Boundary Properties Research Articles

The Effect of Solute Elements Co-Segregation on Grain Boundary Energy and the Mechanical Properties of Aluminum by First-Principles Calculation

The segregation of solute atoms at grain boundary (GB) has an important effect on the GB characteristics and the properties of materials. The study of multielement co-segregation in GBs is still in progress and deserves further research at the atomic scale. In this work, first-principles calculations were carried out to investigate the effect of Mg and Cu co-segregation on the energetic and mechanical properties of the Al Σ5(210) GB. The segregation tendency of Mg at the GB in the presence of Cu is characterized, indicating a preference for substitutional segregation far away from Cu atoms. Cu segregation can facilitate the segregation of Mg due to their mutual attractive energy. The GB energy results show that Mg and Cu co-segregation significantly decreases GB energy and thus enhances the stability of the Al Σ5(210) GB. First-principles tensile test calculations indicate that Cu effectively counteracts the weakening effect of Mg segregation in the GB, particularly with the high concentration of Cu segregation. The phenomenon of Cu compensating the strength of the GB is attributed to an increase of charge density and the formation of newly formed Cu-Al bonds. Conversely, Mg segregation weakens the strengthening effect of Cu on the GB, but it can increase the strength of the GB when high concentrations of Cu atoms are present in the GB. The ICOHP and Bader charge analysis exhibits that the strengthening effect of Mg is attributed to charge transfer with surrounding Al and Cu, which enhances the Cu-Al and Al-Al bonds. The results provide a further understanding of the interplay between co-segregated elements and its influence on the energetic and mechanical properties of grain boundary.

Exploring alternative polymer materials for joint liners: a software-guided material selection

This study explores the alternative polymer materials and selection process for joint implant liners, focusing on applying CES Selector software to identify suitable polymer materials. CES Selector provides an easy-to-use interface. It offers multiple selection methods, including boundary values and property constraints. Seven materials were excluded from the analysis, resulting in 19 potential candidates, including unconventional options like EVOH, PCTA, PESU, PI, PPA, PPC, PPSU, and PSU. The materials underwent evaluation based on key criteria, including tensile strength, Young’s modulus, compressive strength, fatigue strength, and fracture toughness. Overall, TPU exhibited a remarkable combination of high mechanical strength and adaptable Young’s modulus, making it a top contender. However, in other evaluation criteria, PI surpassed TPU, solidifying its potential as a superior choice. This systematic approach provides valuable insights for engineers and designers seeking innovative materials for joint implant liners. The study results broaden the range of materials used in implant manufacturing, providing potential alternatives that offer better long-term durability and performance.

Evaluating the effect of A- and B-site cobalt doping on the structural, morphological, dielectric, and non-ohmic properties of CaCu3Ti4O12 ceramics prepared by the hydrothermal method

CaCu3Ti4O12 (CCTO), CaCu3-xCoxTi4O12 (CCCxTO) and CaCu3Ti4-xCoxO12 (CCTCxO) ceramics with x = 0.1 were synthesized by the hydrothermal process at 200°C for 24 hours. The influence of cobalt substitution on the copper and titanium sites in CaCu3Ti4O12 on the structural, morphological, and physical properties was investigated. It was shown through the analysis of X-ray diffractograms of CCTO, CCCxTO, and CCTCxO compounds that they crystallized in a pure perovskite structure without the presence of secondary phases. The refinement of the spectra using the Rietveld method showed an efficient formation of the crystalline phase of the cubic structure (Im3¯), which remains unchanged, with an increase in the unit cell due to the substitution of Co2+/Co3+ in the Cu2+ and Ti4+ sites of the CCTO ceramic. Raman spectroscopy was used as a complementary characterization method to XRD in order to detect vibrational bands and highlight any changes in the crystal lattice. SEM results showed that cobalt insertion increased the average grain size. The dielectric properties were studied by complex impedance spectroscopy in a frequency range from 1 kHz to 1 MHz at different temperatures, where the insertion of cobalt in the Cu2+ and Ti4+ sites has a significant effect on the permittivity value (εr) and dielectric losses (tanδ). The non-ohmic characteristics showed that the change in grain size due to cobalt incorporation is beneficial to improving the breakdown strength (Eb) and nonlinear coefficient (α), which can be attributed to the grain boundary properties of the Internal Barrier Layer Capacitor (IBLC) model and the behavior of the Schottky barrier.

