Formation Of Microcracks Research Articles

A Study on the Microstructure Regulation Effect of Niobium Doping on LiNi0.88Co0.05Mn0.07O2 and the Electrochemical Performance of the Composite Material under High Voltage.

High-nickel ternary materials are currently the most promising lithium battery cathode materials due to their development and application potential. Nevertheless, these materials encounter challenges like cation mixing, lattice oxygen loss, interfacial reactions, and microcracks. These issues are exacerbated at high voltages, compromising their cyclic stability and safety. In this study, we successfully prepared Nb5+-doped high-nickel ternary cathode materials via a high-temperature solid-phase method. We investigated the impact of Nb5+ doping on the microstructure and electrochemical properties of LiNi0.88Co0.05Mn0.07O2 ternary cathode materials by varying the amount of Nb2O5 added. The experimental results suggest that Nb5+ doping does not alter the crystal structure but modifies the particle morphology, yielding radially distributed, elongated, rod-like structures. This morphology effectively mitigates the anisotropic volume changes during cycling, thereby bolstering the material's cyclic stability. The material exhibits a discharge capacity of 224.4 mAh g-1 at 0.1C and 200.3 mAh g-1 at 1C, within a voltage range of 2.7 V-4.5 V. Following 100 cycles at 1C, the capacity retention rate maintains a high level of 92.9%, highlighting the material's remarkable capacity retention and cyclic stability under high-voltage conditions. The enhancement of cyclic stability is primarily due to the synergistic effects caused by Nb5+ doping. Nb5+ modifies the particle morphology, thereby mitigating the formation of microcracks. The formation of high-energy Nb-O bonds prevents oxygen precipitation at high voltages, minimizes the irreversibility of the H2-H3 phase transition, and thereby enhances the stability of the composite material at high voltages.

Comparative Evaluation of ProTaper Gold, TruNatomy, and XP-endo Shaper Instruments on Dentinal Microcrack Formation: Scanning Electron Microscope Study

Comparative Evaluation of ProTaper Gold, TruNatomy, and XP-endo Shaper Instruments on Dentinal Microcrack Formation: Scanning Electron Microscope Study

To Enhance the Performance of LiNi0.5Co0.2Mn0.3O2 Aqueous Electrodes by the Coating Process.

The Li+/H+ cation exchange reactions occur when the cathode is exposed to water and can cause the degradation of battery performance, posing a significant challenge in the preparation of cathode aqueous electrodes. In this study, kh570 [3-(trimethoxysilyl)propyl methacrylate] is used to coat and modify the surface of LiNi0.5Co0.2Mn0.3O2 cathode particles. During the coating process, kh570 undergoes hydrolysis to generate silanol groups, which are subsequently bonded onto the surface of cathode particles and undergo self-polymerization through condensation reactions. As a result, a coating layer forms on the surface of the cathode. This change alters the surface properties of the cathode particles from hydrophilic to hydrophobic, thereby increasing their resistance to water. The coating layers reduce direct contact with water and minimizes internal particle microcracks formation in aqueous electrode processing. After the preparation of aqueous electrodes, the modified cathode exhibits lower transfer resistance and lower polarization, improving both the current rate performance and the cycling performance of the battery.

Suppressing formation of microcracks in laser powder bed fusion manufactured AA6061 aluminum alloy by introducing mechanical alloyed Al-25at%Ti particles

A novel approach which incorporates mechanical alloyed Al-25at%Ti particles into an AA6061 aluminum alloy powder feedstock has been used to suppress pronounced hot cracking that normally occurs in laser powder bed fusion (LPBF) manufactured AA6061 alloy. Investigation of the microstructure and tensile properties of the Ti-modified AA6061 sample fabricated by LPBF confirms the effectiveness of this approach. The suppression of microcrack formation is associated with the transition of a coarse columnar structure to fine equiaxed structure facilitated by heterogeneous nucleation of the grains on Al3Ti nanoparticles. This crack-free microstructure also results in excellent tensile properties of 252 MPa in yield strength, 361 MPa in ultimate tensile strength, and 9.7 % in elongation to fracture.

