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2019-01-27 | Computational search for ultrasmall and fast skyrmions in the Inverse Heusler family | Skyrmions are magnetic excitations that are potentially ultrasmall and
topologically protected, making them interesting for high-density
all-electronic ultrafast storage applications. While recent experiments have
confirmed the existence of various types of skyrmions, their typical sizes are
much larger than traditional domain walls, except at very low temperature. In
this work, we explore the optimal material parameters for hosting ultra-small,
fast, and room temperature stable skyrmions. As concrete examples, we explore
potential candidates from the inverse Heusler family. Using first-principles
calculations of structural and magnetic properties, we identify several
promising ferrimagnetic inverse Heusler half-metal/near half-metals and analyze
their phase space for size and metastability. | 1901.09446v1 |
2019-01-28 | Magnetotransport properties and giant anomalous Hall angle in half-Heusler compound TbPtBi | Magnetic lanthanide half-Heuslers ($R$PtBi; $R$ being the lanthanide)
represent an attractive subgroup of the Heusler family and have been identified
as ideal candidates for time reversal symmetry breaking topological Weyl
semimetals. In this paper, we present the detailed analysis of the
magnetotransport properties of frustrated antiferromagnet TbPtBi. This material
shows large, non-saturating magnetoresistance (MR) with unusual magnetic field
dependence. The MR of TbPtBi is significantly anisotropic with respect to the
magnetic field, applied along different crystallographic directions and
indicates the anisotropic nature of the Fermi surface. The chiral anomaly
induced negative longitudinal magnetoresistance confirms the presence of Weyl
fermions. At low temperature, Berry phase driven large anomalous Hall
conductivity has been observed. The calculated anomalous Hall angle is the
largest reported so far. | 1901.09534v1 |
2012-09-27 | Fabrication and characterization of semiconducting half Heusler YPtSb thin films | The semiconducting half Heusler compound YPtSb was predicted theoretically to
be capable of changing into topological insulator under proper strain. In this
work, p type semiconducting half-Heusler YPtSb thin films were prepared by
magnetron co-sputtering method from a specially designed target for the first
time. Textured structure with (111) plane paralleling with (001) of MgO
substrate was observed when YPtSb thin films were grown on MgO (100) substrate
at 600{\deg}C.Electrical measurements show that the resistivity of YPtSb films
decreases with increasing temperature, indicating a semiconductor-like
behavior. The carrier density is as high as 1.15 X 10^21 cm-3 at 300 K. The
band gap of YPtSb thin films obtained by infrared spectroscopy is around 0.1 -
0.15 eV, which is well in agreement with the theoretical prediction and the
value measured in bulk YPtSb. | 1209.6288v2 |
2020-04-26 | High thermoelectric performance of half-Heusler compound BiBaK with intrinsically low lattice thermal conductivity | Half-Heusler compounds usually exhibit relatively higher lattice thermal
conductivity that is undesirable for thermoelectric applications. Here we
demonstrate by first-principles calculations and Boltzmann transport theory
that the BiBaK system is an exception, which has rather low thermal
conductivity as evidenced by very small phonon group velocity and relaxation
time. Detailed analysis indicates that the heavy Bi and Ba atoms form a
cage-like structure, inside which the light K atom rattles with larger atomic
displacement parameters. In combination with its good electronic transport
properties, the BiBaK shows a maximum n-type ZT value of 1.9 at 900 K, which
outperforms most half-Heusler thermoelectric materials. | 2004.12324v1 |
2020-08-11 | Anomalous Hall effect in half-metallic Heusler compound Co$_{2}$Ti$X$ ($X$=Si, Ge) | Though Weyl fermions have recently been observed in several materials with
broken inversion symmetry, there are very few examples of such systems with
broken time reversal symmetry. Various Co$_{2}$-based half-metallic
ferromagnetic Heusler compounds are lately predicted to host Weyl type
excitations in their band structure. These magnetic Heusler compounds with
broken time reversal symmetry are expected to show a large momentum space Berry
curvature, which introduces several exotic magneto-transport properties. In
this report, we present systematic analysis of experimental results on
anomalous Hall effect (AHE) in Co$_2$Ti$X$ ($X$=Si and Ge). This study is an
attempt to understand the role of Berry curvature on AHE in Co$_2$Ti$X$ family
of materials. The anomalous Hall resistivity is observed to scale quadratically
with the longitudinal resistivity for both the compounds. The detailed analysis
indicates that in anomalous Hall conductivity, the intrinsic Karplus-Luttinger
Berry phase mechanism dominates over the extrinsic skew scattering and
side-jump mechanism. | 2008.04837v1 |
2020-08-17 | Interaction between skyrmions and antiskyrmions in a coexisting phase of a Heusler material | Coexisting phases of magnetic skyrmions and antiskyrmions have proposed to
exhibit a variety of fascinating properties, owing to interactions between
them. The recent discovery of the coexisting phase in a Heusler material could
offer a platform for skyrmion-antiskyrmion-based spintronics. Here we report
Lorentz electron microscopy experiments and micromagnetic simulations in a
similar Heusler material, Mn$_{1.3}$Pt$_{1.0}$Pd$_{0.1}$Sn. Around $B_c \sim$
420$\,$mT, we find a stochastic reversible transformation and a room
temperature coexisting phase of elliptical skyrmions and square-shaped
antiskyrmions. The closeness of the energy competition is sensitive to the
exchange stiffness constants and sample thickness. Furthermore, we reveal
isotropic long-range repulsive interaction between the skyrmions and
antiskyrmions regardless of their shapes and the skyrmion helicities, in stark
contrast to conventional thought of angle- and helicity-dependent short-range
pairwise interactions. The observed interaction possibly results from the
topological protection against the intrusion of magnetic flux density coming
from skyrmions (antiskyrmions) into antiskyrmions (skyrmions). Our results
provide new insight into interacting skyrmions and antiskyrmions and a guide
for developing skyrmion-antiskyrmion-based spintronics. | 2008.07272v2 |
2020-08-31 | Giant magnetocaloric effect driven by first-order magneto-structural transition in cosubstituted Ni-Mn-Sb Heusler compounds: predictions from \textit{Ab initio} and Monte Carlo calculations | Using Density Functional Theory and a thermodynamic model [Physical Review B
86, 134418 (2012)], in this paper, we provide an approach to systematically
screen compounds of a given Heusler family to predict ones that can yield giant
magnetocaloric effect driven by a first-order magneto-structural transition. We
apply this approach to two Heusler series
Ni$_{2-x}$Fe$_{x}$Mn$_{1+z-y}$Cu$_{y}$Sb$_{1-z}$ and
Ni$_{2-x}$Co$_{x}$Mn$_{1+z-y}$Cu$_{y}$Sb$_{1-z}$, obtained by cosubstitution at
Ni and Mn sites. We predict four new compounds with potentials to achieve the
target properties. Our computations of the thermodynamic parameters, relevant
for magnetocaloric applications, show that the improvement in the parameters in
the predicted cosubstituted compounds can be as large as four times in
comparison to the off-stoichiometric Ni-Mn-Sb and a compound derived by single
substitution at the Ni site, where magnetocaloric effects have been observed
experimentally. This work establishes a protocol to select new compounds that
can exhibit large magnetocaloric effects and demonstrate cosubstitution as a
route for more flexible tuneability to achieve outcomes, better than the
existing ones. | 2008.13479v1 |
2016-03-10 | Pairing of j=3/2 fermions in half-Heusler superconductors | We theoretically consider the superconductivity of the topological
half-Heusler semimetals YPtBi and LuPtBi. We show that pairing occurs between
j=3/2 fermion states, which leads to qualitative differences from the
conventional theory of pairing between j=1/2 states. In particular, this
permits Cooper pairs with quintet or septet total angular momentum, in addition
to the usual singlet and triplet states. Purely on-site interactions can
generate s-wave quintet time-reversal symmetry-breaking states with
topologically nontrivial point or line nodes. These local s-wave quintet pairs
reveal themselves as d-wave states in momentum space. Furthermore, due to the
broken inversion symmetry in these materials, the s-wave singlet state can mix
with a p-wave septet state, again with topologically-stable line nodes. Our
analysis lays the foundation for understanding the unconventional
superconductivity of the half-Heuslers. | 1603.03376v3 |
2016-03-27 | Thermoelectric properties of half-Heusler $\mathrm{ZrNiPb}$ by using first principles calculations | We investigate electronic structures and thermoelectric properties of recent
synthetic half-Heusler $\mathrm{ZrNiPb}$ by using generalized gradient
approximation (GGA) and GGA plus spin-orbit coupling (GGA+SOC). Calculated
results show that $\mathrm{ZrNiPb}$ is a indirect-gap semiconductor. Within the
constant scattering time approximation, semi-classic transport coefficients are
performed through solving Boltzmann transport equations. It is found that the
SOC has more obvious influence on power factor in p-type doping than in n-type
doping, leading to a detrimental effect in p-type doping. These can be
explained by considering the SOC influences on the valence bands and conduction
bands near the Fermi level. The lattice thermal conductivity as a function of
temperature is calculated, and the corresponding lattice thermal conductivity
is 14.5 $\mathrm{W m^{-1} K^{-1}}$ at room temperature. By comparing the
experimental transport coefficients with calculated ones, the scattering time
is attained for 0.333 $\times$ $10^{-14}$ s. Finally, the thermoelectric figure
of merit $ZT$ can be attained, and the $ZT$ value can be as high as 0.30 at
high temperature by choosing appropriate doping level. It is possible to reduce
lattice thermal conductivity by point defects and boundaries, and make
half-Heusler $\mathrm{ZrNiPb}$ become potential candidate for efficient
thermoelectricity. | 1603.08203v1 |
2016-12-19 | Completely compensated ferrimagnetism and sublattice spin crossing in the half-metallic Heusler compound Mn1.5FeV0.5Al | The Slater-Pauling rule states that L21 Heusler compounds with 24 valence
electrons do never exhibit a total spin magnetic moment. In case of strongly
localized magnetic moments at one of the atoms (here Mn) they will exhibit a
fully compensated half-metallic ferrimagnetic state instead, in particular,
when symmetry does not allow for antiferromagnetic order. With aid of magnetic
and anomalous Hall effect measurements it is experimentally demonstrated that
Mn1.5V0.5FeAl follows such a scenario. The ferrimagnetic state is tuned by the
composition. A small residual magnetization, that arises due to a slight
mismatch of the magnetic moments in the different sublattices results in a
pronounced change of the temperature dependence of the ferrimagnet. A
compensation point is confirmed by observation of magnetic reversal and sign
change of the anomalous Hall effect. Theoretical models are presented that
correlate the electronic structure and the compensation mechanisms of the
different half-metallic ferrimagnetic states in the Mn-V-Fe-Al Heusler system. | 1612.06300v1 |
2017-06-01 | Prediction of triple point fermions in simple half-Heusler topological insulators | We predict the existence of triple point fermions in the band structure of
several half-Heusler topological insulators by $ab~initio$ calculations and the
Kane model. We find that many half-Heusler compounds exhibit multiple triple
points along four independent $C_3$ axes, through which the doubly degenerate
conduction bands and the nondegenerate valence band cross each other linearly
nearby the Fermi energy. When projected from the bulk to the (111) surface,
most of these triple points are located far away from the surface
$\bar{\Gamma}$ point, as distinct from previously reported triple point fermion
candidates. These isolated triple points give rise to Fermi arcs on the
surface, that can be readily detected by photoemission spectroscopy or scanning
tunneling spectroscopy. | 1706.00200v1 |
2020-06-09 | Detection of antiskyrmions by topological Hall effect in Heusler compounds | Heusler compounds having $\textit{D}$${}_{2d}$ crystal symmetry gained much
attention recently due to the stabilization of a vortex-like spin texture
called antiskyrmions in thin lamellae of Mn${}_{1.4}$Pt${}_{0.9}$Pd${}_{0.1}$Sn
as reported in the work of Nayak $\textit{et al.}$ [Nature (London) 548, 561
(2017)]. Here we show that bulk Mn${}_{1.4}$Pt${}_{0.9}$Pd${}_{0.1}$Sn
undergoes a spin-reorientation transition from a collinear ferromagnetic to a
noncollinear configuration of Mn moments below 135 K, which is accompanied by
the emergence of a topological Hall effect. We tune the topological Hall effect
in Pd and Rh substituted Mn${}_{1.4}$PtSn Heusler compounds by changing the
intrinsic magnetic properties and spin textures. A unique feature of the
present system is the observation of a zero-field topological Hall resistivity
with a sign change which indicates the robust formation of antiskyrmions. | 2006.05190v1 |
2020-10-22 | Anomalous Quantum Oscillations in Spin-3/2 Topological Semimetal YPtBi | The proposed high-spin superconductivity in the half-Heusler compounds
changes the landscape of superconductivity research. While superconducting
instability is possible only in systems with quantum mechanically coherent
quasiparticles, it has not been verified for any proposed high-spin Fermi
surfaces. Here we report an observation of anomalous Shubnikov-de Haas effect
in half-Heusler YPtBi, which is compatible with a coherent $j=3/2$ Fermi
surface. The quantum oscillation (QO) signal in cubic YPtBi manifests extreme
anisotropy upon rotation of the magnetic field from [100] to [110]
crystallographic direction where the QO signal drastically vanishes near [110].
