Boundary Structure Research Articles

Controls of sedimentary-diagenetic evolution on rock physics properties in Precambrian-Lower Paleozoic ancient carbonate reservoirs

The Precambrian-Lower Paleozoic ancient carbonate reservoirs are pivotal for onshore hydrocarbon exploration in China. Nevertheless, their intricate diagenetic history leads to apparent inter- and intra-reservoir heterogeneity, strongly impacting the physical responses. Deciphering the rock physical characteristics compatible with geological processes is imperative for interpreting the geophysical responses of these reservoirs. To address this, rock physical experiments under reservoir conditions were conducted for carbonate rocks formed in different sedimentary systems from a geological perspective. The results illustrated that sedimentary-diagenetic evolution determines the material composition, dolomite genesis, and pore evolution, ultimately defining the two most critical parameters, load-bearing frame, and pore structure, controlling the physical properties of ancient carbonate rocks. Reservoir properties (porosity and permeability) are enhanced by strong hydrodynamic conditions that facilitate primary pore development, penecontemporaneous dissolution leading to secondary dissolved pores, early-stage dolomitization preserving pre-existing pores, and multi-stage tectonic movement forming microcracks (at the plug scale) with superior transport capacity. Concerning seismic properties, the slight decrease in P-wave velocity reflects that dissolution shapes the pores into a larger but stiffer shape. The significant decrease in P-wave velocity could be attributed to two factors, including weaker crystal contact boundary types formed due to different provenance, strong evaporation and silicification, and microcracks developed in regions with intense tectonic activities. Furthermore, these crystal contact boundary and pore structure types can be effectively identified by the difference in VP/VS ratio. This study enhances the understanding of rock physics in ancient carbonate reservoirs, which is relevant to the exploration of such reservoirs.

Machine learning interatomic potential with DFT accuracy for general grain boundaries in α-Fe

AbstractTo advance the development of high-strength polycrystalline metallic materials towards achieving carbon neutrality, it is essential to design materials in which the atomic level control of general grain boundaries (GGBs), which govern the material properties, is achieved. However, owing to the complex and diverse structures of GGBs, there have been no reports on interatomic potentials capable of reproducing them. This accuracy is essential for conducting molecular dynamics analyses to derive material design guidelines. In this study, we constructed a machine learning interatomic potential (MLIP) with density functional theory (DFT) accuracy to model the energy, atomic structure, and dynamics of arbitrary grain boundaries (GBs), including GGBs, in α-Fe. Specifically, we employed a training dataset comprising diverse atomic structures generated based on crystal space groups. The GGB accuracy was evaluated by directly comparing with DFT calculations performed on cells cut near GBs from nano-polycrystals, and extrapolation grades of the local atomic environment based on active learning methods for the entire nano-polycrystal. Furthermore, we analyzed the GB energy and atomic structure in α-Fe polycrystals through large-scale molecular dynamics analysis using the constructed MLIP. The average GB energy of α-Fe polycrystals calculated by the constructed MLIP is 1.57 J/m2, exhibiting good agreement with experimental predictions. Our findings demonstrate the methodology for constructing an MLIP capable of representing GGBs with high accuracy, thereby paving the way for materials design based on computational materials science for polycrystalline materials.

Cold Sintered ZnO-Polystyrene (PS) Composites with Modified Interfacial Structures and Properties.

Lightweight and integrated electronic devices with high performance have become an inevitable trend in the development of power electronic systems. However, it is challenging to obtain lightweight and miniaturized varistors due to the low threshold electric field. Herein, (1 - x)ZnO-xPS composites with a high threshold electric field are prepared through a cold sintering process at 220 °C for 50 min, utilizing lightweight PS to modulate the grain boundary structures of ZnO varistors. With PS content ≤1.5 wt %, the relative densities of cold sintered composites exceed 95%. PS thin layers with a thickness of 2-10 nm are distributed at the grain boundaries of ZnO, forming the Schottky barrier, which triggers nonlinear current-voltage responses. With the addition of PS, the threshold electric field is dramatically enhanced from 135 to 2703 V·mm-1, higher than that of commercial ZnO varistors, which is further demonstrated by the electric field simulation of the Finite Element Method. The interfacial resistance obtained from impedance analysis increases with the increase of the PS content, and the activation energy of (1 - x)ZnO-xPS composites is higher than that of pure ZnO ceramics. This study provides a promising approach for the development of lightweight and cost-effective varistor materials.

