publicationDate stringlengths 1 2.79k | title stringlengths 1 36.5k ⌀ | abstract stringlengths 1 37.3k ⌀ | id stringlengths 9 47 |
|---|---|---|---|
2018-05-14 | Structure and glass-forming ability of simulated Ni-Zr alloys | Binary Cu-Zr system is a representative bulk glassformer demonstrating high
glass forming ability due to pronounced icosahedral local ordering. From the
first glance, Ni-Zr system is the most natural object to expect the same
behavior because nickel and copper are neighbours in the periodic table and
have similar physicochemical properties. However, doing molecular dynamics
simulations of $\rm Ni_{\alpha}Zr_{1-\alpha}$ alloys described by embedded atom
model potential, we observe different behaviour. We conclude that the Ni-Zr
system has the same glass-forming ability as an additive binary Lennard-Jones
mixture without any chemical interaction. The structural analysis reveals that
icosahedral ordering in Ni-Zr alloys is much less pronounced than that in the
Cu-Zr ones. We suggest that lack of icosahedral ordering due to peculiarities
of interatomic interactions is the reason of relatively poor glass-forming
ability of Ni-Zr system. | 1805.05113v1 |
2018-05-28 | Universal correlation between electronic factors and solute-defect interactions in bcc refractory metals | The interactions between solute atoms and crystalline defects such as
vacancies, dislocations, and grain boundaries play an essential role in
determining physical, chemical and mechanical properties of solid-solution
alloys. Here we present a universal correlation between two electronic factors
and the solute-defect interaction energies in binary alloys of
body-centered-cubic (bcc) refractory metals (such as W and Ta) with
transition-metal substitutional solutes. One electronic factor is the
bimodality of the d-orbital local density of states for a matrix atom at the
substitutional site, and the other is related to the hybridization strength
between the valance sp- and d-bands for the same matrix atom. Remarkably, the
correlation is independent of the types of defects and the locations of
substitutional sites, following a linear relation for a particular pair of
solute-matrix elements. Our findings provide a novel and quantitative guidance
to engineer the solute-defect interactions in alloys based on electronic
structures. | 1805.10760v2 |
2018-05-30 | Short-range antiferromagnetic correlations in the superconducting state of filled skutterudite alloys Pr$_{1-x}$Eu$_x$Pt$_4$Ge$_{12}$ | Motivated by current research efforts towards exploring the interplay between
magnetism and superconductivity in multiband electronic systems, we have
investigated the effects of Eu substitution through thermodynamic measurements
on the superconducting filled skutterudite alloys
Pr$_{1-x}$Eu$_x$Pt$_4$Ge$_{12}$. An increase in Eu concentration leads to a
suppression of the superconducting transition temperature consistent with an
increase of magnetic entropy due to Eu local moments. While the low-temperature
heat capacity anomaly is present over the whole doping range, we find that in
alloys with $x\leq0.5$ the Schottky peaks in the heat capacity in the
superconducting state appear to be due to Zeeman splitting by an internal
magnetic field. Our theoretical modeling suggests that this field is a result
of the short-range antiferromagnetic correlations between the europium ions.
For the samples with $x > 0.5$, the peaks in the heat capacity signal the onset
of antiferromagnetic (AFM) ordering of the Eu moments. | 1805.12012v1 |
2018-06-01 | Hidden orders in amorphous structures: extraction of nearest neighbor networks of amorphous Nd-Fe alloys with Gabriel graph analyses | Using the scheme of Delaunay and Gabriel graphs, we analyzed the amorphous
structures of computationally created Nd-Fe alloys for several composition
ratios based on melt quench simulations with finite temperature
first-principles molecular dynamics.By the comparison of the radial
distribution functions of the whole system and those derived from the Delaunay
and Gabriel graphs, it was shown that the Gabriel graphs represent the first
nearest neighbor networks well in the examined amorphous systems. From the
Gabriel graph analyses, we examined the coordination structures of amorphous
Nd-Fe alloys statistically. We found that the ranges of distributions of
coordination numbers vary depending on the composition ratio. The angular
distributions among three adjacent atoms were also analyzed, and it was found
that the angular distributions behave differently in the Nd-rich and Fe-rich
samples. We found that the orders in the amorphous system becomes stronger as
increasing the Nd ratio, which corresponds to the appearance of crystalline
grain boundary phases at high Nd composition ratio [T. T. Sasaki et al., Acta
Mater. 115, 269-277 (2016)]. | 1806.00240v4 |
2018-06-11 | Lateral heterostructures of hexagonal boron nitride and graphene: BCN alloy formation and microstructuring mechanism | Integration of individual two-dimensional materials into heterostructures is
a crucial step which enables development of new and technologically interesting
functional systems of reduced dimensionality. Here, well-defined lateral
heterostructures of hexagonal boron nitride and graphene are synthesized on
Ir(111) by performing sequential chemical vapor deposition from borazine and
ethylene in ultra-high vacuum. Low-energy electron microscopy (LEEM) and
selected-area electron diffraction ({\mu}-LEED) show that the heterostructures
do not consist only of hexagonal boron nitride (an insulator) and graphene (a
conductor), but that also a 2D alloy made up of B, C, and N atoms (a
semiconductor) is formed. Composition and spatial extension of the alloy can be
tuned by controlling the parameters of the synthesis. A new method for in situ
fabrication of micro and nanostructures based on decomposition of hexagonal
boron nitride is experimentally demonstrated and modeled analytically, which
establishes a new route for production of BCN and graphene elements of various
shapes. In this way, atomically-thin conducting and semiconducting components
can be fabricated, serving as a basis for manufacturing more complex devices. | 1806.03892v1 |
2018-06-17 | Dislocation interactions and crack nucleation in a fatigued near-alpha titanium alloy | Dislocation interactions at the crack nucleation site were investigated in
near-alpha titanium alloy Ti-6242Si subjected to low cycle fatigue. Cyclic
plastic strain in the alloy resulted in dislocation pile-ups in the primary
alpha grains, nucleated at the boundaries between the primary alpha and the
two-phase regions. These two phase regions provided a barrier to slip transfer
between primary alpha grains. We suggest that crack nucleation occurred near
the basal plane of primary alpha grains by the subsurface double-ended pile-up
mechanism first conceived by Tanaka and Mura. Superjogs on the basal <a>
dislocations were observed near the crack nucleation location. The two phase
regions showed direct transmission of a3 dislocations between secondary alpha
plates, transmitted through the beta ligaments as a[010], which then decompose
into (a/2)<111> dislocation networks in the beta. The beta ligaments themselves
do not appear to form an especially impenetrable barrier to slip, in agreement
with the micropillar and crystal plasticity investigations of Zhang et al. | 1806.06367v1 |
2018-09-18 | Twinning-induced pseudoelastic behavior in (MoW)$_{85}$(TaTi)$_{7.5}$Zr$_{7.5}$ | We provide a critical atomistic evidence of pseudoelastic behavior in complex
solid-solution BCC Mo-W-Ta-Ti-Zr alloy. Prior to this work, only limited
single-crystal BCC solids of pure metals and quaternary alloys have shown
pseudoelastic behavior at low temperatures and high strain rates. The
deformation mechanisms investigated using classical molecular simulations under
tensile-compressive loading reveal temperature-dependent pseudoelastic behavior
aided by twinning during the loading-unloading cycle. The pseudoelasticity is
found to be independent of loading directions with identical cyclic deformation
characteristics during uniaxial loading. Additionally, temperature variation
from 77 to 1500 K enhances the elastic strain recovery in the alloy. | 1809.06822v1 |
2018-09-27 | Kinetic Pathways of Phase Decomposition Using Steepest-Entropy-Ascent Quantum Thermodynamics Modeling. Part I: Continuous and Discontinuous Transformations | The decomposition kinetics of a solid-solution into separate phases are
analyzed with an equation of motion initially developed to account for
dissipative processes in quantum systems. This equation and the
steepest-entropy-ascent quantum thermodynamic framework of which it is a part
make it possible to track kinetic processes in systems in non-equilibrium,
while retaining the framework of classical equilibrium thermodynamics. The
general equation of motion is particularized for the case of the decomposition
of a binary alloy, and a solution model is used to build an approximate energy
eigenstructure, or pseudo-eigenstructure, for the alloy system. This equation
is then solved with the pseudo-eigenstructure to obtain a unique reaction path
and the decomposition kinetics of the alloy. For a hypothetical solid-solution
with a miscibility gap at low temperatures, the conditions under which this
framework predicts a continuous transformation path (spinodal decomposition) or
a discontinuous one (nucleation and growth) are demonstrated. | 1809.10627v1 |
2019-11-14 | Electron spin mediated distortion in metallic systems | The deviation of positions of atoms from their ideal lattice sites in
crystalline solid state systems causes distortion and can lead to variation in
structural [1] and functional properties [2]. Distortion in molecular systems
has been traditionally understood in the term of Jahn-Teller distortion [3],
while for the one-dimensional chain of metals, the Peierls distortion mechanism
has been proposed [4]. In a real three dimensional metallic systems, a
fundamental description of the distortion is missing, which we need to design
alloys with attractive structural properties. The present investigation
presents the evolution of distortion in metallic systems in terms of
magnetovolume effects arising due to magnetic ground-state of the system.
Particularly the significant distortion in the case of Cr due to presence of
other transition metals is seen. Cr alloyed with transition metals as a
candidate system to study the correlation between charge disproportion,
spin-flip, magnetovolume effects and Fermi surface nesting. This study provides
a novel explanation of strengthening effect of Cr observed in alloys due to its
unique magnetic properties. | 1911.05950v1 |
2019-11-27 | Enhancement of the electronic thermoelectric properties of bulk strained silicon-germanium alloys using the scattering relaxation times from first principles | We use first-principles electronic structure methods to calculate the
electronic thermoelectric properties (i.e. due to electronic transport only) of
single-crystalline bulk $n$-type silicon-germanium alloys vs Ge composition,
temperature, doping concentration and strain. We find excellent agreement to
available experiments for the resistivity, mobility and Seebeck coefficient.
These results are combined with the experimental lattice thermal conductivity
to calculate the thermoelectric figure of merit $ZT$, finding very good
agreement with experiment. We predict that 3% tensile hydrostatic strain
enhances the $n$-type $ZT$ by 50% at carrier concentrations of $n=10^{20}$
cm$^{-3}$ and temperature of $T=1200K$. These enhancements occur at different
alloy compositions due to different effects: at 50% Ge composition the
enhancements are achieved by a strain induced decrease in the Lorenz number,
while the power factor remains unchanged. These characteristics are important
for highly doped and high temperature materials, in which up to 50% of the heat
is carried by electrons. At 70% Ge the increase in $ZT$ is due to a large
increase in electrical conductivity produced by populating the high mobility
$\Gamma$ conduction band valley, lowered in energy by strain. | 1911.12149v1 |
2020-01-04 | Observation of spin-motive force in ferrimagnetic GdFeCo alloy films | Non-uniform magnetic structures produce emergent electromagnetic phenomena
such as the topological Hall effect and the spin-motive force (SMF). The
experimental reports on the SMF, however, are very few and the relationship
between the SMF and material parameters is still unclear. In this study, we
investigated the SMF in ferrimagnetic GdFeCo alloy films using the
spin-torque-induced ferromagnetic resonance method and clarified the
relationship. The amplitude of the detected SMF becomes larger than that of the
transition metal alloy FeCo by the Gd doping and reaches the maximum near a Gd
composition of the boundary between in-plane and perpendicularly magnetized
films. According to the analytical calculation, the enhancement is related to
the trajectory of the magnetization precession. Moreover, we find that the SMF
induced by the magnetic resonance is inversely proportional to the square of
the damping constant. | 2001.01042v2 |
2020-01-13 | Interactions between basal dislocations and $β_1'$ precipitates in Mg-4Zn alloy: mechanisms and strengthening | The mechanisms of dislocation/precipitate interaction as well as the critical
resolved shear stress were determined as a function of temperature in a Mg-4
wt. % Zn alloy by means of micropillar compression tests. It was found that the
mechanical properties were independent of the micropillar size when the
cross-section was $>$ 3 x 3 $\mu$m$^2$. Transmission electron microscopy showed
that deformation involved a mixture of dislocation bowing around the
precipitates and precipitate shearing. The initial yield strength was
compatible with the predictions of the Orowan model for dislocation bowing
around the precipitates. Nevertheless, precipitate shearing was dominant
afterwards, leading to the formation of slip bands in which the rod
precipitates were transformed into globular particles, limiting the strain
hardening. The importance of precipitate shearing increased with temperature
and was responsible for the reduction in the mechanical properties of the alloy
from 23C to 100C. | 2001.04380v1 |
2020-01-19 | Development of Interatomic Potential for Al-Tb Alloy by Deep Neural Network Learning Method | An interatomic potential for Al-Tb alloy around the composition of Al90Tb10
was developed using the deep neural network (DNN) learning method. The atomic
configurations and the corresponding total potential energies and forces on
each atom obtained from ab initio molecular dynamics (AIMD) simulations are
collected to train a DNN model to construct the interatomic potential for Al-Tb
alloy. We show the obtained DNN model can well reproduce the energies and
forces calculated by AIMD. Molecular dynamics (MD) simulations using the DNN
interatomic potential also accurately describe the structural properties of
Al90Tb10 liquid, such as the partial pair correlation functions (PPCFs) and the
bond angle distributions, in comparison with the results from AIMD.