This radical anisotropy for a cubic system cannot be explained by trivial
scenarios for QO involving effective mass or impurity scattering, but it is
naturally explained by the warping feature of the $j=3/2$ Fermi surface YPtBi.
Our results prove the high-spin nature of the quasiparticle in the half-Heusler
compounds, which makes the realization of the unprecedented high-spin
superconductivity more plausible. | 2010.12085v2 |
2020-11-12 | Anomalous Hall effect and negative longitudinal magnetoresistance in half-Heusler topological semimetal candidates TbPtBi and HoPtBi | Half-Heusler compounds have attracted significant attention because of their
topologically non-trivial electronic structure, which leads to unusual electron
transport properties. We thoroughly investigated the magnetotransport
properties of high-quality single crystals of two half-Heusler phases, TbPtBi
and HoPtBi, in pursuit of the characteristic features of topologically
non-trivial electronic states. Both studied compounds are characterized by the
giant values of transverse magnetoresistance with no sign of saturation in
magnetic field up to 14 T. HoPtBi demonstrates the Shubnikov-de Haas effect
with two principal frequencies, indicating a complex Fermi surface; the
extracted values of carrier effective masses are rather small, $0.18\,m_e$ and
$0.27\,m_e$. The investigated compounds exhibit negative longitudinal
magnetoresistance and anomalous Hall effect, which likely arise from a nonzero
Berry curvature. Both compounds show strongly anisotropic magnetoresistance,
that in HoPtBi exhibits a butterfly-like behavior. | 2011.06290v1 |
2021-04-22 | Chemical bonding origin of the thermoelectric power factor in Half-Heusler semiconductors | Intermetallic semiconductors with the cubic Half-Heusler structure (XYZ) have
excellent thermoelectric properties. This has been attributed to the high
degeneracy of the carrier pockets in the band structure, but large differences
are found between different material compositions. Half-Heuslers are often
interpreted within Zintl chemistry, making a clear distinction between an
electropositive cation ($X^{n+}$) and an extended polyanion ($YZ^{n-}$). Based
on quantitative real space chemical bonding analysis, we unravel large degrees
of covalent bonding between the formal cation and anion, making the Zintl
distinction clearly invalid. This covalence is shown to strongly affect the
band structure, thermoelectric properties and response properties in the
materials, with improved thermoelectric properties observed for those materials
that least follow the Zintl concept. This expands our knowledge of the chemical
bonding motifs governing physical properties, and gives a critical view on the
simplistic chemical concepts too often applied for design of complex materials. | 2104.11281v1 |
2021-04-29 | Nonlinear Hall Effect in Antiferromagnetic Half-Heusler Materials | It has recently been demonstrated that various topological states, including
Dirac, Weyl, nodal-line, and triple-point semimetal phases, can emerge in
antiferromagnetic (AFM) half-Heusler compounds. However, how to determine the
AFM structure and to distinguish different topological phases from transport
behaviors remains unknown. We show that, due to the presence of combined
time-reversal and fractional translation symmetry, the recently proposed
second-order nonlinear Hall effect can be used to characterize different
topological phases with various AFM configurations. Guided by the symmetry
analysis, we obtain the expressions of the Berry curvature dipole for different
AFM configurations. Based on the effective model, we explicitly calculate the
Berry curvature dipole, which is found to be vanishingly small for the
triple-point semimetal phase, and large in the Weyl semimetal phase. Our
results not only put forward an effective method for the identification of
magnetic orders and topological phases in AFM half-Heusler materials, but also
suggest these materials as a versatile platform for engineering the non-linear
Hall effect. | 2104.14127v1 |
2022-01-08 | Atomic disorder and Berry phase driven anomalous Hall effect in Co2FeAl Heusler compound | Co2-based Heusler compounds are the promising materials for the spintronics
application due to their high Curie temperature, large spin-polarization, large
magnetization density, and exotic transport properties. In the present
manuscript, we report the anomalous Hall effect (AHE) in a polycrystalline
Co2FeAl Heusler compound using combined experimental and theoretical studies.
The Rietveld analysis of high-resolution synchrotron x-ray diffraction data
reveals a large degree (~50 %) of antisite disorder between Fe and Al atoms.
The analysis of anomalous transport data provides the experimental anomalous
Hall conductivity (AHC) about 227 S/cm at 2 K with an intrinsic contribution of
155 S/cm, which has nearly constant variation with temperature. The detailed
scaling analysis of anomalous Hall resistivity suggests that the AHE in Co2FeAl
is governed by the Berry phase driven intrinsic mechanism. Our theoretical
calculations reveal that the disorder present in Co2FeAl compound enhances the
Berry curvature induced intrinsic AHC. | 2201.02864v1 |
2022-07-15 | Band splitting induced Berry flux and intrinsic anomalous Hall conductivity in NiCoMnGa quaternary Heusler compound | The anomalous transport properties of Heusler compounds become a hotspot of
research in recent years due to their unique band structure and possible
application in spintronics. In this paper, we report the anomalous Hall effect
in polycrystalline NiCoMnGa quaternary Heusler compound by experimental means
and theoretical calculations. The experimental anomalous Hall conductivity
(AHC) was found at about 256 S/cm at 10K with an intrinsic contribution of ~
121 S/cm. The analysis of Hall data reveals the presence of both extrinsic and
intrinsic contributions in AHE. Our theoretical calculations show that a pair
of spin-orbit coupled band formed by the band splitting due to spin-orbit
interaction (SOI) at the Fermi level produces a finite Berry flux in the system
that provides the intrinsic AHC about 100 S/cm, which is in good agreement with
the experiment. | 2207.07313v1 |
2022-08-04 | Ab-initio study of stable 3d, 4d and 5d transition metal based Quaternary Heusler compounds | The realization of the stable structure of Heusler compounds and the study of
different properties is an important step for their potential application in
spintronics and magnetoelectronic devices. In this paper, using the plane-wave
pseudopotential method within the framework of density functional theory (DFT),
we investigate 25 Quaternary Heusler compounds for their electronic, magnetic,
and mechanical properties. The Open Quantum Materials Database (OQMD) is used
to screen a large number of compounds to narrow down the possible synthesizable
materials. The convex-hull distance and elastic constants are exploited to
confirm the thermodynamic and mechanical stability of the compounds. The
careful study of the different structures suggests that 5 of the compounds
crystallize in type-1 structure whereas 20 compounds adopt type-3 structure.
The possible explanation for the observed behavior is made by invoking
electronegativity arguments and through the study of individual spin magnetic
moments in different structures. The compounds with diverse electronic and
magnetic properties such as half-metallicity, spin gapless semiconducting
behavior, and non-magnetic semi-conducting property have been identified. | 2208.02401v2 |
2024-03-01 | Spin-gapped metals: A novel class of materials -- the case of semi-Heusler compounds | Gapped metals, a recently discovered new class of materials, possess a band
gap slightly above or below the Fermi level. These materials are intrinsic p-
or n-type semiconductors eliminating the need for extrinsic doping. Inspired by
this concept, we propose the so-called "spin-gapped metals" exhibiting
intrinsic p- or n-type behavior for each spin channel independently. Their
properties would be similar to the dilute magnetic semiconductors eliminating
the requirement for transition metal doping. Here, we demonstrate this novel
concept in semi-Heusler compounds using first principles electronic band
structure calculations. We comprehensively analyze their electronic and
magnetic properties, paving the way for novel technological applications of
Heusler compounds. | 2403.00936v1 |
2002-12-17 | Charge Distributions in Metallic Alloys: a Charge Excess Functional theory approach | Charge Distributions in Metallic Alloys: a Charge Excess Functional theory
approach | 0212398v1 |
2009-03-08 | Alloy Stabilized Wurtzite Ground State Structures of Zinc-Blende Semiconducting Compounds | The ground state structures of the A$_x$B$_{1-x}$C wurtzite (WZ) alloys with
$x=$0.25, 0.5, and 0.75 are revealed by a ground state search using the
valence-force field model and density-functional theory total energy
calculations. It is shown that the ground state WZ alloy always has a lower
strain energy and formation enthalpy than the corresponding zinc-blende (ZB)
alloy. Therefore, we propose that the WZ phase can be stabilized through
alloying. This novel idea is supported by the fact that the WZ
AlP$_{0.5}$Sb$_{0.5}$, AlP$_{0.75}$Sb$_{0.25}$, ZnS$_{0.5}$Te$_{0.5}$, and
ZnS$_{0.75}$Te$_{0.25}$ alloys in the lowest energy structures are more stable
than the corresponding ZB alloys. To our best knowledge, this is the first
example where the alloy adopts a structure distinct from both parent phases. | 0903.1449v1 |
2014-04-18 | Mn$_m$Tc$_n$ nanoalloy clusters obey Vegard's law : A first principles prediction | With a view to gain an understanding about the alloying tendency of
bimetallic nano alloy clusters of isoelectronics constituents, we studied the
structural and mixing behaviors of Mn$_m$Tc$_n$ alloy clusters with $m+n =$13
for all possible compositions, using first principles electronic structure
calculations. Our study reports a favorable mixing tendency for the alloy
clusters. The average bond lengths of the minimum energy structures show an
overall linear variation with concentrations, indicating a Vegard's law like
variation for the nano alloy clusters, though the optimized structures undergo
a structural transition from a closed and compact structure for the Mn-rich
alloy clusters to an open layered like structure for the Tc-rich alloy
clusters. We figure out a continuous and smooth interplay between hybridization
and magnetization properties of the alloy clusters, which plays a vital role
for the Vegard's law like variation in their average bond lengths. | 1404.4703v1 |
2014-07-01 | Electronic band structure and ambipolar electrical properties of Cu2O based semiconductor alloys | Tuning the opto-electronic properties through alloying is essential for
semiconductor technology. Currently, mostly isovalent and isostructural alloys
are used (e.g., group-IV and III-V), but a vast and unexplored space of novel
functional materials is conceivable when considering more complex alloys by
mixing aliovalent and heterostructural constituents. The real challenge lies in
the quantitative property prediction for such complex alloys to guide their
experimental exploration. We developed an approach to predict compositional
dependence of both band-structure and electrical properties from ab-initio
calculations by extending conventional dilute defect model to higher (alloy)
concentrations. Considering alloying of aliovalent (Mg, Zn, Cd) cations and
isovalent anions (S, Se) into Cu2O, we predict tunability of band-gap energies
and doping levels over a wide range, including the type conversion from p- to
n-type. Initial synthesis and characterization of Zn and Se substituted Cu2O
support the defect model, suggesting these alloys as promising novel oxide
semiconductor materials. | 1407.0101v1 |
2021-07-01 | Elastic energy of multi-component solid solutions and strain origins of phase stability in high-entropy alloys | The elastic energy of mixing for multi-component solid solutions is derived
by generalizing Eshelby's sphere-in-hole model for binary alloys. By surveying
the dependence of the elastic energy on chemical composition and lattice
misfit, we propose a lattice strain coefficient {\lambda}*. Applying to several
high-entropy alloys and superalloys, we found that most solid solution alloys
are stable when {\lambda}*<0.16, analogous to the Hume-Rothery atomic-size rule
for binary alloys. We also reveal that the polydispersity index {\delta},
frequently used for describing strain in multi-component alloys, is directly
related to the elastic energy (e) with e=q{\delta}^2, q being an elastic
constant. Furthermore, the effects of (i) the number and (ii) the atomic-size
distribution of constituting elements on the phase stability of high-entropy
alloys were quantified. The present derivations open for richer considerations
of elastic effects in high-entropy alloys, offering immediate support for
quantitative assessments of their thermodynamic properties and studying related
strengthening mechanisms. | 2107.00514v1 |
2019-04-09 | Alloy Design for Mechanical Properties: Conquering the Length Scales | Predicting the structural response of advanced multiphase alloys and
understanding the underlying microscopic mechanisms that are responsible for it
are two critically important roles modeling plays in alloy development. An
alloys demonstration of superior properties, such as high strength, creep
resistance, high ductility, and fracture toughness, is not sufficient to secure
its use in widespread application. Still, a good model is needed, to take
measurable alloy properties, such as microstructure and chemical composition,
and forecast how the alloy will perform in specified mechanical deformation
conditions, including temperature, time, and rate. In this bulletin, we
highlight recent achievements by multiscale modeling in elucidating the coupled
effects of alloying, microstructure, and the dynamics of mechanisms on the
mechanical properties of polycrystalline alloys. Much of the understanding
gained by these efforts relied on integration of computational tools that
varied over many length and time scales, from first principles density
functional theory, atomistic simulation methods, dislocation and defect theory,
micromechanics, phase field modeling, single crystal plasticity, and
polycrystalline plasticity. | 1904.04569v1 |
2018-12-05 | Influence of composition and heating schedules on compatibility of FeCrAl alloys with high-temperature steam | FeCrAl alloys are proposed and being intensively investigated as alternative
accident tolerant fuel (ATF) cladding for nuclear fission application. Herein,
the influence of major alloy elements (Cr and Al), reactive element effect and
heating schedules on the oxidation behavior of FeCrAl alloys in steam up to
1500{\deg}C was examined. In case of transient ramp tests, catastrophic
oxidation, i.e. rapid and complete consumption of the alloy, occurred during
temperature ramp up to above 1200{\deg}C for specific alloys. The maximum
compatible temperature of FeCrAl alloys in steam increases with raising Cr and
Al content, decreasing heating rates during ramp period and doping of yttrium.