A computational study of the effects of graphene additions on electrical properties of polycrystalline copper

The addition of graphene has recently shown promise as a route for the significant improvement of the bulk electrical properties of metallic materials. We explore the effects these additions have on the net electrical conductivity of fabricated copper-graphene (Cu-Gr) nanocomposites as a function of grain structure and grain boundary properties. Synthetic 3D microstructures were generated to represent polycrystalline copper with different average grain diameters and twinned grain boundary fractions. Then, the Poisson equation of electrical transport was solved using a finite difference method in order to predict the net electrical conductivity of each microstructure. In this context, the potential effect of graphene on the conductivity of the composite was evaluated as a function of the number of affected grain boundaries. The results of these calculations indicate that 1.) as supported by literature, net electrical conductivity decreases with decreasing grain size, 2.) the presence of twinned grain boundaries results in smaller loss of conductivity than would otherwise be expected, and 3.) the presence of graphene on the grain boundaries can be expected to lead to improvements in net electrical conductivity. However, we also find that 4.) when the Cu grain structure becomes sufficiently refined, the addition of graphene could conceivably result in significant improvements in electrical conductivity over and above coarse-grained Cu. It is estimated from our calculations that, assuming microstructures with average grain sizes between 100 nm and 100 μm and graphene conductivity 1000 to 10,000 that of a typical Cu grain boundary, an improvement in electrical conductivity of approximately 17 % over that of bulk Cu may be attainable. Therefore, by performing this study we suggest a possible route for the improvement of Cu electrical properties through the addition of graphene.

Misshaped boundary classifier model for license plate detection in haze weather using entropy CNN

Weather that creates haze can cover up car license plates, creating warped lines that make it difficult to see and identify them. This paper suggests a novel Primitive Boundary Classifier Model (PBCM) that uses the unique properties of bright and dark boundaries to solve this problem. Iteratively extracting characteristics from the input image, the PBCM draws volatile borders and ends linearity at particular pixel positions. To detect irregular boundaries in the hidden layers through changes in entropy and regularity terminations, this procedure is combined with linear entropy learning, which is accomplished by altering a convolutional neural network. Identifying the license plate area and its related embedding is possible by finding these terminating border pixel locations. The model evaluates its performance during validation by considering similarity and false rate metrics. The comparative analysis, this model improves the 7.34% detection precision with 15.98% high similarity and 8.95% less false rate for the maximum epochs performance ratio of 90.1% and error rate of 11.2%.

Using Extensive Core‐Reflected Phases to Constrain Sharp Inner Core Boundary Beneath East Asia

AbstractThe physical properties of the Earth's inner core boundary (ICB) are crucial for understanding inner core growth and geodynamo generation. In this study, we analyze the differential travel time residuals (DTTRs) and waveform similarities of the core‐reflected phases (PKiKP and PcP) to investigate fine‐scale seismic structures of the ICB. To study the ICB beneath East Asia, we collect a total of 4,272 PKiKP and PcP phase pairs from 37 earthquakes occurring from January 2009 to December 2018 recorded by permanent stations in the Chinese Digital Seismic Network (CDSN). This extensive PKiKP dataset allows for a geographically continuous depiction of the ICB beneath East Asia, revealing a diverse scope on its topography and sharpness. There are three main findings in our study. First, we collect a comprehensive PKiKP and PcP dataset with extensive ray coverage across East Asia. Numerous weak precritical PKiKP signals are detected, enabling robust constraints on the ICB across wide regions. Second, the PKiKP‐PcP DTTRs exhibit an average offset of −0.25 s (ranging from −1.5 to 1.0 s) relative to the PREM model, suggesting the outer core is approximately 1.3 km thinner than predicted by the PREM model, although it remains largely consistent with it. Third, the bin‐stacked PKiKP and PcP waveforms show high similarity across most sampled areas, indicating that the ICB thickness is no more than 2 km mostly beneath East Asia, which aligns with the hypothesis of a rapid transition from the solid inner core to the liquid outer core in our study region.