Furthermore, the developed DNN interatomic potential predicts the formation
energies of crystalline phases of Al-Tb system with the accuracy comparable to
ab initio calculations. The structure factor of Al90Tb10 metallic glass
obtained by MD simulation using the developed DNN interatomic potential is also
in good agreement with the experimental X-ray diffraction data. | 2001.06762v3 |
2020-01-19 | Dephasing of Transverse Spin Current in Ferrimagnetic Alloys | It has been predicted that transverse spin current can propagate coherently
(without dephasing) over a long distance in antiferromagnetically ordered
metals. Here, we estimate the dephasing length of transverse spin current in
ferrimagnetic CoGd alloys by spin pumping measurements across the compensation
point. A modified drift-diffusion model, which accounts for spin-current
transmission through the ferrimagnet, reveals that the dephasing length is
about 4-5 times longer in nearly compensated CoGd than in ferromagnetic metals.
This finding suggests that antiferromagnetic order can mitigate spin dephasing
-- in a manner analogous to spin echo rephasing for nuclear and qubit spin
systems -- even in structurally disordered alloys at room temperature. We also
find evidence that transverse spin current interacts more strongly with the Co
sublattice than the Gd sublattice. Our results provide fundamental insights
into the interplay between spin current and antiferromagnetic order, which are
crucial for engineering spin torque effects in ferrimagnetic and
antiferromagnetic metals. | 2001.06918v5 |
2020-01-28 | First-principles calculation of electronic density of states and Seebeck coefficient in transition-metal-doped Si-Ge alloys | High $ZT$ value and large Seebeck coefficient have been reported in the
nanostructured Fe-doped Si-Ge alloys. In this work, the large Seebeck
coefficient in Fe-doped Si-Ge systems is qualitatively reproduced from the
computed electronic density of states, where a hybrid functional, HSE06, is
used for an exchange-correlation functional, as well as a special quasi-random
structure (SQS) for a disordered atomic configuration. Furthermore, by
replacing Fe with other transition metals, such as Mn, Co, Ni, Cu, Zn, and Au,
a better dopant that produces a larger Seebeck coefficient in Si-Ge alloy
systems is explored. | 2001.10191v1 |
2021-07-02 | Deformation mechanisms of Mg-Ca-Zn alloys studied by means of micropillar compression tests | The effect of Ca and Zn in solid solution on the critical resolved shear
stress (CRSS) of <a> basal slip, tensile twinning and <c+a> pyramidal slip in
Mg alloys has been measured through compression tests on single crystal
micropillars with different orientations. The solute atoms increased the CRSS
for basal slip to ~ 13.5 MPa, while the CRSS for pyramidal slip was lower than
85 MPa, reducing significantly the plastic anisotropy in comparison with pure
Mg. Moreover, the CRSSs for twin nucleation and growth were very similar (~ 37
MPa) and the large value of the CRSS for twin growth hindered the growth of
twins during thermo-mechanical processing. Finally, evidence of <a> prismatic
slip and cross-slip between basal and prismatic dislocations was found. It is
concluded that the reduction of plastic anisotropy, the activation of different
slip systems and cross-slip and the weak basal texture promoted by the large
CRSS for twin growth are responsible for the improved ductility and formability
of Mg-Ca-Zn alloys. | 2107.00878v1 |
2021-07-17 | Transition from high-entropy to conventional $(TiZrNbCu)_{1-x}Co_x$ metallic glasses | A new amorphous alloy system $(TiZrNbCu)_{1-x}Co_x$ covering a broad
composition range from the high-entropy (HEA) to Co rich alloys (x$\leqslant$
0.43) has been fabricated, characterized and investigated. A comprehensive
study of the chemical compositions, homogeneity, thermal stability, electronic
structure and magnetic and mechanical properties has been performed. All
properties change their variations with x within the HEA range. In particular,
the average atomic volume deviates from the Vegard's law for x$\ge 0.2$, where
also the average atomic packing fraction suddenly changes. The valence band
structure, studied with ultraviolet photoemission spectroscopy, shows a
split-band shape with 3d-states of Co approaching the Fermi level on increasing
x. Due to onset of magnetic correlations magnetic susceptibility rapidly
increases for x$\ge 0.25$. Very high microhardness increases rapidly with x.
The results are compared with those for similar binary and quinary metallic
glasses and with those for Cantor type of crystalline alloys. | 2107.08239v1 |
2021-07-24 | Electron-Phonon Scattering governs both Ultrafast and Precessional Magnetization Dynamics in Co-Fe Alloys | Recent investigations have advanced the understanding of how
structure-property relationships in ferromagnetic metal alloys affect the
magnetization dynamics on nanosecond time-scales. A similar understanding for
magnetization dynamics on femto- to pico-second time-scales does not yet exist.
To address this, we perform time-resolved magneto optic Kerr effect (TRMOKE)
measurements of magnetization dynamics in Co-Fe alloys on femto- to nano-second
regimes. We show that Co-Fe compositions that exhibit low Gilbert damping
parameters also feature prolonged ultrafast demagnetization upon
photoexcitation. We analyze our experimental TR-MOKE data with the
three-temperature-model (3TM) and the Landau-Lifshitz-Gilbert equation. These
analyses reveal a strong compositional dependence of the dynamics across all
time-scales on the strength of electron-phonon interactions. Our findings are
beneficial to the spintronics and magnonics community, and will aid in the
quest for energy-efficient magnetic storage applications. | 2107.11699v1 |
2017-04-04 | An ab initio based approach to optical properties of semiconductor heterostructures | A procedure is presented that combines density functional theory computations
of bulk semiconductor alloys with the semiconductor Bloch equations, in order
to achieve an ab initio based prediction of the optical properties of
semiconductor alloy heterostructures. The parameters of an eight-band
kp-Hamiltonian are fitted to the effective band structure of an appropriate
alloy. The envelope function approach is applied to model the quantum well
using the kp-wave functions and eigenvalues as starting point for calculating
the optical properties of the heterostructure. It is shown that Luttinger
parameters derived from band structures computed with the TB09 density
functional reproduce extrapolated values. The procedure is illustrated by
computing the absorption spectra for a (AlGa)As/Ga(AsP)/(AlGa)As quantum well
system with varying phosphide content in the active layer. | 1704.00983v1 |
2017-04-05 | Unifying first principle theoretical predictions and experimental measurements of size effects on thermal transport in SiGe alloys | In this work, we demonstrate the correspondence between first principle
calculations and experimental measurements of size effects on thermal transport
in SiGe alloys. Transient thermal grating (TTG) is used to measure the
effective thermal conductivity. The virtual crystal approximation under the
density functional theory (DFT) framework combined with impurity scattering is
used to determine the phonon properties for the exact alloy composition of the
measured samples. With these properties, classical size effects are calculated
for the experimental geometry of reflection mode TTG using the
recently-developed variational solution to the phonon Boltzmann transport
equation (BTE), which is verified against established Monte Carlo simulations.
We find agreement between theoretical predictions and experimental measurements
in the reduction of thermal conductivity (as much as $\sim$ 25\% of the bulk
value) across grating periods spanning one order of magnitude. This work
provides a framework for the tabletop study of size effects on thermal
transport. | 1704.01386v2 |
2017-04-25 | On the compressibility of the transition-metal carbides and nitrides alloys Zr_xNb_{1-x}C and Zr_xNb_{1-x}N | The 4d-transition-metals carbides (ZrC, NbC) and nitrides (ZrN, NbN) in the
rocksalt structure, as well as their ternary alloys, have been recently studied
by means of a first-principles full potential linearized augmented plane waves
method within the local density approximation. These materials are important
because of their interesting mechanical and physical properties, which make
them suitable for many technological applications. Here, by using a simple
theoretical model, we estimate the bulk moduli of their ternary alloys
Zr$_x$Nb$_{1-x}$C and Zr$_x$Nb$_{1-x}$N in terms of the bulk moduli of the end
members alone. The results are comparable to those deduced from the
first-principles calculations. | 1704.07587v1 |
2017-05-03 | Quaternary two-dimensional (2D) transition metal dichalcogenides (TMDs) with tunable bandgap | Alloying/doping in two-dimensional material has been important due to wide
range band gap tunability. Increasing the number of components would increase
the degree of freedom which can provide more flexibility in tuning the band gap
and also reduced the growth temperature. Here, we report synthesis of
quaternary alloys MoxW1-xS2ySe2(1-y) using chemical vapour deposition. The
composition of alloys has been tuned by changing the growth temperatures. As a
result, we can tune the bandgap which varies from 1.73 eV to 1.84 eV. The
detailed theoretical calculation supports the experimental observation and
shows a possibility of wide tunability of bandgap. | 1705.01245v1 |
2017-05-10 | Rigidity of branching microstructures in shape memory alloys | We analyze generic sequences for which the geometrically linear energy
\[E_\eta(u,\chi):= \eta^{-\frac{2}{3}}\int_{B_{0}(1)} \left| e(u)-
\sum_{i=1}^3 \chi_ie_i\right|^2 d x+\eta^\frac{1}{3} \sum_{i=1}^3
|D\chi_i|(B_{0}(1))\] remains bounded in the limit $\eta \to 0$. Here $ e(u)
:=1/2(Du + Du^T)$ is the (linearized) strain of the displacement $u$, the
strains $e_i$ correspond to the martensite strains of a shape memory alloy
undergoing cubic-to-tetragonal transformations and $\chi_i:B_{0}(1) \to
\{0,1\}$ is the partition into phases. In this regime it is known that in
addition to simple laminates also branched structures are possible, which if
austenite was present would enable the alloy to form habit planes.
In an ansatz-free manner we prove that the alignment of macroscopic
interfaces between martensite twins is as predicted by well-known rank-one
conditions. Our proof proceeds via the non-convex, non-discrete-valued
differential inclusion \[e(u) \in \bigcup_{1\leq i\neq j\leq 3}
\operatorname{conv} \{e_i,e_j\}\] satisfied by the weak limits of bounded
energy sequences and of which we classify all solutions. In particular, there
exist no convex integration solutions of the inclusion with complicated
geometric structures. | 1705.03664v2 |
2017-05-20 | The Spin-Orbit Torque from a Magnetic Heterostructure with High-Entropy Alloy | High-entropy alloy (HEA) is a family of metallic materials with nearly equal
partitions of five or more metals, which might possess mechanical and transport
properties that are different from conventional binary or tertiary alloys. In
this work, we demonstrate current-induced spin-orbit torque (SOT) magnetization
switching in a Ta-Nb-Hf-Zr-Ti HEA-based magnetic heterostructure with
perpendicular magnetic anisotropy (PMA). The maximum damping-like SOT
efficiency from this particular HEA-based magnetic heterostructure is further
determined to be $|\zeta^{\operatorname{HEA}}_{DL}|\approx0.033$ by hysteresis
loop shift measurements, while that for the Ta control sample is
$|\zeta^{\operatorname{Ta}}_{DL}|\approx0.04$. Our results indicate that
HEA-based magnetic heterostructures can serve as a new group of potential
candidates for SOT device applications. | 1705.07248v1 |
2018-06-24 | Ni-P coatings electroplating - A review, Part I: Pure Ni-P alloy | In the electroplating industry Ni-P coatings are extensively employed owing
to their excellent properties which enable substrate protection against
corrosion and wear. Depending on their composition and structure, as-plated
deposits demonstrate good mechanical, tribological and electrochemical
features, catalytic activity but also beneficial magnetic characteristics. With
subsequent thermal treatment hardness of Ni-P metal-metalloid system can
approach or be even higher than that of hard Cr coatings. The purpose of this
paper is to provide a general survey of the research work dealing with the
electrodeposition of Ni-P binary alloy coatings. Proposed phosphorus
incorporation mechanisms, Ni-P alloy microstructure before and after thermal
treatment, its mechanical, tribological, corrosion, catalytic and magnetic
properties are considered, so are the key process variables influencing
phosphorus content in the deposits and the roles of the main electrolytic bath
constituents. Findings on the merits of employing pulse plating and fabrication
of unconventional (layered and functionally graded) structures are succinctly
explored. | 1807.04693v1 |
2018-07-27 | Thermodynamics and kinetics of core-shell versus appendage co-precipitation morphologies: An example in the Fe-Cu-Mn-Ni-Si system | What determines precipitate morphologies in co-precipitating alloy systems?