Isothermal oxidation resulted in catastrophic oxidation at 1400{\deg}C for all
examined alloys. However, formation of a protective alumina scale at
1500{\deg}C was ascertained despite partial melting. The occurrence of
catastrophic oxidation seems to be controlled by dynamic competitive mechanisms
between mass transfer of Al from the substrate and transport of oxidizing gas
through the scale both toward the metal/oxide scale interface. | 1812.01850v1 |
2020-04-14 | Nanoporous AuPt and AuPtAg alloy co-catalysts formed by dewetting-dealloying on ordered TiO2 nanotube surface lead to significantly enhanced photocatalytic H2 generation | Effective co-catalysts are of key importance for photocatalytic H2 generation
from aqueous environments. An attractive co-catalyst candidate are AuPt
(metastable) alloys due to the synergistic electronic and chemical interaction
of the constituents in the charge transfer and H2 evolution process. Here we
introduce the fabrication of AuPt alloy nanoparticles with nanoporosity (pore
size of 2-5 nm) fabricated on spaced TiO2 nanotubes. By dewetting a layered
AgAuPt coating, we form AuPtAg alloy nanoparticles. From these alloys, Ag can
selectively be dissolved leading to the desired nanoporous AuPt alloy particles
with diameter in the range of 10-70 nm deposited as a gradient on the TiO2
nanotubes. A significant enhancement of photocatalytic H2 generation is
obtained compared to the same loading of monometallic or nonporous alloy. The
nanoporous AuPt particles provide not only a large surface area to volume ratio
(and are thus more effective) but also show the intrinsic synergy of a AuPt
alloy for H2 generation. | 2005.01486v1 |
2022-03-18 | Designing a thermodynamically stable and intrinsically ductile refractory alloy | Developing ductile refractory BCC alloys has remained a challenge. The
intrinsic ductility (D) of an alloy is the ratio of surface energy ($\gamma_s$)
and unstable stacking fault energy ($\gamma_{usfe}$). Lowering the valence
electron concentration has been shown to improve the intrinsic ductility of
refractory alloys. However, Re has been widely used to ductilize W, contrary to
the low valency criteria suggested in the literature. Here we use density
functional theory to calculate the enthalpy of formation, $\gamma_{usfe}$ and
$\gamma_s$ of Group IV, V, VI elements and their 25 equiatomic binary alloys in
BCC crystal structure. We found that positive enthalpy leads to a considerable
reduction in $\gamma_{usfe}$ compared to composition averaged value, resulting
in improved intrinsic ductility. Enthalpy is maximum at the equiatomic
concentrations indicating the highly repulsive interaction between the alloy
constituents and vicer-versa. We found that the repulsive interaction between
the alloy constituents leads to a reduction in $\gamma_{usfe}$, making alloys
intrinsically ductile. | 2203.09949v3 |
2016-03-11 | Mechanocaloric effects in Shape Memory Alloys | Shape memory alloys are a class of ferroic materials which undergo a
structural (martensitic) transition where the associated ferroic property is a
lattice distortion (strain). The sensitiveness of the transition to the
conjugated external field (stress), together with the latent heat of the
transition gives rise to giant mechanocaloric effects. In non-magnetic shape
memory alloys, the lattice distortion is mostly described by a pure shear and
the martensitic transition in this family of alloys is strongly affected by
uniaxial stress whereas it is basically insensitive to hydrostatic pressure. As
a result, non-magnetic alloys exhibit giant elastocaloric effects but
negligible barocaloric effects. By contrast, in a number of magnetic shape
memory alloys, the lattice distortion at the martensitic transition involves a
volume change in addition to the shear strain. Those alloys are affected by
both uniaxial stress and hydrostatic pressure and they exhibit giant
elastocaloric and barocaloric effects. The paper aims at providing a critical
survey of available experimental data on elastocaloric and barocaloric effects
in magnetic and non-magnetic shape memory alloys. | 1603.03658v1 |
2017-02-09 | First-principles high-throughput screening of shape-memory alloys based on energetic, dynamical, and structural properties | First-principles-based materials screening is systematically performed to
discover new combinations of chemical elements possibly making shape-memory
alloys (SMAs). The B2, D03, and L21 crystal structures are considered as the
parent phases, and the 2H and 6M structures are considered as the martensitic
phases. 3,384 binary and 3,243 ternary alloys (6,627 in total) with
stoichiometric composition ratios are investigated by the materials screening
in terms of energetic and dynamical stabilities of the martensitic phases as
well as structural compatibility between the parent and the martensitic phases.
187 alloys are found to survive after the screening. Some of the surviving
alloys are constituted by the chemical elements already widely used in SMAs,
but other various metallic elements are also found in the surviving alloys. The
energetic stability of the surviving alloys is further analyzed by comparison
with the data in Materials Project Database (MPD) to examine the alloys which
may occur phase separation or transition. | 1702.02734v1 |
2017-10-24 | Evaluation of microstructure and mechanical property variations in AlxCoCrFeNi high entropy alloys produced by a high-throughput laser deposition method | Twenty-one distinct AlxCoCrFeNi alloys were rapidly prepared by laser
alloying an equiatomic CoCrFeNi substrate with Al powder to create an alloy
library ranging x=0.15-1.32. Variations in crystal structure, microstructure
and mechanical properties were investigated using X-ray diffraction, scanning
electron microscopy, scanning transmission electron microscopy and
nanoindentation. With increasing Al content, the crystal structure transitioned
from a disordered FCC to a mixture of disordered BCC and ordered B2 structures.
While the onset of BCC/B2 formation was consistent with previously reported
cast alloys, the FCC structure was observed at larger Al contents in the laser
processed materials, resulting in a wider two phase regime. The FCC phase was
primarily confined to the BCC/B2 grain boundaries at these high Al contents.
The nanoindentation modulus and hardness of the FCC phase increased with Al
content, while the properties of the BCC/B2 structure were insensitive to
composition. The structure and mechanical properties of the laser-processed
alloys were surprisingly consistent with reported results for cast alloys,
demonstrating the feasibility of applying this high-throughput methodology to
multicomponent alloy design. | 1710.08855v1 |
2021-05-06 | Anticorrosion and biocompatibility of a functionalized layer formed on ZK60 Mg alloy via hydroxyl ion implantation | Magnesium and its alloys have aroused tremendous interests because of their
promising mechanical properties and biocompatibility. However, their
excessively fast corrosion rate hinders the development of Mg alloys in the
biomedical fields. Inspired by conventional ion implantation, a less-toxic
functional group (hydroxyl) is used as the ion source to bombard the ZK60 Mg
alloy surface to form a functionalized oxide layer. This functionalized oxide
layer significantly facilitates the corrosion resistance of the ZK60 Mg alloy
substrate and the proliferation of MC3T3-E1 cells, which is confirmed by
electrochemical, immersion, and in vitro cytocompatibility tests. In comparison
with results of ZK60 alloy implanted with carboxyl ions in our previous work,
it is concluded that hydroxyl-treated alloys exhibit slightly higher corrosion
rate while better biocompatibility. In summary, less-toxic functional ion
implantation can be an effective strategy for inhibiting corrosion of Mg alloy
implants and promoting their biocompatibility. | 2105.02558v1 |
2022-01-12 | Hydrogen trapping and embrittlement in high-strength Al-alloys | Ever more stringent regulations on greenhouse gas emissions from
transportation motivate efforts to revisit materials used for vehicles.
High-strength Al-alloys often used in aircrafts could help reduce the weight of
automobiles, but are susceptible to environmental degradation. Hydrogen (H)
"embrittlement" is often pointed as the main culprit, however, the mechanisms
underpinning failure are elusive: atomic-scale analysis of H inside an alloy
remains a challenge, and this prevents deploying alloy design strategies to
enhance the materials' durability. Here we successfully performed near-atomic
scale analysis of H trapped in second-phase particles and at grain boundaries
in a high-strength 7xxx Al-alloy. We used these observations to guide atomistic
ab-initio calculations which show that the co-segregation of alloying elements
and H favours grain boundary decohesion, while the strong partitioning of H
into the second-phases removes solute H from the matrix, hence preventing
H-embrittlement. Our insights further advance the mechanistic understanding of
H-assisted embrittlement in Al-alloys, emphasizing the role of H-traps in
retarding cracking and guiding new alloy design. | 2201.04490v1 |
2022-05-18 | Atomistic Investigation of Elementary Dislocation Properties Influencing Mechanical Behaviour of $Cr_{15}Fe_{46}Mn_{17}Ni_{22}$ alloy and $Cr_{20}Fe_{70}Ni_{10}$ alloy | In this work, molecular dynamics (MD) simulations were used to investigate
elementary dislocation properties in a Co-free high entropy (HEA) model alloy
($Cr_{15}Fe_{46}Mn_{17}Ni_{22}$ at. %) in comparison with a model alloy
representative of Austenitic Stainless Steel (ASS) ($Cr_{20}Fe_{70}Ni_{10}$ at.
%). Recently developed embedded-atom method (EAM) potentials were used to
describe the atomic interactions in the alloys. Molecular Statics (MS)
calculations were used to study the dislocation properties in terms of local
stacking fault energy (SFE), dissociation distance while MD was used to
investigate the dissociation distance under applied shear stress as a function
of temperature and strain rate. It was shown that higher critical stress is
required to move dislocations in the HEA alloy compared with the ASS model
alloy. The theoretical investigation of simulation results of the dislocation
mobility shows that a simple constitutive mobility law allows to predict
dislocation velocity in both alloys over three orders of magnitude, covering
the phonon drag regime and the thermally activated regime induced by
dislocation unpinning from local hard configurations. | 2205.08798v1 |
2022-05-25 | Ensemble averages of ab initio optical, transport, and thermoelectric properties of hexagonal Si$_x$Ge$_{1-x}$ alloys | We present a comprehensive first-principles investigation of optical,
transport, and thermoelectric properties of pure and doped hexagonal
Si$_x$Ge$_{1-x}$ alloys based on density-functional theory calculations, the
Boltzmann transport equation, and the generalized quasi-chemical approximation
to obtain alloy averages of electronic properties. At low temperature, phase
decomposition into the hexagonal elementary crystals is thermodynamically
favored, but around and above room temperature random alloys are predicted to
be stable. While hexagonal Si has an indirect band gap, the gap of hexagonal Ge
is direct with very weak optical transitions at the absorption edge. The alloy
band gap remains direct for a Si content below 45\,\% and the oscillator
strength of the lowest optical transitions is efficiently enhanced by alloying.
