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.

Prediction of metastable phase formation in an immiscible Cu–Cr system from interatomic potential and ab initio calculation

2003 ◽  
Vol 18 (10) ◽  
pp. 2300-2303 ◽  
Author(s):  
H. R. Gong ◽  
L. T. Kong ◽  
B. X. Liu
Keyword(s):  
Ab Initio ◽  
Interatomic Potential ◽  
Metastable Phase ◽  
The Body ◽  
Face Centered Cubic ◽  
The Face ◽  
Bcc Structure ◽  
Face Centered ◽  
Dynamics Simulations ◽  
Cr System

Ab initio calculation was performed to predict the structures, lattice constants, and cohesive energies of metastable Cu75Cr25 and Cu50Cr50 phases. An n-body Cu–Cr potential was derived through fitting to some ab initio calculated results and was capable of reproducing some intrinsic properties of the Cu–Cr system. Based on the derived potential, molecular dynamics simulations predicted that for a Cu100−xCrx alloy, the face-centered-cubic structure is more stable than the body-centered-cubic (bcc) one when 0 ≤ x ≤ 25, while the bcc structure becomes energetically favored when 25 < x ≤ 100. Interestingly, the predictions match well with the experimental observations.

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 Ab Initio Phase Diagram of Copper

Crystals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 537
Author(s):  
Samuel R. Baty ◽  
Leonid Burakovsky ◽  
Daniel Errandonea
Keyword(s):  
Molecular Dynamics ◽  
Phase Diagram ◽  
Ab Initio ◽  
Solid Phase ◽  
Quantum Molecular Dynamics ◽  
Face Centered Cubic ◽  
Melting Curves ◽  
Solid Phases ◽  
Face Centered ◽  
Dynamics Simulations

Copper has been considered as a common pressure calibrant and equation of state (EOS) and shock wave (SW) standard, because of the abundance of its highly accurate EOS and SW data, and the assumption that Cu is a simple one-phase material that does not exhibit high pressure (P) or high temperature (T) polymorphism. However, in 2014, Bolesta and Fomin detected another solid phase in molecular dynamics simulations of the shock compression of Cu, and in 2017 published the phase diagram of Cu having two solid phases, the ambient face-centered cubic (fcc) and the high-PT body-centered cubic (bcc) ones. Very recently, bcc-Cu has been detected in SW experiments, and a more sophisticated phase diagram of Cu with the two solid phases was published by Smirnov. In this work, using a suite of ab initio quantum molecular dynamics (QMD) simulations based on the Z methodology, which combines both direct Z method for the simulation of melting curves and inverse Z method for the calculation of solid–solid phase boundaries, we refine the phase diagram of Smirnov. We calculate the melting curves of both fcc-Cu and bcc-Cu and obtain an equation for the fcc-bcc solid–solid phase transition boundary. We also obtain the thermal EOS of Cu, which is in agreement with experimental data and QMD simulations. We argue that, despite being a polymorphic rather than a simple one-phase material, copper remains a reliable pressure calibrant and EOS and SW standard.

Voids in Irradiated Tungsten and Molybdenum

1969 ◽  
Vol 27 ◽  
pp. 190-191
Author(s):  
Robert C. Rau ◽  
Robert L. Ladd
Keyword(s):  
Melting Point ◽  
Fast Neutron ◽  
Neutron Irradiation ◽  
Elevated Temperatures ◽  
Irradiation Temperature ◽  
The Body ◽  
Face Centered Cubic ◽  
Body Centered Cubic ◽  
Cubic Metals ◽  
Face Centered

Recent studies have shown the presence of voids in several face-centered cubic metals after neutron irradiation at elevated temperatures. These voids were found when the irradiation temperature was above 0.3 Tm where Tm is the absolute melting point, and were ascribed to the agglomeration of lattice vacancies resulting from fast neutron generated displacement cascades. The present paper reports the existence of similar voids in the body-centered cubic metals tungsten and molybdenum.

MINIMAL KNOTTING NUMBERS

2009 ◽  
Vol 18 (08) ◽  
pp. 1159-1173 ◽  
Author(s):  
CASEY MANN ◽  
JENNIFER MCLOUD-MANN ◽  
RAMONA RANALLI ◽  
NATHAN SMITH ◽  
BENJAMIN MCCARTY
Keyword(s):  
The Body ◽  
Computer Algorithm ◽  
Face Centered Cubic ◽  
Body Centered Cubic ◽  
Cubic Lattice ◽  
The Face ◽  
Face Centered ◽  
Body Centered Cubic Lattice

This article concerns the minimal knotting number for several types of lattices, including the face-centered cubic lattice (fcc), two variations of the body-centered cubic lattice (bcc-14 and bcc-8), and simple-hexagonal lattices (sh). We find, through the use of a computer algorithm, that the minimal knotting number in sh is 20, in fcc is 15, in bcc-14 is 13, and bcc-8 is 18.

