Face-centered-cubic solid-phase theory of the nucleus

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.

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Metastable–solid phase diagrams derived from polymorphic solidification kinetics

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2017809118 ◽

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.

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Preparation and Certification of Standard Reference Materials to be Used in the Determination of Retained Austenite in Steels

Advances in X-ray Analysis ◽

10.1154/s0376030800012398 ◽

1982 ◽

Vol 26 ◽

pp. 137-140

Author(s):

George E. Hicho ◽

Earl E. Eaton

Keyword(s):

Reference Materials ◽

Retained Austenite ◽

Solid Phase ◽

Standard Reference Materials ◽

Face Centered Cubic ◽

X Ray Diffraction ◽

X Ray ◽

Face Centered ◽

Materials Used ◽

Steel Hardening

In the steel hardening process, steel is heated to a temperature where a face-centered-cubic solid phase called austenite is formed. After a stabilization period, the steel is quenched into a medium which transforms the austenite into a metastable, body-centered-tetragonal solid phase called martensite. On occasion the austenite is not entirely transformed into martensite and some austenite remains. This untransformed (retained) austenite is sometimes detrimental to the finished product, and often there are requirements as to the amount of retained austenite permitted In the finished product.X-ray diffraction procedures (XRD) are normally used to determine the amount of retained austenite and this paper describes the preparation and characterization of the Standard Reference Materials used to calibrate x-ray diffraction units.

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Ti(C, N)-Based Cermets with Two Kinds of Core-Rim Structures Constructed by β-Co Microspheres

Advances in Materials Science and Engineering ◽

10.1155/2020/4684529 ◽

2020 ◽

Vol 2020 ◽

pp. 1-11

Author(s):

Hui Yan ◽

Ying Deng ◽

Yong Yao Su ◽

Shan Jiang ◽

Qiao Wang Chen ◽

...

Keyword(s):

Manufacturing Industry ◽

Solid Phase ◽

High Energy ◽

Binder Phase ◽

Solid Phase Reaction ◽

Phase Reaction ◽

Face Centered Cubic ◽

Black Core ◽

Face Centered ◽

And Performance

Ti(C, N)-based cermet materials represent the best choice of materials for the manufacturing industry and military products. In this study, we use cubic β-cobalt(β-Co) as the binder phase to strengthen constructed cermets. At the same time, to optimize the microstructure, (Ti, W, Mo, Ta) (C, N) powders are added to form two kinds of core-rim morphologies. Here, β-cobalt powders with face-centered cubic structures are obtained by the solid-phase reaction of high-energy ball milling. A solid-phase chemical reaction and a carbothermic reduction-nitridation method are used to prepare the (Ti, W, Mo, Ta) (C, N) powders. In our process, first we mix the cobalt and (Ti, W, Mo, Ta) (C, N) powders; then we press the powder mixtures into rectangular samples and sinter them in a pressure sintering furnace to obtain Ti(C, N)-based cermets with two kinds of core-rim structure, that is, black core/white rim and white core/gray rim. The results show that the new cermets demonstrate excellent toughness and performance.

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Reentrant Behavior of the Density vs. Temperature of Indium Islands on GaAs(111)A

Nanomaterials ◽

10.3390/nano10081512 ◽

2020 ◽

Vol 10 (8) ◽

pp. 1512

Author(s):

Artur Tuktamyshev ◽

Alexey Fedorov ◽

Sergio Bietti ◽

Shiro Tsukamoto ◽

Roberto Bergamaschini ◽

...

Keyword(s):

Phase Transition ◽

Deposition Temperature ◽

Solid Phase ◽

Face Centered Cubic ◽

Complex Behavior ◽

Cubic Crystal ◽

Solid Phase Transition ◽

Face Centered ◽

Expected Increase ◽

Island Density

We show that the density of indium islands on GaAs(111)A substrates have a non-monotonic, reentrant behavior as a function of the indium deposition temperature. The expected increase in the density with decreasing temperature, indeed, is observed only down to 160 °C, where the indium islands undertake the expected liquid-to-solid phase transition. Further decreasing the temperature causes a sizable reduction of the island density. An additional reentrant increasing behavior is observed below 80 °C. We attribute the above complex behavior to the liquid–solid phase transition and to the complex island–island interaction which takes place between crystalline islands in the presence of strain. Indium solid islands grown at temperatures below 160 °C have a face-centered cubic crystal structure.

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Ab Initio Phase Diagram of Copper

Crystals ◽

10.3390/cryst11050537 ◽

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.

