publicationDate stringlengths 1 2.79k | title stringlengths 1 36.5k ⌀ | abstract stringlengths 1 37.3k ⌀ | id stringlengths 9 47 |
|---|---|---|---|
2018-10-19 | Magnon properties of random alloys | We study magnon properties in terms of spin stiffness, Curie temperatures and
magnon spectrum of Fe-Ni, Co-Ni and Fe-Co random alloys using a combination of
electronic structure calculations and atomistic spin dynamics simulations.
Influence of the disorder are studied in detail by use of large supercells with
random atomic arrangement. It is found that disorder affects the magnon
spectrum in vastly different ways depending on the system. Specifically, it is
more pronounced in Fe-Ni alloys compared to Fe-Co alloys. In particular, the
magnon spectrum at room temperature in Permalloy (Fe$_{20}$Ni$_{80}$) is found
to be rather diffuse in a large energy interval while in Fe$_{75}$Co$_{25}$ it
forms sharp branches. Fe-Co alloys are very interesting from a technological
point of view due to the combination of large Curie temperatures and very low
calculated Gilbert damping of $\sim$0.0007 at room temperature for Co
concentrations around 20--30\%. | 1810.08487v1 |
2019-01-08 | Crystallographic relationships of T-/S-phase aggregates in an Al-Cu-Mg-Ag alloy | T-(Al20Cu2Mn3) phase dispersoids are important for limiting recovery and
controlling grain growth in Al-Cu alloys. However, these dispersoids can also
reduce precipitation hardening by acting as heterogeneous nucleation sites and
may lead to increased susceptibility towards pitting corrosion when
galvanically coupled with S-(Al2CuMg) phase precipitates. The interplay between
T- and S-phases is therefore important for understanding their effect on the
mechanical and electrochemical properties of Al-Cu-Mg alloys. Here, the
crystallographic relationships between the T-phase, S-phase, and surrounding Al
matrix were investigated in an Al-1.31Cu-1.14Mg-0.13Ag-0.10Fe-0.28Mn (at.%)
alloy by combining scanning precession electron diffraction with misorientation
analysis in 3-dimensional axis-angle space and correlated high-resolution
transmission electron microscopy. Orientation relationships are identified
between all three phases, revealing S-T orientation relationships for the first
time. Differences in S-Al orientation relationships for precipitates formed at
T-phase interfaces compared to their non-interfacial counterparts were also
identified. These insights provide a comprehensive assessment of the
crystallographic relationships in T-/S-phase aggregates, which may guide future
alloy design. | 1901.02266v1 |
2019-01-16 | Chemical Ordering and Crystal Nucleation at the Liquid Surface: A Comparison of $\rm{Cu}_{50}\rm{Zr}_{50}$ and $\rm{Ni}_{50}\rm{Al}_{50}$ Alloys | We study the influence of the liquid-vapor surface on the crystallization
kinetics of supercooled metal alloys. While a good glass former,
$\rm{Cu}_{50}\rm{Zr}_{50}$, shows no evidence of surface enhancement of
crystallization, $\rm{Ni}_{50}\rm{Al}_{50}$ exhibits an increased rate of
crystallization due to heterogeneous nucleation at the free liquid surface. The
difference in the compositional fluctuations at the interface is proposed as
the explanation of the distinction between the two alloys. Specifically, we
observe compositional ordering at the surface of $\rm{Ni}_{50}\rm{Al}_{50}$
while the $\rm{Cu}_{50}\rm{Zr}_{50}$ alloy only exhibits a diffuse adsorption
of the Cu at the interface. We argue that the general difference in composition
susceptibilities at planar surfaces represents an important factor in
understanding the difference in the glass forming ability of the two alloys. | 1901.05160v1 |
2019-01-29 | Disorder-Induced Weyl Semimetal Phase and Sequential Band Inversions in PbSe-SnSe Alloys | The search for topological systems has recently broadened to include random
substitutional alloys, which lack the specific crystalline symmetries that
protect topological phases, raising the question whether topological properties
can be preserved, or are modified by disorder. To address this question, we
avoid methods that assumed at the outset high (averaged) symmetry, using
instead a fully-atomistic, topological description of alloy. Application to
PbSe-SnSe alloy reveals that topology survives in an interesting fashion: (a)
spatial randomness removes the valley degeneracy (splitting larger than 150
meV), leading to a sequential inversion of the split valley components over a
range of compositions; (b) absence of inversion lifts spin degenerates, leading
to a Weyl semimetal phase without the need of external magnetic field, an
unexpected result, given that the alloy constituent compounds are
inversion-symmetric. (a) and (b) underpin the topological physics at low
symmetry and complete the missing understanding of possible topological phases
within the normal-topological insulator transition. | 1901.10575v2 |
2019-04-18 | High Entropy Alloys Mined From Phase Diagrams | High entropy alloys (HEA) show promise as a new type of high-performance
structural material. Their vast degrees of freedom provide for extensive
opportunities to design alloys with tailored properties. However, the
compositional complexities of HEAs present great challenges for alloy design.
Current approaches have shown limited reliability in accounting for the
compositional regions of single solid solution and composite phases. We present
a phenomenological method, analyzing binary phase diagrams to predict HEA phase
formation on the hypothesis that the structural stability of HEAs is encoded
within. Accordingly, we introduce a small number of phase-diagram inspired
parameters and employ machine learning to partition the formation region of
500+ reported HEA compositions. The model achieved a single phase HEA
prediction rate >80 %. To validate our method, we demonstrated the capability
of this method in predicting HEA solid solution phases with and without
intermetallics in 30 randomly selected complex compositions, with a success
rate of 77 %. The presented efficient search approach with high predictive
capability can be exploited to complement computation-intense methods in
providing a powerful platform for the design of high entropy alloys. | 1904.08880v1 |
2019-04-19 | Epitaxial Stabilisation of ${\bf \mathrm{Ge_{1-x}Sn_x}}$ Alloys | The thermodynamic stability of germanium tin $\mathrm{Ge_{1-x}Sn_x}$ alloys
is investigated across the composition range $0 \le x \le 1$ by applying
density functional theory (DFT) together with the cluster expansion formalism
(CE). It is known that GeSn alloys are immiscible and that non-equilibrium
growth techniques are required to produce metastable films and nanostructures.
Insight into the driving forces behind component segregation is gained by
investigating the equilibrium thermodynamics of GeSn systems. The alloy free
energy of mixing is computed by combining enthalpies from CE with entropy terms
for configurational and vibrational degrees of freedom. Volume deformations due
to the large mismatch in ionic radii are readily found to be the key driving
force for immiscibility at all temperatures of relevance. This leads to a study
of epitaxial stabilisation by employing latticed matched substrates to favour
growth of alloys with fractional compositions of $\mathrm{x=0}$, approximately
$\mathrm{x=0.5}$ and $\mathrm{x=1}$. Reduction of the free energy of mixing due
to epitaxial strain in thin films is quantified for each substrate leading to
indicators for growth of kinetically stable films. | 1904.09147v4 |
2019-10-24 | GaSbBi alloys and heterostructures: fabrication and properties | Dilute bismuth (Bi) III-V alloys have recently attracted great attention, due
to their properties of band-gap reduction and spin-orbit splitting. The
incorporation of Bi into antimonide based III-V semiconductors is very
attractive for the development of new optoelectronic devices working in the
mid-infrared range (2-5 $\mu$m). However, due to its large size, Bi does not
readily incorporate into III-V alloys and the epitaxy of III-V dilute bismides
is thus very challenging. This book chapter presents the most recent
developments in the epitaxy and characterization of GaSbBi alloys and
heterostructures. | 1910.11210v1 |
2018-02-01 | Topological Weyl semimetals in $\rm Bi$$_{1-x}$$\rm Sb$$_{x}$ alloys | We have investigated the Weyl semimetal (WSM) phases in bismuth antimony
($\rm Bi$$_{1-x}$$\rm Sb$$_{x}$) alloys by the combination of atomic
composition and arrangement. Via first principles calculations, we have found
two WSM states with the Sb concentration of $x=0.5$ and $x=0.83$ with specific
inversion symmetry broken elemental arrangement. The Weyl points are close to
the Fermi level in both of these two WSM states. Therefore, it has a good
opportunity to obtain Weyl points in Bi-Sb alloy. The WSM phase provides a
reasonable explanation for the current transport study of BiSb alloy with the
violation of Ohm's law [Dongwoo Shin, et al., Nature Materials 16, 1096
(2017)]. This work shows that the topological phases in Bi-Sb alloys depend on
both elemental composition and their specific arrangement. | 1802.00288v1 |
2018-08-03 | Combined ab initio and empirical model of the thermal conductivity of uranium, uranium-zirconium, and uranium-molybdenum | In this work we developed a practical and general modeling approach for
thermal conductivity of metals and metal alloys that integrates ab initio and
semiempirical physics-based models to maximize the strengths of both
techniques. The approach supports creation of highly accurate, mechanistic, and
extensible thermal conductivity modeling of alloys. The model was demonstrated
on {\alpha}-U and U-rich U-Zr and U-Mo alloys, which are potential fuels for
advanced nuclear reactors. The safe use of U-based fuels requires quantitative
understanding of thermal transport characteristics of the fuel. The model
incorporated both phonon and electron contributions, displayed good agreement
with experimental data over a wide temperature range, and provided insight into
the different physical factors that govern the thermal conductivity under
different temperatures. This model is general enough to incorporate more
complex effects like additional alloying species, defects, transmutation
products, and noble gas bubbles to predict the behavior of complex metallic
alloys like U-alloy fuel systems under burnup. | 1808.01271v1 |
2018-12-10 | Microscopic Geometry Rules Ordering Tendency for Multicomponent Disordered Alloys | Short-range ordering (SRO) tendency for disordered alloys is considered as
competition between chemical ordering and geometric (mainly, difference in
atomic radius for constituents) effects. Especially for multicomponent
(including the so-called high entropy alloys (HEAs) near equiatomic
composition), it has been considered as difficult to systematically
characterize the SRO tendency only by geometric effects, due mainly to the fact
that (i) chemical effects typically plays significant role, (ii) near
equiatomic composition, we cannnot classify which elements belong to solute or
solvent, and (iii) underlying lattice for pure elements can typically differ
from each other. Despite these facts, we here show that SRO tendency for seven
fcc-based alloys including subsystems of Ni-based HEAs, can be well
characterized by geometric effects, where corresponding atomic radius is
defined based on atomic configuration with special fluctuation, measured from
ideally random structure. The present findings strongly indicate the
significant role of geometry in underlying lattice on SRO for multicomponent
alloys. | 1812.03690v1 |
2019-02-19 | Mixed structural face-centered cubic and body-centered cubic orders in near stoichiometric Fe2MnGa alloys | Magnetic and transport properties of near-stoichiometric metastable FexMnyGaz
alloys (46<x<52, 17<y25, 26<z<30) with face-centered cubic (FCC), body-centered
cubic (BCC), and two-phase (FCC+BCC) structures are investigated. The
experimental results are analyzed in terms of first-principles calculations of
stoichiometric Fe2MnGa alloy with the L21, L12, and the tetragonally distorted
L21 structural orderings. It is shown that the pure BCC and FCC phases have
distinct magnetic and transport properties. Two-phase Fe2MnGa alloys have
magnetic and transport properties typical of the mixed BCC and FCC phases.