Self-diffusion in < 100 > symmetrical tilt grain boundaries in tungsten: Molecular dynamics simulation

The structure and energy of grain boundaries, the energies of point defects formation in them and grain-boundary self-diffusion coefficients in 18 < 100 > symmetrical tilt grain boundaries in tungsten have been determined by atomistic simulation. The dependences of grain boundary energies, defect formation energies in them and activation energy of grain-boundary self-diffusion on the misorientation angle have been calculated. A structural phase transformation has been discovered in Σ5(310) and Σ5(210) boundaries, which affected the diffusion properties of these grain boundaries. The calculations performed are compared with the available experimental data on self-diffusion in grain boundaries of tungsten.

Atomic-scale investigation on the structures and mechanical properties of metastable grain boundaries in aluminum

Grain boundary (GB) structural transition in pure metals open up new possibilities for material microstructure design. By managing the distribution of ground-state and metastable GB structures, the beneficial effects of GBs on materials can be maximised. However, the application of GB transitions to develop high-performance aluminum is limited by the inadequate understanding of the metastable GB structure in aluminium and its associated plastic deformation mechanisms. In this work, we firstly used a high-throughput GB generation method to construct multiple GB structure for a given misorientation angle, and screen out the ground-state and metastable GB structures according to the energy principle. Six typical symmetrically tilted GBs were investigated, including Σ5(210), Σ17(410) and Σ17(530) GBs around <001> tilt axis, and Σ9(221), Σ11(332), Σ17(223) GBs around <110> axis. Then, molecular dynamics simulations were carried out to perform uniaxial tensile tests on the six GBs and their corresponding metastable GBs at different temperatures. The results show that the tensile strength of <001> metastable GBs differs slightly from the ground-state GB at various temperatures, but for <110> GBs, the strength of most metastable GBs is significantly stronger or weaker compared to that of ground-state GB at 10 K. An increase in temperature reduced this difference in tensile strength of <110> GBs. According to atomic analysis of the GB structural characteristics, it was found that stress and temperature-induced GB structural transition, GB strain localization, and the prevention of dislocation nucleation or propagation from the dissociated structure are the main causes of the differences in tensile responses between the ground-state and metastable GBs.

Effect of Doping Strategy on Electrochemical Performance of Grain Boundaries of Complex Perovskite Proton Conductor Ba3Ca1.18Nb1.82O−δ

In this study, the electrical conductivity and electrochemical performance of Ba3Ca1.18Nb1.82O9−δwere improved by substituting niobium (Nb) element with bismuth (Bi) and ytterbium (Yb) elements. Three different proton conductors, namely, Ba3Ca1.18Nb1.82O9−δ (BCN), Ba3Ca1.18Nb1.72Bi0.1O9−δ (BCNB), and Ba3Ca1.18Nb1.72Yb0.1O9−δ (BCNYb) were prepared by solid state sintering. The electrochemical performance of BCNYb was found to be the best at 400–800 °C in the wet atmosphere. Their ion transport properties were studied by using the defect equilibrium model. The results show the improvement in proton conductivity of BCNYb. Analysis of distribution of relaxation time reveals the improvement in the grain boundary properties of BCNYb. Single cells were prepared with BCN, BCNB, and BCNYb electrolytes, and the performance of the resulting fuel cells was tested. The BCNYb-based fuel cell shows excellent electrochemical performance, indicating its promising potential as a solid-state electrolyte with excellent properties.

