Implementation of an Effective Bond Energy Formalism in the Multicomponent Calphad Approach

Most models currently used for complex phases in the calculation of phase diagrams (Calphad) method are based on the compound energy formalism. The way this formalism is presently used, however, is prone to poor extrapolation behavior in higher-order systems, especially when treating phases with complex crystal structures. In this paper, a partition of the Gibbs energy into effective bond energies, without changing its confgurational entropy expression, is proposed, thereby remarkably improving the extrapolation behavior. The proposed model allows the use of as many sublattices as there are occupied Wyckoff sites and has great potential for reducing the number of necessary parameters, thus allowing shorter computational time. Examples for face centered cubic (fcc) ordering and the σ phase are given.

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Cutting Edge of High-Entropy Alloy Superconductors from the Perspective of Materials Research

Metals ◽

10.3390/met10081078 ◽

2020 ◽

Vol 10 (8) ◽

pp. 1078

Author(s):

Jiro Kitagawa ◽

Shusuke Hamamoto ◽

Naoki Ishizu

Keyword(s):

Material Design ◽

High Entropy Alloy ◽

Face Centered Cubic ◽

Simple Material ◽

Σ Phase ◽

High Entropy ◽

Cscl Type ◽

Materials Research ◽

Face Centered ◽

New Phenomena

High-entropy alloys (HEAs) are a new class of materials which are being energetically studied around the world. HEAs are characterized by a multicomponent alloy in which five or more elements randomly occupy a crystallographic site. The conventional HEA concept has developed into simple crystal structures such as face-centered-cubic (fcc), body-centered-cubic (bcc) and hexagonal-closed packing (hcp) structures. The highly atomic-disordered state produces many superior mechanical or thermal properties. Superconductivity has been one of the topics of focus in the field of HEAs since the discovery of the bcc HEA superconductor in 2014. A characteristic of superconductivity is robustness against atomic disorder or extremely high pressure. The materials research on HEA superconductors has just begun, and there are open possibilities for unexpectedly finding new phenomena. The present review updates the research status of HEA superconductors. We survey bcc and hcp HEA superconductors and discuss the simple material design. The concept of HEA is extended to materials possessing multiple crystallographic sites; thus, we also introduce multisite HEA superconductors with the CsCl-type, α-Mn-type, A15, NaCl-type, σ-phase and layered structures and discuss the materials research on multisite HEA superconductors. Finally, we present the new perspectives of eutectic HEA superconductors and gum metal HEA superconductors.

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Effect of Molybdenum Additives on Corrosion Behavior of (CoCrFeNi)100−xMox High-Entropy Alloys

Entropy ◽

10.3390/e20120908 ◽

2018 ◽

Vol 20 (12) ◽

pp. 908 ◽

Cited By ~ 9

Author(s):

Wenrui Wang ◽

Jieqian Wang ◽

Honggang Yi ◽

Wu Qi ◽

Qing Peng

Keyword(s):

Corrosion Behavior ◽

Compressive Strain ◽

Compressive Yield Strength ◽

High Entropy Alloys ◽

Face Centered Cubic ◽

Σ Phase ◽

High Entropy ◽

Passivation Film ◽

Face Centered ◽

Mo Content

The present work investigates the influence of micro-alloyed Mo on the corrosion behavior of (CoCrFeNi)100−xMox high-entropy alloys. All of the (CoCrFeNi)100−xMox alloys exhibit a single face-centered cubic (FCC) solid solution. However, the (CoCrFeNi)97Mo3 alloy exhibits an ordered sigma (σ) phase enriched in Cr and Mo. With the increase of x (the Mo content) from 1 to 3, the hardness of the (CoCrFeNi)100−xMox alloys increases from 124.8 to 133.6 Vickers hardness (HV), and the compressive yield strength increases from 113.6 MPa to 141.1 MPa, without fracture under about a 60% compressive strain. The potentiodynamic polarization curve in a 3.5% NaCl solution indicates that the addition of Mo has a beneficial effect on the corrosion resistance to some certain extent, opposed to the σ phase. Furthermore, the alloys tend to form a passivation film in the 0.5 M H2SO4 solution in order to inhibit the progress of the corrosion reaction as the Mo content increases.

