Unique Microstructure Research Articles

Enhanced properties of fine‐grain titanium diboride with high dislocation density fabricated by high‐pressure sintering

AbstractFor the purpose of the densification of ceramics with high melting points, the traditional preparation method requires long‐term heating above 2000°C, which inevitably leads to severe grain growth and high energy consumption. In this study, TiB2 ceramics with a high density (98.9%) and a fine grain size (2.15 µm) were prepared under the pressure of 200 MPa at the low temperature of 1650°C in a carbon fiber reinforced sintering mold with reliable strength. The high‐pressure sintered sample possessed a high hardness of 30.1 GPa and a high dislocation density of 3.64 × 1014 m−2. The mechanical properties of TiB2 ceramics could be significantly improved by high‐pressure induced unique microstructures. This sintering process provides insights into subsequent sintering of other ceramics with high melting points.

Self‐Supported Ni/Ni(OH)2 Electrodes for High‐Performance Alkaline and AEM Water Electrolysis

AbstractA novel tape‐cast Ni/Ni(OH)2 electrode is developed for water electrolysis applications. Through precise control of sintering temperature and in situ formation of Ni(OH)2 nanosheets, the electrode achieves an optimized hierarchical porous structure with interconnected channels, facilitating efficient gas bubble transport and release. The electrode exhibits remarkable hydrogen evolution reaction activity with overpotentials of 40 and 124 mV at 10 and 100 mA cm−2, respectively, comparable to noble metal catalysts. The unique microstructure enables rapid bubble detachment and enhanced mass transport, leading to a high current density of 0.91 A cm−2 at 1.8 V in alkaline water electrolysis. The inherent Ni/Ni(OH)2 composition demonstrates excellent stability over 1500 h of continuous operation and maintains consistent performance under intermittent conditions, making it particularly suitable for renewable energy integration. For anion exchange membrane water electrolysis, the electrode's smooth surface morphology prevents membrane damage while maintaining efficient mass transport, delivering 0.4 A cm−2 at 1.8 V. This study demonstrates that rational design of electrode microstructure through tape‐casting offers a promising pathway toward high‐performance, durable, and cost‐effective water electrolyzers.

Engineered ionic polymer metal composites (eIPMCs) under dynamic compression loading conditions: theory and experiments

Abstract Engineered Ionic Polymer Metal Composites (eIPMCs) represent the next generation of IPMCs, soft electro-chemo-mechanically coupled smart materials used as actuators and sensors. Recent studies indicate that eIPMC sensors, featuring unique microstructures at the interface between the ionic polymer membrane and the electrode, exhibit enhanced electrochemical behavior and sensitivity under compression, as compared to traditional IPMCs. However, a complete and experimentally-validated model of how eIPMCs behave under dynamic compression loads is currently missing. In this paper, we develop an analytical model for eIPMC sensors, elucidating the role of the engineered interface, modeled as a separate material layer with unique mechanical and electrochemical properties. Theoretical predictions focus on the mechanical-to-electrochemical transduction response under dynamic compressive loads. Experimental verification is conducted on conventional IPMC and novel eIPMC samples fabricated using the polymer abrading technique. Electrochemical impedance spectroscopy is performed to study the effect of the engineered interface on the electrochemical properties. Open-circuit voltage and short-circuit current are measured under external compressive loads in different loading scenarios to demonstrate sensing performance. Results show good qualitative agreement between experimental trends and model predictions. Experiments over the frequency range 1-18 Hz demonstrate an increase of 220-290% in open-circuit voltage and 17-166% in short-circuit current sensitivity for eIPMCs over IPMCs.