Laser-inherent porosity defects in additively manufactured Ti–6Al–4V implant: Formation, distribution, and effect on fatigue performance

Porosity defects are inherently present in Ti–6Al–4V (Ti6-4) parts produced using additive manufacturing (AM) methods like laser powder-bed fusion (LPBF). This work aims to investigate different laser-inherent porosity defects at various LPBF parameter settings and assess their impact on the fatigue behaviour of Ti6-4 implants processed by LPBF. The presence of LPBF-inherent porosity defects with different shapes and sizes was established using microstructural examination and X-ray micro-CT analysis. These mostly comprise lack-of-fusion porosity (LoFP), gas-entrapped porosity (GeP), and pores-induced microcracks. Volumetric porosity defects were seen to range from 1.9 × 104 to 9.52 × 105 μm3. The L-1 specimen exhibited the lowest defect, while the L-6 specimen displayed the largest number of defects. While LoFP defects predominate in L-6, there was a notable presence of GeP defects in the specimens processed using the factory default condition (L-D). Upon examination of the majority of specimens, GeP and LoFP coalesced to form clusters, leading to the formation of pores-induced microcracks. This ultimately leads to a decrease in fatigue performance. By maintaining the power at the default setting and increasing the scan speed by 8% of the default value, a specimen (L-1) with minimal porosity defects and superior fatigue performance is achieved. L-6 exhibits defects with significant dimensions and irregular form. Consequently, it displays inferior fatigue characteristics.

Effect of Size and Morphology of Different ZnO Nanostructures on the Performance of Dye-Sensitized Solar Cells

In this study, the influence of zinc oxide (ZnO) nanostructures with various morphologies on the performance of dye-sensitized solar cells (DSSCs) was investigated. Photo-electrodes were fabricated incorporating ZnO transport layers of distinct nanoscale morphologies—namely nanoparticles, microballs, spiky microballs, belts, and triangles—and their respective current–voltage characteristics were evaluated. It was observed that the DSSCs employing the triangular ZnO nanostructures, with a side length of approximately 30 nm, achieved the highest power conversion efficiency of 2.62%. This was closely followed by the DSSCs using spherical nanoparticles with an average diameter of approximately 20 nm, yielding an efficiency of 2.54%. In contrast, the efficiencies of DSSCs with microball and spiky microball ZnO nanostructures were significantly lower, measuring 0.31 and 1.79%, respectively. The reduction in efficiency for the microball-based DSSCs is attributed to the formation of micro-cracks within the thin film during the fabrication process. All DSSC configurations maintained a uniform active area of 4 mm². Remarkably, the highest fill factor of 59.88% was recorded for DSSCs utilizing the triangular ZnO morphology, with the spherical nanoparticles attaining a marginally lower fill factor of 59.38%. This investigation corroborates the hypothesis that reduced particle size in the transport layer correlates with enhanced DSSC performance, which is further amplified when the nanoparticles possess pointed geometries that induce strong electric fields due to elevated charge concentrations.

Stress field evolution on rebar coupling connection at uniaxial tension

Rebar coupling connections are widely used for joints, and it is necessary to get information about the stress field distribution on the coupling surface at uniaxial tension to characterize operation of such joints.Purpose: The aim of the work is to study the stress-strain state of rebar connections under tension, full-scale junctions of the type A500 rods, and the deformation influence on the steel microstructure of grade С1020.Methodology: Non-contact three-dimensional imaging system VIC-3D and digital image correlation and tracking for studying stress-strain state of rebar connection; transmission electron microscopy for studying the steel microstructure.Research findings: Load-displacement curves are suggested for the valve coupling, and three deformation stages are identified: 1) elastic deformation of the coupling connection, 2) parabolic hardening, 3) preceding the coupling connection destruction. The analysis of the strain field distribution on the coupling connection shows that at any time, plastic strain localizes in certain zones of the sample. The stress field evolution on the coupling connection correlates with the indicated deformation stages. The compliance of the rebar joint made of seamless hot-deformed tube with an outer and inner diameters 51 and 32 mm, respectively, made of С1020 steel grade, induces 500 MPa stress in the normal section of rebar under the tensile axial load.Value: It is shown that during uniaxial tension of 0 to 5 %, perlite fractures, which is accompanied by further polarization of the dislocation structure. The internal stress amplitude increases and at 5% tension, far-range stresses grow as compared with those induced forest dislocations. The main contribution to far-range stresses and their change at 5 % tension is made by the elastic component, that promotes to the microcrack formation.