We focus on alloys of two precipitating phases, with precipitates of the
fast-precipitating phase acting as heterogeneous nucleation sites for a second
phase manifesting slower kinetics. We study a FeCuMnNiSi alloy using the
combination of atom probe tomography and kinetic Monte Carlo simulations. It is
shown that the interplay between interfacial and ordering energies, plus active
diffusion paths, strongly affect the selection of core-shell verses appendage
morphologies. Specifically, the ordering energy reduction of the MnNiSi phase
heterogeneously nucleated on a pre-existing copper-rich precipitate exceeds the
energy penalty of a predominantly Fe/Cu interface, leading to initial
appendage, rather than core-shell, formation. Diffusion of Mn, Ni and Si around
and through the Cu core towards the ordered phase results in subsequent
appendage growth. We further show that in cases with higher primary precipitate
interface energies and/or suppressed ordering, the core-shell morphology is
favored. | 1807.10644v1 |
2018-07-31 | New room-temperature ferromagnet: B-added Pd0.75Mn0.25 alloy | Mn-based room-temperature ferromagnets attract considerable attention due to
their high ordered Mn moment. We have found that a Pd0.75Mn0.25 alloy with
added B (Pd0.75Mn0.25Bx) shows room-temperature soft ferromagnetism, whereas
the parent Pd0.75Mn0.25 alloy is a spin-glass system. The saturated Mn moment
at room temperature systematically increases to 2.68\muB/Mn as x increases to
0.125. The maximum Curie temperature of 390 K is also realized at an x of
0.125. The experimental results suggest a tunable soft ferromagnetism, which is
governed only by the boron concentration. Our results will pave the way in
chemical control of room-temperature bulk ferromagnetism in Mn compounds based
on the addition of an atom with a small atomic radius. | 1807.11640v1 |
2018-07-31 | Study of the solute clusters/enrichment at early stage of ageing in Mg-Zn-Gd alloys by atom probe tomography | The chemical enrichment/ordering of solute atoms in Mg matrix are crucial to
understand the formation mechanism of long-period stacking ordered (LPSO)
structures. In this study, three-dimensional distribution of solute elements in
an Mg-Zn-Gd alloy during ageing process is quantitatively characterized by
three-dimensional atom probe (3DAP) tomography. Based on the radius
distribution function, it is found that Zn-Gd solute pairs in Mg matrix appear
mainly in two peaks at early stage of ageing and the separation distance
between Zn and Gd atoms is well rationalized by the first-principles
calculation. Moreover, the fraction of Zn-Gd solute pairs increases first and
decreases subsequently due to the precipitation of LPSO structures. Moreover,
the composition of structural unit in LPSO structure and the solute enrichment
around it are quantified. It is found that Zn and Gd elements are synchronized
in the LPSO structure, and solute segregation of pure Zn or Gd is not observed
at the transformation front of the LPSO structure in this alloy. In addition,
the crystallography of transformation front is further determined by 3DAP data. | 1807.11791v1 |
2018-10-05 | Phase transitions in the binary-alloy Hubbard model: insight from strong-coupling perturbation theory | In the binary-alloy with composition A$_x$B$_{1-x}$ of two atoms with ionic
energy scales $\pm\Delta$, an apparent Ander- son insulator (AI) is obtained as
a result of randomness in the position of atoms. Using our recently developed
technique that combines the local self-energy from strong-coupling perturbation
theory with the transfer matrix method, we are able to address the problem of
adding a Hubbard $U$ to the binary alloy problem for millions of lattice sites
on the honeycomb lattice. By adding the Hubbard interaction $U$, the resulting
AI phase will become metallic which in our formulation can be clearly
attributed to the screening of disorder by Hubbard $U$. Upon further increase
in $U$, again the AI phase emerges which can be understood in terms of the
suppressed charge fluctuations due to residual Hubbard interaction of which the
randomness takes advantage and localizes the quasi-particles of the metallic
phase. The ultimate destiny of the system at very large $U$ is to become a Mott
insulator (MI). We construct the phase diagram of this model in the plane of
($U,\Delta$) for various compositions $x$. | 1810.02505v1 |
2018-10-12 | Breakdown of coherence in Kondo alloys: crucial role of concentration vs band filling | We study the low energy states of the Kondo alloy model (KAM) as function of
the magnetic impurity concentration per site, x, and the conduction electron
average site occupation, nc. In previous works, two different Fermi liquid
regimes had been identified at strong Kondo coupling JK, that may be separated
by a transition at x=nc. Here, we analyze the KAM for finite JK on a Bethe
lattice structure. First, using the mean-field coherent potential approximation
(DMFT-CPA) which is exact at lattice coordination Z=infty, we show that the
real part of the local potential scattering may be located outside the
conduction electron band, revealing a possible breakdown of Luttinger 'theorem'
for intermediate values of impurity concentration x. Unusual physical
signatures are expected, e.g., in ARPES experiments. In order to take into
account fluctuations associated with finite dimensionality,i.e., finite Z, we
extend this analyze by also studying the KAM with an adaptation of the
statistical-DMFT method that was developped elsewhere. We review the
distributions of local potential scattering and their evolution with model
parameters: concentration, strength of Kondo coupling, coordination number,
local site neighborhood, connection with percolation issue. Relevence for Kondo
alloys material with f-electrons is also discussed. | 1810.05383v1 |
2018-10-12 | First principles characterization of reversible martensitic transformations | Reversible martensitic transformations (MTs) are the origin of many
fascinating phenomena, including the famous shape memory effect. In this work,
we present a fully ab initio procedure to characterize MTs in alloys and to
assess their reversibility. Specifically, we employ ab initio molecular
dynamics data to parametrize a Landau expansion for the free energy of the MT.
This analytical expansion makes it possible to determine the stability of the
high- and low-temperature phases, to obtain the Ehrenfest order of the MT, and
to quantify its free energy barrier and latent heat. We apply our model to the
high-temperature shape memory alloy Ti-Ta, for which we observe remarkably
small values for the metastability region (the interval of temperatures in
which the high-and low-temperature phases are metastable) and for the barrier:
these small values are necessary conditions for the reversibility of MTs and
distinguish shape memory alloys from other materials. | 1810.05489v2 |
2018-10-15 | A structural modeling approach to solid solutions based on the similar atomic environment | Solid solution is an important way to enhance the structural and functional
performances of materials. In this work, we develop a structural modeling
approach to solid solutions based on the similar atomic environment (SAE). We
propose the similarity function associated with any type of atom cluster to
describe quantitatively the configurational deviation from the desired solid
solution structure that is fully disordered or contains short-range order
(SRO). In this manner, the structural modeling for solid solution is
transferred to a minimization problem in the configuration space. Moreover, we
pay efforts to enhance the practicality and functionality of this approach. The
approach and implementation are demonstrated by the cross-validations with the
special quasi-random structure (SQS) method. We apply the SAE method to the
typical quinary CoCrFeMnNi high-entropy alloy, continuous binary Ta-W alloy and
ternary CoCrNi medium-entropy alloy with SRO as prototypes. In combination with
ab initio calculations, we investigate the structural properties and compare
the calculation results with experiments. | 1810.06144v3 |
2018-10-25 | Impact of lattice relaxations on phase transitions in a high-entropy alloy studied by machine-learning potentials | Recently, high-entropy alloys (HEAs) have attracted wide attention due to
their extraordinary materials properties. A main challenge in identifying new
HEAs is the lack of efficient approaches for exploring their huge compositional
space. Ab initio calculations have emerged as a powerful approach that
complements experiment. However, for multicomponent alloys existing approaches
suffer from the chemical complexity involved. In this work we propose a method
for studying HEAs computationally. Our approach is based on the application of
machine-learning potentials based on ab initio data in combination with Monte
Carlo simulations. The high efficiency and performance of the approach are
demonstrated on the prototype bcc NbMoTaW HEA. The approach is employed to
study phase stability, phase transitions, and chemical short-range order. The
importance of including local relaxation effects is revealed: they
significantly stabilize single-phase formation of bcc NbMoTaW down to room
temperature. Finally, a so-far unknown mechanism that drives chemical order due
to atomic relaxation at ambient temperatures is discovered. | 1810.10820v2 |
2019-01-15 | Composition Susceptibility and the Role of One, Two and Three Body Interactions in Glass Forming Alloys: Cu$_{50}$Zr$_{50}$ vs Ni$_{50}$Al$_{50}$ | In this paper we compare the composition fluctuations and interaction
potentials of a good metallic glass former, Cu$_{50}$Zr$_{50}$, and a poor
glass former, Ni$_{50}$Al$_{50}$. The Bhatia-Thornton correlations functions
are calculated. Inspired by the observation of chemical ordering at the NiAl
surface, we derive a new property, R$_{cn}$( q ), corresponding to linear
susceptibility of concentration to a perturbation in density. We present a
direct comparison of the potentials for the two model alloys, using a 2nd order
density expansion, establish that the one body energy plays a crucial role in
stabilizing the crystal relative to the liquid in both alloys but that the
three body contribution to the heat of fusion is significantly larger in NiAl
that CuZr. | 1901.04664v1 |
2019-01-17 | Precipitation during high temperature aging of Al-Cu alloys: a multiscale analysis based on first principles calculations | Precipitation during high temperature aging of Al-Cu alloys is analyzed by
means of the integration of classical nucleation theory and phase-field
simulations into a multiscale modelling approach based on well-established
thermodynamics principles. In particular, thermal stability of ${\theta}''$,
${\theta}'$ and ${\theta}$ precipitates was assessed from first principles
calculations of the Helmholtz free energy while homogeneous and heterogeneous
nucleation of ${\theta}''$ and ${\theta}'$ was analysed using classical
nucleation theory. Precipitate growth was finally computed by means of
mesoscopic phase-field model. The model parameters that determine
quantitatively the driving forces for each transformation were obtained by
means of first principles calculations and computational thermodynamics. The
predictions of the models were in good agreement with experimental results and
provided a comprehensive understanding of the precipitation pathway in Al-Cu
alloys. It is envisaged that the strategy presented in this investigation can
be used in the future to design optimum microstructures based on the
information of the different energy contributions obtained from first
principles calculations. | 1901.05729v1 |
2019-01-18 | Origins of the transformability of Nickel-Titanium shape memory alloys | The near equiatomic NiTi alloy is the most successful shape memory alloy by a
large margin. It is widely and increasingly used in biomedical devices. Yet,
despite having a repeatable superelastic effect and excellent shape-memory,
NiTi is very far from satisfying the conditions that characterize the most
reversible phase transforming materials. Thus, the scientific reasons
underlying its vast success present an enigma. In this work, we perform
rigorous mathematical derivation and accurate DFT calculation of transformation
mechanisms to seek previously unrecognized twin-like defects that we term
involution domains, and we observe them in real space in NiTi by the
aberration-corrected scanning transmission electron microscopy. Involution
domains lead to an additional 216 compatible interfaces between phases in NiTi,
and we theorize that this feature contributes importantly to its reliability.