Poisson's Ratio for Central-Force Polycrystals

1976 ◽  
Vol 31 (12) ◽  
pp. 1539-1542 ◽  
Author(s):  
H. M. Ledbetter
Keyword(s):  
Electron Energy ◽  
Poisson Ratio ◽  
The Body ◽  
Central Force ◽  
Face Centered Cubic ◽  
Polycrystalline Aggregate ◽  
Body Centered Cubic ◽  
The Face ◽  
Predicted Values ◽  
Face Centered

Abstract The Poisson ratio υ of a polycrystalline aggregate was calculated for both the face-centered cubic and the body-centered cubic cases. A general two-body central-force interatomatic potential was used. Deviations of υ from 0.25 were verified. A lower value of υ is predicted for the f.c.c. case than for the b.c.c. case. Observed values of υ for twenty-three cubic elements are discussed in terms of the predicted values. Effects of including volume-dependent electron-energy terms in the inter-atomic potential are discussed.

scholarly journals Generalization of the Unified Analytic Melt-Shear Model to Multi-Phase Materials: Molybdenum as an Example

Crystals ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 86 ◽  
Author(s):  
Leonid Burakovsky ◽  
Darby Luscher ◽  
Dean Preston ◽  
Sky Sjue ◽  
Diane Vaughan
Keyword(s):  
Shear Modulus ◽  
Solid Phase ◽  
Model Parameters ◽  
Quantum Molecular Dynamics ◽  
Face Centered Cubic ◽  
Shear Model ◽  
Bcc Structure ◽  
Face Centered ◽  
Multi Phase ◽  
Theoretical Results

The unified analytic melt-shear model that we introduced a decade ago is generalized to multi-phase materials. A new scheme for calculating the values of the model parameters for both the cold ( T = 0 ) shear modulus ( G ) and the melting temperature at all densities ( ρ ) is developed. The generalized melt-shear model is applied to molybdenum, a multi-phase material with a body-centered cubic (bcc) structure at low ρ which loses its dynamical stability with increasing pressure (P) and is therefore replaced by another (dynamically stable) solid structure at high ρ . One of the candidates for the high- ρ structure of Mo is face-centered cubic (fcc). The model is compared to (i) our ab initio results on the cold shear modulus of both bcc-Mo and fcc-Mo as a function of ρ , and (ii) the available theoretical results on the melting of bcc-Mo and our own quantum molecular dynamics (QMD) simulations of one melting point of fcc-Mo. Our generalized model of G ( ρ , T ) is used to calculate the shear modulus of bcc-Mo along its principal Hugoniot. It predicts that G of bcc-Mo increases with P up to ∼240 GPa and then decreases at higher P. This behavior is intrinsic to bcc-Mo and does not require the introduction of another solid phase such as Phase II suggested by Errandonea et al. Generalized melt-shear models for Ta and W also predict an increase in G followed by a decrease along the principal Hugoniot, hence this behavior may be typical for transition metals with ambient bcc structure that dynamically destabilize at high P. Thus, we concur with the conclusion reached in several recent papers (Nguyen et al., Zhang et al., Wang et al.) that no solid-solid phase transition can be definitively inferred on the basis of sound velocity data from shock experiments on Mo. Finally, our QMD simulations support the validity of the phase diagram of Mo suggested by Zeng et al.

Investigation of Crystalline and Amorphous Forms of Aluminum and Its Alloys: Computational Modeling and Experiment

NANO ◽  
2018 ◽  
Vol 13 (03) ◽  
pp. 1850026
Author(s):  
Sergey Shityakov ◽  
Norbert Roewer ◽  
Carola Y. Förster ◽  
Hai T. Tran ◽  
Wenjun Cai ◽  
...  
Keyword(s):  
Metal Structure ◽  
Dislocation Nucleation ◽  
Al Alloys ◽  
Atomic Scale ◽  
Face Centered Cubic ◽  
Stress Strain ◽  
The Face ◽  
Tension And Compression ◽  
Face Centered ◽  
Dynamics Simulations

The purpose of this study is to investigate polycrystalline lattices of aluminum (Al) under the stress–strain conditions in all-atom molecular dynamics simulations and Al alloys using X-ray diffraction. Isothermal uniaxial tension and compression of these polycrystalline lattices showed no dislocation nucleation peaks, which correspond only to the Al monocrystal form. The best tensile and compressive resistance characteristics were observed for a material with the highest grain number ([Formula: see text]) due to the significant reduction of the face-centered cubic lattice in the metal structure. This process is mainly driven by the gradual elevation of the system’s kinetic energy. In the experiment, the amorphous Al alloys with higher manganese composition (20.5%) were investigated, matching the simulated amorphous structures. Overall, the results suggest that the increase in number of grains in Al lattices diminishes the stress–strain impact due to a more disordered atomic-scale (amorphous) metal composition.

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