Study of mechanical and metallurgical properties of wire arc additively manufactured inconel 718 alloy

The current research work deals with the investigation of mechanical, wetting transition on grain boundary (GB) and metallurgical properties of Inconel 718 alloy used in aerospace industrial applications. The fabrication of thin-wall structure (multilayer structure) is fabricated using wire arc additive manufacturing (WAAM) technique. The novelty of this method is that gas metal arc welding (GMAW) is used as energy source and cold metal transfer (CMT) is used as mode of droplet transfer. Four tensile samples are extracted asper ASTM E8/E8M standards and three microstructure samples are extracted from thin wall structure. Optical microscopy (OM), SEM, EDAX, and EBSD analysis were carried out. In addition, Hardness and tensile tests, as well as fractography analysis were conducted. The grain boundary wetting transition (GBWT) analysis is also carried out. SEM analysis reveals that Nb-rich MC-type carbide contains grain boundaries of droplets, indicating incomplete wetting. Laves and delta (δ) phases are also identified as liquids of a continuous layer separated by Ni elements, indicating complete wetting. EBSD analysis indicates the average grain size as 251.2 μm. The average value of micro hardness as 417.3 HV and UTS as 609.75 MPa are achieved.

Deciphering the relationships among phase boundary, domain structure, and excellent electrical properties of ternary Bi0.5Na0.5TiO3-Bi0.2Sr0.7TiO3-NaNbO3 ferroelectrics

Bi0.5Na0.5TiO3-based ferroelectric ceramics have broad application prospects due to their excellent electrical properties and are considered to be one of the most promising functional materials to supersede lead-based materials. Here, 0.9Bi0.5Na0.5TiO3-0.1Bi0.2Sr0.7TiO3-xNaNbO3 (BNT-BST-xNN) ternary lead-free ferroelectric ceramics were prepared, and the origin of their excellent dielectric properties was investigated in terms of phase boundary and domain structure. The introduction of NN led to a phase transition from the ferroelectric rhombohedral phase (R3c) to the relaxor tetragonal phase (P4bm), and the two phases coexisted in the BNT-BST-xNN ternary solid solution with x ranging from 0.06 to 0.2. Meanwhile, the macroscopic domain of BNT-BST was destroyed and replaced by highly active polar nano-regions (PNRs) of the P4bm phase, leading to an increase in local structural disorder and enhanced relaxor behavior. A dielectric constant (εr) of ∼1765 (150 °C) with Δε/ε150 °C less than 15 % over a broad range from 80 to 328 °C was achieved in the BNT-BST-0.15NN, and an excellent energy storage property (Wrec = 3.3 J/cm3) was obtained under a low electric field (190 kV/cm). More specifically, the relationship among phase boundary, domain structure, and excellent electrical properties was achieved based on Rietveld refinements and the dielectric/ferroelectric characterizations. This work provides a deep insight into the phase evolution and its impact on the electrical properties of the BNT-based relaxor ferroelectrics.