Among the investigated alloys, Fe46Mn24Ga30 has a martensitic transformation
accompanied by significant changes in its magnetic and transport properties. | 1902.06968v1 |
2019-02-22 | Optical properties of Fe-Mn-Ga alloys | The first-principles calculations of the electronic structures and the
interband optical conductivity (OC) spectra have been performed for the
stoichiometric Fe$_{2}$MnGa alloy with L2$_{1}$ and L1$_{2}$ types of atomic
ordering. The calculated optical properties of Fe$_{2}$MnGa alloy for the
L2$_{1}$ and L1$_{2}$ phases are complemented by the experimental OC spectra
for bulk and thin film Fe-Mn-Ga alloy samples near the stoichiometry 2:1:1 with
L2$_{1}$ and L1$_{2}$ (for bulks) as well as the body-centered-cubic and
face-centered-cubic (for films) structures, respectively. A reasonable
agreement between experimental and calculated interband OC spectra was obtained
for both phases of the alloy. The experimental data show no significant
difference in the OC spectra with respect to the degrees of atomic and magnetic
orders of the samples. | 1902.08450v1 |
2019-02-26 | Au-Ge alloys for wide-range low-temperature on-chip thermometry | We present results of a Au-Ge alloy that is useful as a resistance-based
thermometer from room temperature down to at least \SI{0.2}{\kelvin}. Over a
wide range, the electrical resistivity of the alloy shows a logarithmic
temperature dependence, which simultaneously retains the sensitivity required
for practical thermometry while also maintaining a relatively modest and
easily-measurable value of resistivity. We characterize the sensitivity of the
alloy as a possible thermometer and show that it compares favorably to
commercially-available temperature sensors. We experimentally identify that the
characteristic logarithmic temperature dependence of the alloy stems from
Kondo-like behavior induced by the specific heat treatment it undergoes. | 1902.10111v2 |
2019-06-11 | Characterisation of Li in the surface film of a corrosion resistant Mg-Li(-Al-Y-Zr) alloy | The surface film formed upon Mg-Li(-Al-Y-Zr) following aqueous immersion and
air-exposure was investigated. This alloy (which contains 30.3 at. % Li)
possesses a bcc crystal structure and has been reported as being corrosion
resistant. It was determined that the principal components of the surface film
were Li2CO3 and Mg(OH)2 as characterised by grazing incidence X-ray diffraction
(GIXRD). The detection of hcp grains near the alloy surface was observed by
GIXRD and selected area electron diffraction (SAED). The spatial distribution
of Li and Mg in the surface film was characterised by electron energy loss
spectroscopy (EELS) and the distribution of other major elements in the alloy
was characterised by scanning transmission electron microscopy (STEM) and
energy dispersive X-ray spectroscopy (EDXS). It was observed that Li was
distributed throughout the alloy surface film and with an elevated
concentration in the so-called outer layer. | 1906.04508v1 |
2019-06-13 | Astra Version 1.0: Evaluating Translations from Alloy to SMT-LIB | We present a variety of translation options for converting Alloy to SMT-LIB
via Alloy's Kodkod interface. Our translations, which are implemented in a
library that we call Astra, are based on converting the set and relational
operations of Alloy into their equivalent in typed first-order logic (TFOL). We
investigate and compare the performance of an SMT solver for many translation
options. We compare using only one universal type to recovering Alloy type
information from the Kodkod representation and using multiple types in TFOL. We
compare a direct translation of the relations to predicates in TFOL to one
where we recover functions from their relational form in Kodkod and represent
these as functions in TFOL. We compare representations in TFOL with unbounded
scopes to ones with bounded scopes, either pre or post quantifier expansion.
Our results across all these dimensions provide directions for portfolio
solvers, modelling improvements, and optimizing SMT solvers. | 1906.05881v1 |
2019-06-15 | Effect of tungsten on vacancy behaviors in Ta-W alloys from first-principles | Alloying elements play an important role in the design of plasma facing
materials with good comprehensive properties. Based on first-principles
calculations, the stability of alloying element W and its interaction with
vacancy defects in Ta-W alloys are studied. The results show that W tends to
distribute dispersedly in Ta lattice, and is not likely to form precipitation
even with the coexistence of vacancy. The aggregation behaviors of W and
vacancy can be affected by their concentration competition. The increase of W
atoms has a negative effect on the vacancy clustering, as well as delays the
vacancy nucleation process, which is favorable to the recovery of point
defects. Our results are in consistent with the defect evolution observed in
irradiation experiments in Ta-W alloys. Our calculations suggest that Ta is a
potential repairing element that can be doped into Ta-based materials to
improve their radiation resistance. | 1906.06610v1 |
2020-04-08 | Benchmarking of spin-orbit torque switching efficiency in Pt alloys | We systematically survey on Pt$_{x}$Cu$_{1-x}$/Co/MgO magnetic
heterostructure with perpendicular magnetic anisotropy and report a significant
improvement on spin-orbit torque switching efficiency in Pt-Cu alloy system.
The largest damping-like spin-orbit torque efficiency determined by hysteresis
loop shift measurement is about 0.44 for Pt$_{0.57}$Cu$_{0.43}$, which is
originated from the higher resistivity tuned by alloying. Moreover, from the
results of current-induced switching measurements, a lower critical switching
current density is achieved by proper alloying due to the simultaneous
enhancement of spin-orbit torque efficiency and reduction of coercivity of the
Co layer. Finally, the ability to lower power consumption and preserve good
thermal stability using Pt$_{x}$Cu$_{1-x}$ alloy is demonstrated, which
suggests that Pt$_{x}$Cu$_{1-x}$ is an attractive candidate for future SOT-MRAM
applications. | 2004.03962v2 |
2020-04-11 | Coupling Physics in Machine Learning to Predict Properties of High-temperatures Alloys | High-temperature alloy design requires a concurrent consideration of multiple
mechanisms at different length scales. We propose a workflow that couples
highly relevant physics into machine learning (ML) to predict properties of
complex high-temperature alloys with an example of the 9-12 wt.% Cr steels
yield strength. We have incorporated synthetic alloy features that capture
microstructure and phase transformations into the dataset. Identified high
impact features that affect yield strength of 9Cr from correlation analysis
agree well with the generally accepted strengthening mechanism. As part of the
verification process, the consistency of sub-datasets has been extensively
evaluated with respect to temperature and then refined for the boundary
conditions of trained ML models. The predicted yield strength of 9Cr steels
using the ML models is in excellent agreement with experiments. The current
approach introduces physically meaningful constraints in interrogating the
trained ML models to predict properties of hypothetical alloys when applied to
data-driven materials. | 2004.05424v2 |
2020-05-07 | Detecting quadrupole: a hidden source of magnetic anisotropy for Manganese alloys | Mn-based alloys exhibit unique properties in the spintronics materials
possessing perpendicular magnetic anisotropy (PMA) beyond the Fe and Co-based
alloys. It is desired to figure out the quantum physics of PMA inherent to
Mn-based alloys, which have never been reported. Here, the origin of PMA in
ferrimagnetic Mn$_{3-{\delta}}$Ga ordered alloys is investigated to resolve
antiparallel-coupled Mn sites using x-ray magnetic circular and linear
dichroism (XMCD/XMLD) and a first-principles calculation. We found that the
contribution of orbital magnetic moments in PMA is small from XMCD and that the
finite quadrupole-like orbital distortion through spin-flipped electron hopping
is dominant from XMLD and theoretical calculations. These findings suggest that
the spin-flipped orbital quadrupole formations originate from the PMA in
Mn$_{3-{\delta}}$Ga and bring the paradigm shift in the researches of PMA
materials using x-ray magnetic spectroscopies. | 2005.03249v1 |
2020-05-10 | Glass formation in binary alloys with different atomic symmetries | Prediction of the glass forming ability (GFA) of alloys remains a major
challenge. We are not able to predict the composition dependence of the GFA of
even binary alloys. To investigate the effect of each element's propensity to
form particular crystal structures on glass formation, we focus on binary
alloys composed of elements with the same size, but different atomic symmetries
using the patchy-particle model. For mixtures with atomic symmetries that
promote different crystal structures, the minimum critical cooling rate $R_c$
is only a factor of $5$ lower than that for the pure substances. For mixtures
with different atomic symmetries that promote local crystalline and icosahedral
order, the minimum $R_c$ is more than $3$ orders of magnitude lower than that
for pure substances. Results for $R_c$ for the patchy-particle model are in
agreement with those from embedded atom method simulations and sputtering
experiments of NiCu, TiAl, and high entropy alloys. | 2005.04654v1 |
2020-05-20 | Automated Copper Alloy Grain Size Evaluation Using a Deep-learning CNN | Moog Inc. has automated the evaluation of copper (Cu) alloy grain size using
a deep-learning convolutional neural network (CNN). The proof-of-concept
automated image acquisition and batch-wise image processing offers the
potential for significantly reduced labor, improved accuracy of grain
evaluation, and decreased overall turnaround times for approving Cu alloy bar
stock for use in flight critical aircraft hardware. A classification accuracy
of 91.1% on individual sub-images of the Cu alloy coupons was achieved. Process
development included minimizing the variation in acquired image color,
brightness, and resolution to create a dataset with 12300 sub-images, and then
optimizing the CNN hyperparameters on this dataset using statistical design of
experiments (DoE).
Over the development of the automated Cu alloy grain size evaluation, a
degree of "explainability" in the artificial intelligence (XAI) output was
realized, based on the decomposition of the large raw images into many smaller
dataset sub-images, through the ability to explain the CNN ensemble image
output via inspection of the classification results from the individual smaller
sub-images. | 2005.09634v1 |
2020-05-29 | Mn-site doping and its effect on inverted hysteresis and thermomagnetic irreversibility behavior of antiferromagnetic Mn$_5$Si$_3$ alloy | The structural and magnetic behavior of Mn-site doped intermetallic manganese
silicide alloys of nominal compositions Mn$_{5-x}$A$_x$Si$_3$ ($x$ = 0.05, 0.1,
0.2 and A = Ni, Cr) have been investigated with a focus to the inverted
hysteresis behavior and thermomagnetic irreversibility. Room temperature x-ray
powder diffraction data confirm that all the doped alloys crystallize in
hexagonal $D8_8$ type structure with space group $P6_3/mcm$. The doped alloys
are found to show paramagnetic (PM) - collinear antiferromagnetic (AFM2) -
noncollinear antiferromagnetic (AFM1) transitions during cooling from room
temperature. A significant decrease in the critical values of both AFM1-AFM2
transition temperatures and fields have been observed with the increasing Ni/Cr
concentration. Inverted hysteresis loop, field-induced arrest, and
thermomagnetic arrest, the key features of the undoped Mn$_5$Si$_3$ alloy, are
found to be significantly affected by the Mn-site doping and eventually
vanishes with 4\% doping. | 2005.14368v1 |
2020-05-29 | Uncertainty Quantification and Composition Optimization for Alloy Additive Manufacturing Through a CALPHAD-based ICME Framework | During powder production, the pre-alloyed powder composition often deviates
from the target composition leading to undesirable properties of additive
manufacturing (AM) components. Therefore, we developed a method to perform
high-throughput calculation and uncertainty quantification by using a
CALPHAD-based ICME framework (CALPHAD: calculations of phase diagrams, ICME:
integrated computational materials engineering) to optimize the composition,
and took the high-strength low-alloy steel (HSLA) as a case study. We analyzed
the process-structure-property relationships for 450,000 compositions around
the nominal composition of HSLA-115. Properties that are critical for the
performance, such as yield strength, impact transition temperature, and
weldability, were evaluated to optimize the composition. With the same
uncertainty as the initial composition, an optimized average composition has
been determined, which increased the probability of achieving successful AM
builds by 44.7%. The present strategy is general and can be applied to other
alloy composition optimization to expand the choices of alloy for additive
manufacturing. Such a method also calls for high-quality CALPHAD databases and
predictive ICME models. | 2005.14371v2 |
2020-08-05 | Ab-initio based models for temperature-dependent magneto-chemical interplay in bcc Fe-Mn alloys | Body-centered cubic (bcc) Fe-Mn systems are known to exhibit a complex and
atypical magnetic behaviour from both experiments and 0 K electronic-structure
calculations, which is due to the half-filled 3d-band of Mn. We propose
effective interaction models for these alloys, which contain both atomic spin
and chemical variables. They were parameterized on a set of key density
functional theory (DFT) data, with the inclusion of non-collinear magnetic
configurations being indispensable. Two distinct approaches, namely a
knowledge-driven and a machine-learning approach have been employed for the
fitting. Employing these models in atomic Monte Carlo simulations enables the
prediction of magnetic and thermodynamic properties of the Fe-Mn alloys, and
their coupling, as functions of temperature. This includes the decrease of
Curie temperature with increasing Mn concentration, the temperature evolution
of the mixing enthalpy and its correlation with the alloy magnetization. Also,
going beyond the defect-free systems, we determined the binding free energy
between a vacancy and a Mn atom, which is a key parameter controlling the
atomic transport in Fe-Mn alloys. | 2008.02013v1 |
2021-03-01 | Phase field simulation of grain size effects in nanograined Ti-Nb shape memory alloys | Titanium-based shape memory alloys, such as Ti2448, have attracted enormous
attention owing to their unique thermomechanical properties and potential
biomedical applications. In this study, we develop a polycrystalline phase
field to investigate the grain size dependence of the martensitic
transformation and associated mechanical properties of nanograined Ti-Nb
alloys. It is shown that a reduction of the average grain size strengthens the
suppression of the martensitic transformation (MT), leading to an increase of
the transformation stress, shrinkage of the stress hysteresis, and elimination
of residual strain. The time-temperature-transformation curves of nano-grained
Ti-Nb alloys with different average grain sizes are obtained and the validity
of Hall-Petch relation is also confirmed in all studied grain sizes.