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CVD Growth of Graphene on Three Types of Epitaxial Metal Films on Sapphire Substrate

MRS Proceedings ◽

10.1557/opl.2011.639 ◽

2011 ◽

Vol 1284 ◽

Author(s):

Katsuya Nozawa ◽

Nozomu Matsukawa ◽

Kenji Toyoda ◽

Shigeo Yoshii

Keyword(s):

Metal Film ◽

Graphene Layer ◽

Solid Phase ◽

Chemical Vapor ◽

Metal Films ◽

Face Centered Cubic ◽

Graphene Growth ◽

Graphene Layers ◽

Complex Crystal Structure ◽

Face Centered

ABSTRACTGraphene growth by chemical vapor deposition (CVD) was studied on three types of epitaxial metal films with different crystal structures on sapphire. Nickel (face-centered-cubic: fcc), Ru (hexagonal-closed-pack: hcp), and Co (fcc at temperature for graphene growth and hcp at R.T.) were deposited on c-face sapphire substrates and annealed in a furnace for solid phase epitaxial growth. Graphene layers were grown by CVD with methane gas on the epitaxial metal film. The graphene layer uniformity was consistent with the structural simplicity of the metal film. The Ru sample had a single domain in the metal film and the highest graphene uniformity. The Co sample had a very complex crystal structure in the metal film and the poorest uniformity in graphene. The Ni sample had two types of stacking domains in the metal film and the graphene layer was uniform on each domain, but inhomogeneity was observed at domain boundaries.

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Voids in Irradiated Tungsten and Molybdenum

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100062865 ◽

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.

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A study of interface sliding at F.C.C.-B.C.C. boundaries in a Cu-Zn alloy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100109252 ◽

1978 ◽

Vol 36 (1) ◽

pp. 422-423

Author(s):

F. Monchoux ◽

A. Rocher ◽

J.L. Martin

Keyword(s):

Face Centered Cubic ◽

Creep Tests ◽

High Voltage Electron Microscopy ◽

Diffusion Treatment ◽

Voltage Electron ◽

The Face ◽

Face Centered ◽

Interface Sliding ◽

Zn Alloy ◽

Made In

Interphase sliding is an important phenomenon of high temperature plasticity. In order to study the microstructural changes associated with it, as well as its influence on the strain rate dependence on stress and temperature, plane boundaries were obtained by welding together two polycrystals of Cu-Zn alloys having the face centered cubic and body centered cubic structures respectively following the procedure described in (1). These specimens were then deformed in shear along the interface on a creep machine (2) at the same temperature as that of the diffusion treatment so as to avoid any precipitation. The present paper reports observations by conventional and high voltage electron microscopy of the microstructure of both phases, in the vicinity of the phase boundary, after different creep tests corresponding to various deformation conditions.Foils were cut by spark machining out of the bulk samples, 0.2 mm thick. They were then electropolished down to 0.1 mm, after which a hole with thin edges was made in an area including the boundary

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Microstructure of Electro-Eroded Cemented Carbide Surfaces

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100101165 ◽

1968 ◽

Vol 26 ◽

pp. 284-285

Author(s):

V. N. Filimonenko ◽

M. H. Richman ◽

J. Gurland

Keyword(s):

Surface Layer ◽

Cobalt Content ◽

Cemented Carbides ◽

Face Centered Cubic ◽

X Ray Diffraction ◽

Metallographic Examination ◽

Standard Procedures ◽

Face Centered ◽

Diamond Paste ◽

Plastic Carbon

The high temperatures and pressures that are found in a spark gap during electrical discharging lead to a sharp phase transition and structural transformation in the surface layer of cemented carbides containing WC and cobalt. By means of X-ray diffraction both W2C and a high-temperature monocarbide of tungsten (face-centered cubic) were detected after electro-erosion. The W2C forms as a result of the peritectic reaction, WC → W2C+C. The existence and amount of the phases depend on both the energy of the electro-spark discharge and the cobalt content. In the case of a low-energy discharge (i.e. C=0.01μF, V = 300v), WC(f.c.c.) is generally formed in the surface layer. However, at high energies, (e.g. C=30μF, V = 300v), W2C is formed at the surface in preference to the monocarbide. The phase transformations in the surface layer are retarded by the presence of larger percentages of cobalt.Metallographic examination of the electro-eroded surfaces of cemented carbides was carried out on samples with 5-30% cobalt content. The specimens were first metallographically polished using diamond paste and standard procedures and then subjected to various electrical discharges on a Servomet spark machining device. The samples were then repolished and etched in a 3% NH4OH electrolyte at -0.5 amp/cm2. Two stage plastic-carbon replicas were then made and shadowed with chromium at 27°.

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