Exploring the coupled effects of interfaces and grain size gradients in heterogeneous laminate and gradient structures via a multiple mechanism based constitutive model

Abstract As two promising types of heterogeneous materials, gradient structures and heterogeneous laminates possess superior mechanical properties, such as a combination of high strength and exceptional ductility, which can be attributed to back stress strengthening and strain hardening arising from their heterogeneous microstructures. Recent efforts have been made to combine these two unique microstructures to further improve their properties and performance. However, how heterogeneous interfaces and grain size gradients interplay with each other remains unknown. Therefore, this work aims at exploring the coupled effects of interfaces and grain size gradients in copper–bronze heterogeneous laminate and gradient samples via multiple mechanism-based constitutive modeling incorporating statistically stored dislocations, geometrically necessary dislocations, back stress and deformation twinning. It is revealed that different grain size gradients have profound influence on the deformation mechanisms and mechanical behaviors of the material: a monotonic grain size gradient in the copper layers strengthens the material yet reduces its ductility as a result of diminished back stress hardening due to weakened interface effects; a symmetric grain size gradient in the bronze layers leads to an increase in ductility and a decrease in strength; only by introducing a symmetric grain size gradient into the copper layers can the strength and ductility of the material be improved simultaneously, which is accredited to stronger back stress and grain boundary strengthening due to the synergistic effects between the interfaces and the grain size gradients. In addition, the distinct propensities for twinning in the copper and bronze layers can be attributed to both their different stacking fault energies and grain sizes.

PH-Triggered Phase Transitions, Coexposure of (001) and (110) Facets, and Oxygen Vacancies in BiOCl Photocatalysts.

Bismuth oxychloride (BiOCl) is known for its unique layered microstructure, which plays a pivotal role in enhancing its photocatalytic properties. This study introduces a novel strategy for controlling the phase composition, facet orientation, and oxygen vacancy formation in BiOCl through precise pH adjustment during the synthesis. By employing a hydrothermal method, we systematically varied the pH to produce distinct BiOCl phases and conducted detailed structural and photocatalytic analyses. Remarkably, BiOCl synthesized at pH = 7 demonstrated superior photocatalytic activity on rhodamine B (RhB) degradation, which can be attributed to the coexposure of the (001) and (110) facets, as well as an increased concentration of oxygen vacancies. Density functional theory study also revealed that a high concentration of oxygen vacancies leads to enhanced charge separation, which is beneficial for photocatalytic activity. These results indicate that optimizing the pH during synthesis is a viable approach to enhancing the photocatalytic efficiency of BiOCl, offering significant potential for advanced applications in environmental remediation and solar energy conversion.

Examining Market Quality on the Egyptian Exchange (EGX): An Intraday Liquidity Analysis

This study examines the intraday dynamics of liquidity and trading activity on the Egyptian Exchange (EGX) to assess its market quality. Using reconstructed five-minute limit order book data, this study measures liquidity dimensions and explores anomalies through interval-of-day and day-of-week models. Key findings reveal an inverted J-shaped pattern in spreads due to information asymmetry, a U-shaped pattern in total depth, and a J-shaped market depth pattern. Additionally, significant day-of-week effects are observed, with Sundays showing the lowest liquidity and Thursdays the highest trading activity. These patterns highlight the impact of the EGX’s unique microstructure, including tick sizes and a preference for limit orders. This study underscores the influence of market structure on liquidity, trading efficiency, and cost, emphasizing the need for tailored regulatory and trading strategies. It provides valuable insights for investors optimizing trading strategies and policymakers seeking to enhance market integrity. Concluding, this research offers a foundation for understanding intraday liquidity patterns in emerging markets like the EGX and proposes future exploration of how information flows and trading mechanisms affect price discovery and market efficiency.

Mineralogical analysis of plutonic and volcanic rocks at selected slope sections of the Kuala Lumpur-Karak Highway

The Kuala Lumpur-Karak Highway (KL-KH) is a key route connecting Kuala Lumpur to the East Coast states of Peninsular Malaysia. It passes through three distinct geological formations: the Kuala Lumpur Granite, Genting Sempah Complex, and Bentong Raub Suture Zone. These formations feature unique rock mineral compositions and microstructures that influence the strength and behavior of rock masses. This study used X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) to analyze the mineralogical properties of plutonic and volcanic rock samples from the highway. The plutonic sample from KM29 (GKM29) consists of quartz, muscovite, and albite, while the volcanic sample from KM93 (LKM93) is rhyolite, containing quartz, albite, muscovite, and biotite. While both samples share similar minerals, they differ in texture, mineral proportions, and carbon content. The GKM29 sample has a more granular texture, while the LKM93 sample is finer. These differences in mineral composition and texture affect the mechanical properties of the rocks, including strength and durability, which are crucial for slope stability. Understanding these variations is essential for assessing slope stability and potential geological hazards along the highway. This study emphasizes the importance of early geological assessments for effective slope management and road safety, enabling better planning and maintenance strategies.