The optical spectra show clear trends and both absorption edges and prominent
peaks can be tuned with composition. The dependence of transport coefficients
on carrier concentration and temperature is similar in cubic and hexagonal
alloys. However, the latter display anisotropic response due to the reduced
hexagonal symmetry. In particular, the transport mass exhibits a significant
directional dependence. Seebeck coefficients and thermoelectric power factors
of $n$-doped alloys show non-monotonous variations with the Si content
independently of temperature. | 2205.12612v1 |
2022-09-11 | A map of single-phase high-entropy alloys | High-entropy alloys have shown much interest and unusual materials
properties. The stability of equimolar single-phase solid solution of five or
more elements is likely to be rare and identifying the existence of such alloys
has been very challenging because of the very large space of possible
combinations. Herein, based on high-throughput density-functional theory
calculations, we construct a chemical map of single-phase equimolar high
entropy alloys by investigating over 650000 equimolar quinary alloys through a
binary regular solid-solution model. We identify more than 30000 potential
single-phase equimolar alloys (5% of the possible combinations) forming mainly
in body-centered cubic structures. We unveil the chemistries that are likely to
form high-entropy alloys, and identify the complex interplay among mixing
enthalpy, intermetallics formation, and melting point that drives the formation
of these solid solutions. We demonstrate the power of our method by predicting
the existence of two new high entropy alloys, i.e. the body-centered cubic
AlCoMnNiV and the face-centered cubic CoFeMnNiZn, which are successfully
synthesized. | 2209.04803v3 |
2022-10-17 | A new alloy for Al-chalcogen system: AlSe surface alloy on Al (111) | Metal chalcogenide is a promising material for studying novel underlying
physical phenomena and nanoelectronics applications. Here, we systematically
investigate the crystal structure and electronic properties of the AlSe surface
alloy on Al (111) using scanning tunneling microscopy, angle-resolved
photoelectron spectrometer, and first-principle calculations. We reveal that
the AlSe surface alloy possesses a hexagonal closed-packed structure. The AlSe
surface alloy comprises two atomic sublayers (Se sublayer and Al sublayer) with
1.16 A along the z direction. The dispersion shows two hole-like bands for AlSe
surface alloy located at about -2.2 eV, far below the Fermi level, which is
sharply different from other metal chalcogenide and binary alloys. These two
bands mainly derive from the in-plane orbital of AlSe (px and py). These
results provide implications for related Al-chalcogen interface. Meanwhile,
AlSe alloy have an advantage of large-scale atomic flatness and a wide band gap
near the Fermi level in serving as an interface for two-dimensional materials. | 2210.08739v1 |
2023-07-31 | Structural and Magnetic Properties of V-Ti-Si Alloy Superconductors | The structural and magnetic properties of the as-cast and annealed
V$_{0.6-x}$Si$_x$Ti$_{0.4}$ ($x$ = 0, 0.05, 0.10, 0.15) alloy superconductors
are reported here. It is found that addition of silicon to the V-Ti alloys
results in eutectic precipitation of Ti$_{5}$Si$_3$-phase in the body centred
cubic (bcc) $\beta$-V-Ti matrix. In the as-cast V$_{0.6-x}$Si$_x$Ti$_{0.4}$
alloys, the superconducting transition temperature (T$_{C}$) changes
non-monotonically with increasing silicon content whereas after annealing, it
is about 7.7 K for all the alloys. On the other hand, the upper critical field
decreases and the coherence length increases after annealing in the x = 0.10
alloy. The variations in the superconducting properties in the alloys are
related to the solubility of 6 at.% Si in the V$_{0.60}$Ti$_{0.40}$ alloy and
the vanadium enrichment in the $\beta$ matrix due to the precipitation of
Ti$_{5}$Si$_3$ phase. | 2307.16623v2 |
2023-10-06 | Multi-principal element alloy discovery using directed energy deposition and machine learning | Multi-principal element alloys open large composition spaces for alloy
development. The large compositional space necessitates rapid synthesis and
characterization to identify promising materials, as well as predictive
strategies for alloy design. Additive manufacturing via directed energy
deposition is demonstrated as a high-throughput technique for synthesizing
alloys in the Cr-Fe-Mn-Ni quaternary system. More than 100 compositions are
synthesized in a week, exploring a broad range of compositional space. Uniform
compositional control to within +/-5 at% is achievable. The rapid synthesis is
combined with conjoint sample heat treatment (25 samples vs 1 sample), and
automated characterization including X-ray diffraction, energy-dispersive X-ray
spectroscopy, and nano-hardness measurements. The datasets of measured
properties are then used for a predictive strengthening model using an active
machine learning algorithm that balances exploitation and exploration. A
learned parameter that represents lattice distortion is trained using the alloy
compositions. This combination of rapid synthesis, characterization, and active
learning model results in new alloys that are significantly stronger than
previous investigated alloys. | 2310.04021v1 |
1999-08-03 | The Fermi surfaces of Metallic Alloys and the Oscillatory Magnetic Coupling between Magnetic Layers separated by such Alloy Spacers | We review the theory of oscillatory magnetic coupling in Metallic Multilayers
across alloy spacers. We illustrate the relationship between the frequencies of
the oscillations and the extremal caliper vectors of the Fermi surface of the
spacer by explicit calculations for Cu$_{(1-x)}$Ni$_x$, Cr$_{(1-x)}$V$_x$ and
Cr$_{(1-x)}$Mo$_x$ alloys. We argue the measurement of the frequencies of such
oscillations can be an extremely useful and cheap probe of the Fermi surface of
random alloys. | 9908035v1 |
2004-01-31 | Comparison among the local atomic order of amorphous TM-Ti alloys (TM=Co, Ni, Cu) produced by Mechanical Alloying studied by EXAFS | We have investigated the local atomic structure of amorphous TM-Ti alloys (TM
= Co, Ni, Cu) produced by Mechanical Alloying by means of EXAFS analyses on TM
and Ti K-edges. Coordination numbers and interatomic distances for the four
alloys where found and compared. EXAFS results obtained indicated a shortening
in the unlike pairs TM-Ti as the difference between $d$ electrons of TM and Ti
atoms increases, suggesting an increase in the chemical short range order
(CSRO) from TM = Co to Cu. | 0402013v1 |
2006-12-13 | Tuning alloy disorder in diluted magnetic semiconductors in high fields to 89 T | Alloy disorder in II-VI diluted magnetic semiconductors (DMS) is typically
reduced when the local magnetic spins align in an applied magnetic field. An
important and untested expectation of current models of alloy disorder,
however, is that alloy fluctuations in many DMS compounds should increase again
in very large magnetic fields of order 100 tesla. Here we measure the disorder
potential in a Zn$_{.70}$Cd$_{.22}$Mn$_{.08}$Se quantum well via the low
temperature photoluminescence linewidth, using a new magnet system to 89 T.
Above 70 T, the linewidth is observed to increase again, in accord with a
simple model of alloy disorder. | 0612332v1 |
2006-12-26 | Compaction of bulk amorphous Fe40Ni40P14B6 alloys | The consolidations of two bulk amorphous Fe40Ni40P14B6 alloy discs are
performed via hot pressing for a short time in its supercooled liquid region
under a pressure of ~1.2 GPa. When the consolidated temperature Ts is lower,
the conjunction of two bulk amorphous Fe40Ni40P14B6 alloy discs cannot be
achieved. Only when Ts get to the vicinity of 675 K, two amorphous
Fe40Ni40P14B6 alloy discs have low viscosity enough to be fully fused together
in a short time and the resulting compacts retain ~90% amorphous phase. To
further improve the consolidated temperature Ts, a vast amount of
crystallization will occur and result in the embrittlement of amorphous alloy. | 0612628v2 |
2008-05-21 | Model Checking Event-B by Encoding into Alloy | As systems become ever more complex, verification becomes more main stream.
Event-B and Alloy are two formal specification languages based on fairly
different methodologies. While Event-B uses theorem provers to prove that
invariants hold for a given specification, Alloy uses a SAT-based model finder.
In some settings, Event-B invariants may not be proved automatically, and so
the often difficult step of interactive proof is required. One solution for
this problem is to validate invariants with model checking. This work studies
the encoding of Event-B machines and contexts to Alloy in order to perform
temporal model checking with Alloy's SAT-based engine. | 0805.3256v2 |
2008-12-03 | Relationship between the magnetic hyperfine field and the magnetic moment | Based on experimental data it is shown, for some chosen alloys and compounds
of iron, that there is no one unique relationship between the 57Fe-site
magnetic hyperfine field, Bhf, and the magnetic moment per Fe atom, m. Instead,
the Bhf-m plot consists of several branches, each of them being characteristic
of a given alloy or compound. Consequently, the effective proportionality
constant (hyperfine coupling constant) depends on the alloy system or compound,
and for a given alloy system or compound it depends on the composition or even
on the lattice site. Consequently, the scaling of Bhf into the underlying m
cannot be done a priopri. | 0812.0671v1 |
2009-06-08 | Multicomponent multisublattice alloys, nonconfigurational entropy and other additions to the Alloy Theoretic Automated Toolkit | A number of new functionalities have been added to the Alloy Theoretic
Automated Toolkit (ATAT) since it was last reviewed in this journal in 2002.
ATAT can now handle multicomponent multisublattice alloy systems,
nonconfigurational sources of entropy (e.g. vibrational and electronic
entropy), Special Quasirandom Structures (SQS) generation, tensorial cluster
expansion construction and includes interfaces for multiple atomistic or ab
initio codes. This paper presents an overview of these features geared towards
the practical use of the code. The extensions to the cluster expansion
formalism needed to cover multicomponent multisublattice alloys are also
formally demonstrated. | 0906.1608v1 |
2010-02-26 | Investigation on Vibrational, Optical and Structural Properties of an Amorphous Se$_{0.80}$S$_{0.20}$ Alloy Produced by Mechanical Alloying | An amorphous Se$_{0.80}$S$_{0.20}$ alloy produced by Mechanical Alloying was
studied by Raman spectroscopy, x-ray diffraction, extended x-ray absorption
fine structure (EXAFS) and optical absorption spectroscopy, and also through
reverse Monte Carlo simulations of its total structure factor and EXAFS data.
Its vibrational modes, optical gap and structural properties as average
interatomic distances and average coordination numbers were determined and
compared to those found for an amorphous Se$_{0.90}$S$_{0.10}$ alloy. The
results indicate that coordination numbers, interatomic distances and also the
gap energy depend on the sulphur concentration. | 1002.5006v1 |
2018-02-27 | Fitting of the TB-SMA interatomic potentials for Pt/Cu(111) surface alloy | In this paper we present new parameters of the TB-SMA interatomic potentials
for the Pt/Cu(111) surface alloy. The parameters are fitted using both the
experimental and {\it ab initio} data. The potentials reproduce not only the
bulk properties of copper and platinum, but also the energy characteristics of
the Pt/Cu(111) surface alloy. The potentials can be used for the simulations of
the growth of the Pt/Cu(111) surface alloy on the atomic scale. | 1802.09965v1 |
2020-04-27 | Analytic binary alloy volume-concentration relations and the deviation from Zen`s law | Alloys expand or contract as concentrations change, and the resulting
relationship between atomic volume and alloy content is an important property
of the solid. While a well-known approximation posits that the atomic volume
varies linearly with concentration (Zen`s law), the actual variation is more
complicated. Here we use an apparent size of the solute (solvent) atom and the
elasticity to derive explicit analytical expressions for the atomic volume of
binary solid alloys. Two approximations, continuum and terminal, are proposed.
Deviations from Zen`s law are studied for 22 binary alloy systems. | 2004.12966v1 |
2020-05-17 | Band structures and direct-to-indirect bandgap transitions in BAlN and BGaN alloys: a first principle study | In this work, the energy band structures of BGaN and BAlN alloys are
systematically studied through first-principles calculation using HSE hybrid
density functional theory by MedeA-VASP. Direct-indirect bandgap transition of
BGaN alloys at B content around 44% and that of BAlN alloys at B content about
24% have been identified. The variation of electron and hole effective masses
of both materials at different B compositions have also been demonstrated. A
large change in hole effective masses of BGaN and BAlN alloys from B=0% to 25%
has been observed. Finally, a picture of energy bandgap versus lattice constant
of III-nitride family with boron is shown. | 2005.08274v1 |
2020-03-09 | Uncommon clustering in dilute Ti-Fe alloys | We present the results of ab initio modeling of structure of dilute Ti-Fe, a
typical representative of quenched Ti-based transition-metal alloys. We have
demonstrated that beyond the solubility limit this alloy cannot be described in
common terms of substitutional and interstitial alloys. Instead, very stable
local clusters are formed in both low-temperature hcp and high-temperature bcc
phases of alloys, with almost identical local structures. This gives an example
of geometrically frustrated state and explains unusual concentration behavior
of M\"ossbauer spectra discovered long ago for this system. | 2003.03939v1 |
2020-09-24 | Design using randomness: a new dimension for metallurgy | High entropy alloys add a new dimension, atomic-scale randomness and the
associated scale-dependent composition fluctuations, to the traditional
metallurgical axes of time-temperature-composition-microstructure. Alloy
performance is controlled by the energies and motion of defects (dislocations,
grain boundaries, vacancies, cracks, ...). Randomness at the atomic scale can
introduce new length and energy scales that can control defect behavior, and
hence control alloy properties. The axis of atomic-scale randomness combined
with the huge compositional space in multicomponent alloys thus enables, in
tandem with still-valid traditional principles, a new broader alloy design
strategy that may help achieve the multi-performance requirements of many
engineering applications. | 2009.11740v1 |
2024-02-19 | High-entropy alloy TiV2ZrCrMnFeNi for hydrogen storage at room temperature with full reversibility and good activation | The development of alloys that are hydrogenated and dehydrogenated quickly
and actively at room temperature is a challenge for the safe and compact
storage of hydrogen. In this study, a new high-entropy alloy (HEA) with AB-type
configuration (A: hydride-forming elements, B: inert-to-hydrogen elements) was
designed by considering valence electron concentration, electronegativity
difference and atomic-size mismatch of elements. The alloy TiV2ZrCrMnFeNi had
dual C14 Laves and BCC phases, in which C14 stored hydrogen and BCC/C14
interphase boundaries contributed to activation. The alloy absorbed 1.6 wt% of
hydrogen at room temperature without any activation treatment and exhibited
fast kinetics and full reversibility. | 2402.11781v1 |
2017-11-17 | First principles second harmonic generation of transition metal dichalcogenides and boron nitride alloys: from monolayers and nanotubes to Haeckelites and Schwarzites | In order to shed light on the second harmonic generation (SHG) of new 2-D
systems, first principles methods are used to calculate the second order
susceptibility \chi(2) for different types of layered alloys such as monolayers
of transition metal dichalcogenide (TMD) alloys, TMD Haeckelite alloys,
nanotubes of TMD alloys, hexagonal boron nitride (h-BN) systems which include
BxNyCz alloys, BN and BNC2 nanotubes, BxNxCy Haeckelites and BN Schwarzites
(porous BN). It is found that the tungsten based alloys possess higher \chi(2)
than Mo based at high photon energies, but at low energies, one type of MoSSe
dominates. The hypothetical TMD Haeckelites NbSSe and Nb0.5Ta0.5S2 reveal the
highest \chi(2) of all the calculated structures. Zigzag TMD alloy nanotubes
show higher \chi(2) as the diameter is reduced and approximate to the monolayer
for big diameters. BNC alloys exhibit a higher \chi(2) than the h-BN monolayer
and are comparable to TMD alloys, except for one case which doubles its
intensity. The BN tubes show an increase of \chi(2) as the diameter decreases,
similarly to the TMD nanotubes. BxNxCy Haeckelites possess a very high \chi(2)
and may shed light on the role of extended defects in nonlinear optical
properties. One of the BN Schwarzites exhibits a higher \chi(2) than already
known 3-D materials. | 1711.06751v1 |
2019-01-07 | Mechanistic origin of high retained strength in refractory BCC high entropy alloys up to 1900K | The body centered cubic (BCC) high entropy alloys MoNbTaW and MoNbTaVW show
exceptional strength retention up to 1900K. The mechanistic origin of the
retained strength is unknown yet is crucial for finding the best alloys across
the immense space of BCC HEA compositions. Experiments on Nb-Mo, Fe-Si and
Ti-Zr-Nb alloys report decreased mobility of edge dislocations, motivating a
theory of strengthening of edge dislocations in BCC alloys. Unlike pure BCC
metals and dilute alloys that are controlled by screw dislocation motion at low
temperatures, the strength of BCC HEAs can be controlled by edge dislocations,
and especially at high temperatures, due to the barriers created for edge glide
through the random field of solutes. A parameter-free theory for edge motion in
BCC alloys qualitatively and quantitatively captures the strength versus
temperature for the MoNbTaW and MoNbTaVW alloys. A reduced analytic version of
the theory then enables screening over >600,000 compositions in the
Mo-Nb-Ta-V-W family, identifying promising new compositions with high retained
strength and/or reduced mass density. Overall, the theory reveals an unexpected
mechanism responsible for high temperature strength in BCC alloys and paves the
way for theory-guided design of stronger high entropy alloys. | 1901.02100v3 |
2020-05-23 | Mixed ground state in Fe-Ni Invar alloys | We investigate the ground state properties of Invar alloys via detailed study
of the electronic structure of Fe$_{1-x}$Ni$_x$ alloys ($x$ = 0.2, 0.3, 0.4,
0.5, 0.6, 0.7, 0.9) employing $x$-ray photoelectron spectroscopy (XPS). While
all the alloys exhibit soft ferromagnetic behavior with Curie temperature much
higher than the room temperature, the results for invar alloy,
Fe$_{0.6}$Ni$_{0.4}$ exhibit anomalous behavior. Moreover, the
magneto-resistance of the Invar alloy becomes highly negative while the end
members possess positive magneto-resistance. The core level spectra of the
Invar alloy exhibit emergence of a distinct new feature below 20~K while all
other Fe-Ni alloys exhibit no temperature dependence down to 10~K.