A New XPS Test Material for More Reliable Analysis of Microstructures

ABSTRACTA reference material is required for small‐area XPS because it has been used more frequently for surface control in recent years and many operators use incorrect field of views. To address this problem, we developed a test material starting in 2019. We optimised this XPS test material dedicated to the control of analysis position on the sample, with respect to the following factors: type of XPS instruments available on the market, the manufacturing process and sample handling. Test structures are now aligned along lines instead of on a circle radius, so that the individual structures can be accessed more quickly and easily. In addition, a larger test structure of 300 μm and another one in an intermediate size of 18 μm were added. Smaller test structures under 50 μm have been annotated with finder grids/arrows around them so that they are easier to find. Further, the manufacturing process was changed from e‐beam lithography to a mask process to be able to offer the test material at a favourable price. The use of masks also had to be adapted for the new manufacturing process so that the smallest square structures are also realised as such and do not show any distortion of the structure boundaries. The quality control using a metrological SEM confirmed a very reproducible manufacturing process. It is demonstrated that the test material can be successfully employed to find the most suitable beam size of the XPS system used for the analysis of small (μm range) surface features.

Analysis of Vibration Characteristics for Rotating Braided Fiber-Reinforced Composite Annular Plates with Perforations

In the current study, a comprehensive numerical model for analyzing the vibrational characteristics of braided fiber-reinforced composite (BFRC) rotating annular plate with perforations under diverse boundary constraints was introduced. This model employs the differential quadrature finite element method (DQFEM), which was developed based on the first-order shear deformation theory (FSDT) and coordinate transformation approach. The BFRC material, specifically a two-dimensional biaxial orthogonal fabric, was utilized to fabricate the annular plate with two distinct types of holes: circular and sector-shaped. The model’s convergence, accuracy, numerical stability, and reliability were confirmed through comparative assessments utilizing data from the literature, from ABAQUS software, and from experimental findings. The analysis focuses on studying the influences of structural properties, material parameters, and boundary restraints on the frequencies of vibration for BFRC rotating annular plates with holes. This theoretical model helps provide scientific basis and technical guidance for the stability and lightweight design of rotating annular plates, such as rotor structures in aircraft engines.

On the atomistic origin of internal length scale in strain-gradient plasticity models: The case of grain boundary structures and energies

On the atomistic origin of internal length scale in strain-gradient plasticity models: The case of grain boundary structures and energies

Design optimization of continuous fiber composites with thermo-mechanical coupling and load uncertainties

This paper introduces a theoretical framework for the design optimization of continuous fiber composites reinforced with continuous fiber trajectories subject to thermo-mechanical coupling and load uncertainties. Different uniform temperature variations are applied in the structure to investigate the influence of ambient temperature change on the structural performance. To consider the external load uncertainties, a robust design optimization model is proposed where the loads are modeled as hybrid variables, namely magnitudes as random variables and directions as interval variables, with the robust objective determined through a hybrid orthogonal polynomial expansion method. Furthermore, we use a level-set function to represent the structural boundary, with its evolution driven by shape derivatives calculated based on uncertainty analysis. The continuous fiber paths are subsequently determined by the level-set isoline extracted from the structural boundary, which in turn influences the structural mechanical performance due to the material anisotropy of composites. The continuity of continuous fiber and the equal space between adjacent trajectories largely ensure the additive manufacturability of the composites. Three numerical examples are presented to demonstrate the effectiveness of the developed framework. The results show that the ambient temperature variations and load uncertainties largely impact the optimized topology and fiber infill patterns of composites, thus are important to be considered in the design stage. Moreover, the optimized structure can have a 5-fold stiffness per unit mass compared with the initial design thus largely increasing the material efficiency in carrying external uncertain loads.

Metaharvesting: emergent energy harvesting by piezoelectric metamaterials

Vibration energy harvesting is a technology that enables electric power generation by augmenting vibrating materials or structures with piezoelectric elements. In a recent work, we quantified the intrinsic energy-harvesting availability (EHA) of a piezoelectric phononic crystal (Piezo-PnC) by calculating its damping ratio across the Brillouin zone and subtracting off the damping ratio of the corresponding non-piezoelectric version of the phononic crystal. It was highlighted that the resulting quantity indicates the amount of useful energy available for harvesting and is independent of the finite structure size and boundary conditions and of any forcing conditions. Here, we investigate the intrinsic EHA of two other material systems chosen to be statically equivalent to a given Piezo-PnC: a piezoelectric locally resonant metamaterial (Piezo-LRM) and a piezoelectric inertially amplified metamaterial (Piezo-IAM). Upon comparing with the intrinsic EHA of the Piezo-PnC, we observe an emergence of energy-harvesting capacity, a phenomenon we refer to as metaharvesting. This is analogous to the concept of metadamping, except the quantity evaluated is associated with piezoelectric energy harvesting rather than raw dissipation. Our results show that the intrinsic EHA is enhanced by local resonances and enhanced further by inertial amplification. These findings offer a new paradigm for the design—at the fundamental level—of architectured piezoelectric materials with superior energy-harvesting capacity.