Comprehensive Study of Sub-micron Porous Titanium-zirconium Scaffolds Fabricated by Liquid Metal Dealloying

This article investigates the microstructure, mechanical properties and biocompatibility of ultrafine porous titanium-zirconium (TiZr) alloys synthesized by the liquid metal dealloying (LMD) at a temperature of 1023K for various immersion times. The dealloying of Ti20Zr20Cu60 precursors in molten magnesium causes to self-organize three-dimensional hcp-α structures by surface diffusion mechanism, wherein the ligament size, density and porosity range from 130 to 280nm, 2.8 to 3.2g/cm3 and 0.43 to 0.5, respectively. The compression test results of porous products indicate a perfect combination of high compressive strength (415−620MPa) and low elastic modulus (2.1−3.2GPa) matching that of the human bone. The maximum ligament size (280nm), density (3.2g/cm3) and compressive strength (620MPa) corresponds to immersion time of 600s; thereby, the mechanical characteristics can be tailored by modifying the process parameters. Meanwhile, the elastic modulus and compressive strength enhance almost linearly with increasing the relative density in accordance with the Gibson and Ashby model. The in-vitro experiments with MG-63 osteoblast cells also suggests the immersion time of 600s to better support the bone tissue ingrowth. The porous TiZr alloy fabricated by the new dealloying method can be considered as a novel biomaterial for dental implants owing to its unique microstructure, compressive features and biocompatibility.

Achieving high strength in Mg-Gd-Ag-Zr alloy through heterogeneous microstructure with multimodal grain structure and hierarchical precipitates

The development of high-strength Magnesium (Mg) alloys is a key research focus due to their relatively low strength compared to other structural metals. In this paper, a high-strength Mg-13.4Gd-2.2Ag-0.4Zr wt% alloy is achieved by carefully designing a multimodal grain structure combined with hierarchical precipitates, using a processing route of hot rolling followed by aging. The multimodal grain structure, characterized by three distinct grain size distributions and a strong basal texture, arises from partial dynamic recrystallization during hot rolling. The hierarchical precipitates include microscale rod-like and particle-like β phase at grain boundaries, twins, and deformation bands, as well as nanoscale β phase precipitates (~63nm) dispersed within the grain interiors. The fully β precipitates also demonstrate a modified precipitation pathway, differing from the β' and γ'' nanoprecipitates observed in conventional Mg-Gd-Ag alloys. This unique microstructure results in an ultimate tensile strength of 447MPa, primarily attributable to the strong basal texture, hierarchical precipitates, hetero-deformation-induced (HDI) strengthening, and high dislocation density.

High density lath twins lead to high thermoelectric conversion efficiency in Bi2Te3 modules.

Thermoelectric (TE) generators based on bismuth telluride (Bi2Te3) are recognized as a credible solution for low-grade heat harvesting. In this study, an combinative doping strategy of both the donor (Ag) and the acceptor (Ga) in Ag9GaTe6 as dopants is developed to modulate the microstructure and improve the ZT value of p-type Bi0.4Sb1.6Te3. Specifically, the distribution of Ag and Ga in the matrix synergistically introduces multiple phonon scattering centers including lath twins, triple junction boundaries, and Sb-rich nanoprecipitates, leading to an obviously suppressed lattice thermal conductivity of 0.50 W m-1 K-1 at 300 K. At the same time, such unique microstructures of lath twins synergistically enhance the room-temperature power factor to 48.8 μW cm-1 K-2 and improve the Vickers hardness to 0.90 GPa. Consequently, a high ZT of 1.40 at 350 K and ZTave of 1.24 (300-500 K) are achieved in the Bi0.4Sb1.6Te3 + 0.03 wt% Ag9GaTe6 sample. Based on that, a competitive conversion efficiency of 6.5% at ΔT = 200 K is obtained in the constructed 17-couple TE module, which exhibits no significant change in the output property after 30 thermal cycle tests benefiting from the stable microstructure.

