting from a preponderance of chemical short-range ordering, expressed by Warren–Cowley parameter and increasing abundance of icosahedral motifs with increasing Cu content. In addition, their strong impact on mass transport properties as well as the excess entropy has been detected which exhibits nonlinear compositional behaviour. Thus, we find that the Stokes–Einstein relation is unsuitable for atom transport properties determination at investigated Cu concentration range, while the Green–Kubo formalism can fully account for the experimentally observed physical phenomena. We obtain a compact and compatible view onto the structure and chemical behaviour, including atom kinetics and thermodynamics, of Al–Cu liquid alloys, which allowed us to find another hard-sphere-like metallic system in which transport properties and thermodynamics are strongly affected by packing effects. The hybrid approach presented herein gave a broader and deeper look into the liquid state of the Al–Cu alloys being missing in the literature.
Highlights
Precise determination of structural and chemical properties of metallic systems is strenuous, and sometimes, even impossible, due to the technical limitations of the experimental set-up
Rybicki et al [15] were the first to experimentally study the structure of the liquid Al83Cu17 alloy, observing how the atomic groups are linked to each other. This melt was the subject of computational investigations, including ab initio molecular dynamics (AIMD) [16] and classical molecular dynamics studies [5], employing modified embedded atom model (MEAM) potentials [17]
As it has been shown in a recent study on liquid Al–Zn alloys [4], a combination of molecular dynamics simulations (MD) simulations with thermodynamics-based modelling can successfully account for experimental data and describe the relationship between the structure and thermophysical properties
Summary
Precise determination of structural and chemical properties of metallic systems is strenuous, and sometimes, even impossible, due to the technical limitations of the experimental set-up. A pronounced maximum in viscosity was observed for Al–Cu alloy composition close to intermetallic phases existing in the solid state of the Al–Cu system, which could suggest ‘‘associates’’ influence This issue has not been discussed in the literature with regard to structure and diffusivity investigations. Apart from that, no detailed study on the topology of local atom environment and its relationship with chemistry and atom kinetics has been given yet, which could play a vital role in the investigation of glass or crystal state stability As it has been shown in a recent study on liquid Al–Zn alloys [4], a combination of MD simulations with thermodynamics-based modelling can successfully account for experimental data and describe the relationship between the structure and thermophysical properties. The main scope of the present work is building a bridge between MD-based simulations and CALPHAD-type modelling based on quasichemical approximation for a weakly compoundforming molten alloy [29] and tests it on liquid Al–Cu alloys that will be helpful in discussion of structure and chemistry of the Al–Cu system liquid state
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