Temperature-dependent damage of magnesium alloy with ratchetting–fatigue interaction effects: Experiments and mesomechanical theory

Fatigue failure is a significant concern for magnesium (Mg) alloy components. However, fatigue damage mechanisms of Mg alloys, particularly in the case of ratchetting–fatigue interaction at elevated temperatures, are still not well understood. In this paper, we combine experiments and theoretical analysis to investigate the high-temperature damage mechanisms of the extruded AZ31 Mg alloy, specifically focusing on the effects of ratchetting–fatigue interaction. We reveal a distinct demonstration of damage, namely the formation of microvoids in the alloy due to significant ratchetting deformation, defined as ratchetting damage. Notably, this ratchetting damage is more prevalent at higher temperatures. Considering the mesomechanics-based energy mechanisms associated with grain boundaries (or twin boundaries), a mesomechanical damage model is established to capture the ratchetting damage under elevated temperatures and large ratchetting deformations. This model can reasonably simulate the intricate process of damage evolution and predict the critical condition of microvoid or microcrack formation. This work has the potential to serve as a theoretical tool for the safety design of structures made from Mg alloys under complex mechanical and thermal conditions.

Hybrid Fiber Influence on the Crack Permeability of Cracked Concrete Exposed to Freeze-Thaw Cycles.

This paper describes hybrid fiber's influence on the crack permeability of cracked concrete exposed to freeze-thaw cycles. A permeability setup and a laser-scanning setup have been designed to measure the crack permeability and the fractured surface roughness of cracked hybrid fiber-reinforced concrete, containing polypropylene fiber and steel fiber, under a splitting tensile load. The results show that, when the effective crack width of the specimens is less than 25 μm, the rough crack surface significantly reduces the concrete's crack permeability. As the crack width increases, the effect of the concrete crack surface on crack permeability gradually decreases, and the crack permeability of the concrete is closer to the Poiseuille flow model. The permeability parameter α derived from the Poiseuille flow model is effective for assessing the crack permeability of concrete. Compared to the modified factor ξ of crack permeability, the permeability parameter α can effectively evaluate and quantify the development trend of crack permeability within a certain range of crack widths. The permeability parameter α of SF20PP2.3, subjected to the same freeze-thaw cycles, decreases by 16.3-94.8% compared to PP4.6 and SF40, and SF20PP2.3 demonstrates a positive synergistic effect on the crack impermeability of cracked concrete. The crack impermeability of SF40PP2.3, subjected to the same freeze-thaw cycles, lies between that of PP6.9 and SF60. The roughness of crack surface (X) and the crack permeability (Y) are highly correlated and follow an exponential curve (Y = 1.0415 × 107·e-6.025·X) in concrete. This demonstrates that hybrid fibers enhance crack impermeability by increasing the crack surface roughness. Furthermore, the combination of polypropylene fiber and steel fiber effectively promotes the formation of micro-cracks and facilitates the propagation of multiple cracks in the concrete matrix. This combination increases the head loss of water flow through the concrete and decreases the crack permeability.

Realizing Dual Functions through Y2O3 Modification to Enhance the Electrochemical Performance of LiNi0.8Co0.1Mn0.1O2 Material

In recent years, the remarkable energy density of high-nickel ternary materials has captured considerable attention. Nevertheless, the high-nickel ternary cathode material encounters several challenges, including cationic mixing, microcrack formation, poor cycling capability, and limited thermal stability. Coating, as a viable approach, proves to be effective in enhancing the material properties. In this study, the LiNi0.8Co0.1Mn0.1O2 (NCM811) sample underwent a dry grinding process, followed by Y2O3 coating and subsequent sintering at varying temperatures. The microstructure, morphology, and electrochemical properties of the materials were meticulously examined, and the underlying mechanism of coating modification was meticulously explored. The outcomes demonstrate the attainment of dual coating and doping effects through Y2O3 modification. Y2O3 coating mitigates the direct interaction between the NCM811 surface and the electrolyte, thereby inhibiting undesired side reactions at the interface. Moreover, the Y element infiltrates the crystal structure, imparting stability at elevated sintering temperatures. Remarkably, the Y2O3-coated cathode materials exhibit significantly enhanced cycling stability, discharge capacity, and rate performance. These findings can provide novel insights that can be harnessed to improve the energy density cathode material of NCM811.