Nonporous TiO2@C microsphere with a highly integrated structure for high volumetric lithium storage and enhance initial coulombic efficiency

To enhance the volumetric energy density and initial coulombic efficiency (ICE) of titanium oxide (TiO2) as anode electrode material for lithium-ion batteries (LIB), this study employed a surface-confined in-situ inter-growth mechanism to prepare a TiO2 embedded carbon microsphere composite. The results revealed that the composite exhibited a highly integrated structure of TiO2 with oxygen vacancies and carbon, along with an exceptionally small specific surface area of 11.52 m2/g. Due to its unique microstructure, the composite demonstrated remarkable lithium storage properties, including a high ICE of 75%, a notable capacity of 426.8 mAh/g after 200 cycles at 0.2 A/g, superior rate performance of 210.1 mAh/g at 5 A/g, and an outstanding cycle life, with a capacity decay rate of only 0.003% per cycle over 2000 cycles. Furthermore, electrochemical kinetic studies further validated the advantages of this microstructure.

Synthesis and Complex Dielectric Properties of Ba0.4Sr0.6SnO3 Ceramics with Thorn-like Microstructure.

In this study, we synthesized perovskite Ba0.4Sr0.6SnO3 ceramics with a unique thorn-like microstructure using the solid-state reaction method. The structural and complex dielectric properties were investigated in detail. X-ray diffraction was employed to characterize the phase purity, while X-ray photoelectron spectroscopy was used to analyze the chemical state of the components. The frequency and temperature dependence of the dielectric properties indicates that both the dielectric constant and loss are influenced by A-site ion doping as well as the presence of the thorn-like microstructure. The observed dielectric behavior can be explained by the interfacial polarization and dielectric relaxation processes, which arise from the existing Sn4+-Sn2+ pairs, oxygen vacancies, and defects with activation energies of 0.38 eV, 0.73 eV, and 0.54 eV, respectively. The resistances of grain boundaries, grains, and the thorn-like structure were revealed by the impedance spectra. These findings provide valuable insights into understanding structure-property relationships in perovskite stannate ceramics.

Structured Polymers Enable the Sustained Delivery of Glucocorticoids within the Intra-Articular Space.

Intra-articular glucocorticoid injections are effective in controlling inflammation and pain in arthritides but restricted by short duration of action and risk of joint degeneration. Controlled drug release using biocompatible hydrogels offers a unique solution, but limitations of in situ gelation restrict their application. Gellan sheared hydrogels (GSHs) retain the advantages of hydrogels, however their unique microstructures lend themselves to intra-articular application - capable of shear thinning under force but restructuring at rest to enhance residence. This study examined GSHs for extended intra-articular glucocorticoid delivery of prednisolone (10 mgmL-1); demonstrating links between material mechanics, steroid release, and preclinical assessment of efficacy in synoviocyte culture and transgenic(TNF)197Gkl (TNFtg) murine model of arthritis. GSHs demonstrated sustained release, with typical Fickian profiles over 18 days. Moreover, systems showed good stability under extended culture, with inherent cell-compatibility and suppression of inflammatory synoviocyte activation. In TNFtg animals, GSHs suppressed synovitis (70.08%, p < 0.05), pannus formation (45.01%, p < 0.05), and increased articular cartilage (82.23%, p < 0.05) relative to vehicle controls. The extended profile of steroid release from injectable GSH formulations holds promise in the treatment and management of inflammatory arthritides such as rheumatoid and osteoarthritis, representing a step-change in intra-articular drug delivery to suppress long-term joint inflammation.

Evolution of Precipitates and Microhardness of L-PBF Inconel 625 Through Relevant Thermal Treatment

Laser powder bed fusion (L-PBF) is a metal additive manufacturing (AM) technique that produces a unique microstructure significantly different from wrought microstructure. Inconel 625 (IN625) is an alloy widely used to manufacture complex parts, but it comes with its own unique challenges. The alloy is prone to precipitation under elevated temperatures, which makes designing suitable heat treatment to tailor the desired microstructure and mechanical properties critical. Traditional heat treatment for wrought IN625 cannot be applied to L-PBF IN625; therefore, it is vital to understand the evolution of precipitates on the way to complete recrystallization. This study focuses on these precipitates in IN625 produced by the L-PBF technique. Heat treatments at 700 °C, 900 °C, and 1050 °C were performed separately to encourage the precipitation of strengthening γ″, the detrimental δ phase, and the dissolution of precipitates, respectively. γ″ precipitates were found in the as-printed condition and at 700 °C. δ precipitates were detected at 700 and 900 °C. Carbides and Al-rich oxides were observed in all conditions of L-PBF IN625. Texture analysis showed grain growth along the build direction with strong (100) texture at temperatures up to 900 °C. Weak and random texture with equiaxed grains was observed at 1050 °C, which is similar to wrought IN625.