The evolution of grain boundary structure mediated by disclinations in magnesium alloys under superplastic deformation

Superplastic deformation in metals and alloys, characterized by ultrahigh ductility (exceeding 300%) without cracking at elevated temperatures, is a critical process for manufacturing complex-shaped components. While a few grain-boundary (GB)-mediated deformation mechanisms have been identified as essential contributors to superplasticity in fine-grained polycrystals (grain size is typically less than 10 μm), it is still a challenge to maintain a steady fine-grained microstructure and sustainable plastic flow at high temperatures. Partially due to the lack of a quantitative description of dislocation-GB reactions, it has not been well recognized how grain coarsening can be suppressed by the external loading during superplastic deformation. In this work, we address this challenge by formulating a disclination-dislocation coupling equation within the Lie-algebra framework, providing a quantitative understanding of the interactions between disclinations, dislocations, and GBs. Using quasi-in-situ electron backscattered diffraction (EBSD) analysis in Mg alloys, we systematically investigate the multiscale interactions of the defects and their impact on grain structure evolution. Three key mechanisms that suppress conventional grain coarsening have been identified, i.e., disclination-assisted GB accommodation, disclination-GB pinning, and disclination-induced sub-GB crossing, all of which are captured by the proposed equation. This study contributes to the broader field of plasticity by linking macroscopic deformation behavior with microscopic mechanisms, offering new insights into the theory of superplastic deformation in metals and alloys.

Correlations between local chemical fluctuations and grain boundary strength in Ti-Zr-Nb-Ta-Mo refractory multi-principal element alloys

Ti-Zr-Nb-Ta-Mo refractory multi-principal element alloys typically exhibit high yield strength while tensile ductility tends to be poor. In this study, we found that even after solid solution treatment of Ti-Zr-Nb-Ta-Mo alloys, significant change in ductility occur due to the local chemical fluctuations. Ta's dramatic chemical fluctuations cause variations in atomic-scale strain fields, leading to reduced grain boundary strength and brittle fracture. First-principles calculations show that (Ti, Zr)-rich at the grain boundaries increases the delocalization of valence electrons, leading to longer bond lengths and reduced crystal orbital bond index values, thereby causing grain boundary embrittlement. Our findings explore the root causes of brittleness in Ti-Zr-Nb-Ta-Mo alloys at the atomic and electronic scales, providing not only a method to analyze grain boundary embrittlement using bond length, electronic localization function and crystal orbital bond index, but also a theoretical guidance for improving the mechanical properties via grain boundary structure optimization.

Polarization pinning at antiphase boundaries in multiferroic YbFeO3

Abstract The switching characteristics of ferroelectrics and multiferroics are influenced by the interaction of topological defects with domain walls. We report on the pinning of polarization due to antiphase boundaries in thin films of the multiferroic hexagonal YbFeO3. We have directly resolved the atomic structure of a sharp antiphase boundary (APB) in YbFeO3 thin films using a combination of aberration-corrected scanning transmission electron microscopy (STEM) and total energy calculations based on density-functional theory (DFT). We find the presence of a layer of FeO6 octahedra at the APB that bridges the adjacent domains. STEM imaging shows a reversal in the direction of polarization on moving across the APB, which DFT calculations confirm is structural in nature as the polarization reversal reduces the distortion of the FeO6 octahedral layer at the APB. Such APBs in hexagonal perovskites are expected to serve as domain-wall pinning sites and hinder ferroelectric switching of the domains.

Correlation between microstructure properties and the effect of WC addition on the interface, hardness and corrosion performance of thermally sprayed NiCrBSi-WC coating

ABSTRACT Ni super-alloy is based on a powder coating of NiCrBSi – WC from flexicord wire feedstock material. The role of the CMoAlNi thick layer on the microstructure and interface properties of the coating was examined. The microstructure and interface properties were analyzed for both NiCrBSi-WC and NiCrBSi-WC/CMoAlNi thick layer using optical microscopy (OM), scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS), X-ray diffraction analysis (XRD). The mechanical property was evaluated by a Vickers hardness and nano-indentation measurement under 3N and 100mN, respectively. The performance of corrosion interface coatings was investigated in 3.5% of bentonite solution. The applied layer has a flame-spray morphology with unmelted and deformed particles associated with voids and porosities. In contrast, after CMoAlNi under-layers, the interface is a more compact boundary structure with no porosity or cracks. The as-sprayed NiCrBSi-WC coating exhibits high hardness (HIT≈6 GPa), and high Young's modulus (EIT≈ 240 GPa) The ability to resist cracking is significantly higher for the NiCrBSi-WC coating concerning the NiCrBSi-WC/CMoAlNi coating, 7.21 compared to 2.88 (GPA−3) x106. The electrochemical potentiodynamic polarisation results show that the NiCrBSi-WC coating's corrosion resistance is higher than that of the NiCrBSi-WC / CMoAlNi coating.