They are expected to arise in other transformations and to alter the
conventional interpretation of the mechanism of the martensitic transformation. | 1901.06332v2 |
2019-01-25 | icet - A Python library for constructing and sampling alloy cluster expansions | Alloy cluster expansions (CEs) provide an accurate and computationally
efficient mapping of the potential energy surface of multi-component systems
that enables comprehensive sampling of the many-dimensional configuration
space. Here, we introduce \textsc{icet}, a flexible, extensible, and
computationally efficient software package for the construction and sampling of
CEs. \textsc{icet} is largely written in Python for easy integration in
comprehensive workflows, including first-principles calculations for the
generation of reference data and machine learning libraries for training and
validation. The package enables training using a variety of linear regression
algorithms with and without regularization, Bayesian regression, feature
selection, and cross-validation. It also provides complementary functionality
for structure enumeration and mapping as well as data management and analysis.
Potential applications are illustrated by two examples, including the
computation of the phase diagram of a prototypical metallic alloy and the
analysis of chemical ordering in an inorganic semiconductor. | 1901.08790v1 |
2019-04-16 | Strengthening in multi-principal element alloys with local-chemical-order roughened dislocation pathways | High-entropy alloys (HEAs) were presumed to have a configurational entropy as
high as that of an ideally mixed solid solution (SS) of multiple elements in
near-equal proportions. However, enthalpic interactions inevitably render such
chemically disordered SSs rare and metastable, except at very high
temperatures. Here we highlight a structural feature that sets these
concentrated SSs apart from traditional solvent-solute ones: the HEAs possess a
wide variety of (local) chemical ordering (LCO). Our atomistic simulations
employing an empirical interatomic potential for NiCoCr reveal that the LCO of
the multi-principal-element SS changes conspicuously with alloy processing
conditions, producing a wide range of generalized planar fault energy in terms
of both its sample-average and spatial variation. We further demonstrate that
the LCO heightens the ruggedness of the energy landscape and raises activation
barriers governing dislocation activities. This not only influences the
selection of dislocation pathways in slip, faulting, twinning, and martensitic
transformation, but also increases the lattice friction to dislocation motion
via a new mechanism of nanoscale segment detrapping that elevates the
mechanical strength. All these open a vast playground not accessible to
ground-state SSs or intermetallics, offering rich opportunities to tune
properties. | 1904.07681v1 |
2019-07-04 | Sharing and Learning Alloy on the Web | We present Alloy4Fun, a web application that enables online editing and
sharing of Alloy models and instances, to be used mainly in an educational
context. By introducing the notion of secret paragraphs and commands in the
models, it also allows the distribution and automatic evaluation of simple
specification challenges, a useful mechanism that enables students to learn
relational logic at their own pace. Alloy4Fun stores all versions of shared and
analyzed models, as well as derivation trees that depict how those models
evolved over time: this wealth of information can be mined by researchers or
tutors to identify, for example, learning breakdowns in the class or typical
mistakes made by students and other Alloy users. A beta version of Alloy4Fun
was already used in two formal methods courses, and we present some results of
this preliminary evaluation. | 1907.02275v1 |
2019-07-09 | Alloy, Janus and core-shell nanoparticles: Numerical modeling of their nucleation and growth in physical synthesis | While alloy, core-shell and Janus binary nanoclusters are found in more and
more technological applications, their formation mechanisms are still poorly
understood, especially during synthesis methods involving physical approaches.
In this work, we employ a very simple model of such complex systems using
Lennard-Jones interactions and inert gas quenching. After demonstrating the
ability of the model to well reproduce the formation of alloy, core-shell or
Janus nanoparticles, we studied their temporal evolution from the gas via
droplets to nanocrystalline particles. In particular, we showed that the growth
mechanisms exhibit qualitative differences between these three chemical
orderings. Then, we determined how the quenching rate can be used to finely
tune structural characteristics of the final nanoparticles, including size,
shape and crystallinity. | 1907.04063v2 |
2019-07-23 | Electron transport in high-entropy alloys: Al$_{x}$CrFeCoNi as a case study | The high-entropy alloys Al$_{x}$CrFeCoNi exist over a broad range of Al
concentrations ($0 < x < 2$). With increasing Al content their structure is
changed from the fcc to bcc phase. We investigate the effect of such structural
changes on transport properties including the residual resistivity and the
anomalous Hall resistivity. We have performed a detailed comparison of the
first-principles simulations with available experimental data. We show that the
calculated residual resistivities for all studied alloy compositions are in a
fair agreement with available experimental data as concerns both the
resistivity values and concentration trends. We emphasize that a good agreement
with experiment was obtained also for the anomalous Hall resistivity. We have
completed study by estimation of the anisotropic magnetoresistance,
spin-disorder resistivity, and Gilbert damping. The obtained results prove that
the main scattering mechanism is due to the intrinsic chemical disorder whereas
the effect of spin polarization on the residual resistivity is appreciably
weaker. | 1907.09731v1 |
2019-07-28 | Strengthening of Al-Cu alloys by Guinier-Preston zones: predictions from atomistic simulations | A scale bridging strategy based in molecular statics and molecular dynamics
simulations in combination with transition state theory has been developed to
determine the flow stress of Al-Cu alloy containing Guinier-Preston zones. The
athermal contribution to the flow stress was determined from the Taylor model,
while the thermal contribution was obtained from the obstacle strength and the
free energy barrier. These two magnitudes were obtained by means of molecular
statics and molecular dynamics simulations of the interaction of edge
dislocations with Guinier-Preston zones in two different orientations. The
predictions of the model were compared with experimental data and were in
reasonable agreement, showing the potential of atomistic simulations in
combination with transition state theory to predict the flow stress of metallic
alloys strengthened with precipitates. | 1907.12053v1 |
2019-10-03 | Muon spin rotation and relaxation in Pr$_{1-x}$Nd$_x$Os$_4$Sb$_{12}$: superconductivity and magnetism in Pr-rich alloys | The Pr-rich end of the alloy series Pr$_{1-x}$Nd$_x$Os$_4$Sb$_{12}$ has been
studied using muon spin rotation and relaxation. The end compound
PrOs$_4$Sb$_{12}$ is an unconventional heavy-fermion superconductor, which
exhibits a spontaneous magnetic field in the superconducting phase associated
with broken time-reversal symmetry. No spontaneous field is observed in the
Nd-doped alloys for x $>$ 0.05. The superfluid density is insensitive to Nd
concentration, and no Nd$^{3+}$ static magnetism is found down to the lowest
temperatures of measurement. Together with the slow suppression of the
superconducting transition temperature with Nd doping, these results suggest
anomalously weak coupling between Nd spins and conduction-band states. | 1910.01757v1 |
2019-10-29 | Laser induced ultrafast 3d and 4f spin dynamics in CoDy ferrimagnetic alloys as a function of temperature | We report on an element- and time-resolved investigation of femtosecond laser
induced ultrafast dynamics of 3d and 4f spins in a ferrimagnetic Co80Dy20 alloy
as a function of temperature. We observe an increase of the Co3d characteristic
demagnetization time and a decrease of the Dy4f demagnetization time when the
temperature is approaching the Curie temperature. It suggests that the critical
slowing down regime, which affects the laser induced ultrafast dynamics in pure
3d transition metals and 4f rare-earth ferromagnetic layers, vanishes for the
Dy sublattice in the CoDy alloy, in line with the theoretical predictions of
the Landau-Lifshitz-Bloch model. | 1910.13143v2 |
2018-02-09 | Effect of Post Weld Heat Treatments on the Elevated Temperature Mechanical Properties of Ti6Al4V Friction Welds | The {\alpha}+\b{eta} titanium alloy (Ti6Al4V) has been successfully joined
using rotary friction welding. To investigate the influence of post weld heat
treatments on the microstructure and mechanical properties of the welds, the
weld joints were heat treated in {\alpha}+\b{eta} and \b{eta} regions, followed
by air cooling and furnace cooling. Subsequent to heat treatment, the specimens
were subjected to stress relieving treatment. The heat treatment temperatures
were selected keeping in view the beta transus temperature of the alloy.
Mechanical properties of the welds are evaluated in the as-welded and post weld
heat treated conditions at the working temperature of this alloy. The results
reported are an average of the values obtained from three tests carried out at
a given set of condition. Joints produced exhibited better mechanical
properties when compared to the parent metal. Coarse transgranular
microstructure and coarse grains in general exhibit better creep and stress
rupture properties, while finer microstructures exhibit better tensile
strengths | 1802.03363v1 |
2018-02-15 | Origin of spin reorientation transitions in antiferromagnetic MnPt-based alloys | Antiferromagnetic MnPt exhibits a spin reorientation transition (SRT) as a
function of temperature, and off-stoichiometric Mn-Pt alloys also display SRTs
as a function of concentration. The magnetocrystalline anisotropy in these
alloys is studied using first-principles calculations based on the coherent
potential approximation and the disordered local moment method. The anisotropy
is fairly small and sensitive to the variations in composition and temperature
due to the cancellation of large contributions from different parts of the
Brillouin zone. Concentration and temperature-driven SRTs are found in
reasonable agreement with experimental data. Contributions from specific
band-structure features are identified and used to explain the origin of the
SRTs. | 1802.05685v2 |
2018-02-19 | Strong enhancement of the spin Hall effect by spin fluctuations near the Curie point of FexPt1-x alloys | Robust spin Hall effects (SHE) have recently been observed in non-magnetic
heavy metal systems with strong spin-orbit interactions. These SHE are either
attributed to an intrinsic band-structure effect or to extrinsic spin-dependent
scattering from impurities, namely side-jump or skew scattering. Here we report
on an extraordinarily strong spin Hall effect, attributable to spin
fluctuations, in ferromagnetic FexPt1-x alloys near their Curie point, tunable
with x. This results in a damping-like spin-orbit torque being exerted on an
adjacent ferromagnetic layer that is strongly temperature dependent in this
transition region, with a peak value that indicates a lower bound 0.34 (+-)
0.02 for the peak spin Hall ratio within the FePt. We also observe a pronounced
peak in the effective spin-mixing conductance of the FM/FePt interface, and
determine the spin diffusion length in these FexPt1-x alloys. These results
establish new opportunities for fundamental studies of spin dynamics and
transport in ferromagnetic systems with strong spin fluctuations, and a new
pathway for efficiently generating strong spin currents for applications. | 1802.06911v1 |
2018-12-03 | Atomic-scale investigation of hydrogen distribution in a Ti-Mo alloy | Ingress of hydrogen is often linked to catastrophic failure of Ti-alloys.
Here, we quantify the hydrogen distribution in fully \b{eta} and
{\alpha}+\b{eta} Ti-Mo alloys by using atom probe tomography. Hydrogen does not
segregate at grain boundaries in the fully \b{eta} sample but segregates at
some {\alpha}/\b{eta} phase boundaries with a composition exceeding 20 at.% in
the {\alpha}+\b{eta} sample. No stable hydrides were observed in either sample.
The hydrogen concentration in \b{eta} phases linearly decreases from ~13 at. %
to ~4 at. % with increasing Mo-content, which is ascribed to the suppression of
hydrogen uptake by Mo addition. | 1812.00981v1 |
2018-12-21 | Ag-Au alloys BCS-like Superconductors? | Prompted by the recent report on the evidence for superconductivity at
ambient temperature and pressure in nanostructures of silver particles embedded
into a gold matrix [arXiv:1807.08572], we have exploited first principles
materials discovery approaches to predict superconductivity in the 3D bulk
crystals and 2D slabs of Ag-Au binary alloys at 1 atm pressure within the
phonon-mediated BCS-like pairing mechanism. In calculations, it turns out that,
the estimated superconducting transition temperatures of the ensued stable and
metastable Ag-Au alloys resulted in Tc as low as one mK. Whereas similar
calculations for the known superconducting intermetallic compounds consisting
of gold, Laves Au2Bi and A15 Nb3Au predict Tc =3.6 K and 10.1 K, respectively,
corroborate with experiments. And, the hitherto unknown silver analogues, Ag2Bi
and Nb3Ag are also found to be superconducting at 6.1 K and 10.8 K,
respectively. Furthermore, we show that, elemental Au in its metastable 9R, and
hcp phases superconduct at Tc =1 mK; but not Ag, in these hexagonal lattices. | 1812.09308v1 |
2019-02-06 | (Fe,Sn)4N alloy as a model spin-glass system with short-range competing interactions on a nonfrustrated simple cubic lattice | The origin of the spin-glass state in (Fe,Sn)4N alloys is studied on the
basis of a Heisenberg Hamiltonian with parameters derived from first principles
within the magnetic force theorem applied in the framework of the disordered
local moments method and local spin-density approximation. We show that in the
alloy concentration range where the spin-glass state is stable only one Fe
sublattice is intrinsically magnetic and the interatomic exchange magnetic
interactions are essentially short ranged due to effects of chemical and
magnetic disorder. The magnetic Fe atoms with well-localized spin moments are
randomly distributed over the nongeometrically frustrated simple cubic lattice.