Stabilizing Interfacial Behaviors of Ni‐rich Cathodes by Upcycling of Oyster Shells Waste

AbstractLayered lithium oxides (LNCM), with over 60% Ni, are promising cathode materials for electric vehicles due to their high capacity. however, reliable cycling retention cannot easily achieved owing to the instability of the interface. Here, recycled oyster shell (OS) is employed as an efficient precursor for the surface modification of LNCM cathodes; subsequently, Ca‐based artificial cathode–electrolyte interphases (CEI) are obtained at the LNCM interfaces through a simple calcination process. When the pulverized OS is calcined with LNCM cathode materials at elevated temperatures, CaCO3 is converted to CaO via thermal decomposition at the LNCM interface, which effectively protects the unstable interface. Microscopic analyses indicate the nanodomain island‐type CEI layers embedded after OS calcination. The OS‐coated LNCM cathode materials increase the cycling retention after 100 cycles (93.8% vs. 62.7%) and decrease the internal cell pressure by preventing electrolyte decomposition. Incorporating Ca into the LNCM cathode materials also inhibits microcrack formation because of the improvement in particle hardness and the remarkable decrease in the irreversible dissolution of transition metals from LNCM cathodes, considering that Ca plays a crucial role in scavenging fluoride species. Consequently, recycling OS as a functional LNCM precursor is an innovative approach for enhanced cycling retention.

The analysis of extension evolution law and damage behavior characteristic for line microcracks on Si3N4 bearing balls

To predict the relation between extension evolution law and damage of line microcracks on silicon nitride bearing balls. Firstly, the 3D point cloud features of line microcracks are obtained based on multi-image 3D reconstruction. Next, the point cloud diagram data is optimized to fit the molecular dynamics geometric model of line microcracks extension process. Then, according to the Si3N4 molecular dynamics deep learning potential, the molecular dynamics mechanical model is established. Finally, Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) is used to numerically solve the extension evolution of line microcracks. The experiment result shows that from the change analysis of single-layer surface mesh, the microcracks extension is concentrated in the central region of the indentation. The new microcracks spread along both sides of the original microcracks. After uniformly distributed load is applied to line microcracks, there is a phenomenon of concentrated swirling microcracks formation under the indentation region. By analyzing the atomic coordination number nephogram, the microcracks extension occurs when the proportion of amorphous atoms is up to 7 % during loading. And the plastic deformation occurs when the proportion of amorphous atoms is dropped to 6 % during unloading. In addition, in the process of indentation loading, plastic deformation and slip zone occur on Si3N4 bearing balls surface. However, the strain is accumulated in the middle region during unloading. The slip zone moves inward and becomes thin, and the elastic deformation partially is recovered.

Monolithic 24 cm2 flexible triple-junction solar cell encapsulated module based on the ipsilateral electrode welding technology

The inverted metamorphic multi-junction solar cell is anticipated to be widely applied in stratospheric flight because of its exceptional properties of flexibility and light weight. We propose an ipsilateral welding technology based on Ti/Au electrodes to simplify the fabrication process of GaInP/GaAs/InGaAs solar cells and encapsulate large-sized flexible solar cells. After annealing at 200°C for 2 h, the Ti/Au electrode achieved a low specific contact resistivity of 2.9×10−7Ω⋅cm2. The performance of the ohmic contact remains stable after the thermal cycling tests. The Ti/Au electrode can require less heat input for welding to reduce the risk of microcrack formation of the solar cells. By employment of this electrode, a 24cm2 solar cell achieved a conversion efficiency of 34.74%. A flexible solar cell module with an efficiency of 32.82% under AM 1.5G illumination was obtained by the ipsilateral electrode welding technology.