Intrinsic symmetry-protected topological mixed state from modulated symmetries and hierarchical structure of boundary anomaly

Intrinsic symmetry-protected topological mixed state from modulated symmetries and hierarchical structure of boundary anomaly

Freestanding Penta-Twinned Pd-Ag Nanosheets.

2D metal nanosheets have attracted significant attention as efficient catalysts for various important chemical reactions. However, the development of metal nanosheets with controlled compositions and morphologies has been slow due to the challenges associated with synthesizing thermodynamically unfavorable 2D structures. Herein, we report a synthesis route of freestanding Pd-Ag penta-twinned nanosheets (Pd-Ag ptNSs) with distinct 5-fold twin boundaries. Through the coreduction of Ag and Pd precursors on presynthesized Pd ptNSs, Ag could be homogeneously alloyed with Pd, leading to the formation of well-defined Pd-Ag ptNSs. The promotional effects of the bimetallic composition, 2D structure, and twin boundaries on catalysis were studied by using Pd-Ag ptNS-catalyzed H2 production from formic acid decomposition as a model reaction. Notably, the catalytic activity of the Pd-Ag ptNSs drastically outperformed those of monometallic, bimetallic, and 3D counterparts, such as Pd ptNSs, Pd-Ag nanosheets without a TB, and Pd-Ag octahedral nanocrystals, demonstrating the promising potential of the integration of twin boundaries and multiple compositions in the development of high-performance 2D nanocatalysts.

Misorientations across interfaces in spark plasma–sintered WC–Co cemented carbides

AbstractThis interdisciplinary work concerns misorientations across various interfaces in spark plasma–sintered (SPSed) WC–Co cemented carbides, as well as how these misorientations affect the intergranular fracture. The whole boundaries in cemented carbides were divided according to the phases on the two sides of the boundary plane, and carbide/carbide grain boundaries were further divided according to the misorientation across the boundary plane. Stereological statistics and five‐parameter analysis were comprehensively performed on the concerned boundary types. For Σ2 carbide/carbide boundaries, multiple boundary structures are observed. How Σ2 twist inhibits intergranular fracture and how such boundary structure is formed are analyzed. For random carbide/carbide boundaries, the habit planes that they are terminated by are calibrated, and their responses to intergranular fracture are examined according to their energy anisotropy. For WC/α‐cobalt and WC/β‐cobalt phase boundaries, misorientations across these boundary planes and the corresponding crack propagation routines are illustrated. On these bases, approaches to improve the fracture strength of SPSed cemented carbides are suggested.

Molecular Dynamics Analysis of Hydrogen Diffusion Behavior in Alpha-Fe Bi-Crystal Under Bending Deformation

The hydrogen embrittlement (HE) phenomenon occurring in drawn pearlitic steel wires sometimes results in dangerous delayed fracture and has been an important issue for a long time. HE is very sensitive to the amount of plastic deformation applied in the drawing process. Hydrogen (H) atom diffusion is affected by ambient thermal and mechanical conditions such as stress, pressure, and temperature. In addition, the influence of stress gradient (SG) on atomic diffusion is supposed to be crucial but is still unclear. Metallic materials undergoing plastic deformation naturally have SG, such as residual stresses, especially in inhomogeneous regions (e.g., surface or grain boundary). In this study, we performed molecular dynamics (MD) simulation using EAM potentials for Fe and H atoms and investigated the behavior of H atoms diffusing in pure iron (α-Fe) with the SG condition. Two types of SG conditions were investigated: an overall gradient established by a bending deformation of the specimen and an atomic-scale local gradient caused by the grain boundary (GB) structure. A bi-crystal model with H atoms and a GB structure was subjected to bending deformation. For a moderate flexure, bending stress is distributed linearly along the thickness of the specimen. The diffusion coefficient of H atoms in the bulk region increased with an increase in the SG value. In addition, it was clearly observed that the direction of diffusion was affected by the existence of the SG. It was found that diffusivity of the H atom is promoted by the reduction in its cohesive energy. From these MD results, we recognize an exponential relationship between the amount of H atom diffusion and the intensity of the SG in nano-sized bending deformation.