Furthermore, when the average grain size becomes ultrasmall, both the
temperature- and stress-induced MTs show the continuous second-order phase
transition behavior. These superior transformation characteristics are
attributed to the high density of grain boundaries and the related dominant
role of the gradient energy at the nanoscale. Our results have profound
implications for the design and control of the properties in nano-grained shape
memory alloys. | 2103.00954v1 |
2021-03-25 | Coexisting superconductivity and ferromagnetism in the (V$_{0.60}$Ti$_{0.40}$)-Gd alloys | We present here, the effect of microstructure on the magnetic, electrical and
thermal properties of (V$_{0.60}$Ti$_{0.40}$)-Gd alloys. The gadolinium is
found to be immiscible and precipitates with a size $<$1.2~$\mu$m in the
(V$_{0.60}$Ti$_{0.40}$)-Gd alloys. These precipitates enhance the grain
boundary density. The (V$_{0.60}$Ti$_{0.40}$)-Gd alloys become ferromagnetic
below $T_{mc}$ = 295~K with an increase in the superconducting transition
temperature ($T_{sc}$). Though the disorder increases with increasing Gd
content, the electronic thermal conductivity ($\kappa_{e} (H = 0)$) reduces by
at most 15\% which is in contrast with the 80\% decrease of the phononic
thermal conductivity ($\kappa_{l} (H = 0)$). Our analysis suggests that the
magnetic moments of Gd precipitates polarize the conduction electrons along and
around the grain boundaries leading to increase in the mean free path of the
electrons. The partial suppression of spin fluctuations in the
(V$_{0.60}$Ti$_{0.40}$)-Gd alloy by the conduction electron polarization
enhances the $T_{sc}$. | 2103.13601v1 |
2022-03-09 | Magnetochemical effects on phase stability and vacancy formation in fcc Fe-Ni alloys | We investigate phase stability and vacancy formation in fcc Fe-Ni alloys over
a broad composition-temperature range, via a density functional theory
parametrized effective interaction model, which includes explicitly spin and
chemical variables. On-lattice Monte Carlo simulations based on this model are
used to predict the temperature evolution of the magnetochemical phase. The
experimental composition-dependent Curie and chemical order-disorder transition
temperatures are successfully predicted. We point out a significant effect of
chemical and magnetic orders on the magnetic and chemical transitions,
respectively. The resulting phase diagram shows a magnetically driven phase
separation around 10-40% Ni and 570-700 K, between ferromagnetic and
paramagnetic solid solutions, in agreement with experimental observations. We
compute vacancy formation magnetic free energy as a function of temperature and
alloy composition. We identify opposite magnetic and chemical disordering
effects on vacancy formation in the alloys with 50% and 75% Ni. We find that
thermal magnetic effects on vacancy formation are much larger in concentrated
Fe-Ni alloys than in fcc Fe and Ni due to a stronger magnetic interaction. | 2203.04688v1 |
2022-03-29 | Absorption spectrum of doped highly mismatched alloys | Highly mismatched alloys (HMA's) are a class of semiconductor alloys with
large electronegativity differences between the alloying elements. We predict
the absorption spectrum due to transitions between the split bands of a doped
highly mismatched alloy with a conduction band anticrossing. We analyze the
joint densities of states for both direct and indirect transitions between the
split bands. The resulting spectrum has features that reveal the unusual state
distribution that is characteristic of HMAs, hence providing valuable insight
into their electronic structure. In particular, we predict a peak near the
absorption edge, which arises due to the suppression of direct transitions at
large momenta. We present analytic forms for the near-absorption-edge and
large-energy spectra, showing that they are qualitatively different from those
in standard parabolic semiconductors. In particular, as a result of suppressed
direct transitions, indirect transitions dominate the spectrum away from the
edge of absorption. | 2203.15528v1 |
2022-03-31 | Towards automated design of corrosion resistant alloy coatings with an autonomous scanning droplet cell | We present an autonomous scanning droplet cell platform designed for
on-demand alloy electrodeposition and real-time electrochemical
characterization for investigating the corrosion-resistance properties of
multicomponent alloys. Automation and machine learning are currently driving
rapid innovation in high throughput and autonomous materials design and
discovery. We present two alloy design case studies: one focusing on a
multi-objective corrosion resistant alloy optimization, and a case study
highlighting the complexity of the multimodal characterization needed to
provide insight into the underlying structural and chemical factors that drive
observed material behavior. This motivates a close coupling between autonomous
research platforms and scientific machine learning methodology that blends
mechanistic physical models and black box machine learning models. This
emerging research area presents new opportunities to accelerate materials
synthesis, evaluation, and hence discovery and design. | 2203.17049v1 |
2016-03-10 | Virtual crystal description of III-V semiconductor alloys in the tight binding approach | We propose a simple and effective approach to construct the empirical
tight-binding parameters of ternary alloys in the virtual crystal
approximation. This combines a new, compact formulation of the strain
parameters and a linear interpolation of the hamiltonians of binary materials
strained to the alloy equilibrium lattice parameter. We show that it is
possible to obtain a perfect description of the bandgap bowing of ternary
alloys in the InGaAsSb family of materials. Furthermore, this approach is in a
good agreement with supercell calculations using the same set of parameters.
This scheme opens a way for atomistic modeling of alloy-based opto-electronic
devices without extensive supercell calculations. | 1603.03227v1 |
2016-12-24 | Localization of electronic states in III-V semiconductor alloys: a comparative study | Electronic properties of III-V semiconductor alloys are examined using first
principles with the focus on the spatial localization of electronic states. We
compare localization at the band edges due to various isovalent impurities in a
host GaAs including its impact on the photoluminescence line widths and carrier
mobilities. The extremity of localization at the band edges is correlated with
the ability of individual elements to change the band gap and the relative band
alignment. Additionally, the formation energies of substitutional defects are
calculated and linked to challenges associated with the growth and formability
of alloys. A spectrally-resolved inverse participation ratio is used to map
localization in prospective GaAs-based materials alloyed with B, N, In, Sb, and
Bi for 1.55 $\mu$m wavelength telecommunication lasers. This analysis is
complemented by a band unfolding of the electronic structure and discussion of
implications of localization on the optical gain and Auger losses.
Correspondence with experimental data on broadening of the photoluminescence
spectrum and charge carrier mobilities show that the localization
characteristics can serve as a guideline for engineering of semiconductor
alloys. | 1612.08218v3 |
2017-02-14 | Computational engineering of sublattice ordering in a hexagonal AlHfScTiZr high entropy alloy | Multi-principle element alloys have enormous potential, but their exploration
suffers from the tremendously large range of configurations. In the last decade
such alloys have been designed with a focus on random solid solutions. Here we
apply an experimentally verified, combined thermodynamic and first-principles
design strategy to reverse the traditional approach and to generate a new type
of hcp Al-Hf-Sc-Ti-Zr high entropy alloy with a hitherto unique structure. A
phase diagram analysis narrows down the large compositional space to a
well-defined set of candidates. First-principles calculations demonstrate the
energetic preference of an ordered superstructure over the competing disordered
solid solutions. The chief ingredient is the Al concentration, which can be
tuned to achieve a D019 ordering of the hexagonal lattice. The computationally
designed D019 superstructure is experimentally confirmed by transmission
electron microscopy and X-ray studies. Our scheme enables the exploration of a
new class of high entropy alloys. | 1702.04038v1 |
2017-10-17 | Gas Eruption Phenomenon Happening from Ga-In Alloy in Electrolyte | We report a gas eruption phenomenon caused by electrolysis of liquid Ga-In
alloy in an electrolyte, especially NaOH solution. A volcanic eruption-like
blowout of gas occurred from the orifice on the alloy surface. In addition to
gas plume, large gas bubbles were also generated and the total gas yield
increased as In ratio was increased. It is found that destructiveness of the
passivation layer on the Ga-In alloy is critical to gas generation. The
mechanism of gas eruption can be ascribed to a galvanic interaction happens
owing to passivation film and alloy with different activity connected as
electrode in electrolyte. Further investigation demonstrated that the lattice
of the film expands because of the incorporation of indium, which brings about
the decrease in band gap and finally enhances more gas generation. These
findings regain the basic understanding of room temperature liquid metal inside
electrolyte. | 1710.08992v1 |
2018-04-17 | Asymmetrical precipitation on {10-12} twin boundary in magnesium alloy | Precipitation on deformation defects is essential for enhancing mechanical
properties of age-hardenable alloys. {10-12} twinning is common in deformed
alloys with hexagonal-close-packed structure. In this work, we revealed how
{10-12} twin boundary (TB) influences beta-Mg17Al12 precipitation in Mg-9Al-1Zn
alloy. The precipitates on the TB are rod-like, while others are lath-shape.
The precipitates hold the Burgers orientation relationship (OR) only with twin
or matrix, contrary to traditional wisdom in others alloys that precipitates on
TB symmetrically keep an OR with both twin and matrix. Moreover, certain
precipitate variants are absent, and a new rule for variant selection on TB is
proposed. | 1804.06134v1 |
2019-05-22 | Treating different bonding situations: Revisiting Au-Cu alloys using the random phase approximation | The ground state equilibrium properties of copper-gold alloys have been
explored with the state of art random phase approximation (RPA). Our estimated
lattice constants agree with the experiment within a mean absolute percentage
error (MAPE) of 1.4 percent. Semi-local functionals such as the generalized
gradient approximation (GGA) of Perdew, Burke, and Ernzerhof (PBE) and strongly
constrained and appropriately normed (SCAN) fail to provide accurate bulk
moduli, which indicate their inability to describe the system in a stretched or
compressed state with respect to the equilibrium geometry. We find that the
non-locality present in RPA is able to describe the transition between two
delocalized electron densities (bulk elemental constituents to crystallized
alloys), as required to provide accurate formation energies. Based on our
results, we conclude that it is difficult to find a universal density
functional which can give accurate results for a wide range of properties of
intermetallic alloys. However, RPA can capture different bonding situations,
often better than other density functionals. It gives accurate results for a
wide range of ground state properties for the alloys, generated from metals
with completely filled d-shells. | 1905.09348v2 |
2019-08-08 | Band structure of strained Ge$_{1-x}$Sn$_x$ alloy: a full-zone 30-band $k\cdot p$ model | We extend the previous 30-band $k$$\cdot$$p$ model effectively employed for
relaxed Ge$_{1-x}$Sn$_{x}$ alloy to the case of strained Ge$_{1-x}$Sn$_{x}$
alloy. The strain-relevant parameters for the 30-band $k$$\cdot$$p$ model are
obtained by using linear interpolation between the values of single crystal of
Ge and Sn that are from literatures and optimizations. We specially investigate
the dependence of band-gap at $L$-valley and $\Gamma$-valley with different Sn
composition under uniaxial and biaxial strain along [100], [110] and [111]
directions. The good agreement between our theoretical predictions and
experimental data validates the effectiveness of our model. Our 30-band
$k$$\cdot$$p$ model and relevant input parameters successfully applied to
relaxed and strained Ge$_{1-x}$Sn$_{x}$ alloy offers a powerful tool for the
optimization of sophisticated devices made from such alloy. | 1908.02958v1 |
2019-08-23 | Magnetic ordering of the martensite phase in Ni-Co-Mn-Sn-based ferromagnetic shape memory alloys | The magnetic state of low temperature martensite phase in Co-substituted
Ni-Mn-Sn-based ferromagnetic shape memory alloys (FSMAs) has been investigated,
in view of numerous conflicting reports of occurrences of spin glass (SG),
superparamagnetism (SPM) or long range anti-ferromagnetic (AF) ordering.