Surface reactivity versus microcracks in Ni-rich layered oxide cathodes: Which is critical for long cycle life？

Capacity fading of Ni-rich cathode is thought to originate from the formation of inactive rock-salt phase induced by surface reactivity and the isolation of active material caused by microcracks due to anisotropic volume contraction of grains. It is generally assumed that inhibiting the formation of microcracks within secondary particle by radially aligned microstructure is a vital aspect for suppressing capacity fading. However, the new researches about reduction of microcracks simply by certain electrolytes call a question on the origin of microcracks and the critical factor for the cycle life of cathodes. Herein, LiNi0.92Co0.04Mn0.04O2 cathodes with different surface characteristic and radially aligned microstructure were synthesized by doping with high valence elements using some hydroxide precursor. The effects of W6+ and/or Mo6+ induced surface phase and microstructure on electrochemical performance were investigated. Despite the inferior radially aligned, size-refined primary grains and higher degree of microcracks, W6+ doped cathode still possesses alleviated parasitic reactions, higher crystal structural stability and capacity retention than Mo6+ doped materials, because of the enhanced cathode-electrolyte interfacial stability. The results contend that the consequence of surface reactivity on determining cycle life of Ni-rich cathodes is more critical than that of microcracks, and efforts relating to constructing intact and uniform stable surface phase will exhibit greater potential to promote the performance of Ni-rich cathodes than microstructural refinement.

Advancements in Addressing Microcrack Formation in Ni–Rich Layered Oxide Cathodes for Lithium–Ion Batteries

AbstractNickel–rich layered oxides of LiNi1–x–yCoxMn(Al)yO2 (where 1–x–y>0.6) are considered promising cathode active materials for lithium‐ion batteries (LIBs) due to their high reversible capacity and energy density. However, the widespread application of NCM(A) is limited by microstructural degradation caused by the anisotropic shrinkage and expansion of primary particles during the H2→H3 phase transition. In this mini–review, we comprehensively discuss the formation of microcracks, subsequent material degradation, and related alleviation strategies in nickel–rich layered NCM(A). Firstly, theories on microcracks′ formation and evolution mechanisms are presented and critically analyzed. Secondly, recent advancements in mitigation strategies to prevent degradation in Ni–rich NCM/NCA are highlighted. These strategies include doping, surface coating, structural optimization, and morphology engineering. Finally, we provide an outlook and perspective to identify promising strategies that may enable the practical application of Ni–rich NCM/NCA in commercial settings.

Influence of coating microstructure on the corrosion behavior of Inconel 625 coatings fabricated by different thermal spraying processes

Inconel 625 coatings with dense microstructures (porosity <2 %) were fabricated on AISI 304L stainless steel substrates by flame spraying (F), twin-wire arc spraying (A), plasma spraying (P), and high-velocity oxygen fuel spraying (H). The quantity of oxide within the coating layers followed the descending order of F > A > P > H, with Cr2O3 identified as the predominant oxide in the Inconel 625 coating layers. The corrosion resistance of the Inconel 625 coating specimens decreased in the order of H > A > P > F. The outstanding corrosion resistance of the Inconel 625 coating prepared by high-velocity oxygen fuel spraying was attributed to the compact coating layer with a very low oxide content. It is suggested that the localized galvanic corrosion around the oxide/matrix interface may deteriorate the corrosion resistance of the coating layer, which is the primary factor contributing to the low corrosion resistance of the F specimen. Although the P specimen exhibited a lower oxide content than the A specimen, it demonstrated inferior corrosion resistance. This phenomenon can be attributed to the significant formation of microcracks within the P specimen, creating penetration tunnels for the corrosive solution and consequently reducing its corrosion resistance.