The magnetic frustration, which generally is believed to be an essential
ingredient of the spin-glass state formation condition, may occur only due to
the competition of the two nearest-neighbor interactions. We thus argue that
(Fe,Sn)4N is a rare example of a spin-glass system where the mechanism of
spin-glass state formation might be studied in the framework of the minimal
random-site model on a simple cubic lattice with competing interactions, while
the effects of the geometrical frustration can be excluded. | 1902.02230v1 |
2019-01-29 | Automated Image Analysis and Contiguity Estimation for Liquid Phase Sintered Tungsten Heavy Alloys | In this study an automated software model using digital image processing
techniques is proposed for extracting the image characteristics and contiguity
of liquid phase sintered tungsten heavy alloys. The developed model takes a
typical image as input and processes it with no human intervention and provides
the corresponding image characteristics and contiguity value. The image
processing algorithm includes segmentation, binding point extraction, phase
connection, particle count and contiguity estimation stages. For the output,
microstructural parameters such as tungsten particle size, amount of tungsten
phase and contiguity are determined. The model is implemented by using 6
different scanning electron microscope images of liquid phase sintered
90W-7Ni-3Fe and 93W-4.9Ni-2.1Fe allloys. The results indicate that relative to
the manual measurements, the automated model can correctly estimate the
contiguity with an error in the vicinity of 5.6% - 2.9% for these two alloys.
The developed software can easily be adapted to be used for other
microstructures. It is also provided as open-source and available for other
researchers. | 1902.05382v1 |
2019-02-27 | Single-Phase High-Entropy Intermetallic Compounds (HEICs): Bridging High-Entropy Alloys and Ceramics | High-entropy intermetallic compounds (HEICs) were fabricated by mechanical
alloying and spark plasma sintering to fill a knowledge gap between the
traditional high-entropy alloys (HEAs) and emerging high-entropy ceramics
(HECs). Notably, several four- or five-component equimolar aluminides, such as
the B2-phase (Fe1/5Co1/5Ni1/5Mn1/5Cu1/5)Al, have been made into single-phase
HEICs for the first time. Thermodynamic modeling and a reversible,
temperature-dependent, phase-stability experiment suggest that such B2-phase
HEICs are entropy-stabilized phases. The structure of these HEICs resembles
that of HECs with high-entropy mixing of four or five elements of nearly equal
fractions in one and only one sublattice, but with significant (~10%) anti-site
defects (differing from typical HECs). A new phase stability rule for forming
single B2-phase HEICs is proposed. Five additional HEICs of predominantly D022
phases have also been made. This study broadens the families of equimolar,
single-phase, high-entropy materials that have been successfully fabricated. | 1902.10420v1 |
2019-06-04 | Estudio del crecimiento del Sn/Ag(111): explorando la posibilidad de formacion de estaneno | In recent years, 2D materials have attracted increasing attention from the
scientific community due to their superlative properties. The stanene, a
graphene like compound formed by Sn atoms, may have unique properties because
of the spin-orbit coupling SOC (such as the Quantum Spin Hall Effect QSH,
topological superconductivity, among others), that could eventually have
applications in spintronics and quantum computing. In the experiment stanene
epitaxial growth was explored by evaporating Sn onto a Ag(111) substrate.
Partial results using spectroscopic techniques such as LEED and XPS agreed with
literature. Regarding measurements made with UPS/ARPES, dispersion relations
were obtained for the surface state of the Sn/Ag(111) sample: for 1/3ML of Sn
they matched with the reported results for the surface alloy Ag$_2$Sn;
conversely, for (1/3+0,5)ML of Sn they mismatched with the reported parabolic
relation for the stanene, particularly, they were indistinguishable from the
surface alloy one. Probably, lack of formation of stanene was caused by an
excessive heating during the sample preparation process, that could have
produced an increase in the surface alloy Ag$_2$Sn thickness. | 1906.01159v1 |
2019-06-07 | Machine learning modeling of high entropy alloy: the role of short-range order | The development of machine learning sheds new light on the traditionally
complicated problem of thermodynamics in multicomponent alloys. Successful
application of such a method, however, strongly depends on the quality of the
data and model. Here we propose a scheme to improve the representativeness of
the data by utilizing the short-range order (SRO) parameters to survey the
configuration space. Using the improved data, a pair interaction model is
trained for the NbMoTaW high entropy alloy using linear regression. Benefiting
from the physics incorporated into the model, the learned effective Hamiltonian
demonstrates excellent predictability over the whole configuration space. By
including pair interactions within the 6th nearest-neighbor shell, this model
achieves an $R^2$ testing score of 0.997 and root mean square error of 0.43
meV. We further perform a detailed analysis on the effects of training data,
testing data, and model parameters. The results reveal the vital importance of
representative data and physical model. On the other hand, we also examined the
performance neural networks, which is found to demonstrate a strong tendency to
overfit the data. | 1906.02889v1 |
2019-06-10 | Exchange Splitting of a Hybrid Surface State and Ferromagnetic Order in a 2D Surface Alloy | Surface alloys are highly flexible materials for tailoring the spin-dependent
properties of surfaces. Here, we study the spin-dependent band structure of a
DyAg$_2$ surface alloy formed on an Ag(111) crystal. We find a significant
exchange spin-splitting of the localized Dy 4f states pointing to a
ferromagnetic coupling between the localized Dy moments at $40\,$K. The
magnetic coupling between these moments is mediated by an indirect, RKKY-like
exchange coupling via the spin-polarized electrons of the hole-like Dy-Ag
hybrid surface state. | 1906.03780v4 |
2019-06-26 | Concentration tuned tetragonal strain in alloys: application to magnetic anisotropy of FeNi$_{1-x}$Co$_x$ | We explore an opportunity to induce and control tetragonal distortion in
materials. The idea involves formation of a binary alloy from parent compounds
having body-centered and face-centered symmetries. The concept is illustrated
in the case of FeNi$_{1-x}$Co$_x$ magnetic alloy formed by substitutional
doping of the L1$_0$ FeNi magnet with Co. Using electronic structure
calculations we demonstrate that the tetragonal strain in this system can be
controlled by concentration and it reaches maximum for $x=0.5$. This finding is
then applied to create a large magnetocrystalline anisotropy (MAE) in
FeNi$_{1-x}$Co$_x$ system by considering an interplay of the tetragonal
distortion with electronic concentration and chemical anisotropy. In
particular, we identify a new ordered FeNi$_{0.5}$Co$_{0.5}$ system with MAE
larger by a factor 4.5 from the L1$_0$ FeNi magnet. | 1906.11329v1 |
2020-04-04 | Solute-Vacancy Clustering in Aluminum | We present an extensive first-principles database of solute-vacancy,
homoatomic, heteroatomic solute-solute, and solute-solute-vacancy binding
energies of relevant alloying elements in aluminum. We particularly focus on
the systems with major alloying elements in aluminum, i.e., Cu, Mg, and Si. We
consider physical factors such as solute size and formation energies of
intermetallic compounds to correlate with binding energies. Systematic studies
of the homoatomic solute-solute-vacancy and heteroatomic (Cu, Mg, or
Si)-solute-vacancy complexes reveal the overarching effect of the vacancy in
stabilizing solute-solute pairs. The computed binding energies of the
solute-solute-vacancy triplet successfully explain several experimental
observations that remained unexplained by the reported pair binding energies in
literature. The binding energy database presented here elucidates the
interaction between solute cluster and vacancy in aluminum, and it is expected
to provide insight into the design of advanced Al alloys with tailored
properties. | 2004.01931v2 |
2020-04-06 | Solute drag forces from equilibrium interface fluctuations | The design of polycrystalline alloys hinges on a predictive understanding of
the interaction between the diffusing solutes and the motion of the constituent
crystalline interfaces. Existing frameworks ignore the dynamic multiplicity of
and transitions between the interfacial structures and phases. Here, we develop
a computationally-accessible theoretical framework based on short-time
equilibrium fluctuations to extract the drag force exerted by the segregating
solute cloud. Using three distinct classes of computational techniques, we show
that the random walk of a solute-loaded interface is necessarily non-classical
at short time-scales as it occurs within a confining solute cloud. The much
slower stochastic evolution of the cloud allows us to approximate the
short-time behavior as an exponentially sub-diffusive Brownian motion in an
external trapping potential with a stiffness set by the average drag force. At
longer time-scales, the interfacial and bulk forces lead to a gradual recovery
of classical random walk of the interface with a diffusivity set by the
extrinsic mobility. The short-time response is accessible via {\it ab-initio}
computations, offering a firm foundation for high throughput, rational design
of alloys for controlling microstructural evolution in polycrystals, and in
particular for nanocrystalline alloys-by-design. | 2004.02394v1 |
2020-04-08 | Tunability of martensitic behavior through coherent nanoprecipitates and other nanostructures | Molecular dynamics simulations show that coherent precipitates can
significantly affect the properties of martensitic transformations in
Ni$_{63}$Al$_{37}$ alloys. The precipitates, consisting of non-martensitic
Ni$_{50}$Al$_{50}$, modify the free energy landscape that governs the phase
transformation and result in a significant reduction of the thermal hysteresis,
at comparably minor expense of transformation strain, and modification of
transformation temperatures. Importantly, this paper shows that free energy
landscape engineering is possible with nanostructures potentially accessible
through standard metallurgical processing routes. The atomistic-level
nucleation and transformation mechanisms within the nanoprecipitate systems are
explored and compared with epitaxial nanolaminates and nanowires. The
simulations reveal three distinct regimes of transformation mechanisms and
martensitic nanostructure as a function of volume fraction of the
non-martensitic phase. Free energy landscape engineering is generally
applicable and could contribute to the design of new shape memory alloys with
novel properties, such as light weight alloys that operate at room temperature. | 2004.04288v1 |
2020-04-14 | High-intensity pulsed ion beam treatment of amorphous iron-based metal alloy | Abstract The results of intense pulsed ion beam (IPIB) treatment of the soft
magnetic amorphous alloy of a FINEMET-type are presented. Foil produced from
the alloy was irradiated with short (about 100 ns) pulses of carbon ions and
protons with energy of up to 300 keV and an energy density of up to 7 J/cm2.
X-ray diffraction, M\"ossbauer spectroscopy and magnetic measurements were used
to investigate structural and magnetic properties of irradiated foils. It is
shown that the foil remains intact after the treatment, and the crystal
structure still amorphous. Spontaneous magnetization vector is found to lie
almost along perpendicular to the foil plane after irradiation, whereas for the
initial amorphous foil it belongs to the plane. The magnetic properties of the
foil undergo changes: the coercive force decreases, the saturation induction
increases slightly, and the magnetization curve has shallower slope. | 2004.06410v1 |
2020-04-23 | The role of 2s Bloch wave state excitations on STEM-HAADF intensity in quantitative analysis of alloys | In this work, we emphasize the important contribution of the 2s Bloch wave
state to the properties of a STEM electron probe propagating on an atomic
column. For a strong enough column potential, the confinement of the 2s state
leads to a long-period oscillation of the electron wave function, which is
reflected in the resulting STEM-HAADF intensity. We show how this influences
STEM composition quantification even at large thicknesses. We found
additionally that the excitation of the 2s state affects the intensity of
alloys where long-range order phenomena are present, which in turn provides a
way to probe the degree of order in alloys. | 2004.11191v1 |
2020-04-27 | Boron Liquid Metal Alloy Ion Sources For Special FIB Applications | Focused Ion Beam (FIB) processing has been established as a well-suited and
promising technique in R&D in nearly all fields of nanotechnology for
patterning and prototyping on the micro and nanometer scale and below. Among
other concepts, liquid metal alloy ion sources (LMAIS) are one of the
alternatives to conventional gallium beams to extend the FIB application field.
To meet the rising demand for light ions, different boron containing alloys
were investigated in this work. A promising solution was found in a Co31Nd64B5
based LMAIS which will be introduced in more detail. Besides cobalt as a
ferromagnetic element and the rare earth element neodymium, boron in particular
is of interest for special FIB applications like local p-type doping, for which
resolution of about 30 nm has been achieved so far. | 2004.12722v1 |
2020-05-03 | BAlN alloy for enhanced two-dimensional electron gas characteristics of GaN-based high electron mobility transistor | The emerging wide bandgap BAlN alloys have potentials for improved
III-nitride power devices including high electron mobility transistor (HEMT).