Combination of dc magnetization, ac susceptibility and small angle neutron
scattering (SANS) studies provide a clear evidence for AF order in martensitic
phase of Ni45Co5Mn38Sn12 alloy and rule out SPM and SG orders. Identical
studies on another alloy of close composition of Ni44Co6Mn40Sn10 point to
presence of SG order in martensitic phase and absence of SPM behavior, contrary
to earlier report. SANS results do show presence of nanometre-sized clusters
but they are found to grow in size from 3 nm at 30 K to 11 nm at 300 K, and do
not correlate with magnetism in these alloys. | 1908.08860v2 |
2020-03-04 | Magnetism in Rb$_{x}$Sr$_{1-x}$C novel alloy | We report a study on the electronic and magnetic properties of a novel
Rb$_{x}$Sr$_{1-x}$C alloy. We find that the variation of the lattice parameter
as function of Rb composition exhibits a deviation from the Vegard's law of
about 0.4 {\AA}. The total energy results predict a ferromagnetic ordering for
Sr-rich alloy, and antiferromagnetic ordering for RbC-rich alloy with a total
magnetic moment ranging from 2 to 3$\mu_\text{B}$ per cation. As for the parent
compounds, RbC and SrC, the origin of magnetism arises from the polarization of
the carbon $p$-orbitals. From the spin-polarized calculations, we note that the
half-metallicity in the Rb$_{x}$Sr$_{1-x}$C alloy is confirmed for $x<0.875$.
On the other hand, a direct band gap is observed in the semiconducting spin
part, in contrast to the pure parent compounds. | 2003.02047v1 |
2020-03-04 | Dislocation loops growth and radiation growth in neutron irradiated Zr-Nb alloys: rate theory modelling | A generalized model to study dislocation loops growth in irradiated binary
Zr-based alloys is presented. It takes into account temperature effects,
efficiencies of loops to absorb point defects dependent on the loop size, an
influence of locality of grain boundary sink strength, and concentration of the
alloying element. This model is used to describe the dynamics of loop radii
growth in zirconium-niobium alloys under neutron irradiation at reactor
conditions. A growth of both loop radii and strains is studied at different
grain sizes, location from grain boundaries, and concentration of niobium. It
is shown that locality of grain boundary sinks results in a non-uniform
deformation of the crystal inside the grains. Additionally, an introduction of
niobium as an alloying element decreases the loop radii but promotes the growth
of local strains inside the grains. | 2003.02060v1 |
2020-03-09 | New approach to model the yield strength of body centered cubic solid solution refractory high entropy alloys | A simple fitting approach is used for modeling the compressive yield strength
of body centered cubic (bcc) solid solution high entropy alloys in
Al-Hf-Nb-Mo-Ta-Ti-V-Zr system. It is proposed that the yield strength could be
modeled by a polynomial where the experimental data can be used for finding the
polynomial coefficients. The results show that the proposed polynomial could
model the yield strength of solid solution alloys relatively well. The
developed polynomial is used for predicting the strength of RHEAs in
Hf-Mo-Nb-Ta-Ti-V-Zr system. It is observed that the yield strength of alloys
within this system increases with the additions of Mo and Zr and decreases with
the addition of Ti. Furthermore, the model predicts that the yield strength
increases with increasing the value of parameters valence electron
concentration (VEC) and atomic size difference (ASD). Although the developed
polynomial does not consider the mechanisms involved in the strengthening of
alloys, it can be considered as a straightforward method for assessing the
strength of solid solution RHEAs. | 2003.04042v2 |
2020-07-01 | Trial of a search for a face-centered-cubic high-entropy alloy superconductor | With the aim of the discovery of face-centered-cubic (fcc) high-entropy alloy
(HEA) superconductor, we have carried out materials research on Nb or
Pb-containing multi-component alloys. Although the X-ray diffraction (XRD)
patterns of some Nb-containing samples exhibited the dominant fcc phases, no
superconducting signals were observed down to 3 K. Examination with an energy
dispersive X-ray spectrometer revealed that all samples were multi-phase, but
the existence of several new Nb-containing HEA phases was found in them. It was
confirmed that the synthesis of Pb-containing an HEA or quaternary alloy would
be difficult, probably due to the large differences in the crystal structure
and atomic radius among constituent elements, low reaction temperature and the
lack of a rapid cooling process in the synthesis. Despite the negative results
in this research, some hints for an improved strategy for the search for an fcc
HEA superconductor are provided. Moreover, our results are useful as
fundamental data for future HEA predictions or for studies of phase relations
in Nb or Pb-containing multi-component alloys based on the CALPHAD (calculation
of phase diagram) method. | 2007.00788v1 |
2020-07-25 | Microstructure evolution and densification during spark plasma sintering of nanocrystalline W-5wt.%Ta alloy | The present work reports the effect of Ta on densification and microstructure
evolution during non-isothermal and spark plasma sintering of nanocrystalline
W. Nanocrystalline W-5wt.%Ta alloy powder was synthesized using mechanical
alloying. The nanocrystalline powder was characterized thoroughly using X-ray
diffraction line profile analysis. Furthermore, the shrinkage behavior of
nanocrystalline powder was investigated during non-isothermal sintering using
dilatometry. Subsequently, the alloy powder was consolidated using spark plasma
sintering up to 1600 {\deg}C. The role of Ta on stabilizing the microstructure
during spark plasma sintering of nanocrystalline W was investigated in detail
using electron backscatter diffraction. The average grain size of spark plasma
sintered W-5wt.%Ta alloy was observed as 1.73 micron. | 2007.12947v1 |
2020-07-28 | A Novel Compact Si-B-N Barrier on Mg-Li Alloys via Plasma Treatment | Mg-Li alloys have attracted much attention due to their superior properties.
However, it is a great challenge to improve their inferior oxidation and
corrosion resistance. We report a novel Si-B-N ceramic film deposited on the
Mg-9.6Li alloy surface as an effective barrier against oxidation and corrosion.
The films were deposited by using plasma enhanced chemical vapor deposition
from a N2-B2H6-SiH4 gas mixtures, showing compact structure and adhesive
attachment to the alloy surface. The barrier revealed excellent protection
against oxidation in humid air for 500 days, and no observable changes were
found in immersion test of the 3.5 wt.% NaCl solution for 10 min. The superior
oxidation and corrosion resistance are attributed to the excellent material
property of Si-B-N coatings with compact structure via plasma treatment.
Moreover, it is found that moderate proportion of B_2 H_6 in the source gas
mixture is beneficial to the protection of alloys, where the hydrogen release
reaction nearly disappeared and no bubbles were generated on the surface in the
immersion test. | 2007.14170v1 |
2020-09-03 | Disorder broadening of even denominator fractional quantum Hall states in the presence of a short-range alloy potential | We study energy gaps of the $\nu=7/2$ and $\nu=5/2$ fractional quantum Hall
states in a series of two-dimensional electron gases containing alloy disorder.
We found that gaps at these two filling factors have the same suppression rate
with alloy disorder. The dimensionless intrinsic gaps in our alloy samples
obtained from the model proposed by Morf and d'Ambrumenil are consistent with
numerical results, but are larger than those obtained from experiments on
pristine samples published in the literature. The disorder broadening parameter
has large uncertainties. However, a modified analysis relying on shared
intrinsic gaps yields consistent results for both the $\nu=5/2$ and $7/2$
fractional quantum Hall states and establishes a linear relationship between
the disorder broadening parameter and alloy concentration. Furthermore, we find
that we can separate contributions to the disorder broadening of the long-range
and short-range scattering. | 2009.01873v1 |
2020-11-17 | Effect of surface mechanical treatment on the oxidation behavior of FeAl-model alloy | Fe based alloys are commonly used in almost every sector of human life. For
different reasons, the surfaces of the real parts are prepared using different
methods, e.g., mirror-like polishing, grit-blasting, etc. The purpose of the
present work is to answer the question how the surface preparation influences
the oxidation behavior of Fe-based alloys. To answer this question, a high
purity model alloy, Fe 5 wt Al, was isothermally oxidized in a
thermogravimetrical furnace. The post-exposure analysis included SEM/EDS (WDS)
and XRD. The surface roughness was determined by a contact and laser
profilometer. The obtained results demonstrate that the mechanical surface
preparation influences oxidation kinetics as well as the microstructure of the
oxide scale formed on the alloy at both studied temperatures. Namely, polishing
and grinding caused local formation of Fe-rich nodules and sub-layer of
protective Al2O3. In contrast, gritblasting leads to the formation of a thick
outer Fe-oxide and internal aluminum nitridation. A significant increase in the
oxidation rate of the material after gritblasting was attributed to grain
refinement in the near-surface region, resulting in an increase in easy
diffusion paths, namely grain boundaries. | 2011.08913v1 |
2020-12-27 | Microscopic origin of immiscibility and segregation in liquid binary alloys | Microscopic description in the study of immiscibility and segregating
properties of liquid metallic binary alloys has gained a renewed scientific and
technological interests during the last eight years for the physicists,
metallurgists and chemists. Especially, in understanding the basic mechanisms,
from the point of interionic interaction, and how and why segregation in some
metallic alloys takes place at and under certain thermodynamic state specified
by temperature and pressure. An overview of the theoretical and experimental
works done by different authors or groups in the area of segregation combining
electronic theory of metals, statistical mechanics and the perturbative
approach is presented in this review. Main attention in this review is focused
on the static effects such as the effects of energy of mixing, enthalpy of
mixing, entropy of mixing and understanding the critical behaviour of
segregation of alloys from the microscopic theoretical approach. Investigation
of segregating properties from the dynamic effects such as from the effects of
shear viscosity and diffusion coefficient is just becoming available. However,
we have restricted this review only on static effects and their variation of
impacts on different alloys. | 2012.13897v2 |
2021-02-07 | Multi-principal element grain boundaries: Stabilizing nanocrystalline grains with thick amorphous complexions | Amorphous complexions have recently been demonstrated to simultaneously
enhance the ductility and stability of certain nanocrystalline alloys. In this
study, three quinary alloys (Cu-Zr-Hf-Mo-Nb, Cu-Zr-Hf-Nb-Ti, and Cu-Zr-Hf-Mo-W)
are studied to test the hypothesis that increasing the chemical complexity of
the grain boundaries will result in thicker amorphous complexions and further
stabilize a nanocrystalline microstructure. Significant boundary segregation of
Zr, Nb, and Ti is observed in the Cu-Zr-Hf-Nb-Ti alloy, which creates a
quaternary interfacial composition that limits average grain size to 63 nm even
after 1 week at ~97% of the melting temperature. This high level of thermal
stability is attributed to the complex grain boundary chemistry and amorphous
structure resulting from multi-component segregation. High resolution
transmission electron microscopy reveals that the increased chemical complexity
of the grain boundary region in the Cu-Zr-Hf-Nb-Ti alloy results in an average
amorphous complexion thickness of 2.44 nm, approximately 44% and 32% thicker
than amorphous complexions previously observed in Cu-Zr and Cu-Zr-Hf alloys. | 2102.03925v3 |
2021-02-17 | Dislocation dynamics prediction of the strength of Al-Cu alloys containing shearable $θ''$ precipitates | The critical resolved shear stress of an Al 4 wt. \% Cu alloy containing a
homogeneous distribution of $\theta''$ precipitates was determined by means of
dislocation dynamics simulations. The size distribution, shape, orientation and
volume fraction of the precipitates in the alloy were obtained from
transmission electron microscopy observations while the parameters controlling
the dislocation/precipitate interactions (elastic mismatch, transformation
strains, dislocation mobility and cross-slip probability, etc.) were calculated
from atomistic simulations. The precipitates were assumed to be either
impenetrable or shearable by the dislocations, the latter characterized by a
threshold shear stress that has to be overcome to shear the precipitate. The
predictions of the simulations in terms of the critical resolved shear stress
and of the dislocation/precipitate interaction mechanisms were in good
agreement with the experimental results. It was concluded that the optimum
strength of this alloy is attained with a homogeneous distribution of
$\theta''$ precipitates whose average size ($\approx$ 40 nm) is at the
transition between precipitate shearing and looping. Overall, the dislocation
dynamics strategy presented in this paper is able to provide quantitative
predictions of precipitate strengthening in metallic alloys. | 2102.08875v1 |
2021-04-06 | Thermodynamics of vacancies in concentrated solid solutions: From dilute Ni-alloys to the Cantor system | The vacancy concentration at finite temperatures is studied for a series of
(CoCrFeMn)$_{1-x_\mathrm{Ni}}$Ni$_{x_\mathrm{Ni}}$ alloys by grand-canonical
Monte-Carlo (MC) simulations. The vacancy formation energies are calculated
from a classical interatomic potential and exhibit a distribution due to the
different chemical environments of the vacated sites. In dilute alloys, this
distribution features multiple discrete peaks, while concentrated alloys
exhibit an unimodal distribution as there are many different chemical
environments of similar vacancy formation energy. MC simulations using a
numerically efficient bond-counting model confirm that the vacancy
concentration even in concentrated alloys may be calculated by the established
Maxwell-Boltzmann equation weighted by the given distribution of formation
energies. We calculate the variation of vacancy concentration as function of Ni
content in the (CoCrFeMn)$_{x_\mathrm{Ni}}$Ni$_{1-x_\mathrm{Ni}}$ and prove the
excellent agreement of the thermodynamic model and the results from the
grand-canonical Monte-Carlo simulations. | 2104.02697v2 |
2021-06-07 | Modeling refractory high-entropy alloys with efficient machine-learned interatomic potentials: defects and segregation | We develop a fast and accurate machine-learned interatomic potential for the
Mo-Nb-Ta-V-W quinary system and use it to study segregation and defects in the
body-centred cubic refractory high-entropy alloy MoNbTaVW. In the bulk alloy,
we observe clear ordering of mainly Mo-Ta and V-W binaries at low temperatures.
