arXiv subjects

V. Ankudinov

Publications and source records attributed to V. Ankudinov.

5 recordsLinked to original sources

arXiv2022

Competition of glass and crystal: phase-field model

The phase-field model for the description of the solidification processes with the glass-crystal competition is suggested. The model combines the first-order phase transition model in the phase-field formalism and gauge-field theory of glass transition. We present a self-consistent system of stochastic motion equations for unconserved order parameters describing the crystal-like short-range ordering and vitrification. It is shown, that the model qualitatively describes the glass-crystal competition during quenching with finite cooling speed. The nucleation of the crystalline phase at slow cooling speeds and low undercoolings proceeds by a fluctuation mechanism. The model demonstrates the tendency to amorphization with the increase of its cooling rate.

cond-mat.mtrl-sci↗

arXiv2022

Structural phase-field crystal model for Lennard-Jones pair interaction potential

A modification of structural phase-field crystal (XPFC) model for an arbitrary pair interaction potential is presented. Formation of 1D and 2D structures for the Lennard-Jones (LJ) potential was studied numerically. The equilibrium lattice parameters for the presented structures were found consistent to the correspondent LJ-distance parameters. The lattice parameter of 2D triangle's structure matches the periodical in 1D, which shown to be consistent with the theory of freezing from the isotropic liquids. Numerically obtained XPFC phase diagram of two-dimensional structures qualitatively reproduces classical PFC diagram and coincides with the melting region of high-temperature part of LJ diagram.

cond-mat.mtrl-sci↗

arXiv2022

Numerical simulation of thermal conductivity of stainless steel and Al-12Si powders for additive manufacturing

A three-dimensional model of a partially melted powder bed with particles stochastically distributed in size and space coordinates has been developed. Numerical simulation of temperature distributions in stainless steel AISI 316L and Al-12Si powders in vacuum, air and argon has been performed to analyze unsteady heat transfer in a porous medium. The numerical model demonstrates a large effect of heat transfer through the gas phase in case of powders with low thermal conductivities like stainless steels. At the porosity level of 65\% and above, the mechanism of heat transfer drastically changes and a linear dependence of thermal conductivity on porosity frequently used in literature becomes incorrect. The effects of the consolidation coefficient and size distribution on effective heat transfer in powders are discussed. The obtained dependencies of the effective thermal conductivity on porosity and the consolidation coefficient could be used in additive manufacturing applications.

cond-mat.mtrl-sci↗

arXiv2020

The uncertainty of glass transition temperature in molecular dynamics simulations and numerical algorithm for its unique determination

When the cooling rate $v$ is smaller than a certain material-dependent threshold, the glass transition temperature $T_g$ becomes to a certain degree the "material parameter" being nearly independent on the cooling rate. The common method to determine $T_g$ is to extrapolate viscosity $ν$ of the liquid state at temperatures not far above the freezing conditions to lower temperatures where liquid freezes and viscosity is hardly measurable. It is generally accepted that the glass transition occurs when viscosity drops by $13\leq n\leq17$ orders of magnitude. The accuracy of $T_g$ depends on the extrapolation quality. We propose here an algorithm for a unique determining of $T_g$. The idea is to unambiguously extrapolate $ν(T)$ to low temperatures without relying upon a specific model. It can be done using the numerical analytical continuation of $ν(T)$-function from above $T_g$ where it is measurable, to $T\gtrsim T_g$. For numerical analytical continuation, we use the Pade approximant method.

physics.chem-ph↗

arXiv2020

Freezing of two-length-scale systems: complexity, universality and prediction

Two-length-scale pair potentials arise ubiquitously in condensed matter theory as effective interparticle interactions in molecular, metallic and soft matter systems. The existence of two different bond lengths generated by the shape of potential causes complex behavior in even one-component systems: polymorphism in solid and liquid states, water-like anomalies, the formation of quasicrystals and high stability against crystallization. Here we address general properties of freezing in one-component two-length-scale systems and argue that the formation of solid phases during cooling a liquid is essentially determined by the radial distribution function (RDF) of the liquid. We show that different two-length-scale systems having similar RDF freeze into the same solid phases. In most cases, the similarity between RDFs can be expressed by the proximity of two dimensionless effective parameters: the ratio between effective bond lengths, $λ$, and the fraction of short-bonded particles $ϕ$. We validate this idea by studying the formation of different solid phases in different two-length-scale systems. The method proposed allows predicting effectively the formation of solid phases in both numerical simulations and self-assembling experiments in soft matter systems with tunable interactions.

physics.chem-ph↗