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Nano-Scaled Creep Response of TiAlV Low Density Medium Entropy Alloy at Elevated Temperatures

Materials ◽

10.3390/ma13010036 ◽

2019 ◽

Vol 13 (1) ◽

pp. 36

Author(s):

Xiangkai Zhang ◽

Hanting Ye ◽

Jacob C. Huang ◽

Taiyou Liu ◽

Pinhung Lin ◽

...

Keyword(s):

Elevated Temperatures ◽

Peierls Stress ◽

Dislocation Creep ◽

Calphad Approach ◽

Low Density ◽

Face Centered Cubic ◽

Specific Strength ◽

Phase Constituent ◽

Fcc Alloys ◽

Face Centered

A low density, medium entropy alloy (LD-MEA) Ti33Al33V34 (4.44 g/cm3) was successfully developed. The microstructure was found to be composed of a disordered body-centered-cubic (BCC) matrix and minor ordered B2 precipitates based on transmission electron microscopy characterization. Equilibrium and non-equilibrium modeling, simulated using the Calphad approach, were applied to predict the phase constituent. Creep behavior of {110} grains at elevated temperatures was investigated by nanoindentation and the results were compared with Cantor alloy and Ti-6Al-4V alloy. Dislocation creep was found to be the dominant mechanism. The decreasing trend of hardness in {110} grains of BCC TiAlV is different from that in {111} grains of face-centered-cubic (FCC) Cantor alloy due to the different temperature-dependence of Peierls stress in these two lattice structures. The activation energy value of {110} grains was lower than that of {111} grains in FCC Cantor alloy because of the denser atomic stacking in FCC alloys. Compared with conventional Ti-6Al-4V alloy, TiAlV possesses considerably higher hardness and specific strength (63% higher), 83% lower creep displacement at room temperature, and 50% lower creep strain rate over the temperature range from 500 to 600 °C under the similar 1150 MPa stress, indicating a promising substitution for Ti-6Al-4V alloy as structural materials.

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Kinetic Competition During Duplex Partitionless Solidification in Ni-V Alloys

MRS Proceedings ◽

10.1557/proc-398-57 ◽

1995 ◽

Vol 398 ◽

Cited By ~ 2

Author(s):

D.R. Allen ◽

J.H. Perepezko

Keyword(s):

Face Centered Cubic ◽

Duplex Structure ◽

Containerless Processing ◽

Transmission Electron Microscopy Analysis ◽

Simultaneous Formation ◽

Σ Phase ◽

Transmission Electron ◽

Electron Microscopy Analysis ◽

Microscopy Analysis ◽

Face Centered

ABSTRACTA structure composed of both partitionless face-centered cubic (α-fcc) and body-centered cubic (β-bcc) phases has been observed following high undercooling solidification of nickel-vanadium (Ni-V) alloys in the composition range 47-51.7 at.% V. Containerless processing and rapid solidification suppresses the formation of the equilibrium σ phase and results in the simultaneous formation of partitionless fcc and bec phases. Transmission electron microscopy analysis has identified regions in which 0.1-1 μηι a and β grains co-exist in a duplex structure. A nucleation and growth kinetics analysis has been developed to describe the conditions under which this structure may form. Thermodynamic and kinetic arguments have been used to provide bounds on various kinetic parameters. These bounds indicate that the nucleation rates for a and β must be larger than about 1027 m−3 s−3 to account for the number of grains observed in the time available for nucleation, and the growth rates are constrained to be larger than about 1 m/s to account for complete solute trapping.