Interestingly, the shallow core level spectra (3$s$, 3$p$) of Fe and Ni of the
Invar alloy reveal stronger deviation at low temperatures compared to the deep
core levels (2$s$, 2$p$) indicating crystal field effect. It appears that there
is a large precipitation of antiferromagnetic $\gamma^\prime$ phase below 20 K
possessing low magnetic moment (0.5$\mu_B$) on Fe within the $\alpha$ phase.
The discovery of negative magneto-resistance, anomalous magnetization at low
temperature and the emergence of unusual new features in the core levels at low
temperature provide an evidence of mixed phase in the ground state of Invar
alloys. | 2005.11493v1 |
2020-08-24 | Bond Synergy Model for Bond Energies in Alloy Oxides | In this work we introduce a metal-oxide bond-energy model for alloy oxides
based on pure-phase bond energies and bond synergy factors that describe the
effect of alloying on the bond energy between cations and oxygen, an important
quantity to understand formation and stability of passive films. This model is
parameterized for binary cation-alloy oxides using density-functional theory
energies and is shown to be directly transferable to multi-component alloy
oxides. We parameterized the model for alloy oxide energies with metal cations
that form the basis of corrosion resistant alloys, including Fe, Ni, Cr, Mo,
Mn, W, Co, and Ru. We find that isoelectronic solutes allow quantification of
pure-phase bond energies in oxides and that the calculated bond energy values
give sensible results compared to common experience, including the role of Cr
as the passive-layer former in Fe-Ni-Cr alloys for corrosion applications.
Additionally, the bond synergy factors give insights into the mutual
strengthening and weakening effects of alloying on cation-oxygen bonds and can
be related to enthalpy of mixing and charge neutrality constraints. We
demonstrate how charge neutrality can be identified and achieved by the
oxidation states that the different cations assume depending on alloy
composition and the presence of defects. | 2008.10172v1 |
2021-11-23 | Atomic and mesoscopic structure of Dy-based surface alloys on noble metals | Surface alloys are a highly tunable class of low dimensional materials with
the opportunity to tune and control the spin and charge carrier functionalities
on the nanoscale. Here, we focus on the atomic and mesoscopic structural
details of three distinctive binary rare-earth-noble metals (RE/NM) surface
alloys by employing scanning tunneling microscopy (STM) and low energy electron
diffraction (LEED). Using Dysprosium as the guest element on fcc(111) noble
metal substrates, we identify the formation of non-commensurate surface alloy
superstructures which exhibit homogeneous moir\'e patterns for DyCu2/Cu (111)
and DyAu2/Au(111), while an inhomogeneous one is found for DyAg2/Ag(111). The
variations in the local structure are analyzed for all three surface alloys and
the observed differences are discussed in the light of the lattice mismatches
of the alloy layer with respect to the underlying substrate. For the
particularly intriguing case of a Dy-Ag surface alloy, the surface alloy layer
does not show a uniform long-range periodic structure, but consists of local
hexagonal tiles separated by extended domain walls. These domain walls exist to
relief the in-plane strain within the DyAg2 surface alloy layer. Our findings
clearly demonstrate that surface alloying is an intriguing tool to tailor both
the local atomic, but also the mesoscopic moir\'e structures of metallic
heterostructures. | 2111.11877v2 |
2023-04-09 | High-throughput Alloy and Process Design for Metal Additive Manufacturing | Designing alloys for additive manufacturing (AM) presents significant
opportunities. Still, the chemical composition and processing conditions
required for printability (ie., their suitability for fabrication via AM) are
challenging to explore using solely experimental means. In this work, we
develop a high-throughput (HTP) computational framework to guide the search for
highly printable alloys and appropriate processing parameters. The framework
uses material properties from state-of-the-art databases, processing
parameters, and simulated melt pool profiles to predict process-induced
defects, such as lack-of-fusion, keyholing, and balling. We accelerate the
printability assessment using a deep learning surrogate for a thermal model,
enabling a 1,000-fold acceleration in assessing the printability of a given
alloy at no loss in accuracy when compared with conventional physics-based
thermal models. We verify and validate the framework by constructing
printability maps for the CoCrFeMnNi Cantor alloy system and comparing our
predictions to an exhaustive 'in-house' database. The framework enables the
systematic investigation of the printability of a wide range of alloys in the
broader Co-Cr-Fe-Mn-Ni HEA system. We identified the most promising alloys that
were suitable for high-temperature applications and had the narrowest
solidification ranges, and that was the least susceptible to balling,
hot-cracking, and the formation of macroscopic printing defects. A new metric
for the global printability of an alloy is constructed and is further used for
the ranking of candidate alloys. The proposed framework is expected to be
integrated into ICME approaches to accelerate the discovery and optimization of
novel high-performance, printable alloys. | 2304.04149v1 |
2016-10-07 | Computational Investigation of Half-Heusler Compounds for Spintronics Applications | We present first-principles density functional calculations of the electronic
structure, magnetism, and structural stability of 378 $\textit{XYZ}$
half-Heusler compounds (with $X=$ Cr, Mn, Fe, Co, Ni, Ru, Rh, $Y=$ Ti, V, Cr,
Mn, Fe, Ni, $Z=$ Al, Ga, In, Si, Ge, Sn, P, As, Sb). We find that a
"Slater-Pauling density of states" with a gap or pseudogap at three states per
atom below the gap in at least one spin channel is a common feature in
half-Heusler compounds. We find that the presence of such a gap at the Fermi
energy in one or both spin channels contributes greatly to the stability of a
half-Heusler compound. We calculate the formation energy of each compound and
systematically investigate its stability against all other phases in the Open
Quantum Materials Database (OQMD). We represent the thermodynamic phase
stability of each compound as its distance from the convex hull of stable
phases in the respective chemical space and show that the hull distance of a
compound is a good measure of the likelihood of its experimental synthesis. We
identify 26 18-electron semiconductors, 45 half-metals, and 34 near half-metals
with negative formation energy, that follow the Slater-Pauling rule of three
electrons per atom. Our calculations predict new thermodynamically stable
semiconducting phases NiScAs, RhTiP, and RuVAs, which merit further
experimental exploration. Further, two interesting zero-moment half-metals,
CrMnAs and MnCrAs, are calculated to have negative formation energy. In
addition, our calculations predict a number of new, hitherto unreported,
semiconducting (e.g., CoVGe, FeVAs), half-metallic (e.g., RhVSb), near
half-metallic (e.g., CoFeSb, CoVP) half-Heusler compounds to lie close to the
respective convex hull of stable phases, and thus may be experimentally
realized under suitable synthesis conditions, resulting in potential candidates
for various spintronics applications. | 1610.02444v2 |
2017-12-06 | Computational Investigation of Inverse-Heusler compounds for Spintronics Applications | First-principles calculations of the electronic structure, magnetism and
structural stability of inverse-Heusler compounds with the chemical formula
\textit{X$_2$YZ} are presented and discussed with a goal of identifying
compounds of interest for spintronics. Compounds for which the number of
electrons per atom for \textit{Y} exceed that for \textit{X} and for which
\textit{X} is one of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, or Cu; \textit{Y} is one of
Ti, V, Cr, Mn, Fe, Co, Ni, Cu, or Zn; and \textit{Z} is one of Al, Ga, In, Si,
Ge, Sn, P, As or Sb were considered. The formation energy per atom of each
compound was calculated. By comparing our calculated formation energies to
those calculated for phases in the Inorganic Crystal Structure Database (ICSD)
of observed phases, we estimate that inverse-Heuslers with formation energies
within 0.052 eV/atom of the calculated convex hull are reasonably likely to be
synthesizable in equilibrium. The observed trends in the formation energy and
relative structural stability as the \textit{X}, \textit{Y} and \textit{Z}
elements vary are described. In addition to the Slater-Pauling gap after 12
states per formula unit in one of the spin channels, inverse-Heusler phases
often have gaps after 9 states or 14 states. We describe the origin and
occurrence of these gaps. We identify 14 inverse-Heusler semiconductors, 51
half-metals and 50 near half-metals with negative formation energy. In
addition, our calculations predict 4 half-metals and 6 near half-metals to lie
close to the respective convex hull of stable phases, and thus may be
experimentally realized under suitable synthesis conditions, resulting in
potential candidates for future spintronics applications. | 1712.02278v1 |
2017-04-06 | A critical study of the elastic properties and stability of Heusler compounds: Cubic Co$_{2}YZ$ compounds with $L2_{1}$ structure | Elastic constants and their derived properties of various cubic Heusler
compounds were calculated using first-principles density functional theory. To
begin with, Cu$_2$MnAl is used as a case study to explain the interpretation of
the basic quantities and compare them with experiments. The main part of the
work focuses on Co$_2$-based compounds that are Co$_2$Mn$M$ with the main group
elements $M=$~Al, Ga, In, Si, Ge, Sn, Pb, Sb, Bi, and Co$_2TM$ with the main
group elements Si or Ge, and the $3d$ transition metals $T=$~Sc, Ti, V, Cr, Mn,
and Fe. It is found that many properties of Heusler compounds correlate to the
mass or nuclear charge $Z$ of the main group element.
Blackman's and Every's diagrams are used to compare the elastic properties of
the materials, whereas Pugh's and Poisson's ratios are used to analyze the
relationship between interatomic bonding and physical properties. It is found
that the {\it Pugh's criterion} on brittleness needs to be revised whereas {\it
Christensen's criterion} describes the ductile--brittle transition of Heusler
compounds very well. The calculated elastic properties give hint on a metallic
bonding with an intermediate brittleness for the studied Heusler compounds.
The universal anisotropy of the stable compounds has values in the range of
$0.57 <A_U <2.73$. The compounds with higher $A_U$ values are found close to
the middle of the transition metal series. In particular, Co$_2$ScAl with
$A_U=0.01$ is predicted to be an isotropic material that comes closest to an
ideal Cauchy solid as compared to the remaining Co$_2$-based compounds. Apart
from the elastic constants and moduli, the sound velocities, Debye
temperatures, and hardness are predicted and discussed for the studied systems.