In damaged crystals, our simulations reveal clear segregation of vanadium, the
smallest atom in the alloy, to compressed interstitial-rich regions like
radiation-induced dislocation loops. Vanadium also dominates the population of
single self-interstitial atoms. In contrast, due to its larger size and low
surface energy, niobium segregates to spacious regions like the inner surfaces
of voids. When annealing samples with supersaturated concentrations of defects,
we find that in complete contrast to W, interstitial atoms in MoNbTaVW cluster
to create only small ($\sim 1$ nm) experimentally invisible dislocation loops
enriched by vanadium. By comparison to W, we explain this by the reduced but
three-dimensional migration of interstitials, the immobility of dislocation
loops, and the increased mobility of vacancies in the high-entropy alloy, which
together promote defect recombination over clustering. | 2106.03369v2 |
2021-06-07 | Accelerated Corrosion of High Entropy Alloys under Tensile Stress | High entropy alloys are finding significant scientific interest due to their
exotic microstructures and exceptional properties resulting thereof. These
alloys have excellent corrosion resistance and may find broad range of
applications from bio-implants, aerospace components and nuclear industry. A
critical performance metric that determines the application worthiness of the
alloys is the resilience of stressed structural members in a corrosive
environment. This study reports the results from a novel experimental setup to
quantify the corrosion rate under uniaxial tensile stress in a single phase fcc
Al0.1CoCrFeNi high entropy alloy rods. Under a uniform uniaxial applied stress
of 600 MPa, the corrosion current density was observed to increase by three
orders of magnitude and ~150 mV drop in corrosion potential. The mechanism of
accelerated corrosion is identified as surface passivation layer breakdown, pit
initiation on un-passivated surface and rapid pit-propagation along the loading
direction. | 2106.03690v1 |
2021-06-17 | Emergence of near-boundary segregation zones in face-centered cubic multi-principal element alloys | Grain boundaries have been shown to dramatically influence the behavior of
relatively simple materials such as monatomic metals and binary alloys. The
increased chemical complexity associated with multi-principal element alloys is
hypothesized to lead to new grain boundary phenomena. To explore the
relationship between grain boundary structure and chemistry in these materials,
hybrid molecular dynamics/Monte Carlo simulations of a faceted {\Sigma}11 <110>
tilt boundary, chosen to sample both high- and low-energy boundary
configurations, are performed in face-centered cubic CrFeCoNiCu and CrFeCoNi
equiatomic alloys. Unexpected enrichment of Fe is discovered in the
face-centered cubic regions adjacent to the interface and found to be
correlated with a structurally-distinct region of reduced atomic volume.
Comparison with the boundary of the same type in monatomic Cu demonstrates that
altered near-boundary regions exist in simpler systems as well, with the
chemical complexity of the multi-principal element alloys highlighting its
existence and importance. | 2106.09492v3 |
2021-08-16 | Highly fcc-textured Pt-Al alloy films grown on MgO(001) showing enhanced spin Hall efficiency | We report on a systematic comparative study of the spin Hall efficiency
between highly face-centered cubic (fcc)-textured Pt-Al alloy films grown on
MgO(001) and poorly-crystallized Pt-Al alloy films grown on SiO$_2$. Using
CoFeB as the detector, we show that for Al compositions centering around $x =
25$, mainly L1$_{2}$ ordered Pt$_{100-x}$Al$_x$ alloy films grown on MgO
exhibit outstanding charge-spin conversion efficiency. For
Pt$_{78}$Al$_{22}$/CoFeB bilayer on MgO, we obtain damping-like spin Hall
efficiency as high as $\xi_\textrm{DL} \sim +0.20$ and expect up to seven-fold
reduction of power consumption compared to the polycrystalline bilayer of the
same Al composition on SiO$_2$. This work demonstrates that improving the
crystallinity of fcc Pt-based alloys is a crucial step for achieving large spin
Hall efficiency and low power consumption in this material class. | 2108.06927v1 |
2021-09-12 | Neural network based order parameter for phase transitions and its applications in high-entropy alloys | Phase transition is one of the most important phenomena in nature and plays a
central role in materials design. All phase transitions are characterized by
suitable order parameters, including the order-disorder phase transition.
However, finding a representative order parameter for complex systems is
nontrivial, such as for high-entropy alloys. Given variational autoencoder's
(VAE) strength of reducing high dimensional data into few principal components,
here we coin a new concept of "VAE order parameter". We propose that the
Manhattan distance in the VAE latent space can serve as a generic order
parameter for order-disorder phase transitions. The physical properties of the
order parameter are quantitatively interpreted and demonstrated by multiple
refractory high-entropy alloys. Assisted by it, a generally applicable alloy
design concept is proposed by mimicking the nature mixing of elements. Our
physically interpretable "VAE order parameter" lays the foundation for the
understanding of and alloy design by chemical ordering. | 2109.05598v1 |
2021-10-07 | A Modern-day Alchemy: Double Glow Plasma Surface Metallurgy Technology | In the long history of science and technology development, one goal is to
diffuse solid alloy elements into the surface of steel materials to form
surface alloys with excellent physical and chemical properties. On the basis of
plasma nitriding technology, double glow plasma surface metallurgy technology
has answered this challenge. This technology, which seems to be a modern-day
alchemy, can use any element in the periodic table of chemical elements,
including solid metal elements and their combinations, to form many types of
surface alloyed layers with high hardness, wear resistance, corrosion
resistance and high temperature oxidation resistance on various metal
materials. For examples, nickel base alloys, stainless steels and high speed
steels are formed on the surfaces of ordinary carbon steels; and high hardness,
wear resistance and high temperature oxidation resistance alloy are formed on
the surface of titanium alloy.This article briefly introduces the formation and
principle of double glow plasma surface metallurgy technology, and summarizes
the experimental results and industry application. The significance and
development prospect of this technology are discussed. | 2110.03236v1 |
2021-10-22 | REACH: Refining Alloy Scenarios by Scope | Writing declarative models has numerous benefits, ranging from automated
reasoning and correction of design-level properties be-fore systems are built,
to automated testing and debugging of their implementations after they are
built. Alloy is a declarative modeling language that is well suited for
verifying system designs. A key strength of Alloy is its scenario-finding
toolset, the Analyzer, which allows users to explore all valid scenarios that
adhere to the model's constraints up to a user-provided scope. In Alloy, it is
common for users to desire to first validate smaller scenarios, then once
confident, move onto validating larger scenarios. However, the Analyzer only
presents scenarios in the order they are discovered by the SAT solver. This
paper presents Reach, an extension to the Analyzer which allows users to
explore scenarios by size. Experimental results reveal Reach's enumeration
improves performance while having the added benefit of maintaining a
semi-sorted ordering of scenarios for the user. Moreover, we highlight Reach's
ability to improve the performance of Alloy's analysis when the user makes
incremental changes to the scope of the enumeration. | 2110.11898v1 |
2021-10-23 | Lead Free Alloyed Double Perovskites: An Emerging Class of Materials from Many-Body Perturbation Theory | The discovery of lead free all-inorganic alloyed double perovskites have
revolutionized photovoltaic research, showing promising light emitting
efficiency and its tunability. However, detailed studies regarding optical,
exciton, polaron and transport properties remain unexplored. Here, we report a
theoretical study on the variation of carrier-lattice interaction and
optoelectronic properties of pristine as well as alloyed Cs$_2$AgInCl$_6$
double perovskites. We have employed many-body perturbation theory
(G$_0$W$_0$@HSE06) and density functional perturbation theory (DFPT) to compute
exciton binding energy (E$_\textrm{B}$) and exciton lifetime of different
alloyed double perovskites. We find that phonon scattering limits
charge-carrier mobilities and thus, plays an important role in the development
of high-efficiency perovskite photovoltaics. In view of this, dominant
carrier-phonon scattering is observed via Fr\"{o}hlich mechanism near room
temperature. Moreover, we observe a noticeable increase in hole and electron
mobilities on alloying. We believe that our results will be helpful to gain a
better understanding of the optoelectronic properties and lattice dynamics of
these double perovskites. | 2110.12146v1 |
2021-12-16 | A Numerical Method for Sharp-Interface Simulations of Multicomponent Alloy Solidification | We present a computational method for the simulation of the solidification of
multicomponent alloys in the sharp-interface limit. Contrary to the case of
binary alloys where a fixed point iteration is adequate, we hereby propose a
Newton-type approach to solve the non-linear system of coupled PDEs arising
from the time discretization of the governing equations, allowing for the first
time sharp-interface simulations of the multialloy solidification. A
combination of spatially adaptive quadtree grids, Level-Set Method, and
sharp-interface numerical methods for imposing boundary conditions is used to
accurately and efficiently resolve the complex behavior of the solidification
front. The convergence behavior of the Newton-type iteration is theoretically
analyzed in a one-dimensional setting and further investigated numerically in
multiple spatial dimensions. We validate the overall computational method on
the case of axisymmetric radial solidification admitting an analytical solution
and show that the overall method's accuracy is close to second order. Finally,
we perform numerical experiments for the directional solidification of a
Co-Al-W ternary alloy with a phase diagram obtained from the PANDAT database
and analyze the solutal segregation dependence on the processing conditions and
alloy properties. | 2112.08650v2 |
2022-01-09 | Resistivity testing of palladium dilution limits in CoPd alloys for hydrogen storage | Palladium satisfies most of the requirements for an effective hydrogen
storage material with two major drawbacks: it has a relatively low gravimetric
hydrogen density and is prohibitively expensive for large-scale applications.