Yet few relevant studies have been carried. In this work, we have investigated
the use of the B0.14Al0.86N alloy as part or entirety of the interlayer between
the GaN buffer and the AlGaN barrier in the conventional GaN-based high
electron mobility transistor (HEMT). The numerical results show considerable
improvement of the two-dimensional electron gas (2DEG) concentration with small
2DEG leakage into the ternary layer by replacing the conventional AlN
interlayer by either the B0.14Al0.86N interlayer or the B0.14Al0.86N/AlN hybrid
interlayer. Consequently, the transfer characteristics can be improved. The
saturation current can be enhanced as well. For instance, the saturation
currents for HEMTs with the 0.5 nm B0.14Al0.86N/0.5 nm AlN hybrid interlayer
and the 1 nm B0.14Al0.86N interlayer are 5.8% and 2.2% higher than that for the
AlN interlayer when VGS-Vth= +3 V. | 2005.01161v1 |
2020-05-14 | The role of minor alloying in the plasticity of bulk metallic glasses | Micro- or minor alloying of metallic glasses is of technological interest. An
originally ductile Pd-based monolithic bulk metallic glass
(Pd$_{40}$Ni$_{40}$P$_{20}$) was selectively manipulated by additions of Fe or
Co. The alloying effects were extreme, showing either exceptional ductility
upon Co addition or immediate catastrophic failure upon Fe addition when tested
under uniaxial compression or 3-point bending. The amorphous structure was
characterized prior to deformation with respect to its medium-range order (MRO)
using variable resolution fluctuation electron microscopy (VR-FEM). We observe
striking differences in the MRO between the ductile and brittle metallic
glasses, with the ductile glasses exhibiting a rich structural diversity and
MRO correlation lengths up to 6 nm. The MRO heterogeneity seems to enable
easier shear banding and hence enhance the deformability. | 2005.06931v4 |
2020-05-15 | An analysis of the influence of the precipitate type on the mechanical behavior of Al-Cu alloys by means of micropillar compression tests | The influence of different types of precipitates (either Guinier-Preston
zones, $\theta''$ or $\theta'$) on the critical resolved shear stress and
strain hardening was determined by means of micropillar compression tests in an
Al - 4 wt. \% Cu alloy. The size, shape and volume fraction of the precipitates
were measured in each case. It was found that size effects were negligible for
micropillars with diameter $\ge$ 5 $\mu$m. Micropillars with Guinier-Preston
zones showed strain localization due to precipitate shearing. The best
mechanical properties were obtained with either a fine dispersion of the
$\theta''$ precipitates or a coarser dispersion of $\theta'$. Both precipitate
shearing and Orowan loops were observed around the $\theta''$ precipitates and
the micropillar strength was compatible with the predictions of the Orowan
model. In the case of the alloy with $\theta'$ precipitates, the strengthening
contribution associated with the transformation strain around the precipitates
has to be included in the model to explain the experimental results. Finally,
the micropillar compression tests in crystals with different orientations were
used to calibrate a phenomenological crystal plasticity. This information was
used to predict the mechanical properties of polycrystals by means of
computational homogeneization. | 2005.07426v1 |
2020-05-18 | Incorporating density jumps and species-conserving dynamics in XPFC binary alloys | This work presents a consistent formulation of the structural
phase-field-crystal model of substitutional binary alloys that allows for the
description phases of unequal densities, a key feature in solidification. We
further develop the dynamics of the model to be consistent with conserved
Langevine dynamics in the true governing species densities. Additionally, this
work expands on the ability to control pressure, so far only implemented in
pure materials, to binary alloys by improving the control system that controls
pressure from previous work. We study the equilibrium properties of the new
model, and demonstrate that control of pressure can drive various kinematic
microscopic processes in materials such as grain boundary pre-melting, phase
instability, and grain or inter-phase boundary motion. | 2005.09049v1 |
2020-08-03 | Intrinsic mechanism for anisotropic magnetoresistance and experimental confirmation in Co$_x$Fe$_{1-x}$ single-crystal films | Using first-principles transport calculations, we predict that the
anisotropic magnetoresistance (AMR) of single-crystal Co$_x$Fe$_{1-x}$ alloys
is strongly dependent on the current orientation and alloy concentration. An
intrinsic mechanism for AMR is found to arise from the band crossing due to
magnetization-dependent symmetry protection. These special $k$-points can be
shifted towards or away from the Fermi energy by varying the alloy composition
and hence the exchange splitting, thus allowing AMR tunability. The prediction
is confirmed by delicate transport measurements, which further reveal a
reciprocal relationship of the longitudinal and transverse resistivities along
different crystal axes. | 2008.00872v1 |
2020-08-25 | Phase behaviour of (Ti:Mo)S$_2$ binary alloys arising from electron-lattice coupling | While 2D materials attract considerable interests for their exotic electronic
and mechanical properties, their phase behaviour is still largely not
understood. This work focuses on (Mo:Ti)S$_2$ binary alloys which have captured
the interest of the tribology community for their good performance in solid
lubrication applications and whose chemistry and crystallography is still
debated. Using electronic structures calculations and statistical mechanics we
predict a phase-separating behaviour for the system and trace its origin to the
energetics of the $d$-band manifold due to crystal field splitting. Our
predicted solubility limits as a function of temperature are in accordance with
experimental data and demonstrate the utility of this protocol in understanding
and designing TMD alloys. | 2008.10927v1 |
2021-02-27 | Bounded Exhaustive Search of Alloy Specification Repairs | The rising popularity of declarative languages and the hard to debug nature
thereof have motivated the need for applicable, automated repair techniques for
such languages. However, despite significant advances in the program repair of
imperative languages, there is a dearth of repair techniques for declarative
languages. This paper presents BeAFix, an automated repair technique for faulty
models written in Alloy, a declarative language based on first-order relational
logic. BeAFix is backed with a novel strategy for bounded exhaustive, yet
scalable, exploration of the spaces of fix candidates and a formally rigorous,
sound pruning of such spaces. Moreover, different from the state-of-the-art in
Alloy automated repair, that relies on the availability of unit tests, BeAFix
does not require tests and can work with assertions that are naturally used in
formal declarative languages. Our experience with using BeAFix to repair
thousands of realworld faulty models, collected by other researchers,
corroborates its ability to effectively generate correct repairs and outperform
the state-of-the-art. | 2103.00327v1 |
2021-03-03 | On-lattice voxelated convolutional neural networks for prediction of phase diagrams and diffusion barriers in cubic alloys | Cluster expansion approximates an on-lattice potential with polynomial
regression. We show that using a convolutional neural network (CNN) instead
leads to more accurate prediction due to the depth of the network. We construct
our CNN potential directly on cubic lattice sites, representing voxels in a 3D
image, and refer to our method as the voxelated CNN (VCNN). The convolutional
layers automatically integrate interaction terms in the regressor; thus, no
explicit definition of clusters is required. As a model system, we combine our
VCNN potential with Monte Carlo simulations on a Ni$_{1-x}$Al$_x$ ($x$ < 30%)
and predict a disordered-to-ordered phase transition with less than 1 meV/atom
error. We also predict the energetic landscape of vacancy diffusion.
Classification of formation energy with respect to short-range-ordering of Al
alloys around a vacancy reveals that the ordering decreases the probability of
Ni diffusion. As the width of our input layer does not depend on the atomic
composition, VCNNs can be applied to study alloys with arbitrary numbers of
elements and empty lattice sites, without additional computational costs. | 2103.02638v1 |
2021-03-20 | Effect of ZrH2 particles on the microstructure and mechanical properties of IN718 manufactured by selective laser melting | The influence of Zr additions (in the form of ZrH2 particles) on the
microstructure and mechanical properties of IN718 Ni-based superalloy
manufactured by selective laser melting was explored. Fully dense alloys could
be obtained by careful selection of the processing parameters. The addition of
ZrH2 did not modify the microstructure of the alloy but introduced a dispersion
of Zr-rich globular particles of approximately 50 nm in diameter which
increased the strength of the as-printed material at ambient (23C) and high
temperature (550C). Heat treatments of solubilisation followed by aging led to
a fine dispersion of gamma" precipitates that controlled the strength of the
alloy, which was independent of the addition of Zr. Moreover, dynamic strain
ageing was found in the heat treated materials when deformed at 550C. Finally,
the strength of the IN718 deformed perpendicular to the building direction was
higher than that along the building direction, regardless of the heat treatment
and temperature. Computational homogenization simulations showed that the
anisotropy was associated with the strong texture. | 2103.11228v1 |
2021-03-26 | The Serrated-Flow Behavior in High-Entropy Alloys | This chapter presents a literature review of the serrated flow phenomenon in
high-entropy alloys (HEAs). The serrated flow is important as it can result in
permanent macroscopic and microstructural changes in HEAs. The literature
reveals several important findings regarding the effect of strain rate and test
temperature on the serrated flow. Furthermore, this chapter explores the
relationship among the composition, microstructure, testing condition, and
serration behavior. Towards the end of the chapter, a concise summary is
presented for the temperature, strain rate, mechanical-testing type
(compression/tension/nanoindentation), and serration type for HEAs. This
chapter also provides an overview of the different types of analytical methods
that have been successfully implemented to model and analyze the serration
behavior in HEAs. Such techniques include the mean-field theory (MFT)
formalism, complexity-analysis method, and multifractal technique. Finally,
future research topics in this area are presented, such as the effects of
twinning and irradiation on the serration behavior. | 2103.14504v1 |
2021-03-31 | Solid state phase transformation kinetics in Zr-base alloys | We present a kinetic model for solid state phase transformation
(alpha<-->beta) of common zirconium alloys used as fuel cladding material in
light water reactors. The model computes the relative amounts of beta or alpha
phase fraction as a function of time or temperature in the alloys. The model
accounts for the influence of excess oxygen (due to oxidation) and hydrogen
concentration (due to hydrogen pickup) on phase transformation kinetics. Two
variants of the model denoted by A and B are presented. Model A is suitable for
simulation of laboratory experiments in which the heating/cooling rate is
constant and is prescribed. Model B is more generic. We compare the results of
our model computations, for both A and B variants, with accessible experimental
data reported in the literature covering heating/cooling rates of up to 100
K/s. The results of our comparison are satisfactory, especially for model A.