The calculated slowness surfaces for sound waves reflect the degree of
anisotropy of the compounds. | 1704.01752v1 |
2018-07-12 | Synthesis and structural characterization of Sb-doped TiFe2Sn Heusler compounds | Heusler compounds form a numerous class of intermetallics, which include two
families of compositions ABC and AB2C, usually referred to as half- and
full-Heusler compounds, respectively. Given their tunable electronic
properties, made possible by adjusting the chemical composition, these
materials are currently considered for the possible use in sustainable
technologies such as solar energy and thermoelectric conversion. According to
theoretical predictions, Sb substitution in the TiFe2Sn full-Heusler compound
is thought to yield band structure modifications that should enhance the
thermoelectric power factor. In this work we tested the phase stability and the
structural and microstructural properties of such heavily-doped compounds. We
synthesized polycrystalline TiFe2Sn1-xSbx samples (x=0,0.1,0.2 and 1.0) by arc
melting, followed annealing. The structural characterization, performed by
x-ray powder diffraction and microscopy analyses, confirmed the formation of
the Heusler AB2C structure (cF16, Fm-3m, prototype: MnCu2Al) in all samples,
with only few percent amounts of secondary phases and only slight deviations
from nominal stoichiometry. With increasing Sb substitution we found a steady
decrease of the lattice parameter, confirming that the replacement takes place
at the Sn site. Quite unusually, the as cast samples exhibited a higher lattice
contraction than the annealed ones. The fully substituted x=1.0 compound, again
adopting the MnCu2Al structure, does not form as stoichiometric phase and
turned out to be strongly Fe deficient.The physical behavior at room
temperature indicated that annealing with increasing temperature is beneficial
for electrical and thermoelectrical transport. Moreover, we measured a slight
improvement of electrical and thermoelectrical properties in the x=0.1 sample
and a suppression in the x=0.2 sample, as compared to the undoped x=0 sample. | 1807.04545v2 |
2004-01-31 | Magnetic properties of amorphous Co$_x$Nb$_{100-x}$ alloys produced by mechanical alloying | Three amorphous Co$_x$Nb$_{100-x}$ alloys, Co$_{25}$Nb$_{75}$,
Co$_{57}$Nb$_{43}$ and Co$_{80}$Nb$_{20}$, were produced by Mechanical Alloying
starting from the elemental powders. Their magnetic properties were determined
using an alternating gradient force magnetometer (AGFM), and the remanent
magnetizations, saturation fields and coercive fields were obtained from the
hysteresis loop. The alloys have a relatively high saturation field, which
decreases as the composition becomes richer in Co. The coercivity and remanent
magnetization reach an optimal value around 57% at.Co, making {\em
a}-Co$_{57}$Nb$_{43}$ the hardest magnetic material among the three alloys.
Further addition of Co produces a soft alloy. | 0402014v1 |
2006-10-12 | Effect of the Fe substitution in Ti-Ni shape memory alloys | Shape memory Ti-Ni alloys attracted much attention in the recent years, since
they are shape memory, intelligent as well as functional materials. In the
present investigation Ti51Ni49 and Ti51Ni45Fe4 alloys were synthesized through
radio frequency (RF) induction melting. The alloy was characterized through
x-ray diffraction (XRD), scanning electron microscopy (SEM), Mossbauer
spectroscopy (MS) and positron annihilation techniques (PAT).The Fe
substitution stabilized the TiNi type cubic (a=2.998 A) phase. The surface
microstructure and presence of the oxide layer in Ti51Ni45Fe4 alloy have been
investigated by SEM. The Positron annihilation measurements indicated a similar
bulk electron density in both the as-cast and annealed (1000 0 C for 30 hrs)
alloys, typically like that of bulk Ti. Mossbauer spectroscopy studies of
as-cast and annealed iron substituted samples showed regions in the samples
where nuclear Zeeman splitting of Fe levels occurred and an oxide phase was
found to be present in as cast Ti51Ni45Fe4 alloy, while annealed sample
indicated the presence of bcc iron phase . | 0610340v1 |
2006-10-12 | On the Evolution of Quasicrystalline and Crystalline Phases in Rapidly Quenched Al-Co-Cu-Ni Alloy | The occurrence of stable decagonal quasicrystalline phase in Al-Co-Ni and
Al-Cu-Co alloys through conventional solidification is well established.
Earlier, we have studied the effect of Cu substitution in place of Co in the
Al70 Co15Ni15 alloy. Here we report the structural/micro-structural changes
with substitution of Cu for Ni in rapidly solidified Al-Co-Ni alloys. The
melt-spun ribbons have been characterized using X-ray diffractometry (XRD),
Scanning and transmission electron microscopy (SEM & TEM). With an increase in
Cu content in the melt spun Al70 Co15Cux Ni15-x (x=0 to 15) alloys, the
relative amount of the decagonal phase decreased up to 10 at% of Cu. At this
composition the quaternary alloy showed the coexistence of decagonal
quasicrystal and superstructure of tau 3 vacancy ordered crystalline phases.
The decagonal phase containing Cu showed more disordering compared to Al-Co-Ni
alloys. The implication of the structural / microstructural changes due to Cu
substitution in stable decagonal quasicrystal will be discussed | 0610347v1 |
2008-06-14 | Formation and stability of icosahedral phase in Al65Ga5Pd17Mn13 alloy | In this work, we present the formation and characterization of a quaternary
(pseudo ternary) icosahedral quasicrystal in Al65Ga5Pd17Mn13 alloy. The X ray
diffraction and transmission electron microscopy confirmed the formation of
icosahedral B2 type and O crystalline (orthorhombic structure) phases in as
cast alloy. The icosahedral phase gets formed after annealing at 800 C for 60
hours. The formation of icosahedral phase in AlGaPdMn quaternary alloy by
present technique has been studied for the first time. The Energy dispersive
X-ray analysis investigations suggest the presence of Ga (5 at) in the alloy.
It is interesting to note that pseudo twelve fold pattern in the as cast alloy
has been observed. Icosahedral AlGaPdMn provides a new opportunity to
investigate the various characteristics including surface characteristics.
Attempts will be made to discuss the micromechanisms for the formation of
quasicrystalline phase in Al-Ga-Pd-Mn alloys. | 0806.2382v1 |
2008-09-17 | Elastic and Chemical Contributions to the Stability of Magnetic Surface Alloys on Ru(0001) | We have used density functional theory to study the structural stability of
surface alloys. Our systems consist of a single pseudomorphic layer of
$M_xN_{1-x}$ on the Ru(0001) surface, where $M$ = Fe or Co, and $N$ = Pt, Au,
Ag, Cd, or Pb. Several of the combinations studied by us display a preference
for atomically mixed configurations over phase-segregated forms. We have also
performed further {\it ab initio} calculations to obtain the parameters
describing the elastic interactions between atoms in the alloy layer, including
the effective atomic sizes at the surface. We find that while elastic
interactions favor alloying for all the systems considered by us, in some cases
chemical interactions disfavor atomic mixing. We show that a simple criterion
(analogous to the Hume-Rothery first law for bulk alloys) need not necessarily
work for strain-stabilized surface alloys, because of the presence of
additional elastic contributions to the alloy heat of formation, that will tend
to oppose phase segregation. | 0809.2908v1 |
2010-03-11 | The Structural Influence on the Rashba-type Spin-Splitting in Surface Alloys | The Bi/Ag(111), Pb/Ag(111), and Sb/Ag(111) surface alloys exhibit a
two-dimensional band structure with a strongly enhanced Rashba-type
spin-splitting, which is in part attributed to the structural asymmetry
resulting from an outward relaxation of the alloy atoms. In order to gain
further insight into the spin-splitting mechanism, we have experimentally
determined the outward relaxation of the alloy atoms in these surface alloys
using quantitative low-energy electron diffraction (LEED). The structure plays
an important role in the size of the spinsplitting as it dictates the potential
landscape, the symmetry as well as the orbital character. Furthermore, we
discuss the band ordering of the Pb/Ag(111) surface alloy as well as the
reproducible formation of Sb/Ag(111) surface alloys with unfaulted
(face-centered cubic) and faulted (hexagonally close-packed) toplayer stacking. | 1003.2351v1 |
2011-02-21 | The energetic and structural properties of bcc NiCu, FeCu alloys: a first-principles study | Using special quasirandom structures (SQS's), we perform first-principles
calculations studying the metastable bcc NiCu and FeCu alloys which occur in
Fe-Cu-Ni alloy steels as precipitated second phase. The mixing enthalpies,
density of state, and equilibrium lattice parameters of these alloys are
reported. The results show that quasi-chemical approach and vegard rule can
well predict the energetic and structural properties of FeCu alloys but fail to
yield that of NiCu. The reason rests with the difference of bond energy
variation with composition between NiCu and FeCu alloys induced by competition
between ferromagnetic and paramagnetic state. Furthermore, the calculated
results show that the energetic and structural properties of these alloys can
well explain the local composition of the corresponding precipitates in ferrite
steels. | 1102.4115v2 |
2011-05-09 | Theoretical Comparison of Rashba Spin-Orbit Coupling in Digitally, Discretely, and Continuously Alloyed Nanostructures | Although most theoretical calculations of quantum wells with non-square
profiles assume that material composition is varied continuously, it is more
common in experiment to grow digital alloys. We compare the Rashba spin-orbit
interaction of triangular wells using continuous, discrete, and digital
alloying profiles in (001)-grown triangular InSb/Al_f(z)In_(1-f(z))Sb, finding
a very large difference between digital alloying and the others, including a
sign change in the Rashba spin-orbit coupling. We find that the interface
contribution to the Rashba spin-orbit coupling is much larger in the
continuously- and discretely-alloyed triangular quantum wells than in the
digitally-alloyed triangular wells, in which it is almost completely absent.
