Molecular dynamic simulations of plasticity and phase transition in Mg polycrystalline under shock compression

2021 ◽  
Author(s):  
Zhiyong Jian ◽  
Yangchun Chen ◽  
Shifang xiao ◽  
Liang Wang ◽  
Xiaofan Li ◽  
...  
Keyword(s):  
Phase Transition ◽  
Grain Boundaries ◽  
Large Scale ◽  
Local Stress ◽  
The Body ◽  
Nonequilibrium Molecular Dynamics ◽  
Dynamic Simulations ◽  
Hexagonal Close Packed ◽  
Dynamics Simulations ◽  
Bcc Phase

Abstract We have investigated the shock-induced plasticity and phase transition in the hexagonal columnar nanocrystalline (HCN) Mg by large-scale nonequilibrium molecular dynamics simulations (NEMD). The preexisting grain boundaries (GBs) induce the nucleation of the {10-12} twins for the local stress relaxation. The twins grow up in grains leading to the orientation rotation. The phase transition from the hexagonal close-packed (HCP) phase to the body-centered cubic (BCC) phase begins when the migrating twin grain boundaries (TGBs) meet in A- and C-type grains, and continues in the plastic deformation regions. The phase-transition pathway involves two steps: the reorientation and phase transformation.

scholarly journals Formation of a single quasicrystal upon collision of multiple grains

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Insung Han ◽  
Kelly L. Wang ◽  
Andrew T. Cadotte ◽  
Zhucong Xi ◽  
Hadi Parsamehr ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Large Scale ◽  
Thin Film Deposition ◽  
Film Deposition ◽  
Decagonal Quasicrystal ◽  
Bulk Crystal Growth ◽  
Computational Discovery ◽  
Dynamics Simulations ◽  
Novel Applications ◽  
Small Misorientation

AbstractQuasicrystals exhibit long-range order but lack translational symmetry. When grown as single crystals, they possess distinctive and unusual properties owing to the absence of grain boundaries. Unfortunately, conventional methods such as bulk crystal growth or thin film deposition only allow us to synthesize either polycrystalline quasicrystals or quasicrystals that are at most a few centimeters in size. Here, we reveal through real-time and 3D imaging the formation of a single decagonal quasicrystal arising from a hard collision between multiple growing quasicrystals in an Al-Co-Ni liquid. Through corresponding molecular dynamics simulations, we examine the underlying kinetics of quasicrystal coalescence and investigate the effects of initial misorientation between the growing quasicrystalline grains on the formation of grain boundaries. At small misorientation, coalescence occurs following rigid rotation that is facilitated by phasons. Our joint experimental-computational discovery paves the way toward fabrication of single, large-scale quasicrystals for novel applications.

scholarly journals Metastable–solid phase diagrams derived from polymorphic solidification kinetics

2021 ◽  
Vol 118 (9) ◽  
pp. e2017809118
Author(s):  
Babak Sadigh ◽  
Luis Zepeda-Ruiz ◽  
Jonathan L. Belof
Keyword(s):  
Large Scale ◽  
Solid Phase ◽  
Metastable Phase ◽  
Extensive Study ◽  
The Body ◽  
Face Centered Cubic ◽  
Nonequilibrium Processes ◽  
Solidification Kinetics ◽  
Face Centered ◽  
Dynamics Simulations

Nonequilibrium processes during solidification can lead to kinetic stabilization of metastable crystal phases. A general framework for predicting the solidification conditions that lead to metastable-phase growth is developed and applied to a model face-centered cubic (fcc) metal that undergoes phase transitions to the body-centered cubic (bcc) as well as the hexagonal close-packed phases at high temperatures and pressures. Large-scale molecular dynamics simulations of ultrarapid freezing show that bcc nucleates and grows well outside of the region of its thermodynamic stability. An extensive study of crystal–liquid equilibria confirms that at any given pressure, there is a multitude of metastable solid phases that can coexist with the liquid phase. We define for every crystal phase, a solid cluster in liquid (SCL) basin, which contains all solid clusters of that phase coexisting with the liquid. A rigorous methodology is developed that allows for practical calculations of nucleation rates into arbitrary SCL basins from the undercooled melt. It is demonstrated that at large undercoolings, phase selections made during the nucleation stage can be undone by kinetic instabilities amid the growth stage. On these bases, a solidification–kinetic phase diagram is drawn for the model fcc system that delimits the conditions for macroscopic grains of metastable bcc phase to grow from the melt. We conclude with a study of unconventional interfacial kinetics at special interfaces, which can bring about heterogeneous multiphase crystal growth. A first-order interfacial phase transformation accompanied by a growth-mode transition is examined.