Magnetic properties of the umbral boundary during sunspot decay

Context. In recent years, the magnetic properties of the umbra-penumbra boundary of sunspots and the boundary of pores at various evolutionary stages have been characterised using datasets from different instruments. Aims. We aim to study the intrinsic differences between the intensity and vector magnetic field properties derived from Hinode/SP and SDO/HMI observations of a decaying sunspot. Methods. We analysed the sunspot embedded in active region NOAA 12797 during six days in 30 SP/Hinode scans and 704 HMI/SDO for both regular maps and maps corrected for scattered light, HMIdcon. We studied the correlation of the magnetic properties and continuum intensity in the datasets within the spot, and we investigated the differences at the umbra-penumbra boundary. We examined the decaying process in detail using the full temporal resolution of the HMIdcon maps. Results. We find a good one-to-one correspondence between the magnetic properties in the SP and HMIdcon maps, but the continuum intensity of the spots in the SP maps is found to be 0.04 IQS brighter than in the HMIdcon maps. The considerable influence of scattered light in the HMI maps makes it the least ideal dataset for studying the boundary of spots without a penumbra. The properties at the umbra-penumbra boundary evolve slowly during the sunspot decay stage, while the penumbra still provides some stability. In contrast, they respond more abruptly to areal changes in the naked-spot stage. During the sunspot decay, we find linear decay in the area and in the magnetic flux. Moreover, the umbra shows two characteristic decaying processes: a slow decay during the first three days, and a sudden fast decay during the final dissipation of the penumbra. We find indications of a 3.5 h lag between the dissipation of the vertical fields in the umbral region and the photometric decay of the umbral area. Conclusions. The differences found in the continuum intensity and in the vertical component of the magnetic field, Bver, between the analysed datasets explain the discrepancies among the Bver values found at the boundaries of umbrae in previous studies.

On Boundary Properties of Conformal Mappings

On Boundary Properties of Conformal Mappings

Effect of In and Sc Co-doping on electrochemical performance on bulk and grain boundaries of La1.9In0.05Sc0.05Ce2O7 proton conductors

In this paper, fluorite-type proton conductors La1.9In0.1Ce2O7, La1.9In0.05Sc0.05Ce2O7 and La1.9Sc0.1Ce2O7 (referred to as LCO-I, LCO-IS and LCO-S), were synthesized by the low-cost solid-state reaction method. The formation process and structure of single-doped LCO-I and LCO-S and co-doped LCO-IS were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The electrochemical performance was studied using alternating current electrochemical impedance spectroscopy (EIS). XRD results showed that the synthesized material had a fluorite structure, without any impurity phase. SEM micrographs showed that LCO-I, LCO-S and LCO-IS had a fairly dense grain. EDS analysis confirmed that the elemental composition of LCO-I, LCO-S and LCO-IS was evenly distributed and contained no impurities. LCO-IS exhibited superior conductivity among related materials, and the total conductivity of LCO-IS in oxygen was 9.49 × 10−3 S cm−1 at 800 °C. The effects of co-doping on bulk and grain boundary properties were analyzed using the distribution of relaxation time (DRT). The bulk and grain boundary conductivity of co-doped LCO-IS was higher than that of single-doped LCO-I and LCO-S. LCO-IS showed good proton conductivity. In the temperature range of 300–800 °C, the proton conductivity was 1.35 × 10−6–4.43 × 10−3 S cm−1. For LCO-I and LCO-IS electrolyte supported symmetric cells (Ag ǀ LCO-I (LCO-IS) ǀ Ag), their open circuit voltages were 0.99 V and 0.97 V, respectively, at 700 °C, and the power densities were 8.8 mW cm−2 and 9.34 mW cm−2. This demonstrates the potential of LCO-IS to be used in various devices as a proton-conducting electrolyte.

Effect of vanadium doping on structural, dielectric, magnetic, and ferroelectric properties of Ba0.95La0.05TiO3 ceramics