Our model B is intended for implementation in fuel rod behavior computer
programs, applicable to a reactor accident situation, in which the Zr-based
fuel cladding may go through alpha<-->beta phase transformation. | 2103.17183v1 |
2022-02-19 | Short-range Atomic Topology of Ab initio Generated Amorphous PdSi Alloys | Since the pioneering efforts of Duwez and coworkers in 1965, when a solid
amorphous phase of Pd-Si ($a$-PdSi) was obtained in the vicinity of the
eutectic concentration, much work has been done. However, some points related
to the atomic structures remain to be systematized. In this work, 8 amorphous
Pd$_{100-c}$Si$_{c}$ alloys (c = 2.5, 5, 10, 13.34, 15, 17.5, 20, and 22 at %)
were generated by molecular dynamics $ab$ $initio$ simulations; the short-range
structure is analyzed using several correlation functions, like Pair
Distribution Functions, reduced Pair Distribution Functions, Plane Angle
Distribution Functions. Other related properties, like nearest-neighbors and
some Frank-Kasper polyhedra are reported. The generated samples correctly
reproduce the scarce experimental pair correlation functions that are reported
in the literature. An unexpected outcome is the appearance of structural
changes in the neighborhood of Pd$_{86.66}$Si$_{13.34}$, which may be related
to the magnetic changes reported in the liquid and amorphous Pd-Si alloys
previously reported. The explicit amorphous topologies are reported. | 2202.09532v2 |
2022-02-22 | Magnetic properties of equiatomic CrMnFeCoNi | Magnetic, specific heat, and structural properties of the equiatomic Cantor
alloy system are reported for temperatures between 5 kelvin and 300 kelvin, and
up to fields of 70 kilo-oersted. Magnetization measurements performed on
as-cast, annealed, and cold-worked samples reveal a strong processing history
dependence and that high-temperature annealing after cold-working does not
restore the alloy to a pristine state. Measurements on known precipitates show
that the two transitions, detected at 43 kelvin and 85 kelvin, are intrinsic to
the Cantor alloy and not the result of an impurity phase. Experimental and ab
initio density functional theory (DFT) computational results suggest that these
transitions are a weak ferrimagnetic transition and a spin-glass-like
transition, respectively, and magnetic and specific heat measurements provide
evidence of significant Stoner enhancement and electron-electron interactions
within the material. | 2202.11073v1 |
2022-02-24 | Predicting binding motifs of complex adsorbates using machine learning with a physics-inspired graph representation | Computational screening in heterogeneous catalysis relies increasingly on
machine learning models for predicting key input parameters due to the high
cost of computing these directly using first-principles methods. This becomes
especially relevant when considering complex materials spaces, e.g. alloys, or
complex reaction mechanisms with adsorbates that may exhibit bi- or
higher-dentate adsorption motifs. Here we present a data-efficient approach to
the prediction of binding motifs and associated adsorption enthalpies of
complex adsorbates at transition metals (TMs) and their alloys based on a
customized Wasserstein Weisfeiler-Lehman graph kernel and Gaussian Process
Regression. The model shows good predictive performance, not only for the
elemental TMs on which it was trained, but also for an alloy based on these
TMs. Furthermore, incorporation of minimal new training data allows for
predicting an out-of-domain TM. We believe the model may be useful in active
learning approaches, for which we present an ensemble uncertainty estimation
approach. | 2202.11866v2 |
2022-03-08 | Colloidal Synthesis of Nanoparticles: from Bimetallic to High Entropy Alloys | At the nanometric scale, the synthesis of a random alloy (i.e. without phase
segregation, whatever the composition) by chemical synthesis remains a not easy
task, even for simple binary type systems. In this context, a unique approach
based on the colloidal route is proposed enabling the synthesis of face-centred
cubic and monodisperse bimetallic, trimetallic, tetrametallic and pentametallic
nanoparticles with diameters around 5 nm as solid solutions. The Fe-Co-Ni-Pt-Ru
alloy and its subsets are considered which is a challenging task as each
element has fairly different physico-chemical properties. Nanoparticles are
prepared by temperature-assisted co-reduction of metal acetylacetonate
precursors in the presence of surfactants. It is highlighted how the
correlation between precursors' degradation temperatures and reduction
potentials values of the metal cations is the driving force to achieve a
homogenous distribution of all elements within the nanoparticles. | 2203.03945v1 |
2022-03-11 | Electrochemical 3D Printing of Ni-Mn and Ni-Co alloy with FluidFM | Additive manufacturing can realize almost any designed geometry, enabling the
fabrication of innovative products for advanced applications. Local
electrochemical plating is a powerful approach for additive manufacturing of
metal microstructures; however, previously reported data have been mostly
obtained with copper, and only a few cases have been reported with other
elements. In this study, we assessed the ability of fluidic force microscopy
(FluidFM) to produce Ni-Mn and Ni-Co alloy structures. Once the optimal
deposition potential window was determined, pillars with relatively smooth
surfaces were obtained. The printing process was characterized by printing
rates in the range of 50-60 nm/s. Cross-sections exposed by focused ion beam
showed highly dense microstructures, while the corresponding face scan with
energy-dispersive X-ray spectroscopy (EDX) spectra revealed a uniform
distribution of alloy components. | 2203.05885v1 |
2022-03-11 | Prediction of stable Li-Sn compounds: boosting ab initio searches with neural network potentials | The Li-Sn binary system has been the focus of extensive research because it
features Li-rich alloys with potential applications as battery anodes. Our
present re-examination of the binary system with a combination of machine
learning and ab initio methods has allowed us to screen a vast configuration
space and uncover a number of overlooked thermodynamically stable alloys. At
ambient pressure, our evolutionary searches identified a new stable Li$_3$Sn
phase with a large BCC-based hR48 structure and a possible high-T LiSn$_4$
ground state. By building a simple model for the observed and predicted Li-Sn
BCC alloys we constructed an even larger viable hR75 structure at an exotic
19:6 stoichiometry. At 20 GPa, new 11:2, 5:1, and 9:2 phases found with our
global searches destabilize previously proposed phases with high Li content.
The findings showcase the appreciable promise machine learning interatomic
potentials hold for accelerating ab initio prediction of complex materials. | 2203.06283v1 |
2022-03-14 | A bond counting model for accurate prediction of lattice parameter of bcc solid solution alloys | Lattice Parameter is an important material feature in High Entropy Alloy
(HEA) Design. Vegards Law is typically used to estimate lattice parameters but
is often inaccurate for metal alloys due to an inability to account for charge
transfer which can affect atomic volumes. The present study used ab initio
simulation to calculate bond lengths between atoms of dissimilar elements in B2
intermetallic compounds which was then combined with a bond counting model to
produce a model to estimate the lattice parameters of Refractory BCC HEAS. The
model was tested using a supercell method which modeled various random solid
solution HEAs. The proposed model produced lattice parameters with superior
accuracy to Vegards Law without the need for large DFT calculations or fitting
parameters. The proposed model had a root mean squared error (RMSE) of 0.006
Angstroms which is half that of Vegards Law RMSE (0.012 Angstrom). | 2203.07137v2 |
2016-03-29 | Static transport properties of random alloys: vertex corrections in conserving approximations | The theoretical formulation and numerical evaluation of the vertex
corrections in multiorbital techniques of theories of electronic properties of
random alloys are analyzed. It is shown that current approaches to static
transport properties within the so-called conserving approximations lead to the
inversion of a singular matrix as a direct consequence of the Ward identity
relating the vertex corrections to one-particle self-energies. We propose a
simple removal of the singularity for quantities (operators) with vanishing
average values for electron states at the Fermi energy, such as the velocity or
the spin torque; the proposed scheme is worked out in details in the
self-consistent Born approximation and the coherent potential approximation.
Applications involve calculations of the residual resistivity for various
random alloys, including spin-polarized and relativistic systems, treated on an
ab initio level, with particular attention paid to the role of different
symmetries (inversion of space and time). | 1603.08677v2 |
2017-02-20 | Impact of carrier localization on recombination in InGaN quantum wells and the efficiency of nitride light-emitting diodes: insights from theory and numerical simulations | We examine the effect of carrier localization due to random alloy
fluctuations on the radiative and Auger recombination rates in InGaN quantum
wells as a function of alloy composition, crystal orientation, carrier density,
and temperature. Our results show that alloy fluctuations reduce individual
transition matrix elements by the separate localization of electrons and holes,
but this effect is overcompensated by the additional transitions enabled by
translational symmetry breaking and the resulting lack of momentum
conservation. Hence, we find that localization increases both radiative and
Auger recombination rates, but that Auger recombination rates increase by one
order of magnitude more than radiative rates. Furthermore, we demonstrate that
localization has an overall detrimental effect on the efficiency-droop and
green-gap problems of InGaN LEDs. | 1702.06009v2 |
2017-06-12 | Determination of grain shape of laser-irradiated FePdCu thin alloy films | The irradiation with the 10 ns pulsed infrared Nd:YAG laser was applied to
transform FePdCu multilayers into chemically ordered L10 phase. The X-ray
diffraction methods (Theta/2Theta scan, psi-scan, omega-scan) were used to
trace the presence of L10 phase after laser annealing with different number of
pulses. The size and shape of crystallites was determined depending on their
orientation with respect to film plane. The (111) oriented crystallites of
constituent metals were built as coherent domains spreading through multilayers
during deposition of films. Laser annealing induced the transformation of
multilayers to alloy, and the ordering of (111) oriented crystallites.
Simultaneously, the (002) oriented crystallites appeared confirming the
transformation to L10 alloy. | 1706.03593v1 |
2017-06-23 | High aspect ratio metal microcasting by hot embossing for X-ray optics fabrication | Metal microstructured optical elements for grating-based X-ray phase-contrast
interferometry were fabricated by using an innovative approach of microcasting:
hot embossing technology with low melting temperature (280{\deg}C) metal alloy
foils and silicon etched templates. A gold-tin alloy (80w%Au / 20w%Sn) was used
to cast micro-gratings with pitch sizes in the range of 2 to 20 micrometers and
depth of the structures up to 80 micrometers. The metal filling of the silicon
template strongly depends on the wetting properties of the liquid metal on the
groove surface. A thin metal wetting layer (20 nm of Ir or Au) was deposited
before the casting in order to turn the template surface into hydrophilic with
respect of the melted metal alloy. Temperature and pressure of the hot
embossing process were optimized for a complete filling of the cavities in a
low viscosity regime of the liquid metal, and for minimizing the shear force
that might damage the silicon structures for small pitch grating. The new
method has relevant advantages, such as being a low cost technique, fast and
easily scalable to large area fabrication. | 1706.07611v1 |
2017-06-28 | First-principles prediction of high-entropy-alloy stability | High entropy alloys (HEAs) are multicomponent compounds whose high
configurational entropy allows them to solidify into a single phase, with a
simple crystal lattice structure. Some HEA's exhibit desirable properties, such
as high specific strength, ductility, and corrosion resistance, while
challenging the scientist to make confident predictions in the face of multiple
competing phases. We demonstrate phase stability in the multicomponent alloy
system of Cr-Mo-Nb-V, for which some of its binary subsystems are subject to
phase separation and complex intermetallic-phase formation. Our
first-principles calculation of free energy predicts that the configurational
entropy stabilizes a single body-centered cubic (BCC) phase from T = 1,700K up
to melting, while precipitation of a complex intermetallic is favored at lower
temperatures. We form the compound experimentally and confirm that it forms as
a single BCC phase from the melt, but that it transforms reversibly at lower
temperatures. | 1706.09282v1 |
2018-04-26 | Superconductivity in equimolar Nb-Re-Hf-Zr-Ti high entropy alloy | Herein, we report the synthesis and detailed superconducting properties of a
new high entropy alloy superconductor with nominal composition
Nb$_{20}$Re$_{20}$Zr$_{20}$Hf$_{20}$Ti$_{20}$ using powder X-ray diffraction
(XRD), energy-dispersive X-ray spectroscopy (EDX), magnetization, transport,
and thermodynamic measurements. The room temperature powder XRD confirms that
the alloy is arranged on a simple body centered cubic crystal lattice with
lattice parameter a = 3.38 (1) $\text{\AA}$. EDX measurement yields an average
composition of Nb$_{21}$Re$_{16}$Zr$_{20}$Hf$_{23}$Ti$_{20}$ (in atomic $\%$).
Transport, magnetic and heat capacity measurements reveal that the material is
a type-II superconductor with the bulk superconducting transition at $T_{c}$ =
5.3 K, lower critical field $H_{c1}$(0) = 33 mT and upper critical field
$H_{c2}$(0) = 8.88 T. Low temperature specific heat measurement indicates that
the sample is a moderately coupled superconductor, and the electronic specific
heat data fits well with the single-gap BCS model. | 1804.10092v1 |
2019-03-19 | H-T Phase Diagram of Rare-Earth -- Transition Metal Alloy in the Vicinity of the Compensation Point | Anomalous hysteresis loops of ferrimagnetic amorphous alloys in high magnetic
field and in the vicinity of the compensation temperature have so far been
explained by sample inhomogeneities. We obtain H-T magnetic phase diagram for
ferrimagnetic GdFeCo alloy using a two-sublattice model in the paramagnetic
rare-earth ion approximation and taking into account rare-earth (Gd) magnetic
anisotropy. It is shown that if the magnetic anisotropy of the $f$-sublattice
is larger than that of the $d$-sublattice, the tricritical point can be at
higher temperature than the compensation point. The obtained phase diagram
explains the observed anomalous hysteresis loops as a result of high-field
magnetic phase transition, the order of which changes with temperature. It also
implies that in the vicinity of the magnetic compensation point the shape of
magnetic hysteresis loop is strongly temperature dependent. | 1903.07941v1 |
2019-05-09 | Alternative interdiffusion theory of many component alloys | We examine the interdiffusion in multicomponent systems using the approach
analogically to one developed earlier for description of interdiffusion in
binary alloys. This approach in opposite to traditional theory, takes into
consideration an active role of vacancies, equilibrium distribution of which is
not supposed. In this case, in equations for flux components there are
contributions conditioned by vacancy concentration gradient. As the vacancy
diffusion coefficient is much larger than those for the components, a
counteraction to this process will equalize the fluxes of components and,
consequently, hinder from increase of deviation of vacancy concentration from
the equilibrium one. If we substitute the expressions for fluxes in the
equation of a continuity then we have the system of diffusion equations for
components and vacancies. This system is solved and we have found a relation
between the interdiffusion coefficients and the corresponding tracer diffusion
coefficients. Interdiffusion coefficient equations sufficiently differ from
traditional one (Darken's approach). The analysis of the possible reasons of
sluggish diffusion in multicomponent alloys is carried out on the basis of the
derived equations for fluxes. | 1905.03402v1 |
2019-05-15 | Gas-induced segregation in Pt-Rh alloy nanoparticles observed by in-situ Bragg coherent diffraction imaging | Bimetallic catalysts can undergo segregation or redistribution of the metals
driven by oxidizing and reducing environments. Bragg coherent diffraction
imaging (BCDI) was used to relate displacement fields to compositional
distributions in crystalline Pt-Rh alloy nanoparticles. 3D images of internal
composition showed that the radial distribution of compositions reverses
partially between the surface shell and the core when gas flow changes between
O2 and H2. Our observation suggests that the elemental segregation of
nanoparticle catalysts should be highly active during heterogeneous catalysis
and can be a controlling factor in synthesis of electrocatalysts. In addition,
our study exemplifies applications of BCDI for in situ 3D imaging of internal
equilibrium compositions in other bimetallic alloy nanoparticles. | 1905.06271v1 |
2019-05-29 | Microstructure and corrosion evolution of additively manufactured aluminium alloy AA7075 as a function of ageing | Additively manufactured high strength aluminium alloy AA7075 was prepared
using selective laser melting. High strength aluminium alloys prepared by
selective laser melting have not been widely studied to date. The evolution of
microstructure and hardness, with the attendant corrosion, were investigated.