Molecular Dynamics Simulations of Nanocrystalline Nickel and Copper Revealing Different Failure Model of FCC Metals

2009 ◽  
Vol 633-634 ◽  
pp. 31-38
Author(s):  
Ajing Cao
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Grain Boundaries ◽  
Large Scale ◽  
Uniaxial Tensile ◽  
Face Centered Cubic ◽  
Triple Junctions ◽  
Fcc Metals ◽  
Face Centered ◽  
Dynamics Simulations

We have previously reported that the fracture behavior of nanocrystalline (NC) Ni is via the nucleation and coalescence of nano-voids at grain boundaries and triple junctions, resulting in intergranular failure mode. Here we show in large-scale molecular dynamics simulations that partial-dislocation-mediated plasticity is dominant in NC Cu with grain size as small as ~ 10 nanometers. The simulated results show that NC Cu can accommodate large plastic strains without cracking or creating damage in the grain interior or grain boundaries, revealing their intrinsic ductile properties compared with NC Ni. These results point out different failure mechanisms of the two face-centered-cubic (FCC) metals subject to uniaxial tensile loading. The insight gained in the computational experiments could explain the good plasticity found in NC Cu not seen in Ni so far.

scholarly journals EQUILIBRIUM MOLECULAR DYNAMICS CALCULATIONS OF THERMAL CONDUCTIVITY: A “HOW-TO” FOR THE BEGINNERS

2020 ◽  
Vol 9 (1) ◽  
pp. 11-25
Author(s):  
Jude S. Alexander ◽  
Christopher Maxwell ◽  
Jeremy Pencer ◽  
Mouna Saoudi
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Large Scale ◽  
Interatomic Potential ◽  
Negative Impact ◽  
Significant Risk ◽  
Nonequilibrium Molecular Dynamics ◽  
Atomistic Modelling ◽  
Dynamics Simulations

The ready availability of codes such as LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator) for molecular dynamics simulations has opened up the realm of atomistic modelling to novice code users with an interest in computational materials modelling but who lack the appropriate theoretical or computational background. As such, there is significant risk of the “user effect” having a negative impact on the quality of results obtained using such codes. Here, we present a “how-to” procedure for equilibrium molecular dynamics-based nuclear fuel thermal conductivity calculations using the Green–Kubo method with an interatomic potential developed by Cooper et al. [ 1 ]. The various steps of the simulation are identified and explained, along with criteria to assess the quality of the intermediate and final results, discussion of some problems that can arise during a simulation, and some inherent limitations of the method. Calculated thermal conductivities for UO2 and ThO2 will be compared with the available experimental data and also with similar thermal conductivity calculations using nonequilibrium molecular dynamics, reported in the open literature.

scholarly journals Large-Scale Molecular Dynamics Simulations of Homogeneous Nucleation of Pure Aluminium

Metals ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 1217 ◽  
Author(s):  
Papanikolaou ◽  
Salonitis ◽  
Jolly ◽  
Frank
Keyword(s):  
Molecular Dynamics ◽  
Large Scale ◽  
Solidification Process ◽  
Md Simulations ◽  
Pure Aluminium ◽  
3 Dimensional ◽  
Hexagonal Close Packed ◽  
Simulation Domain ◽  
Dynamics Simulations ◽  
Insight Into

Despite the continuous and remarkable development of experimental techniques for the investigation of microstructures and the growth of nuclei during the solidification of metals, there are still unknown territories around this topic. The solidification in nanoscale can be effectively investigated by means of molecular dynamics (MD) simulations which can provide a deep insight into the mechanisms of the formation of nuclei and the induced crystal structures. In this study, MD simulations were performed to investigate the solidification of pure Aluminium and the effects of the cooling rate on the final properties of the solidified material. A large number of Aluminium atoms were used in order to investigate the grain growth over time and the formation of stacking faults during solidification. The number of face-centred cubic (FCC), hexagonal close-packed (HCP) and body-centred cubic (BCC) was recorded during the evolution of the process to illustrate the nanoscale mechanisms initiating solidification. The current investigation also focuses on the exothermic nature of the solidification process which has been effectively captured by means of MD simulations using 3 dimensional representations of the kinetic energy across the simulation domain.

scholarly journals Robust quantum-based interatomic potentials for multiscale modeling in transition metals

2006 ◽  
Vol 21 (3) ◽  
pp. 563-573 ◽  
Author(s):  
John A. Moriarty ◽  
Lorin X. Benedict ◽  
James N. Glosli ◽  
Randolph Q. Hood ◽  
Daniel A. Orlikowski ◽  
...  
Keyword(s):  
Transition Metals ◽  
Multiscale Modeling ◽  
Density Functional ◽  
Large Scale ◽  
Dislocation Core ◽  
Dislocation Dynamics ◽  
Interatomic Potentials ◽  
Dynamic Simulations ◽  
Wide Range ◽  
Dynamics Simulations