The electric field contribution, however, is quite similar in all three
systems. Due to a much stronger doping dependence in all three systems, the
electric field contribution dominates at higher dopings, although the very
large offset due to the near absence of interface contribution in
digitally-alloyed wells persists. | 1105.1804v1 |
2012-06-08 | Studies of concentration and temperature dependencies of precipitation kinetics in iron-copper alloys using kinetic monte carlo and stochastic statistical simulations | The earlier-developed ab initio model and the kinetic Monte Carlo method
(KMCM) are used to simulate precipitation in a number of iron-copper alloys
with different copper concentrations x and temperatures T. The same simulations
are also made using the improved version of the earlier-suggested stochastic
statistical method (SSM). The results obtained enable us to make a number of
general conclusions about the dependencies of the decomposition kinetics in
Fe-Cu alloys on x and T. We also show that the SSM describes the precipitation
kinetics in a fair agreement with the KMCM, and employing the SSM in
conjunction with the KMCM enables us to extend the KMC simulations to the
longer evolution times. The results of simulations seem to agree with available
experimental data for Fe-Cu alloys within statistical errors of simulations and
the scatter of experimental results. Comparison of results of simulations to
experiments for some multicomponent Fe-Cu-based alloys enables us to make
certain conclusions about the influence of alloying elements in these alloys on
the precipitation kinetics at different stages of evolution. | 1206.1792v1 |
2013-09-06 | High-Throughput Screening of Perovskite Alloys for Piezoelectric Performance and Formability | We screen a large chemical space of perovskite alloys for systems with the
right properties to accommodate a morphotropic phase boundary (MPB) in their
composition-temperature phase diagram, a crucial feature for high piezoelectric
performance. We start from alloy end-points previously identified in a
high-throughput computational search. An interpolation scheme is used to
estimate the relative energies between different perovskite distortions for
alloy compositions with a minimum of computational effort. Suggested alloys are
further screened for thermodynamic stability. The screening identifies alloy
systems already known to host a MPB, and suggests a few new ones that may be
promising candidates for future experiments. Our method of investigation may be
extended to other perovskite systems, e.g., (oxy-)nitrides, and provides a
useful methodology for any application of high-throughput screening of
isovalent alloy systems. | 1309.1727v1 |
2013-09-27 | A novel Monte Carlo model and simulations of magnetic alloys for nuclear applications | We develop a Magnetic Cluster Expansion (MCE) model for binary bcc and fcc
Fe-Cr alloys, as well as for fcc Fe-Ni alloys, and apply it to the
investigation of magnetic properties of these alloys over a broad interval of
concentrations, and over a broad interval of temperatures extending well over
1000 K. We show how an MCE-based Monte Carlo study describes the magnetic
properties of these alloys, for example the composition and microstructure
dependence of the Curie temperature, the non-collinearity of magnetic
structures found in bcc Fe-Cr alloys, phase transitions between bcc and fcc in
Fe-Cr, and the enthalpy of mixing of Fe-Ni alloys. The results of simulations
are in excellent agreement with experimental observations. | 1309.7197v1 |
2013-10-17 | The Influence of Ca and Y on the Microstructure and Corrosion Resistance of Vacuum Die Casting AZ91 Alloy | The influence of Ca and Y on the microstructure and corrosion resistance of
vacuum die casting AZ91 alloy is investigated using optical microscope,
electron scanning microscope, weight-loss test and electrochemical corrosion
test. The results indicate that the microstructure of AZ91 alloy can be
refined, amount of Mg17Al12 phases is reduced, making Mg17Al12 phases transform
from banding to reticular, and stringer Al2Ca phases and block Al2Y phases are
formed through adding both Ca and Y. The corrosion resistance of AZ91 magnesium
alloy can be increased greatly by adding both Ca and Y. The corrosion rate of
AZ91-1.5Ca-1.0Y alloy is dropped to 16.2% of that of AZ91 alloy immersed in
3.5% NaCl aqueous solution for 24 hours. The corrosion current density of
AZ91-1.5Ca-1.0Y alloy is dropped by one order of magnitude. | 1310.4671v1 |
2013-12-12 | Liquid-Solid Phase Transition Alloy as Reversible and Rapid Molding Bone Cement | Bone cement has been demonstrated as an essential restorative material in the
orthopedic surgery. However current materials often imply unavoidable
drawbacks, such as tissue-cement reaction induced thermal injuries and
troublesome revision procedure. Here we proposed an injectable alloy cement to
address such problems through its liquid-solid phase transition mechanism. The
cement is made of a unique alloy BiInSnZn with a specifically designed low
melting point 57.5{\deg}C. This property enables its rapid molding into various
shapes with high plasticity. Some fundamental characteristics including
mechanical strength behaviors and phase transition-induced thermal features
have been measured to demonstrate the competence of alloy as unconventional
cement with favorable merits. Further biocompatible tests showed that this
material could be safely employed in vivo. In addition, experiments also found
the alloy cement capability as an excellent contrast agent for radiation
imaging. Particularly, the proposed alloy cement with reversible phase
transition feature significantly simplifies the revision of cement and
prosthesis. This study opens the way to implement alloy material as bone cement
to fulfill diverse clinical needs. | 1312.3564v1 |
2014-02-12 | The $ν=5/2$ Fractional Quantum Hall State in the Presence of Alloy Disorder | We report quantitative measurements of the impact of alloy disorder on the
$\nu=5/2$ fractional quantum Hall state. Alloy disorder is controlled by the
aluminum content $x$ in the Al$_x$Ga$_{1-x}$As channel of a quantum well. We
find that the $\nu=5/2$ state is suppressed with alloy scattering. To our
surprise, in samples with alloy disorder the $\nu=5/2$ state appears at
significantly reduced mobilities when compared to samples in which alloy
disorder is not the dominant scattering mechanism. Our results highlight the
distinct roles of the different types of disorder present in these samples,
such as the short-range alloy and the long-range Coulomb disorder. | 1402.2989v2 |
2015-05-23 | Special Quasi-ordered Structures: role of short-range order in the semiconductor alloy (GaN)$_{1-x}$(ZnO)$_x$ | This paper studies short-range order (SRO) in the semiconductor alloy
(GaN)$_{1-x}$(ZnO)$_x$. Monte Carlo simulations performed on a density
functional theory (DFT)-based cluster expansion model show that the
heterovalent alloys exhibit strong SRO because of the energetic preference for
the valence-matched nearest-neighbor Ga-N and Zn-O pairs. To represent the
SRO-related structural correlations, we introduce the concept of Special
Quasi-ordered Structure (SQoS). Subsequent DFT calculations reveal dramatic
influence of SRO on the atomic, electronic and vibrational properties of the
(GaN)$_{1-x}$(ZnO)$_x$ alloy. Due to the enhanced statistical presence of the
energetically unfavored Zn-N bonds with the strong Zn3$d$-N2$p$ repulsion, the
disordered alloys exhibit much larger lattice bowing and band-gap reduction
than those of the short-range ordered alloys. Inclusion of lattice vibrations
stabilizes the disordered alloy. | 1505.06329v2 |
2015-06-28 | Theoretical Modeling for the Interaction of Tin alloying with N-Type Doping and Tensile Strain for GeSn Lasers | We investigate the interaction of tin alloying with tensile strain and n-type
doping for improving the performance of a Ge-based laser for on-chip optical
interconnects. Using a modified tight-binding formalism that incorporates the
effect of tin alloying on conduction band changes, we calculate how threshold
current density and slope efficiency are affected by tin alloying in the
presence of tensile strain and n-type doping. Our results show that while there
exists a negative interaction between tin alloying and n-type doping, tensile
strain can be effectively combined with tin alloying to dramatically improve
the Ge gain medium in terms of both reducing the threshold and increasing the
expected slope efficiency. Through quantitative modeling we find the best
design to include large amounts of both tin alloying and tensile strain but
only moderate amounts of n-type doping if researchers seek to achieve the best
possible performance in a Ge-based laser. | 1506.08402v1 |
2016-02-02 | Exceptional damage-tolerance of a medium-entropy alloy CrCoNi at cryogenic temperatures | High-entropy alloys are an intriguing new class of metallic materials that
derive their properties from being multi-element systems that can crystallize
as a single phase, despite containing high concentrations of five or more
elements with different crystal structures. Here we examine an equiatomic
medium-entropy alloy containing only three elements, CrCoNi, as a single-phase
face-centered cubic (fcc) solid solution, which displays strength-toughness
properties that exceed those of all high-entropy alloys and most multi-phase
alloys. At room temperature the alloy shows tensile strengths of almost 1 GPa,
failure strains of ~70%, and KJIc fracture-toughness values above 200 MPa.m1/2;
at cryogenic temperatures strength, ductility and toughness of the CrCoNi alloy
improve to strength levels above 1.3 GPa, failure strains up to 90% and KJIc
values of 275 MPa.m1/2. Such properties appear to result from continuous steady
strain hardening, which acts to suppress plastic instability, resulting from
pronounced dislocation activity and deformation-induced nano-twinning. | 1602.01155v1 |
2017-07-26 | Amorphous Alloys, Degradation Performance of Azo Dyes: Review | Today freshwater is more important than ever before and it is contaminated
from textile industry. Removal of dyes from effluent of textile using amorphous
alloys has been studied extensively by many researchers. In this review article
it is presented up to date development on the azo dye degradation performance
of amorphous alloys, a new class of catalytic materials. Numerous amorphous
alloys have been developed for increasing higher degradation efficiency in
comparison to conventional ones for the removal of azo dyes in wastewater. One
of the objectives of this review article is to organize the scattered available
information on various aspects on a wide range of potentially effective in the
removal of dyes by using amorphous alloys. This study comprises the affective
removal factors of azo dye such as solution pH, initial dye concentration, and
adsorbent dosage. It was concluded that Fe, Mg, Co, Al and Mn-based amorphous
alloys with wide availability have appreciable for removing several types of
azo dyes from wastewater. Concerning amorphous alloys for future research, some
suggestions are proposed and conclusions have been drawn. | 1709.06941v1 |
2017-12-12 | 3D Characterisation of the Fe-rich intermetallic phases in Al-5%Cu alloys by synchrotron X-ray microtomography and skeletonisation | Synchrotron X-ray microtomography and skeletonisation method were used to
study the true 3D network structures and morphologies of the Fe-rich
intermetallic phases in Al-5.0%Cu-0.6%Mn alloys with 0.5% and 1.0% Fe. It was
found that, the Fe-phases in the 1.0%Fe alloy have node lengths of 5-25m; while
those in the 0.5%Fe alloy are of 3-17 m. The Fe-phases in the 1.0%Fe alloy also
developed sharper mean curvature with wider distribution than those in the
0.5%Fe alloy. Combining SEM studies of the deeply-etched samples, the true 3D
structures of 4 different type Fe-phases in both alloys are also revealed and
demonstrated. | 1712.04102v1 |
2017-12-31 | Microstructure and elevated-temperature mechanical properties of refractory AlMo0.5NbTa0.5TiZr High Entropy Alloy fabricated by powder metallurgy | New approaches for the design of alloy systems with multiprincipal elements
is recently researched in refractory materials field. However, most research
aimed at arc melting process with weakness of coarsening of grains and
inhomogeneous microstructure of segregation of elements during the cooling.
This study aims to design and fabricate high-entropy alloy with powder
metallurgy. In this study, a refractory high entropy alloys with composition
near AlMo0.5NbTa0.5TiZr were produced by powder metallurgy. The alloy consists
of two body-centered cubic (BCC) phases. One phase was disordered BCC enriched
with Mo, Nb and Ta and the other phase was ordered BCC enriched with Al and Zr.
The AlMo0.5NbTa0.5TiZr alloy had a density of 7.46g/cm3 and Vickers
microhardness of 678HV. Its compressive yield strength was 2466MPa at 298K and
964MPa at 1273K. The properties of the alloy and the beneficial effects from
powder metallurgy on the microstructure and properties were outlined. | 1801.00263v1 |
2019-11-27 | Microstructural evolution of a low-alloy steel / nickel superalloy dissimilar metal weld during post-weld heat treatment | The microstructural evolution of a dissimilar metal weld (DMW) obtained by
narrow-gap gas tungsten arc welding (NG-GTAW) was investigated after it was
subjected to a post-weld heat treatment (PWHT). The case studied here is a
joint between low-alloy steel pipes and a stainless steel steam generator using
a nickel based alloy as filler material. The fusion boundary that was the focus
of this work was that between the low-alloy steel (2.25Cr-1Mo) and the nickel
alloy (alloy 82). The difference in matrix phase and chemical composition
between the two alloys leads to a large difference in chemical potential for
carbon, which is mobile at the PWHT temperature. A number of advanced
characterization techniques were used to assess the gradient of composition,
hardness and microstructures across the fusion line, both as welded and after
PWHT. This complete analysis permits to highlight and understand the main
microstructural changes occurring during the PWHT. | 1911.12223v1 |
2018-10-24 | Metallurgical processes in AlSi alloy improved by WC nanoparticles | The influence of a modifier based on WC nanoparticles was investigated using
bulk Al in a real industrial process using a commercial AlSi hypoeutectic
alloy. The modifier was prepared by hot extrusion approach. Its influence was
investigated on Al and on commercial Al A356 alloy. The mechanical properties
of the Al A356 alloy modified with WC nanoparticles was determined after T6
heat treatment and compared with an unmodified specimen of the same alloy. The
results obtained in the modified Al A356 alloy reveal unusual behavior of the
mechanical properties, where the elongation of the alloys improved by 32% 64%,
while the tensile and the yield strengths remained unchanged. This behavior was
attributed to a grain size strengthening mechanism, where strengthening occurs
due to the high concentration of grain boundaries, which prevent the
dislocations motions in the metal lattice. | 1810.10463v1 |
2018-10-26 | 3D characterization of ultrasonic melt processing on the microstructural refinement of Al-Cu alloys by synchrotron X-ray tomography | The effect of ultrasonic melting processing on three-dimensional architecture
of intermetallic phases and pores in two multicomponent cast Al-5.0Cu-0.6Mn-0.5
Fe alloys is characterized using conventional microscopy and synchrotron X-ray
microtomography. The two alloys are found to contain intermetallic phases such
as Al15(FeMn)3Cu2, Al7Cu2Fe, Al3(FeMn), Al6(FeMn), and Al2Cu that have complex
networked morphology in 3D. The application of USP in alloys can obtained
refined and equiaxed microstructures. The grain size of 0.5Fe and 1.0 Fe alloys
is greatly decreased from 16.9 m, 15.8 m without USP to 13.3 m, 12.2 m with
USP, respectively. The results show that USP significantly reduce the volume
fraction, grain size, interconnectivity, and equivalent diameter of the
intermetallic phases in both alloys. The volume fraction of pores in both
alloys is reduced due to the USP degassing effect. The refinement mechanism of
USP induced fragmentation of primary and secondary dendrites via acoustic
bubbles and acoustic streaming flow were discussed. | 1810.11230v1 |
2018-02-21 | Surface texturing of Ti6Al4V alloy using femtosecond laser for superior antibacterial performance | Titanium and its alloy are most widely used implant materials in dental and
orthopaedic fields. However, infections occurring during implantation leads to
implant failure in most of the cases. Here, we have demonstrated antibacterial
behavior of Ti6Al4V alloy achieved when surface modified using femtosecond
laser beam. Post laser treatment conical microstructures were observed on the
Ti6Al4V alloy surface. Generation of different sub-oxide phases of titanium
dioxide were detected on laser treated samples using X-ray diffraction and
X-ray photoelectron spectroscopy. Wettability of Ti6Al4V alloy surface changed
significantly after interaction with the laser. Adhesion and growth of two gram
positive; Staphylococcus aureus and Streptococcus mutans and one gram negative
Pseudomonas aeruginosa bacteria have been explored on pristine, as well as, on
laser textured Ti6Al4V alloy surfaces. In-vitro investigation on agar plate
showed inhibition of bacterial growth on most of the laser treated surface.