Pd-based alloys should be considered as possible alternatives to a pure Pd. The
question is how much one can dilute the Pd concentration in a variety of
candidate materials while preserving hydrogen absorption capability. We
demonstrate that the resistivity measurements of thin-film alloy samples can be
used for a qualitative high-throughput screening and study of the
hydrogen-absorbing properties over the entire range of palladium
concentrations. Contrary to palladium-rich alloys where additional hydrogen
scattering indicates a degree of hydrogen content, the diluted alloy films
respond by a decrease of resistance due to their thickness expansion. Evidence
of significant hydrogen absorption was found in thin CoPd films diluted to just
20% of Pd. | 2201.02974v1 |
2022-06-02 | Growth, characterization, and thermodynamics of III-nitride semiconductors | III-nitride alloys are wide band gap semiconductors with a broad range of
applications in optoelectronic devices such as light emitting diodes and laser
diodes. Indium gallium nitride light emitting diodes have been successfully
produced over the past decade. But the progress of green emission light
emitting devices has been limited by the incorporation of indium in the alloy,
mainly due to phase separation. This difficulty could be addressed by studying
the growth and thermodynamics of these alloys. Knowledge of thermodynamic phase
stabilities and of pressure - temperature - composition phase diagrams is
important for an understanding of the boundary conditions of a variety of
growth techniques. In this dissertation a study of the phase separation of
indium gallium nitride is conducted using a regular solution model of the
ternary alloy system. Graphs of Gibbs free energy of mixing were produced for a
range of temperatures. Binodal and spinodal decomposition curves show the
stable and unstable regions of the alloy in equilibrium. | 2206.01307v1 |
2022-07-15 | Effective Electronic Structure of Monoclinic $β-(Al_xGa_{1-x})_2O_3$ alloy semiconductor | In this article, the electronic band structure $\beta-(Al_xGa_{1-x})_2O_3$
alloy system is calculated with $\beta-Ga_2O_3$ as the bulk crystal. The
technique of band unfolding is implemented to obtain the effective
bandstructure \textit{(EBS)} for aluminium fractions varying between 12.5\% and
62.5\% with respect to the gallium atoms. A 160 atom supercell is used to model
the disordered system that is generated using the technique of special
quasirandom structures which mimics the site correlation of a truly random
alloy and reduces the configurational space that arises due to the vast
enumeration of alloy occupation sites. The impact of the disorder is then
evaluated on the electron effective mass and bandgap which is calculated under
the generalized gradient approximation \textit{(GGA)}. The EBS of disordered
systems gives an insight into the effect of the loss of translational symmetry
on the band topology which manifests as band broadening and can be used to
evaluate disorder induced scattering rates and electron lifetimes. This
technique of band unfolding can be further extended to alloy phonon dispersion
and subsequently phonon lifetimes can also be evaluated from the band
broadening. | 2207.07550v1 |
2022-07-20 | Construction and analysis of surface phase diagrams to describe segregation and dissolution behavior of Al and Ca in Mg alloys | Segregation and dissolution behavior of Mg alloyed with Ca and Al are studied
by performing density functional theory calculations considering an extensive
set of surface structures and compositions. Combining ab initio surface science
approaches with cluster expansion for ordered surface structures we construct
surface phase diagrams for these alloys. We utilize these diagrams to study
segregation phenomena and chemical trends for surfaces in contact with a dry
environment or with an aqueous electrolyte. We show that the presence of water
dramatically impacts the stability and chemical composition of the considered
metallic surfaces. We furthermore find that the two alloying elements behave
qualitatively different: whereas Ca strongly segregates to the surface and
becomes dissolved upon exposure of the surface to water, Al shows an
anti-segregation behavior, i.e., it remains in Mg bulk. These findings provide
an explanation for the experimentally observed increase/decrease in corrosion
rates when alloying Mg with Al/Ca. | 2207.09809v3 |
2022-07-22 | Uncertainty Quantification of Material Properties in Ballistic Impact of Magnesium Alloys | The design and development of cutting-edge light materials for extreme
conditions including high-speed impact remains a continuing and significant
challenge in spite of steady advances. Magnesium (Mg) and its alloys have
gained much attention, due to their high strength-to-weight ratio and potential
of further improvements in material properties such as strength and ductility.
In this paper, we adopt a recently developed computational framework to
quantify the effects of material uncertainties on the ballistic performance of
Mg alloys. The framework is able to determine the largest deviation in the
performance measure resulting from a finite variation in the corresponding
material properties. It can also provide rigorous upper bounds on the
probability of failure using known information about uncertainties and the
system, and then conservative safety design and certification can be achieved.
We specifically focus on AZ31B Mg alloys, and assume that the material is
well-characterized by the Johnson-Cook constitutive and failure models, but the
model parameters are uncertain. We determine the ordering of uncertainty
contributions for model parameters and the corresponding behavior regimes where
those parameters play a crucial role. Finally, we show that how this ordering
provides insight on the improvement of ballistic performance and the
development of new material models for Mg alloys. | 2207.11314v1 |
2022-08-03 | Rapid Production of Accurate Embedded-Atom Method Potentials for Metal Alloys | A critical limitation to the wide-scale use of classical molecular dynamics
for alloy design is the limited availability of suitable interatomic
potentials. Here, we introduce the Rapid Alloy Method for Producing Accurate
General Empirical Potentials or RAMPAGE, a computationally economical procedure
to generate binary embedded-atom model potentials from already-existing
single-element potentials that can be further combined into multi-component
alloy potentials. We present the quality of RAMPAGE calibrated Finnis-Sinclair
type EAM potentials using binary Ag-Al and ternary Ag-Au-Cu as case studies. We
demonstrate that RAMPAGE potentials can reproduce bulk properties and forces
with greater accuracy than that of other alloy potentials. In some simulations,
it is observed the quality of the optimized cross interactions can exceed that
of the original off-the-shelf elemental potential inputs. | 2208.02223v1 |
2022-08-24 | Role of Ni, Si and P on the formation of solute-rich clusters under irradiation in Fe-Cr alloys | After irradiation of Fe-Cr alloys of low purity (model alloys of F-M steels),
minor solute elements as P, Ni and Si have been shown to create solute clusters
which significantly contribute to hardening and might be associated with small
dislocation loops. In order to understand the role of each impurity on the
formation of the nano-features formed under irradiation and the eventual
synergies between the different species, Fe-15at.%Cr-X (X=Si, Ni, P, NiSiP)
alloys of different composition have been ion irradiated and characterized
using atom probe tomography. Irradiation were performed at 300 {\textdegree}C
up to 2.5 dpa in four alloys: Fe15CrNi, Fe15CrSi, Fe15CrP and Fe15CrNiSiP.
Influence of C atoms implanted during irradiation on the nanostructure
evolution is also discussed. The study of the evolution of the nanofeatures
formed under irradiation with the dose as a function of the composition
highlights the role of P and C on the formation of the nano-clusters and
confirm the radiation-induced nature of solute-rich clusters. | 2208.11359v1 |
2022-09-17 | Superfunctional materials by ultra-severe plastic deformation | Superfunctional materials are defined as materials with specific properties
being superior to the functions of engineering materials. Numerous studies
introduced severe plastic deformation (SPD) as an effective process to improve
the functional and mechanical properties of various metallic and non-metallic
materials. Moreover, the concept of ultra-SPD - introducing shear strains over
1000 to reduce the thickness of sheared phases to levels comparable to atomic
distances - was recently utilized to synthesize novel superfunctional
materials. In this article, the application of ultra-SPD for controlling atomic
diffusion and phase transformation and synthesizing new materials with
superfunctional properties is discussed. The main properties achieved by
ultra-SPD include: (i) high-temperature thermal stability in new immiscible
age-hardenable aluminum alloys; (ii) room-temperature superplasticity for the
first time in magnesium and aluminum alloys; (iii) high strength and high
plasticity in nanograined intermetallics; (iv) low elastic modulus and high
hardness in biocompatible binary and high-entropy alloys; (v) superconductivity
and high strength in the Nb-Ti alloys; (vi) room-temperature hydrogen storage
for the first time in magnesium alloys; and (vii) superior photocatalytic
hydrogen production, oxygen production, and carbon dioxide conversion on
high-entropy oxides and oxynitrides as a new family of photocatalysts. | 2209.08295v3 |
2022-10-14 | AI-accelerated Materials Informatics Method for the Discovery of Ductile Alloys | In computational materials science, a common means for predicting macroscopic
(e.g., mechanical) properties of an alloy is to define a model using
combinations of descriptors that depend on some material properties (elastic
constants, misfit volumes, etc.), representative for the macroscopic behavior.
The material properties are usually computed using special quasi-random
structures (SQSs), in tandem with density functional theory (DFT). However, DFT
scales cubically with the number of atoms and is thus impractical for a
screening over many alloy compositions.
Here, we present a novel methodology which combines modeling approaches and
machine-learning interatomic potentials. Machine-learning interatomic
potentials are orders of magnitude faster than DFT, while achieving similar
accuracy, allowing for a predictive and tractable high-throughput screening
over the whole alloy space. The proposed methodology is illustrated by
predicting the room temperature ductility of the medium-entropy alloy Mo-Nb-Ta. | 2210.07683v1 |
2022-11-26 | Engineering ultra-strong Mg-Li-Al-based light-weight alloys from first principles | Light-weight alloys are essential pillars of transportation technologies.
They also play a crucial role to achieve a more green and cost-effective
aerospace technologies. Magnesium-lithium-aluminum (Mg-Li-Al) alloys are
auspicious candidates due to their promising mechanical strengths at low
densities. We herein present a systematic first-principles investigation of the
Mg-Li-Al-based alloys to provide insights for designing ultra-strong
light-weight alloys. Initial analysis indicates that the Mg-Li-Al mixtures are
not thermally stabilized into random-solid solutions. Following this hint, the
base-centered cubic (BCC)-based intermetallics of Mg, Li and Al are
investigated for their thermal and elastic stabilities.Three simple figures of
merits are used to further assess their mechanical strengths. The
most-frequently observed intermetallics are used to predict the yield strength
of the hetero-structures from the recent experimental works. The rule of mixing
works reasonable well to predict the mechanical properties of complex
structures starting from isolated intermetallics. | 2211.14413v1 |
2022-12-08 | Modelling Surface Segregation in Compositionally Complex Alloys with Ab-Initio Accuracy | Compositionally complex alloys or concentrated solid solutions are the latest
frontier in catalyst design, but mixing different elements in one catalyst may
result in surface segregation. Atomistic simulations can predict segregation
patterns, but standard approaches based on mean-field models, cluster
expansion, or classical interatomic potentials are often limited for the
description of multicomponent alloys. We present machine learning potentials
that can describe surface segregation with near DFT accuracy. The method is
used to study a complex Co-Cu-Fe-Mo-Ni quinary alloy. For this alloy, an
unexpected segregation of Co, which has a relatively high surface energy, is
observed. We rationalize this surprising mechanism in terms of simple
transition-metal chemistry. | 2212.04597v1 |
2022-12-12 | Topological insulating phase arising in transition metal dichalcogenide alloy | Transition metal dichalcogenides have been the subject of numerous studies
addressing technological applications and fundamental issues. Single-layer
PtSe2 is a semiconductor with a trivial bandgap, in contrast, its counterpart
with 25% of Se atoms substituted by Hg, Pt2HgSe3 (jacutingaite, a naturally
occurring mineral), is a 2D topological insulator with a large bandgap. Based
on ab-initio calculations, we investigate the energetic stability, and the
topological transition in Pt(HgxSe1-x)2 as a function of alloy concentration,
and the distribution of Hg atoms embedded in the PtSe2 host. Our findings
reveal the dependence of the topological phase with respect to the alloy
concentration and robustness with respect distribution of Hg. Through a
combination of our ab-initio results and a defect wave function percolation
model, we estimate the random alloy concentration threshold for the topological
transition to be only 9%. Our results expand the possible search for
non-trivial topological phases in random alloy systems. | 2212.05863v1 |
2022-12-27 | Natural band alignment of $\rm MgO_{1-x}S_{x}$ alloys | We have calculated formation enthalpies, band gaps, and natural band
alignment for $\rm MgO_{1-x}S_{x}$ alloys by first principles calculation based
on density functional theory. The calculated formation enthalpies show that the
$\rm MgO_{1-x}S_{x}$ alloys exhibit a large miscibilitygap, and a metastable
region was found to occur when the S content was below 18% or over 87%. Effect
of S incorporation for band gaps of $\rm MgO_{1-x}S_{x}$ alloys shows large
bowing parameter (b $ \simeq $ 13 eV) induced. The dependence of the band
lineup of $\rm MgO_{1-x}S_{x}$ alloys on the S content by using two different
methods, and the change in the energy position of valence band maximum (VBM)
was larger than that of conduction band minimum. Based on the calculated VBM
positions, we predicted that $\rm MgO_{1-x}S_{x}$ with S content 10 to 18% can
be surface charge transfer doping by high electron affinity materials. The
present work provides an example to design for p-type oxysulfide materials. | 2212.13330v1 |
2023-03-16 | Phase stability and defect studies of Mg-based Laves phases using defect phase diagrams | Laves phases often form as secondary phases in metallic alloys and have a
significant effect on their structural properties. Thus, phase stability
studies for these chemically and structurally complex phases in addition to
mechanical behavior studies are of great interest. In this work, we use the
concept of metastable bulk phase and defect phase diagrams to augment the
understanding of the bulk phase and defect phase stability in Laves phases in
Mg-based alloys. In this way, we resolve the discrepancy between bulk phase
diagrams and experimental observations regarding the formation of Mg-rich C14
and Al-rich C15 Laves phases in MgAlCa alloys at moderate temperatures.