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Localization of 5f electrons and phase transitions in americium

MRS Proceedings ◽

10.1557/proc-0893-jj01-05 ◽

2005 ◽

Vol 893 ◽

Cited By ~ 1

Author(s):

Michel Pénicaud

Keyword(s):

High Pressure ◽

Phase Transitions ◽

Crystal Structures ◽

Lower Energy ◽

Density Functional ◽

Face Centered Cubic ◽

Hexagonal Close Packed ◽

5F Electrons ◽

Face Centered ◽

Complex Crystal

AbstractDensity-functional electronic calculations have been used to investigate the high-pressure behavior of americium.The phase transitions calculated agree with the recent sequence obtained experimentally under pressure: double hexagonal close packed → face centered cubic → face centered orthorhombic, primitive orthorhombic. In the first three phases the 5f electrons are found localized, only in the fourth phase (Am IV) the 5f electrons are found delocalized. The localization of the 5f electrons is modelled by an anti-ferromagnetic configuration which has a lower energy than the ferromagnetic ones. In this study the complex crystal structures have been fully relaxed.

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Tailoring Compressive Strength and Absorption Energy of Lightweight Multi-Phase AlCuSiFeX (X = Cr, Mn, Zn, Sn) High-Entropy Alloys Processed via Powder Metallurgy

Materials ◽

10.3390/ma14174945 ◽

2021 ◽

Vol 14 (17) ◽

pp. 4945

Author(s):

Ashutosh Sharma ◽

Hansung Lee ◽

Byungmin Ahn

Keyword(s):

Powder Metallurgy ◽

Low Cost ◽

High Strength ◽

Fracture Mechanisms ◽

Solid Solution Phase ◽

Face Centered Cubic ◽

Σ Phase ◽

High Entropy ◽

Face Centered ◽

Fcc Phase

The development of lightweight HEAs with high strength and low cost is an urgent requirement. In this study, equimolar AlCuSiFeX (X = Cr, Mn, Zn, Sn) lightweight HEAs were fabricated by advanced powder metallurgy. The mechanical alloying was performed for 45 h, and the powder compacts were densified at 650 °C. The final results revealed that AlCuSiFeSn lightweight HEA was composed of a single face-centered cubic (FCC) and Cu81Sn22, whereas AlCuSiFeZn showed a dual FCC and body-centered cubic (BCC) structures. Similarly, AlCuSiFeMn alloy contained a BCC + FCC phase with a µ-phase, whereas a σ-phase was present in AlCuSiFeCr in addition to FCC + BCC phases. We also calculated various thermodynamic parameters to predict the solid-solution phase stability of each of the above lightweight HEAs. It was found that lightweight HEAs with additive elements Sn and Zn tend to predominant FCC phases, whereas those with Cr and Mn result in major BCC with hard µ and σ phases, which further improve their mechanical strength. A maximum fracture strain of 23% was obtained for AlCuSiFeSn followed by 19% for AlCuSiFeZn HEA. The compressive fracture mechanisms of these lightweight HEAs are also discussed and reported here.

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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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Faceted antiphase boundaries in GaAs grown on Ge

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010012638x ◽

1987 ◽

Vol 45 ◽

pp. 314-315

Author(s):

N.-H. Cho ◽

S. McKernan ◽

C.B. Carter ◽

K. Wagner

Keyword(s):

Cross Section ◽

Atomic Resolution ◽

Face Centered Cubic ◽

Electrical Behavior ◽

Sphalerite Structure ◽

Antiphase Boundaries ◽

Transmission Electron ◽

Face Centered ◽

Quality Material ◽

Simulated Images

Interest has recently increased in the possibility of growing III-V compounds epitactically on non-polar substrates to produce device quality material. Antiphase boundaries (APBs) may then develop in the GaAs epilayer because it has sphalerite structure (face-centered cubic with a two-atom basis). This planar defect may then influence the electrical behavior of the GaAs epilayer. The orientation of APBs and their propagation into GaAs epilayers have been investigated experimentally using both flat-on and cross-section transmission electron microscope techniques. APBs parallel to (110) plane have been viewed at the atomic resolution and compared to simulated images.Antiphase boundaries were observed in GaAs epilayers grown on (001) Ge substrates. In the image shown in Fig.1, which was obtained from a flat-on sample, the (110) APB planes can be seen end-on; the faceted APB is visible because of the stacking fault-like fringes arising from a lattice translation at this interface.

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