Additively manufactured AA7075 was investigated both in the as-produced
condition and as a function of artificial ageing. The microstructure of
specimens prepared was studied using electron microscopy. Production of AA7075
by selective laser melting generated a unique microstructure, which was altered
by solutionising and further altered by artificial ageing - resulting in
microstructures distinctive to that of wrought AA7075-T6. The electrochemical
response of additively manufactured AA7075 was dependent on processing history,
and unique to wrought AA7075-T6, whereby dissolution rates were generally lower
for additively manufactured AA7075. Furthermore, immersion exposure testing
followed by microscopy, indicated different corrosion morphology for additively
manufactured AA7075, whereby resultant pit size was notably smaller, in
contrast to wrought AA7075-T6. | 1905.12189v1 |
2019-08-01 | Rich diversity of crystallographic phase formation in 2D Rex:Mo1-xS2 (x< 0.5) alloy | We report on the observation of rich variety of crystallographic phase
formation in RexMo1-xS2 alloy for x < 0.5. For x < 0.23, no low dimensional
super-structural modulation is observed and inter-cation hybridization remains
discrete forming dimers to tetramers with increasing Re concentration. For x >
0.23, super-strutural modulaton is observed. Depending on the Re concentrations
(x = 0.23, 0.32, 0.38 and 0.45) and its distributions, various types of cation
hybridization results in rich variety of low dimensional super-structural
modulation as directly revealed by high resolution transmission electron
microscopy. These layered alloy system may be useful for various energy and
novel device applications. | 1908.00201v1 |
2019-08-20 | Comparing all-optical switching in synthetic-ferrimagnetic multilayers and alloys | We present an experimental and theoretical investigation of all-optical
switching by single femtosecond laser pulses. Our experimental results
demonstrate that, unlike rare earth-transition metal ferrimagnetic alloys,
Pt/Co/[Ni/Co]$_N$/Gd can be switched in the absence of a magnetization
compensation temperature, indicative for strikingly different switching
conditions. In order to understand the underlying mechanism, we model the
laser-induced magnetization dynamics in Co/Gd bilayers and GdCo alloys on an
equal footing, using an extension of the microscopic three-temperature model to
multiple magnetic sublattices and including exchange scattering. In agreement
with our experimental observations, the model shows that Co/Gd bilayers can be
switched for an arbitrary thickness of the Co layer, i.e, even far away from
compensating the total Co and Gd magnetic moment. We identify the switching
mechanism in Co/Gd bilayers as a front of reversed Co magnetization that
nucleates at the Co/Gd interface and propagates through the Co layer driven by
exchange scattering. | 1908.07292v2 |
2019-09-10 | Low temperature deformation of MoSi$_2$ and the effect of Ta, Nb and Al as alloying elements | Molybdenum disilicide (MoSi$_2$) is a very promising material for high
temperature structural applications due to its high melting point (2030
{\deg}C), low density, high thermal conductivity and good oxidation resistance.
However, MoSi$_2$ has limited ductility below 900 {\deg}C due to its
anisotropic plastic deformation behaviour and high critical resolved shear
stresses on particular slip systems. Nanoindentation of MoSi$_2$ microalloyed
with aluminium, niobium or tantalum showed that all alloying elements cause a
decrease in hardness. Analysis of surface slip lines indicated the activation
of the additional {1 1 0}<1 1 1> slip system in microalloyed MoSi$_2$, which is
not active below 300 {\deg}C in pure MoSi$_2$. This was confirmed by TEM
dislocation analysis of the indentation plastic zone. Further micropillar
compression experiments comparing pure MoSi$_2$ and the Ta-alloyed sample
enabled the determination of the critical resolved shear stresses of individual
slip systems even in the most brittle [0 0 1] crystal direction. | 1909.04707v1 |
2019-09-19 | Formation of a Te-Ag Honeycomb Alloy: A New Type of Two-Dimensional Material | Inspired by the unique properties of graphene, the focus in the literature is
now on investigations of various two-dimensional (2D) materials with the aim to
explore their properties for future applications. The group IV analogues of
graphene, i.e., silicene, germanene and stanene have been intensively studied
in recent years. However, their semi-metallic band structures hamper their use
in electronic applications. Hence, the synthesis of 2D materials with band gaps
of various sizes has attracted a large interest. Here, we report a successful
preparation of a 2D Te-Ag binary alloy with a honeycomb structure.
Angle-resolved photoelectron spectroscopy (ARPES) in combination with
first-principles calculations using density functional theory (DFT) confirmed
the formation of this binary alloy. The semiconducting property is verified by
the ARPES data and a direct gap of ~0.7 eV is predicted by the DFT
calculations. | 1909.09008v1 |
2019-12-05 | Cluster size effects in the magnetic properties of Fe$_p$-Al$_{q=1-p}$ alloys | A spin-1/2 Ising model, defined in the body centered cubic lattice, is used
to describe some of the thermodynamic properties of Fe$_p$-Al$_q$ alloys, with
$p+q=1$. The model assumes, besides the nearest-neighbor exchange coupling, the
existence of further next-nearest-neighbor superexchange interactions, where
the latter ones depend on the aluminum atoms cluster size. The Ising system so
considered is studied by employing Monte Carlo simulations, using a hybrid
algorithm consisting of one single-spin Metropolis move together with one
single-cluster Wolff algorithm allied, in addition, with single histograms
procedures and finite-size scaling techniques. Quite good fits to the
experimental results of the ordering critical temperature, as a function of Al
concentration in the range $0\le q<0.7$, are obtained and compared to more
recent theoretical approaches done on the same alloys. | 1912.02514v1 |
2019-12-11 | Verification of Short-Range Order and Its Impact on the Properties of the CrCoNi Medium Entropy Alloy | Traditional metallic alloys are mixtures of elements where the atoms of
minority species tend to distribute randomly if they are below their solubility
limit, or lead to the formation of secondary phases if they are above it.
Recently, the concept of medium/high entropy alloys (MEA/HEA) has expanded this
view, as these materials are single-phase solid solutions of generally
equiatomic mixtures of metallic elements that have been shown to display
enhanced mechanical properties. However, the question has remained as to how
random these solid solutions actually are, with the influence of chemical
short-range order (SRO) suggested in computational simulations but not seen
experimentally. Here we report the first direct observation of SRO in the
CrCoNi MEA using high resolution and energy-filtered transmission electron
microscopy. Increasing amounts of SRO give rise to both higher stacking fault
energy and hardness. These discoveries suggest that the degree of chemical
ordering at the nanometer scale can be tailored through thermomechanical
processing, providing a new avenue for tuning the mechanical properties of
MEA/HEAs. | 1912.05610v1 |
2019-12-23 | Vacancy-mediated complex phase selection in high entropy alloys | Phase selection in Ti-Zr-Hf-Al high-entropy alloys was investigated by
in-situ high-energy X$-$ray diffraction, single-crystal X$-$ray diffraction,
and density-functional theory based electronic-structure methods that address
disorder and vacancies, predicting formation enthalpy and chemical short-range
order (SRO). Samples with varying Al content were synthesized, characterized,
and computationally assessed to ascertain the composition-dependent phase
selection, as increased Al content often acts as a stabilizer of a
body-centered-cubic structure. Equiatomic TiZrHfAl was especially interesting
due to its observed bcc superstructure - a variant of $\gamma-$brass with 4
vacancies per cell (not 2 as in $\gamma-$brass). We highlight how vacancy
ordering mediates selection of this variant of $\gamma-$brass, which is driven
by vacancy-atom SRO that dramatically suppress all atomic SRO. As vacancies are
inherent in processing refractory systems, we expect that similar discoveries
await in other high entropy alloys or in revisiting older experimental data. | 1912.11083v2 |
2019-12-31 | Machine Learning the Effective Hamiltonian in High Entropy Alloys | The development of machine learning sheds new light on the problem of
statistical thermodynamics in multicomponent alloys. However, a data-driven
approach to construct the effective Hamiltonian requires sufficiently large
data sets, which is expensive to calculate with conventional density functional
theory (DFT). To solve this problem, we propose to use the atomic local energy
as the target variable, and harness the power of the linear-scaling DFT to
accelerate the data generating process. Using the large amounts of DFT data
sets, various complex models are devised and applied to learn the effective
Hamiltonians of a range of refractory high entropy alloys (HEAs). The testing
$R^2$ scores of the effective pair interaction model are higher than 0.99,
demonstrating that the pair interactions within the 6-th coordination shell
provide an excellent description of the atomic local energies for all the four
HEAs. This model is further improved by including nonlinear and multi-site
interactions. In particular, the deep neural networks (DNNs) built directly in
the local configuration space (therefore no hand-crafted features) are employed
to model the effective Hamiltonian. The results demonstrate that neural
networks are promising for the modeling of effective Hamiltonian due to its
excellent representation power. | 1912.13460v1 |
2020-02-13 | High-Field Magnetization and Magnetic Phase Diagram of Metamagnetic Shape Memory Alloys Ni50-xCoxMn31.5Ga18.5 (x = 9 and 9.7) | Magnetic phase diagrams of the metamagnetic shape memory alloys
Ni50-xCoxMn31.5Ga18.5 (x = 9 and 9.7) were produced from high-field
magnetization measurements up to 56 T. For both compounds, magnetic field
induced martensitic transformations are observed at various temperatures below
300 K. Hysteresis of the field-induced transformation shows unconventional
temperature dependence: it decreases with decreasing temperature after showing
a peak. Magnetic susceptibility measurement, microscopy, and X-ray diffraction
data suggest a model incorporating the magnetic anisotropy and Zeeman energy in
two variants, which qualitatively explains the thermal and the magnetic field
history dependence of the hysteresis in these alloys. | 2002.05303v1 |
2020-03-10 | Bandgap engineering in an epitaxial two-dimensional honeycomb Si$_{6-x}$Ge$_x$ alloy | In this Letter, we demonstrate that it is possible to form a two-dimensional
(2D) silicene-like Si$_5$Ge compound by replacing the Si atoms occupying on-top
sites in the planar-like structure of epitaxial silicene on ZrB$_2$(0001) by
deposited Ge atoms. For coverages below 1/6 ML, the Ge deposition gives rise to
a Si$_{6-x}$Ge$_{x}$ alloy (with $x$ between 0 and 1) in which the on-top sites
are randomly occupied by Si or Ge atoms. The progressive increase of the
valence band maximum with $x$ observed experimentally originates from a
selective charge transfer from Ge atoms to Si atoms. These achievements provide
evidence for the possibility of engineering the bandgap in 2D SiGe alloys in a
way that is similar for their bulk counterpart. | 2003.04612v2 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.