Moreover, the effect of the thermodynamic state of alloys on the competition
between solute-rich hcp-like planar defects and stoichiometric basal stacking
faults is clarified, which determines the brittleness of these alloys.
\end{abstract} | 2303.09576v1 |
2023-06-17 | Superconductivity of Ta-Hf and Ta-Zr alloys: Potential alloys for use in superconducting devices | The electronic properties relevant to the superconductivity are reported for
bulk Ta-Hf and Ta-Zr body centered cubic alloys, in large part to determine
whether their properties are suitable for potential use in superconducting
qbits. The body centered cubic unit cell sizes increase with increasing
alloying. The results of magnetic susceptibility, electrical resistivity and
heat capacity characterization are reported. While elemental Ta is a type I
superconductor, the alloys are type II strong coupling superconductors.
Although decreasing the electron count per atom is expected to increase the
density of electronic states at the Fermi level and thus the superconducting
transition temperature (Tc) in these systems, we find that this is not
sufficient to explain the significant increases in the superconducting Tc's
observed. | 2306.10438v1 |
2023-07-13 | Crucible: Graphical Test Cases for Alloy Models | Alloy is a declarative modeling language that is well suited for verifying
system designs. Alloy models are automatically analyzed using the Analyzer, a
toolset that helps the user understand their system by displaying the
consequences of their properties, helping identify any missing or incorrect
properties, and exploring the impact of modifications to those properties. To
achieve this, the Analyzer invokes off-the-shelf SAT solvers to search for
scenarios, which are assignments to the sets and relations of the model such
that all executed formulas hold. To help write more accurate software models,
Alloy has a unit testing framework, AUnit, which allows users to outline
specific scenarios and check if those scenarios are correctly generated or
prevented by their model. Unfortunately, AUnit currently only supports textual
specifications of scenarios. This paper introduces Crucible, which allows users
to graphically create AUnit test cases. In addition, Crucible provides
automated guidance to users to ensure they are creating well structured,
valuable test cases. As a result, Crucible eases the burden of adopting AUnit
and brings AUnit test case creation more in line with how Alloy scenarios are
commonly interacted with, which is graphically. | 2307.06922v1 |
2023-08-04 | Surface Circular Photogalvanic Effect in Tl-Pb Monolayer Alloys on Si(111) with Giant Rashba Splitting | We have found that surface superstructures made of "monolayer alloys" of Tl
and Pb on Si(111), having giant Rashba effect, produce non-reciprocal
spin-polarized photocurrent via circular photogalvanic effect (CPGE) by
obliquely shining circularly polarized near-infrared (IR) light. CPGE is here
caused by injection of in-plane spin into spin-split surface-state bands, which
is observed only on Tl-Pb alloy layers, but not on single-element Tl nor Pb
layers. In the Tl-Pb monolayer alloys, despite their monatomic thickness, the
magnitude of CPGE is comparable to or even larger than the cases of many other
spin-split thin-film materials. The data analysis has provided the relative
permittivity $\epsilon^{\ast}$ of the monolayer alloys to be $\sim$ 1.0, which
is because the monolayer exists at a transition region between the vacuum and
the substrate. The present result opens the possibility that we can optically
manipulate spins of electrons even on monolayer materials. | 2308.02485v1 |
2023-10-10 | Improved iron-tolerance in recycled aluminum alloys via direct strip casting process | Recycled aluminum alloys are pivotal for sustainable manufacturing, offering
strength, durability, and environmental advantages. However, the presence of
iron (Fe) impurities poses a major challenge, undermining their properties and
recyclability. Conventional manufacturing processes result in coarse Fe-rich
intermetallic compounds that limit the tolerance of Fe content and negatively
influence performance of advanced aluminum alloys. To address this, rapid
solidification techniques like direct strip casting have been explored. In this
work, a detailed study of the strip cast microstructure was conducted by
scanning electron microscopy, electron backscattered diffraction and atom probe
tomography. Our results reveal that alloys produced by DSC exhibit
significantly refined microstructures and are free from coarse Fe-rich
intermetallics, thereby retaining the majority of Fe in solid solution. These
findings indicate that strip casting significantly enhances Fe-tolerance in
aluminum alloys, making it an attractive process for future aluminum recycling,
with implications for sustainable high-performance applications. | 2310.06327v1 |
2023-10-21 | Valley polarization and photocurrent generation in transition metal dichalcogenide alloy MoS$_{2x}$Se$_{2(1-x)}$ | Monolayer transition metal dichalcogenides (TMDCs) constitute the core group
of materials in the emerging semiconductor technology of valleytronics. While
the coupled spin-valley physics of pristine TMDC materials and their
heterstructures has been extensively investigated, less attention was given to
TMDC alloys, which could be useful in optoelectronic applications due to the
tunability of their band gaps. We report here our experimental investigations
of the spin-valley physics of the monolayer and bilayer TMDC alloy,
MoS$_{2x}$Se$_{2(1-x)}$, in terms of valley polarization and the generation as
well as electrical control of a photocurrent utilising the circular
photogalvanic effect. Piezoelectric force microscopy provides evidence for an
internal electric field perpendicular to the alloy layer, thus breaking the
out-of-plane mirror symmetry. The experimental observation is supported by
first principles calculations based on the density functional theory. A
comparison of the photocurrent device, based on the alloy material, is made
with similar devices involving other TMDC materials. | 2310.13924v2 |
2023-10-23 | Preferential Composition during Nucleation and Growth in Multi-Principal Elements Alloys | The crystallization of complex, concentrated alloys can result in
atomic-level short-range order, composition gradients, and phase separation.
These features govern the properties of the resulting alloy. While nucleation
and growth in single-element metals are well understood, several open questions
remain regarding the crystallization of multi-principal component alloys. We
use MD to model the crystallization of a five-element, equiatomic alloy modeled
after CoCrCuFeNi upon cooling from the melt. Stochastic, homogeneous nucleation
results in nuclei with a biased composition distribution, rich in Fe and Co.
This deviation from the random sampling of the overall composition is driven by
the internal energy and affects nuclei of a wide range of sizes, from tens of
atoms all the way to super-critical sizes. This results in short range order
and compositional gradients at nanometer scales. | 2310.15046v1 |
2023-10-30 | Chemo-mechanics in alloy phase stability | We describe a first-principles statistical mechanics method to calculate the
free energies of crystalline alloys that depend on temperature, composition,
and strain. The approach relies on an extension of the alloy cluster expansion
to include an explicit dependence on homogeneous strain in addition to site
occupation variables that track the degree of chemical ordering. The method is
applied to the Si-Ge binary alloy and is used to calculate free energies that
describe phase stability under arbitrary epitaxial constraints. We find that
while the incoherent phase diagram (in which coexisting phases are not affected
by coherency constraints) hosts a miscibility gap, coherent phase equilibrium
predicts ordering and negative enthalpies of mixing. Instead of chemical
instability, the chemo-mechanical free energy exhibits instabilities along
directions that couple the composition of the alloy with a volumetric strain
order parameter. This has fundamental implications for phase field models of
spinodal decomposition as it indicates the importance of gradient energy
coefficients that couple gradients in composition with gradients in strain. | 2310.20085v1 |
2023-11-10 | Experimental investigation of Lord Kelvins isentropic cooling and heating expression in tensile bars for two engineering alloys | Solids when rapidly and elastically stressed change temperature, the effect
proposed by Lord Kelvin is adiabatic thermo-elastic cooling or heating
depending on the sign of the stress. A fast sensitive IR camera has measured
temperature both decreasing and increasing. Temperature measurements made from
the reversible, elastic part of the stress-strain curve during fast uniaxial
tensile loading have been investigated. The isentropic temperature cooling from
the loading curve is recovered by heating after the specimen fractures when the
load is released. These measurements establish for the first time isentropic
thermal recovery in two engineering alloys. The materials tested are an AISI
4340 steel and an aluminum 2024 alloy. Measurements of the isentropic
thermo-elastic stress cooling are -0.61 K/GPa for steel and -1.7 K/GPa for
aluminum alloy. The isentropic thermo-elastic stress heating is -1.16 K/GPa for
steel and -1.6 K/GPa for aluminum alloy. The isentropic, elastic part of the
temperature is fully recoverable even after extensive plastic deformation upon
fracture. | 2311.06371v1 |
2023-11-29 | Ab-initio tensile tests applied to BCC refractory alloys | Refractory metals exhibit high strength at high temperature, but often lack
ductility. Multiprinciple element alloys such as high entropy alloys offer the
potential to improve ductility while maintaining strength, but we don't know
$a-priori$ what compositions will be suitable. A number of measures have been
proposed to predict the ductility of metals, notably the Pugh ratio, the
Rice-Thomson D-parameter, among others. Here we examine direct $ab-initio$
simulation of deformation under tensile strain, and we apply this to a variety
of Nb- and Mo-based binary alloys and to several quaternary alloy systems. Our
results exhibit peak stresses for elastic deformation, beyond which defects
such as lattice slip, stacking faults, transformation, and twinning, relieve
the stress. The peak stress grows strongly with increasing valence electron
count. Correlations are examined among several physical properties, including
the above-mentioned ductility parameters. | 2311.17713v2 |
2023-12-26 | Corrosion-resistant aluminum alloy design through machine learning combined with high-throughput calculations | Efficiently designing lightweight alloys with combined high corrosion
resistance and mechanical properties remains an enduring topic in materials
engineering. To this end, machine learning (ML) coupled ab-initio calculations
is proposed within this study. Due to the inadequate accuracy of conventional
stress-strain ML models caused by corrosion factors, a novel reinforcement
self-learning ML algorithm (accuracy R2 >0.92) is developed. Then, a strategy
that integrates ML models, calculated energetics and mechanical moduli is
implemented to optimize the Al alloys. Next, this Computation Designed
Corrosion-Resistant Al alloy is fabricated that verified the simulation. The
performance (elongation reaches ~30%) is attributed to the H-captured Al-Sc-Cu
phases (-1.44 eV H-1) and Cu-modified {\eta}/{\eta}' precipitation inside the
grain boundaries (GBs). The developed Al-Mg-Zn-Cu interatomic potential (energy
accuracy 6.50 meV atom-1) proves the cracking resistance of the GB region
enhanced by Cu-modification. Conceptually, our strategy is of practical
importance for designing new alloys exhibiting corrosion resistance and
mechanical properties. | 2312.15899v1 |
2024-01-31 | Effect of severe plastic deformation realized by rotary swaging on the mechanical properties and corrosion resistance of near-a-titanium alloy Ti-2.5Al-2.6Zr | The research aims to analyze the impact that severe plastic deformation
arising during Rotary Swaging has on mechanical properties and corrosion
resistance of a near-a-titanium alloy Ti-2.5Al-2.6Zr (Russian industrial name
PT7M). The nature of corrosion decay in fine-grained alloys caused by hot salt
corrosion is known to vary from pit corrosion to intercrystalline corrosion at
the onset of recrystallization processes. Resistance to hot salt corrosion in a
fine-grained titanium alloy Ti-2.5Al-2.6Zr is shown to depend on the
structural-phase state of grain boundaries that varies during their migration
as a result of covering corrosive doping elements (aluminum, zirconium)
distributed in the crystal lattice of a titanium alloy. | 2401.17672v1 |
2024-01-31 | Corrosion fatigue crack initiation in ultrafine-grained near-a titanium alloy PT7M prepared by Rotary Swaging | The study focuses on corrosion fatigue processes taking place in an
ultrafine-grained (UFG) near-a-titanium alloy Ti-2.5Al-2.6Zr (Russian
industrial name PT7M) used in nuclear engineering. UFG structure formed with
Rotary Swaging is found to increase resistance to corrosion fatigue. Parameters
of the Basquin's equation are defined and the slope of the fatigue curve
Sa-lg(N) is shown to depend (nonmonotonic dependence) on the UFG alloy
annealing temperature. This effect can be explained with the patterns of
microstructural evolution in a UFG alloy PT7M during annealing: (1) reduced
density of lattice dislocations, (2) precipitation and dissolution of zirconium
nanoparticles, (3) release of a''-phase particles causing internal stress
fields along interphase (a-a'')-boundaries, and (4) intensive grain growth at
elevated annealing temperatures. It is shown that the fatigue crack closure
effect manifested as changing internal stress fields determined using XRD
method may be observed in UFG titanium alloys. | 2401.17712v1 |
2024-02-15 | Explaining all-optical switching in ferrimagnets with heavy rare-earth elements by varying the spin-flip scattering probability of Gd in Co$_x$Gd$_{100-x}$ alloys and Co/Gd bilayers | Using the microscopic three temperature model, we simulate single-pulse
all-optical switching (AOS) in alloys and bilayers consisting of Co and Gd. In
particular, we investigate its dependence on the spin-flip probability of Gd
$a_\mathrm{sf,Gd}$, a material parameter describing the strength of spin-phonon
coupling. We do so to elucidate the mechanisms behind all-optical switching in
systems where Co is coupled to heavy rare-earth elements with higher damping
such as Tb. In alloys, our observations are twofold. First, an increase of
$a_\mathrm{sf,Gd}$ leads to a broadening of the range of compositions for which
AOS is observed. Second, the ideal Co content is decreased as
$a_\mathrm{sf,Gd}$ is varied. For bilayers, our analysis indicates that
switching is most efficient when $a_\mathrm{sf,Gd}$ takes on small values.