In Situ Laser Direct Writing of Graphene-Based Layered Hybrid Materials with Superhydrophilicity.

Laser-induced graphene (LIG) has attracted extensive attention as an electrode material. However, it usually exhibits limited electrochemical performance in many applications due to the limited electrical conductivity and charge storage properties. Herein, we proposed a simple and environmentally friendly strategy for in situ preparation of flexible Au/LIG/PI layered hybrid materials using laser direct writing. The transformation from hydrophobic to superhydrophilic of hybrid materials was successfully achieved. At a laser power of 6.0 W during laser reirradiation, the contact angle of the prepared Au/LIG/PI layered hybrid material was 0°. Characterizations confirmed a formed continuous Au layer covered on the porous LIG skeleton with a uniform distribution. The superhydrophilicity resulting from this unique microstructure greatly enhanced the electrochemical performance of the microsupercapacitors (MSCs) designed and fabricated based on Au/LIG/PI hybrid materials. Meanwhile, this MSC demonstrated excellent flexibility due to the PI substrate. The in situ preparation of superhydrophilic Au/LIG/PI layered hybrid materials provides a strategy for improving the performance of LIG-based MSCs, thereby enhancing their application potential.

Study on Fatigue Behavior and Fracture Mechanism of LMD Ti-6.5Al-3.5Mo-1.5Zr-0.3Si Alloy Based on Microstructure.

This study explores the fatigue behavior and fracture mechanisms of TC11 titanium alloy formed by laser metal deposition (LMD) and subjected to double annealing. The research focuses on how the alloy's unique microstructure, consisting of alternating equiaxed and columnar crystals, influences its fatigue performance. The microstructure's basket-like α' phase, made up of both plate-shaped and needle-like structures, leads to variations in crack growth behavior, as shown in the relationship between the crack growth rate and the stress intensity. An analysis of slip patterns reveals that equiaxed crystals undergo more frequent deformation, accelerating crack propagation compared to the more evenly distributed deformation in columnar crystals. These findings suggest a new approach for improving the fatigue resistance of 3D-printed titanium alloys by optimizing their microstructure. This study provides valuable insights for enhancing material toughness and extending the lifespan of titanium alloys in applications such as aerospace and biomedical engineering.

Sandwich-Structured Fluorinated Polyimide Aerogel/Paraffin Phase-Change Composites Simultaneously Enables Gradient Thermal Protection and Electromagnetic Wave Transmission.

There is an emerging requirement of advanced functional materials for simultaneous thermal protection and electromagnetic wave-transparent transmission applications. A novel polyimide (PI) aerogel-based sandwich-structural composite is developed to meet such a requirement in this study. This composite is based on a unidirectional fluorinated PI (FPI) aerogel as a lower layer, a nondirectional conventional PI aerogel as a middle layer, and a nondirectional FPI aerogel/paraffin phase-change composite as an upper layer. The lower layer exhibits a unique unidirectional porous microstructure and an ultralow dielectric constant of 1.04. The upper layer possesses a dynamical temperature regulation capability thanks to its loaded paraffin having a high latent heat capacity of 242.7Jg-1. The presence of the nondirectional PI aerogel middle layer can effectively prevent against the leakage of paraffin from the upper layer to the surface of the composite. Through a rational integration of three functional layers, the developed sandwich-structured composite not only can provide gradient thermal protection for hot objects over a long period but also exhibits an excellent wave-transparent capability to establish communication between two electromagnetically shielded electronic devices. With such prominent thermal insulation and wave-transparent functions, the sandwich-structured composite exhibits great potential for specific applications in aircraft, spacecraft, radar systems, and satellite communication.

