Morphology of critically sized crystalline nuclei at shear-induced crystal nucleation in amorphous solid

Abstract

In this work we study morphological characteristics of the critically-sized crystalline nuclei at initial stage of the shear-induced crystallization of a model single-component amorphous (glassy) system. These characteristics are estimated quantitatively through statistical treatment of the nonequilibrium molecular dynamics simulation results for the system under steady shear at various (fixed) values of the shear rateγ and at different temperatures. It is found that the sheared glassy system is crystallized through nucleation mechanism. From analysis of a time-dependent trajectories of the largest crystalline nuclei, the critical size nc and the nucleation time τc were defined. It is shown that the critically-sized nuclei in the system are oriented within the shear-gradient xy-plane at moderate and high shear rates; and a tilt angle of the oriented nuclei depends on the shear rate. At extremely high shear rates and at shear deformation of the system more than 60%, the tilt angle of the nuclei tends to take the value 45 • respective to the shear direction. We found that this feature depends weakly on the temperature. Asphericity of the nucleus shape increases with increasing shear rate, that is verified by increasing value of the asphericity parameter and by the contour of the pair distribution function calculated for the particles of the critically-sized nuclei. The critical size increases with increasing shear rate according to the power-law, nc ∝ (γτc) 1/3 , whereas the shape of the critically-sized nucleus changes from spherical to the elongated ellipsoidal. We found that the nc-dependencies of the nuclei deformation parameter evaluated for the system at different temperatures and shear rates are collapsed into unified master-curve. arXiv:1711.04989v1 [cond-mat.mtrl-sci]

Excellent glass former Ni$_{62}$Nb$_{38}$ crystallizing under combined shear and ultra-high pressure

“…Crystalline nuclei with a non-spherical shape and consisting of several tens of atoms are formed at the initial stage of BMG crystallization. The non-spherical shape of these nuclei is due to the impact of shear strain as it was shown earlier, for example, in Refs [33,41,42]. The formation of these crystal nuclei obeys the Poisson distribution, and this observation is in good agreement with the main postulates of the classical theory of homogeneous stationary nucleation presented in Refs.…”

Mechanical response of mesoporous amorphous NiTi alloy to external deformations

“…where The shear stress simulations are realized via the method of non-equilibrium molecular dynamics in Lammps software package [50,53]. In these simulations, atoms are located inside a triclinic simulation box.…”

Homogeneous Nucleation of Sheared Liquids: Advances and Insights from Simulations and Theory

“…On the other hand, the shape factor, β, (Section 2.3.1) was designed to theoretically account for the ellipsoidal deformation of spherical nuclei in sheared simple liquids. Ellipsoidal shape deformations were also found to occur for single-component glassy systems [141].…”

“…The shear flow is in the x-dimension. (b) Power law fits of the tilt angle, θ, to data for a model glassy system, at various temperatures, as a function of the critical deformation [141]. The critical deformation is defined as the deformation of a critically sized nucleus, which is a dimensionless quantity.…”

“…The direction of the applied shear, and the shear gradient are the x and y directions, respectively. Reproduced from Galimzyanov et al [141], with the permission of AIP Publishing. JUNE 29, 2021 Changes in the shape of solid nuclei due to an imposed flow field have been hypothesized, modelled and reported in theory, simulations, and experiments for diverse systems, notably including polymers [142][143][144][145].…”