Conversely, increasing the value of $a_\mathrm{sf,Gd}$ leads to a general
suppression of AOS. Comparing alloys to bilayers, we find that AOS in alloys
exhibits greater resilience to variations in $a_\mathrm{sf,Gd}$ than it does in
bilayers. | 2402.09878v1 |
2024-02-16 | An energy-based material model for the simulation of shape memory alloys under complex boundary value problems | Shape memory alloys are remarkable 'smart' materials used in a broad spectrum
of applications, ranging from aerospace to robotics, thanks to their unique
thermomechanical coupling capabilities. Given the complex properties of shape
memory alloys, which are largely influenced by thermal and mechanical loads, as
well as their loading history, predicting their behavior can be challenging.
Consequently, there exists a pronounced demand for an efficient material model
to simulate the behavior of these alloys. This paper introduces a material
model rooted in Hamilton's principle. The key advantages of the presented
material model encompass a more accurate depiction of the internal variable
evolution and heightened robustness. As such, the proposed material model
signifies an advancement in the realistic and efficient simulation of shape
memory alloys. | 2402.10655v1 |
2024-02-19 | Significance of interphase boundaries on activation of high-entropy alloys for room-temperature hydrogen storage | The ability of high-entropy alloys (HEAs) for hydrogen storage is a rather
new topic in the hydrogen community. HEAs with the C14 Laves phase have shown a
high potential to reversibly store hydrogen at room temperature, but most of
these alloys require a high-temperature activation treatment. This study
explores the role of interphase boundaries on the easy activation of HEAs at
room temperature. Two chemically similar HEAs with single and dual phases,
TiV1.5ZrCr0.5MnFeNi (C14 + 4 vol% BCC phases) and TiV1.5Zr1.5CrMnFeNi (single
C14 phase), are designed and synthesized. While the dual-phase alloy readily
absorbs hydrogen at room temperature without any activation treatment, the
single-phase alloy requires a high-temperature activation. It is suggested that
interphase boundaries not only provide pathways for easy hydrogen transport and
activation of HEAs at room temperature but also act as active sites for
heterogeneous nucleation of hydride. This study introduces interphase-boundary
generation as an effective strategy to address the activation drawback of HEAs. | 2402.11784v1 |
2024-02-29 | AlloyASG: Alloy Predicate Code Representation as a Compact Structurally Balanced Graph | In the program analysis and automated bug-fixing fields, it is common to
create an abstract interpretation of a program's source code as an Abstract
Syntax Tree (AST), which enables programs written in a high-level language to
have various static and dynamic analyses applied. However, ASTs suffer from
exponential growth in their data size due to the limitation that ASTs will
often have identical nodes separately listed in the tree. To address this
issue, we introduce a novel code representation schema, Complex Structurally
Balanced Abstract Semantic Graph (CSBASG), which represents code as a
complex-weighted directed graph that lists a semantic element as a node in the
graph and ensures its structural balance for almost finitely enumerable code
segments, such as the modeling language Alloy. Our experiment ensures that
CSBASG provides a one-on-one correspondence of Alloy predicates to
complex-weighted graphs. We evaluate the effectiveness and efficiency of our
CSBASG representation for Alloy models and identify future applications of
CSBASG for Alloy code generation and automated repair. | 2403.00170v3 |
1994-04-05 | Effects of atomic clustering on the optical properties of III-V alloys | Self-consistent electronic structure calculations together with a structural
model are used to study the effect of short-range atomic order on the optical
properties of otherwise random Al(0.5)Ga(0.5)As, Ga(0.5)In(0.5)P, and
Al(0.5)In(0.5)As alloys. We find that clustering can reduce the direct band gap
of these alloys by as much as 100 meV. Furthermore, sufficiently strong
clustering is predicted to transform Al(0.5)Ga(0.5)As into a direct gap
material. | 9404006v1 |
1996-10-16 | Ab initio core-level shifts in metallic alloys | Core-level shifts and core-hole screening effects in alloy formation are
studied ``ab initio'' by constrained-density-functional total-energy
calculations. For our case study, the ordered intermetallic alloy MgAu,
final-state effects are essential to account for the experimental Mg 1s shift,
while they are negligible for Au 4f. We explain the differences in the
screening by analyzing the calculated charge density response to the core hole
perturbation. | 9610130v1 |
1996-12-05 | Electronic structure and band gap composition-dependence of the II-VI quaternary alloys | Based on a successful description of II-VI ternary alloys, which introduces
an empirical bowing parameter to the widely used virtual crystal approximation,
we set up a tight-binding Hamiltonian to describe the Zn_{1-y}Cd_ySe_{1-x}Te_x
and Zn_{.9}Cd_{.1}S_{.07}Se_{.93} quaternary alloys. We just use a formula that
can be thought as a straightforward generalization of the virtual crystal
approximation for this case. Our Hamiltonians reproduce very well the change in
the band gap value with the composition observed in recent experimental
reports. | 9612051v1 |
1997-12-10 | Structural and Electronic Properties of a Wide-gap Semiconductor Alloy: Zn_xMg_{1-x}S_ySe_{1-y} | The structural properties of the $Zn_xMg_{1-xS_ySe_{1-y}}$ solid solutions
are determined by a combination of the computational alchemy and the cluster
expansion methods with Monte Carlo simulations. We determine the phase diagram
of the alloy and show that the homogeneous phase is characterized by a large
amount of short-range order occurring among first-nearest neighbors.
Electronic-structure calculations performed using the special quasi-random
structures approach indicate that the energy gap of the alloy is rather
sensitive to this short-range order. | 9712109v1 |
1998-01-11 | Theory of temperature dependence of the Fermi surface-induced splitting of the alloy diffuse-scattering intensity peak | The explanation is presented for the temperature dependence of the fourfold
intensity peak splitting found recently in diffuse scattering from the
disordered Cu3Au alloy. The wavevector and temperature dependence of the
self-energy is identified as the origin of the observed behaviour. Two
approaches for the calculation of the self-energy, the high-temperature
expansion and the alpha-expansion, are proposed. Applied to the Cu3Au alloy,
both methods predict the increase of the splitting with temperature, in
agreement with the experimental results. | 9801089v1 |
1998-06-23 | Electrostatic model of atomic ordering in complex perovskite alloys | We present a simple ionic model which successfully reproduces the various
types of compositional long-range order observed in a large class of complex
insulating perovskite alloys. The model assumes that the driving mechanism
responsible for the ordering is simply the electrostatic interaction between
the different ionic species. A possible new explanation for the anomalous
long-range order observed in some Pb relaxor alloys, involving the proposed
existence of a small amount of Pb^4+ on the B sublattice, is suggested by an
analysis of the model. | 9806273v1 |
1999-06-11 | Induced spin polarisation in a ferromagnetic gadolinium-yttrium alloy | The first direct evidence of an induced spin moment in Gd(62.4)Y(37.6) is
presented. This additional moment, of 0.16 +/- 0.03 Bohr magnetons, arises from
polarisation of Y electrons in the alloy. The moment was detected in a Compton
scattering experiment via the measurement of the one dimensional projection of
the momentum space electron spin density in Gd and in the alloy. The result is
consistent with theoretical predictions calculated using the LMTO method within
the local spin density approximation. | 9906171v1 |
2000-03-13 | Effect of short range order on electronic and magnetic properties of disordered Co based alloys | We here study electronic structure and magnetic properties of disordered CoPd
and CoPt alloys using Augmented Space Recursion technique coupled with the
tight-binding linearized muffin tin orbital (TB-LMTO) method. Effect of short
range ordering present in disordered phase of alloys on electronic and magnetic
properties has been discussed. We present results for magnetic moments, Curie
temperatures and electronic band energies with varying degrees of short range
order for different concentrations of Co and try to understand and compare the
magnetic properties and ordering phenomena in these systems. | 0003206v1 |
2002-06-30 | Theory for effects of pressure on heavy-fermion alloys | The effects of pressure on heavy-fermion alloys are studied in the framework
of Yoshimori-Kasai model under the coherent potential approximation. A unified
picture is presented for both the electron-type heavy-fermion systems and the
hole-type heavy-fermion systems. The density of states of $f$ electrons is
calculated over the whole range of the doping concentration under the applied
pressure. The Kondo temperature, the specific-heat coefficient, and the
electrical resistivity are obtained, in agreement with the experiments
qualitatively. The contrasting pressure-dependent effects for two types of
heavy-fermion alloys are discussed to reveal the coherence in the system under
pressure. | 0207017v1 |
2004-03-21 | Crossover Scaling of Wavelength Selection in Directional Solidification of Binary Alloys | We simulate dendritic growth in directional solidification in dilute binary
alloys using a phase-field model solved with an adaptive-mesh refinement. The
spacing of primary branches is examined for a range of thermal gradients and
alloy compositions and is found to undergo a maximum as a function of pulling
velocity, in agreement with experimental observations. We demonstrate that
wavelength selection is unambiguously described by a non-trivial crossover
scaling function from the emergence of cellular growth to the onset of
dendritic fingers, a result validated using published experimental data. | 0403533v1 |
2004-04-26 | A dilute limit of CeAl$_3$: Emergence of the single-ion Kondo scaling | Strongly diluted Ce$_x$La$_{1-x}$Al$_3$ alloys have been studied by the low
temperature specific heat in order to elucidate the mechanism that determine
their ground state. All alloys with Ce concentrations of $0.0005 \leq x \leq
0.1$ show a $S=1/2$ Kondo behavior. However, the single-ion scaling is observed
only below $x=0.01$. The true single-ion Kondo temperature is small, 0.2 K, and
is identical to that for dilute CeAl$_2$. It is about 20 times smaller than
that for CeAl$_3$, indicating that intersite interactions facilitate
Kondo-screening in CeAl$_3$ and concentrated Ce$_x$La$_{1-x}$Al$_3$ alloys. | 0404595v1 |
2004-05-13 | Cohesive energies of Fe-based glass-forming alloys | We calculate the cohesive energies of Fe-based glass-forming alloys in the
B-Fe-Y-Zr quaternary system. Our {\it ab-initio} calculations fully relax
atomic positions and lattice parameters yielding enthalpies of mixing at T=0K.
We examine both the known equilibrium and metastable phases as well as a
selection of plausible structures drawn from related alloy systems. This
method, generally reproduces experimentally determined phase diagrams while
providing additional information about energetics of metastable and unstable
structures. In particular we can identify crystalline structures whose
formation competes with the metallic glass. In some cases we identify
previously unknown structures or observe possible errors in the experimental
phase diagrams. | 0405298v1 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.