Universal self-assembly of one-component three-dimensional dodecagonal quasicrystals

Using molecular dynamics simulations, we study computational self-assembly of one-component three-dimensional dodecagonal (12-fold) quasicrystals in systems with two-length-scale potentials. Existing criteria for three-dimensional quasicrystal formation are quite complicated and rather inconvenient for particle simulations. So to localize numerically the quasicrystal phase, one should usually simulate over a wide range of system parameters. We show how to universally localize the parameters values at which dodecagonal quasicrystal order may appear for a given particle system. For that purpose, we use a criterion recently proposed for predicting decagonal quasicrystal formation in one-component two-length-scale systems. The criterion is based on two dimensionless effective parameters describing the fluid structure which are extracted from radial distribution function. The proposed method allows reducing the time spent for searching the parameters favoring certain solid structure for a given system. We show that the method works well for dodecagonal quasicrystals; this results is verified on four systems with different potentials: Dzugutov potential, oscillating potential which mimics metal interactions, repulsive shoulder potential describing effective interaction for core/shell model of colloids and embedded-atom model potential for aluminum. Our results suggest that mechanism of dodecagonal quasicrystal formation is universal for both metallic and soft-matter systems and it is based on competition between interparticle scales.Comment: 8 pages, 6 figure

Can we accurately calculate viscosity in multicomponent metallic melts?

Calculating viscosity in multicompoinent metallic melts is a challenging task for both classical and \textit{ab~initio} molecular dynamics simulations methods. The former may not to provide enough accuracy and the latter is too resources demanding. Machine learning potentials provide optimal balance between accuracy and computational efficiency and so seem very promising to solve this problem. Here we address simulating kinematic viscosity in ternary Al-Cu-Ni melts with using deep neural network potentials (DP) as implemented in the DeePMD-kit. We calculate both concentration and temperature dependencies of kinematic viscosity in Al-Cu-Ni and conclude that the developed potential allows one to simulate viscosity with high accuracy; the deviation from experimental data does not exceed 9\% and is close to the uncertainty interval of experimental data. More importantly, our simulations reproduce minimum on concentration dependency of the viscosity at the eutectic point. Thus, we conclude that DP-based MD simulations is highly promising way to calculate viscosity in multicomponent metallic melts.Comment: 11 pages, 7 figure

Laves Phase Formation in High Entropy Alloys

One of the intriguing recent results in the field of high-entropy alloys is the discovery of single-phase equiatomic multi-component Laves intermetallics. However, there is no clear understanding that a combination of chemical elements will form such high-entropy compounds. Here we contribute to understanding this issue by modifying the composition of duodenary TiZrHfNbVCrMoMnFeCoNiAl (12x) alloy in which we recently reported the fabrication of hexagonal C14 Laves phase. We consider three alloys based on 12x: 7x = 12x-VCrMoMnFe, 12x + Sc, 12x + Be and observe that all of them crystalize with the formation of C14 Laves phase as a dominant structure. We report that 12x + Be alloy reveals a single-phase C14 structure with a very high concentration of structural defects and ultra-fine dendritic microstructure with an almost homogenous distribution of the constituted elements over the alloy matrix. The analysis of electrical and magnetic properties reveals that the Laves phases are Curie-Weiss paramagnets, which demonstrate metallic conduction; 7x and 12x alloys also reveal a pronounced Kondo-like anomaly. Analysis of experimental data as well as ab initio calculations suggest that chemical complexity and compositional disorder cause strong s-d band scattering and thus the rather high density of d-states in the conduction band

Self-Diffusion Coefficients of Components in Liquid Binary Alloys of Noble Metals