First-principles generalized pseudopotential theory (GPT) provides a fundamental basis for transferable multi-ion interatomic potentials in transition metals and alloys within density-functional quantum mechanics. In the central body-centered cubic (bcc) metals, where multi-ion angular forces are important to materials properties, simplified model GPT (MGPT) potentials have been developed based on canonical d bands to allow analytic forms and large-scale atomistic simulations. Robust, advanced-generation MGPT potentials have now been obtained for Ta and Mo and successfully applied to a wide range of structural, thermodynamic, defect, and mechanical properties at both ambient and extreme conditions. Selected applications to multiscale modeling discussed here include dislocation core structure and mobility, atomistically informed dislocation dynamics simulations of plasticity, and thermoelasticity and high-pressure strength modeling. Recent algorithm improvements have provided a more general matrix representation of MGPT beyond canonical bands, allowing improved accuracy and extension to f-electron actinide metals, an order of magnitude increase in computational speed for dynamic simulations, and the development of temperature-dependent potentials.

Shock-induced plasticity and phase transformation in single crystal magnesium: An interatomic potential and non-equilibrium molecular dynamics simulations

2021 ◽  
Author(s):  
Zhiyong Jian ◽  
Yangchun Chen ◽  
Shifang Xiao ◽  
Liang Wang ◽  
Xiaofan Li ◽  
...  
Keyword(s):  
Phase Transition ◽  
Molecular Dynamics ◽  
Shear Stress ◽  
Single Crystals ◽  
Interatomic Potential ◽  
The Body ◽  
Shock Strength ◽  
Orientation Relationships ◽  
Elastic Precursor ◽  
Hexagonal Close Packed

Abstract An effective and reliable Finnis-Sinclair (FS) type potential is developed for large-scale molecular dynamics (MD) simulations of plasticity and phase transition of Magnesium (Mg) single crystals under high-pressure shock loading. The shock-wave profiles exhibit a split elastic-inelastic wave in the [0001]HCP shock orientation and a three-wave structure in the [10-10]HCP and [-12-10]HCP directions, namely, an elastic precursor following the plastic and phase-transition fronts. The shock Hugoniot of the particle velocity (Up) vs. the shock velocity (Us) of Mg single crystals in three shock directions under low shock strength reveals apparent anisotropy, which vanishes with increasing shock strength. For the [0001]HCP shock direction, the amorphization caused by strong atomic strain plays an important role in the phase transition and allows for the phase transition from an isotropic stressed state to the daughter phase. The reorientation in the shock directions [10-10]HCP and [-12-10]HCP, as the primary plasticity deformation, leads to the compressed hexagonal close-packed (HCP) phase and reduces the phase-transition threshold pressure. The phase-transition pathway in the shock direction [0001]HCP includes a preferential contraction strain along the [0001]HCP direction, a tension along [-12-10]HCP direction, an effective contraction and shear along the [10-10]HCP direction. For the [10-10]HCP and [-12-10]HCP shock directions, the phase-transition pathway consists of two steps: a reorientation and the subsequent transition from the reorientation hexagonal close-packed phase (RHCP) to the body-centered cubic (BCC). The orientation relationships between HCP and BCC are (0001)HCP á-12-10ñHCP // {110}BCC á001ñBCC. Due to different slipping directions during the phase transition, three variants of the product phase are observed in the shocked samples, accompanied by three kinds of typical coherent twin-grain boundaries between the variants. The results indicate that the highly concentrated shear stress leads to the crystal lattice instability in the elastic precursor, and the plasticity or the phase transition relaxed the shear stress.

scholarly journals Two-step nucleation of the Earth’s inner core

2022 ◽  
Vol 119 (2) ◽  
pp. e2113059119
Author(s):  
Yang Sun ◽  
Feng Zhang ◽  
Mikhail I. Mendelev ◽  
Renata M. Wentzcovitch ◽  
Kai-Ming Ho
Keyword(s):  
Molecular Dynamics ◽  
Inner Core ◽  
Nucleation Mechanism ◽  
Body Centered Cubic ◽  
Hexagonal Close Packed ◽  
Key Factor ◽  
Earth’S Inner Core ◽  
Core Conditions ◽  
Dynamics Simulations ◽  
Bcc Phase

The Earth's inner core started forming when molten iron cooled below the melting point. However, the nucleation mechanism, which is a necessary step of crystallization, has not been well understood. Recent studies have found that it requires an unrealistic degree of undercooling to nucleate the stable, hexagonal, close-packed (hcp) phase of iron that is unlikely to be reached under core conditions and age. This contradiction is referred to as the inner core nucleation paradox. Using a persistent embryo method and molecular dynamics simulations, we demonstrate that the metastable, body-centered, cubic (bcc) phase of iron has a much higher nucleation rate than does the hcp phase under inner core conditions. Thus, the bcc nucleation is likely to be the first step of inner core formation, instead of direct nucleation of the hcp phase. This mechanism reduces the required undercooling of iron nucleation, which provides a key factor in solving the inner core nucleation paradox. The two-step nucleation scenario of the inner core also opens an avenue for understanding the structure and anisotropy of the present inner core.

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