Grain size dependent deformation microstructure evolution and work-hardening in CoCrNi medium entropy alloy

This study clarified the grain size dependence of the deformation microstructure evolution and work-hardening behavior in CoCrNi medium entropy alloy. We fabricated fully recrystallized specimens with coarse-grained (CG) and ultrafine-grained (UFG) specimens by severe plastic deformation and subsequent annealing processes. Tensile deformation was applied to the specimens at room temperature. The UFG specimen exhibited both high strength and high ductility compared to conventional UFG metals due to the high work-hardening ability. In the CG specimen, three distinct types of deformation microstructures consisting of dislocations and deformation twins developed depending on grain orientations, similar to the single-crystalline specimens. In the UFG specimen, widely extended stacking faults and randomly-tangled dislocations were found to coexist in most grains. Deformation twins were found to nucleate without evidence of dislocation reactions regardless of grain orientations, implying abnormal nucleation mechanisms of deformation twins in the UFG specimen. Dislocation densities quantified by in-situ synchrotron XRD measurements during tensile deformation were higher in the UFG specimen than those in the CG specimen and conventional UFG metals. Our analysis showed that the work-hardening behavior of the specimens was primarily controlled by increases in dislocation density as well as the introduction of planar defects during deformation. Through comparisons with the CG specimen and conventional UFG metals, we concluded that the excellent work-hardening ability of the UFG specimen was mainly due to the evolution of unique deformation microstructures and rapid increase in dislocation density, which could be due to inhibited dynamic recovery in the MEA.

Melt-Blown Polypropylene Membrane Modification for Enhanced Hydrophilicity.

Melt-blown, an environmentally friendly technique, is widely used to create high-quality non-woven fabrics by extruding molten polymer resins into interlaced fibers. In the realm of biomedical textiles, its unique microstructure makes it ideal for filtration and wound dressings. Our study focuses on modifying the surfaces of polypropylene melt-blown membranes. An effective, one-step, suitable, and reliable method to graft a bioactive polymer, sodium polystyrene sulfonate-PolyNaSS, onto the membranes has been developed. The process involves UV irradiation to initiate direct and progressive growth of NaSS over the surface through radical polymerization. To assess the efficiency of the grafting, techniques like colorimetry, water contact angle measurements, Fourier-transformed infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) were used. Outcomes related to the grafting were demonstrated by a change in wettability and quantitatively calculated sulfonate groups. Subsequently, grafted PolyNaSS promoted cell adhesion, as evidenced by improved cell morphology. On grafted membranes, fibroblasts exhibited a stretched shape, while non-grafted ones showed inactive round shapes. These findings underscore the chemical and biological reactivity of polypropylene materials, opening exciting possibilities for various applications of melt-blown materials.

Biomimetic biomass-based composite carbon aerogels with excellent mechanical performance for energy storage and pressure sensing in extreme environments.

The poor mechanical properties of biomass-based carbon aerogels after carbonization severely limit their application in pressure sensing and energy storage for wearable devices and electronic skin. In this work, a supramolecular assembly structure was designed inspired by the unique microstructure of natural wood for the preparation of biomass-based carbon aerogels with supercompressibility, elasticity, stable strain electrical signal response, and wide sensitive detection. Bacterial cellulose and lignin were selected as the main components of the biomass-based composite aerogel 'cell wall'. The graphene oxide with an aromatic structure was introduced to induce the assembly of firmly attached lignin and bacterial cellulose. The prepared biomass-based carbon aerogels exhibit supercompressibility (at least 100 cycles at 90% strain), high elasticity (88.88% height retention after 1000 cycles at a strain of 50%), surprising temperature-constant superelasticity and fatigue resistance (shape retention rate greater than 85%) at -196 ℃. In particular, it exhibits temperature-invariant high linear sensitivity over an extremely wide operating pressure range (0-43kPa), allowing accurate detection of human signals. In addition, the prepared carbon aerogels exhibit excellent performance in supercapacitors. It has a specific capacitance of 158F/g at a current density of 1 A/g and an energy density of 18.75 Wh/kg at a high power density of 2500W/g. This strategy also demonstrates its promise as a wearable device in hostile environments.