The polycrystalline different Ba0.95La0.05Ti1-xVxO3 (where, x = 0.00 to 0.12) ceramics were synthesized using solid-state reaction method. The toroid- and pellet-shaped samples were sintered at 1200°C temperature for 4 h. According to the outcomes of the X-ray diffraction (XRD) investigation, each sample possesses a tetragonal crystal structure that includes a few impurity peaks. Extra Raman modes at 327 cm−1 (for x = 0.06 to 0.12) may be attributed to localized phonon vibrations in the vicinity of a (substitutional) defect or as a result of the relaxation of Raman selection rules due to defect-induced disorder. The density showed a progressive increase as the concentration of V increases, reaching its maximum at the x = 0.06 sample, after which it drops. The x = 0.06 sample displayed the highest bulk density, with a value of ρB = 4.01 g/cm3. Scanning Electron Micrograph (SEM) showed gradual agglomeration of the grain with V-content due to magnetic dipole interaction between one particle and other neighboring particles and exposed the porous nature of the samples. The TEM image demonstrates that the particles are well crystalline. For all of the compositions, the dielectric constant was larger in lower frequency areas and remained constant in higher frequency region. The sample with x = 0.06 showed a maximum dielectric constant of 1140 at 102 Hz. AC conductivity increased with increasing frequency. The Nyquist plot suggested an appearance of grain boundary (bulk) property of the material. The constant value of the real part of complex initial permeability over long range of frequency indicated the magnetic stability of the materials. For ceramics with x = 0.03, the largest real part of the initial permeability of 17.29 is evident. From the M − H loop, at room temperature, feeble ferromagnetism was observed with vanadium substitution in BLT ceramics. It is found that the highest saturation magnetization for the x = 0.03 sample is 2.61 emu/g. For the composition of x = 0.06, the highest polarization of 2.80 μC/cm2 is observed.

Bauer simplices and the small boundary property

We show that, for every minimal action of a countably infinite discrete group on a compact metrizable space, if the extreme boundary of the simplex of invariant Borel probability measures is closed and has finite covering dimension then the action has the small boundary property.

Optimal premium pricing in a competitive stochastic insurance market with incomplete information: A Bayesian game-theoretic approach

This paper examines a stochastic one-period insurance market with incomplete information. The aggregate amount of claims follows a compound Poisson distribution. Insurers are assumed to be exponential utility maximizers, with their degree of risk aversion forming their private information. A premium strategy is defined as a mapping between risk-aversion types and premium rates. The optimal premium strategies are denoted by the pure-strategy Bayesian Nash equilibrium, whose existence and uniqueness are demonstrated under specific conditions on the insurer-specific demand functions. Boundary and monotonicity properties for equilibrium premium strategies are derived.

Atomic Structure and Electronic Properties of Pristine and O-Doped Basal-Plane Inversion Domain Boundaries in AlN

Atomic Structure and Electronic Properties of Pristine and O-Doped Basal-Plane Inversion Domain Boundaries in AlN

Polycrystalline silicon, a molecular dynamics study: II. Grains, grain boundaries and their structure

Polycrystalline silicon (poly-Si) is an excellent material for use in microelectronic devices, both in electrical and mechanical applications. Its mechanical and electrical properties are widely adjustable, its processing technology is compatible with existing microcircuit manufacturing technology, and its availability and recyclability are at a high level. Here, we focus on investigating the properties of poly-Si that distinguish it from other forms of silicon, that is, grains, grain boundaries, and the conditions and treatments that determine grain and grain boundary properties. Starting from the molecular dynamics simulations of the deposition of thin poly-Si films under different growth conditions we study the properties of the films, grains, and grain boundaries as a function of growth time, growth temperature, and post-annealing. We aim to get data and information that will form the essential basis for future research on the electrical properties of poly-Si. The main results are: (i) the effect of post-annealing on the distribution of the grain size and grain boundary thickness (ii) the distribution of the grain orientations, and (iii) the density of the 3- and 5-bonded atoms as a function of deposition temperature.

Nonfree almost finite actions for locally finite‐by‐virtually Z${\mathbb {Z}}$ groups

AbstractIn this paper, we study almost finiteness and almost finiteness in measure of nonfree actions. Let be a minimal action of a locally finite‐by‐virtually group on the Cantor set . We prove that under certain assumptions, the action is almost finite in measure if and only if is essentially free. As an application, we obtain that any minimal topologically free action of a virtually group on an infinite compact metrizable space with the small boundary property is almost finite. This is the first general result, assuming only topological freeness, in this direction, and these lead to new results on uniform property and ‐stability for their crossed product ‐algebras. Some concrete examples of minimal topological free (but nonfree) subshifts are provided.