An accurate determination of transport coefficients in liquids, such as diffusivity, is crucial for studying fundamental chemical processes, for constructing and verifying model theories of liquid, and for the optimization of technological processes. However, a reliable experimental determination of the diffusivity is a difficult and sometimes nearly impossible task. In this regard, the development of model theories that allow calculating characteristics of atomic transport is of special interest. Here, the concentration dependencies of the self-diffusion coefficients of the components in Cu-Ag, Cu-Au, and Ag-Au liquid alloys at T = 1423 K and T = 1573 K are calculated in the framework of the linear trajectory approximation in conjunction with the square-well model and the semi-analytical representation of the mean spherical approximation. We reveal that peculiarities in the behavior of the obtained dependencies are related to the peculiarities of the phase diagrams of the alloys under consideration. Additionally, we verify our calculation method on Al80-Cu20 and Al80-Au20 liquid alloys. The results obtained are in good agreement with available experimental and molecular-dynamic simulation data. In the cases when the experimental information is not available, the presented results can be considered as predictive to estimate the quantities under consideration approximately

Self-Diffusion Coefficients of Components in Liquid Binary Alloys of Noble Metals

An accurate determination of transport coefficients in liquids, such as diffusivity, is crucial for studying fundamental chemical processes, for constructing and verifying model theories of liquid, and for the optimization of technological processes. However, a reliable experimental determination of the diffusivity is a difficult and sometimes nearly impossible task. In this regard, the development of model theories that allow calculating characteristics of atomic transport is of special interest. Here, the concentration dependencies of the self-diffusion coefficients of the components in Cu-Ag, Cu-Au, and Ag-Au liquid alloys at T = 1423 K and T = 1573 K are calculated in the framework of the linear trajectory approximation in conjunction with the square-well model and the semi-analytical representation of the mean spherical approximation. We reveal that peculiarities in the behavior of the obtained dependencies are related to the peculiarities of the phase diagrams of the alloys under consideration. Additionally, we verify our calculation method on Al80-Cu20 and Al80-Au20 liquid alloys. The results obtained are in good agreement with available experimental and molecular-dynamic simulation data. In the cases when the experimental information is not available, the presented results can be considered as predictive to estimate the quantities under consideration approximately

Self-assembly of the decagonal quasicrystalline order in simpleă three-dimensional systems

International audienceUsing molecular dynamics simulations we show that a one-component systemă can be driven to a three-dimensional decagonal (10-fold)ă quasicrystalline state just by purely repulsive, isotropic and monotonică interaction pair potential with two characteristic length scales; noă attraction is needed. We found that self-assembly of a decagonală quasicrystal from a fluid can be predicted by two dimensionlessă effective parameters describing the fluid structure. We demonstrateă stability of the results under changes of the potential by obtaining theă decagonal order for three particle systems with different interactionă potentials, both purely repulsive and attractive, but with the sameă values of the effective parameters. Our results suggest that soft matteră quasicrystals with decagonal symmetry can be experimentally observed foră the same systems demonstrating the dodecagonal order for an appropriateă tuning of the effective parameters

Transport Properties of Equiatomic CoCrFeNi High-Entropy Alloy with a Single-Phase Face-Centered Cubic Structure

The key thermophysical properties necessary for the successful design and use of CoCrFeNi alloy in thermophysical applications have been measured experimentally, and the results have been compared with literature values and results previously obtained for commercial Ni-Cr alloys and equiatomic CoCrFeNi alloy. In particular, the thermal diffusivity, coefficient of thermal expansion (CTE), and specific heat capacity were measured for the as-cast and homogenized equiatomic CoCrFeNi alloy over a temperature range allowing the thermal conductivity to be calculated up to 1173 K. The thermal conductivity and thermal diffusivity of the equiatomic CoCrFeNi alloy were found to deviate from monotonic behavior in the temperature range from 773 to 1100 K. Such a deviation was previously observed in the behavior of the temperature dependence of CTE and specific heat capacity of the equiatomic CoCrFeNi alloy. The non-linear behavior is primarily the result of order/disorder phenomena for the as-cast and homogenized sample, as well as non-equilibrium solidification under arc melting conditions for the as-cast sample. The measured data of thermophysical properties are provided for thermally differently treated samples, and it is shown that there is a difference in the behavior of the temperature dependences of CTE, thermal diffusivity, and heat capacity