Superior surface roughness and occurrence of magneli phases of titanium dioxide
on laser treated surface were probably responsible for the antibacterial
behavior exhibited by the laser treated samples. Therefore, femtosecond laser
surface treatment of Ti6Al4V alloy could find potential application in the
development of infection free medical implants for dental and orthopedic
usages. | 1802.07492v1 |
2020-05-16 | Simple approach to model the strength of solid-solution high entropy alloys in Co-Cr-Fe-Mn-Ni system | A simple fitting approach is introduced for modeling the strength (hardness)
of quaternary and quinary face-centered cubic (fcc) solid solution high entropy
alloys (HEAs) in Co-Cr-Fe-Mn-Ni system. It is proposed that the strength of
solid solution HEAs could be modeled by a polynomial equation where
experimental data are used for finding the coefficients of polynomial. It is
observed that the proposed polynomial could model the strength of solid
solution HEAs very well. Effects of constituent elements on the hardness of
quinary Co-Cr-Fe-Mn-Ni alloys are investigated; the results indicate that the
strength of alloys decreases with increasing the Fe content. The softening
effect of Fe is explained by considering its effect on decreasing the shear
modulus of alloys. Furthermore, the effects of parameters enthalpy of mixing
and valence electron concentration on the strength of HEAs are investigated.
The results show that the enthalpy of mixing has a noticeable effect on the
hardness of quinary Co-Cr-Fe-Mn-Ni alloys and the strength increases with
decreasing the enthalpy of mixing. Furthermore, the results show that hardness
of quinary Co-Cr-Fe-Mn-Ni alloys increases with increasing the parameter
valence electron concentration. | 2005.07948v1 |
2022-02-02 | cardiGAN: A Generative Adversarial Network Model for Design and Discovery of Multi Principal Element Alloys | Multi-principal element alloys (MPEAs), inclusive of high entropy alloys
(HEAs), continue to attract significant research attention owing to their
potentially desirable properties. Although MPEAs remain under extensive
research, traditional (i.e. empirical) alloy production and testing is both
costly and time-consuming, partly due to the inefficiency of the early
discovery process which involves experiments on a large number of alloy
compositions. It is intuitive to apply machine learning in the discovery of
this novel class of materials, of which only a small number of potential alloys
has been probed to date. In this work, a proof-of-concept is proposed,
combining generative adversarial networks (GANs) with discriminative neural
networks (NNs), to accelerate the exploration of novel MPEAs. By applying the
GAN model herein, it was possible to directly generate novel compositions for
MPEAs, and to predict their phases. To verify the predictability of the model,
alloys designed by the model are presented and a candidate produced; as
validation. This suggests that the model herein offers an approach that can
significantly enhance the capacity and efficiency of development of novel
MPEAs. | 2202.00966v1 |
2017-06-01 | Tuning the piezoelectric and mechanical properties of the AlN system via alloying with YN and BN | Recent advances in microelectromechanical systems often require
multifunctional materials, which are designed so as to optimize more than one
property. Using density functional theory calculations for alloyed nitride
systems, we illustrate how co-alloying a piezoelectric material (AlN) with
different nitrides helps tune both its piezoelectric and mechanical properties
simultaneously. Wurtzite AlN-YN alloys display increased piezoelectric response
with YN concentration, accompanied by mechanical softening along the
crystallographic c direction. Both effects increase the electromechanical
coupling coefficients relevant for transducers and actuators. Resonator
applications, however, require superior stiffness, thus leading to the need to
decouple the increased piezoelectric response from a softened lattice. We show
that co-alloying of AlN with YN and BN results in improved elastic properties
while retaining most of the piezoelectric enhancements from YN alloying. This
finding may lead to new avenues for tuning the design properties of
piezoelectrics through composition-property maps.
Keywords: piezoelectricity, electromechanical coupling, density functional
theory, co-alloying | 1706.00367v4 |
2017-10-19 | Design of high-strength refractory complex solid-solution alloys | Nickel-based superalloys and near-equiatomic high-entropy alloys containing
Molybdenum are known for higher temperature strength and corrosion resistance.
Yet, complex solid-solution alloys offer a huge design space to tune for
optimal properties at slightly reduced entropy. For refractory Mo-W-Ta-Ti-Zr,
we showcase KKR electronic-structure methods via the coherent-potential
approximation to identify alloys over 5-dimensional design space with improved
mechanical properties and necessary global (formation enthalpy) and local
(short-range order) stability. Deformation is modeled with classical molecular
dynamic simulations, validated from our first-principles data. We predict
complex solid-solution alloys of improved stability with greatly enhanced
modulus of elasticity ($3\times$ at 300 K) over near-equiatomic cases, as
validated experimentally, and with higher moduli above 500~K over commercial
alloys ($2.3\times$ at 2000 K). We also show that optimal complex
solid-solution alloys are not described well by classical potentials due to
critical electronic effects. | 1710.06983v2 |
2020-11-29 | Navigating the Complex Compositional Landscape of High-Entropy Alloys | High-entropy alloys, which exist in the high-dimensional composition space,
provide enormous unique opportunities for realizing unprecedented structural
and functional properties. A fundamental challenge, however, lies in how to
predict the specific alloy phases and desirable properties accurately. This
review article provides an overview of the data-driven methods published to
date to tackle this exponentially hard problem of designing high-entropy
alloys. Various utilizations of empirical parameters, first-principles and
thermodynamic calculations, statistical methods, and machine learning are
described. In an alternative method, the effectiveness of using
phenomenological features and data-inspired adaptive features in the prediction
of the high-entropy solid solution phases and intermetallic alloy composites is
demonstrated. The prospect of high-entropy alloys as a new class of functional
materials with improved properties is featured in light of entropic effects.
The successes, challenges, and limitations of the current high-entropy alloys
design are discussed, and some plausible future directions are presented. | 2011.14403v2 |
2021-01-29 | Simple prediction of immiscible metal alloying based on metastability analysis | It has been known that even though two elemental metals, $X$ and $Y$, are
immiscible, they can form alloys on surfaces of other metal $Z$. In order to
understand such surface alloying of immiscible metals, we study the energetic
stability of binary alloys, $XZ$ and $YZ$, in several structures with various
coordination numbers (CNs). By analyzing the formation energy modified to
enhance the subtle energy difference between metastable structures, we find
that $XZ$ and $YZ$ with B2-type structure (CN$=$8) become energetically stable
when the $X$ and $Y$ metals form an alloy on the $Z$ metal surface. This is
consistent with the experimental results for Pb-Sn alloys on metal surfaces
such as Rh(111) and Ru(0001). Some suitable metal substrates are also predicted
to form Pb-Sn alloys. | 2101.12343v1 |
2021-04-21 | A First-Principles-Based Approach to The High-Throughput Screening of Corrosion-Resistant High Entropy Alloys | The design of corrosion-resistant high entropy alloys (CR-HEAs) is
challenging due to the alloys' virtually astrological composition space. To
facilitate this, efficient and reliable high-throughput exploratory approaches
are needed. Toward this end, the current work reports a first-principles-based
approach exploiting the correlations between work function, surface energy, and
corrosion resistance (i.e., work function and surface energy are, by
definitions, proportional and inversely proportional to an alloy's inherent
corrosion resistance, respectively). Two Bayesian CALPHAD models (or databases)
of work function and surface energy of FCC Co-Cr-Fe-Mn-Mo-Ni are assessed using
discrete surface energies and work functions derived by density-functional
theory (DFT) calculations. The models are then used to rank different
Co-Cr-Fe-Mn-Mo-Ni alloy compositions. It is observed that the ranked alloys
possess chemical traits similar to previously studied corrosion-resistance
alloys, suggesting that the proposed approach can be used to reliably screen
HEAs with potentially good inherent corrosion resistance. | 2104.10590v1 |
2021-10-07 | Design Strength-Ductility Synergy of Metastable High-Entropy Alloys by Tailoring Unstable Fault Energies | Metastable alloys with transformation/twinning-induced plasticity (TRIP/TWIP)
can overcome the strength-ductility trade-off in structural materials.
Originated from the development of traditional alloys, the intrinsic stacking
fault energy (ISFE) has been relied to tailor TRIP/TWIP in high-entropy alloys
(HEA), but with limited quantitative success. Herein, we demonstrate a new
strategy for designing metastable HEAs and validate its effectiveness by
discovering seven new alloys with experimentally observed metastability for
TRIP/TWIP. We propose unstable fault energies as the more effective design
metric and attribute the deformation mechanism of metastable face-centered
cubic alloys to UMFE (unstable martensite fault energy)/UTFE (unstable twin
fault energy) rather than ISFE. Among the studied HEAs and steels, the
traditional ISFE criterion fails in more than half of the cases, while the
UMFE/UTFE criterion accurately predicts the deformation mechanisms in all
cases. The UMFE/UTFE criterion provides a new paradigm for developing
metastable alloys with TRIP/TWIP for enhanced strength-ductility synergy. | 2110.03167v2 |
2021-10-07 | Solid solution and precipitation strengthening effects in basal slip, extension twinning and pyramidal slip in Mg-Zn alloys | A high-throughput methodology is proposed, based on the combination of
diffusion couples and advanced nanomechanical testing methods, to directly
measure alloying effects on the critical resolved shear stress (CRSS) of
individual deformation modes in Mg alloys. The methodology is tested in Mg-Zn
alloys by assessing the alloying effects, up to Zn contents of 2 at.%, on basal
slip, extension twining and pyramidal slip in two metallurgical condition:
as-quenched, for which the Zn solute atoms remain homogenously dispersed in
solid solution; and peak-aged, for which the Zn atoms form rod-shape $MgZn_{2}$
precipitates. A combined approach including micromechanical testing,
transmission Kikuchi diffraction, and high-resolution transmission electron
microscopy was performed to reveal the corresponding deformation mechanisms. It
was found that the CRSS enhancement for basal slip and extension twinning by
$MgZn_{2}$ precipitates is considerably larger than the effect of Zn in solid
solution, while the strengthening of pyramidal slip is similar in both cases.
As a result, the anisotropy ratios remain high and similar to pure Mg in the
solid solution strengthened Mg-Zn alloys. However, they are substantially
reduced in precipitation strengthened Mg-Zn alloys. | 2110.03287v1 |
2021-11-23 | Enhancement of functional properties of V$_{0.6}$Ti$_{0.4}$ alloy superconductor by the addition of yttrium | We show here that the yttrium is immiscible and precipitates with various
sizes in the body centred cubic V$_{0.6}$Ti$_{0.4}$ alloy superconductor. The
number and size of the precipitates are found to depend on the amount of
yttrium added. Precipitates with various sizes up to 30~$\mu$m are found in the
V$_{0.6}$Ti$_{0.4}$ alloy containing 5 at.\% yttrium. The large amount of line
disorders generated by the addition of yttrium in this alloy are found to be
effective in pinning the magnetic flux lines. While the superconducting
transition temperature increases with the increasing amount of yttrium in the
V$_{0.6}$Ti$_{0.4}$ alloy, the critical current density is maximum for the
alloy containing 2 at. \% yttrium, where it is more than 7.5 times the parent
alloy in fields higher than 1~T. We found that the effectiveness of each type
of defect in pinning the flux lines is dependent on the temperature and the
applied magnetic filed. | 2111.11670v1 |
2021-12-20 | Self-diffusion in carbon-alloyed CoCrFeMnNi high entropy alloys | Tracer diffusion of the substitutional components in
(CoCrFeNiMn)$_{1-x}$C$_x$ high-entropy alloys with x = 0.002, 0.005 and 0.008
(in at. fractions) is measured at elevated temperatures from 1173 to 1373 K.
Two different characteristic effects of interstitial carbon addition on
substitutional diffusion in these FCC alloys are distinguished. At the highest
temperature of 1373 K, alloying by C with relatively low concentrations (x =
0.002) retards diffusion of the substitutional elements with respect to those
in the C-free alloy. At lower temperatures and/or higher C concentrations (x >
0.005), an enhancement of the diffusion rates of all substitutional elements is
seen. A model is suggested that relates the self-diffusivities in the
CoCrFeMnNi-C alloys with the lattice distortion imposed by interstitially
dissolved carbon. The experimental results are interpreted in terms of a
decrease of the migration barriers for vacancy-mediated diffusion due to the
presence of interstitial C atoms. | 2112.10507v1 |
2022-04-24 | High-throughput characterization of transition metal dichalcogenide alloys: Thermodynamic stability and electronic band alignment | Alloying offers a way to tune many of the properties of the transition metal
dichalcogenide (TMD) monolayers. While these systems in many cases have been
thoroughly investigated previously, the fundamental understanding of critical
temperatures, phase diagrams and band edge alignment is still incomplete. Based
on first principles calculations and alloy cluster expansions we compute the
phase diagrams 72 TMD monolayer alloys and classify the mixing behavior. We
show that ordered phases in general are absent at room temperature but that
there exists some alloys, which have a stable Janus phase at room temperature.
Furthermore, for a subset of these alloys, we quantify the band edge bowing and
show that the band edge positions for the mixing alloys can be continuously
tuned in the range set by the boundary phases. | 2204.11223v1 |
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