Ultrahigh thermal stability and piezoelectricity of lead-free KNN-based texture piezoceramics

The contradiction between high piezoelectricity and uniquely poor temperature stability generated by polymorphic phase boundary is a huge obstacle to high-performance (K, Na)NbO3 -based ceramics entering the application market as Pb-based substitutes. We possess the phase boundary by mimicking Pb(Zr, Ti)O3’s morphotropic phase boundary structure via the synergistic optimization of diffusion phase boundary and crystal orientation in 0.94(Na0.56K0.44)NbO3−0.03Bi0.5Na0.5ZrO3−0.03(Bi0.5K0.5)HfO3 textured ceramics. As a result, a prominent comprehensive performance is obtained, including giant d33 of 550 ± 30 pC/N and ultrahigh temperature stability (d33 change rate less than 1.2% within 25-150 °C), representing a significant breakthrough in lead-free piezoceramics, even surpassing the Pb-based piezoelectric ceramics. Within the same temperature range, the d33 change rate of the commercial Pb(Zr, Ti)O3−5 ceramics is only about 10%, and more importantly, its d33 (~ 350 pC/N) is much lower than that of the (K, Na)NbO3-based ceramics in this work. This study demonstrates a strategy for constructing the phase boundary with MPB feature, settling the problem of temperature instability in (K, Na)NbO3-based ceramics.

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.

Thermodynamic properties and structure of interfacial boundaries in nonionic fluids from the multilayer quasichemical model

The interfacial properties and structure of nonuniform fluids containing complex chainlike molecules and associating species are very much needed in a variety of different fields, including enhanced oil recovery, drug delivery, pharmacy, cosmetics, food processing, etc.Recently, we described the Multilayer Quasichemical Model (MQuM) of a nonuniform fluid that provides a remarkably detailed structural information, including the local concentration and orientation of functional groups of the molecules, the orientation profiles of the chemical bonds in molecular chains and the orientation profiles of the hydrogen bonds in the mixture.In this work, we focus on the description of thermodynamic properties with the aid of MQuM, including the interfacial tension and the profiles of normal and transverse pressures. Before proceeding to more complex systems, a test is performed through comparison with the previously known results from the Scheutjens-Fleer theory for the planar liquid–vapor interface and spherical droplet in one-component fluid of nonpolar monomeric molecules. The model is applied then for planar interfaces between the liquid phases in mixtures of water with n-alkanes of different chain length and for spherical drops in model systems that contain an associating solvent, a nonpolar chain and a nonionic amphiphile. Our theoretical results are compared with experiment, predictions from iSAFT and MD simulation data from the literature. For the spherical droplets, we discuss the model description of the dependence of the interfacial tension on the curvature and estimate the Tolman length. For the planar interface between the equilibrium liquid phases in water – n-alkane mixtures, the interfacial tensions predicted from the model are in good agreement with experiment.

Critical Review of Physical-Mechanical Principles in Geostructure-Soil Interface Mechanics

AbstractDue to the relatively different mechanical and physical properties of soils and structures, the interface plays a critical role in the transfer of stress and strain between them. The stability and safety of geotechnical structures are thus greatly influenced by the behavior at the soil–structure interface. It is therefore important to focus on the unique characteristics that set the interface apart from other geomaterials while examining the interface behaviour. Understanding the physical mechanism and modelling principles of these interfaces becomes a crucial step for the secure design and investigation of soil-structure interaction (SSI) issues. Moreover, to deal with this soil-environment interaction problem, the classical soil mechanics formulation must be progressively generalised in order to incorporate the effects of new phenomena and new variables on SSI behaviour. Considering the variety of energy geostructures that are emerging nowadays, it is crucial to comprehend the thermo-hydro-mechanical (THM) behaviour of the interface. The objective of this study is to fill this information gap as concisely as possible. A critical review is provided along with the state-of-the-art information on the thermo-hydro-mechanical behaviour of the soil-structure interface, including testing tools and measurement methods, basic principles and deformation mechanisms, constitutive models, as well as their applications in numerical simulations. This study explains how loading influences the mechanisms at the interface and critically examines the effects of boundary conditions, soil properties, environmental factors, and structure type on the THM behaviour of interface zones between soils and structural elements. The validity and reliability of the interface shear stress-displacement models are also covered in this paper. Lastly, the trends and recent advancements are also recommended for the interface research.