Mechanical characterization and strain analysis applied to the heat treatment of wood materials, by means of digital image correlation

Digital image correlation (DIC) was used to examine the strain distribution of heat-treated beech and Uludag fir woods in mechanical testing. It also evaluated the effects of the heat treatment process on the properties of the wood samples. The physical (mass/density loss, dimensional stability, color change, and surface roughness), mechanical (flexure test and compressive strength), morphological, thermal, and structural properties of the heat-treated wood were examined. It was determined that the heat treatment parameters can be optimized using the DIC method. The test results showed that although heat treatment can provide improved physical and thermal properties, it caused micro-crack formations and collapses in the wood cells. As a consequence, the mechanical properties of the heat-treated wood materials decreased with the heat treatment process. There were slight differences in the curves of the samples according to Fourier infrared and X-ray diffraction analyses. Morphological characterization showed that the heat treatment triggered large cracks in the cell wall and lumens and the morphological structure of heat-treated wood was affected at large percentages.

Investigating the physical mechanism of ion-slicing in AlN and hetero-integrating AlN thin film on Si(100) substrate

Heterogeneously integrating the monocrystal AlN thin films on Si(100) substrates by ion-slicing technique provides a promising high-quality material platform to achieve the monolithic integration of Silicon-based CMOS (Complementary Metal Oxide Semiconductor) and high-performance III-nitride devices. Single crystalline AlN bulk materials implanted by hydrogen ions (H+) were used to elucidate the physical mechanism of the blistering formation in hydrogen implanted AlN with different annealing process. XTEM characterization was performed to reveal the formation of H-induced microcracks which eventually leads to the layer splitting. Using the ion-slicing technique, the AlN thin films were capitally transferred to Si(100) substrate. The crystal quality and the microstructure of the transferred AlN thin film were characterized thoroughly, indicating its exceptional crystal quality with the full width at half maximum (FWHM) for (002) XRC as low as 93.6 arcsec.

Effect of PVA Fiber on the Mechanical Properties of Seawater Coral Sand Engineered Cementitious Composites.

The physical and mechanical characteristics of seawater coral sand engineered cementitious composites (SCECC) were examined through uniaxial compression, three-point bending, and splitting tensile tests. The mechanical properties were scrutinized under varying fiber volume fraction conditions (V = 0%, 0.575%, 1.150%, 1.725%, and 2.300%). The experimental results indicated that the compressive strength, three-point bending strength, and split tensile strength of SCECC tended to increase with the rise in fiber volume fraction. The strengths attained their maximum values of 45.88, 12.56, and 3.03 MPa when the fiber volume fraction reached 2.300%. In the compression test, the compressive strength of the 7-day specimen can achieve more than 78.50% of that observed in the 28-day specimen. Three-point bending test has revealed that SCECC exhibits favorable strain-hardening and multi-crack cracking characteristics. Fracture patterns of SCECC exhibited variations corresponding to changes in fiber content, as illustrated by their load-deformation curves, the addition of PVA fibers can change the damage mode of cementitious composites from brittle to ductile. The fracture energy of SCECC further attests to its elevated toughness. This is due to the fact that the fibers delay the formation of microcracks and prevent crack expansion, thus significantly increasing the deformability of the material. By verifying its strength, deformability, fracture energy, and other key performance indicators, the feasibility of SCECC in coastal construction projects has been clarified. The successful development of SCECC provides an innovative and high-performance option for the construction of future island projects.

Investigation of the precipitation behavior and its role on creep deformation and failure mechanisms at high temperatures for a turbine disk alloy

The creep deformation behavior of a turbine disk alloy at high temperatures was studied, and the role of the multi-scale precipitates on the creep deformation and failure mechanisms was revealed. The turbine disk alloy shows a typical microstructure with the micron-scale MC carbides, submicron delta phase, together with nanoscale γ″ and γ' precipitates distributed in the matrix after hot working and aging treatment. The MC carbides are mostly formed from the solidification process due to enrichment of Nb in the inter-dendritic areas. The creep life decreases from 763.5 h to 5.7 h when the creep temperature increases from 953 K to 1023 K at 500 MPa. The fracture surfaces exhibit a transgranular fracture pattern accompanied with the formation of substantial microvoids. Slipping occurs in both unidirectional and bidirectional modes during deformation. The microvoids along the grain boundaries are generated through decohesion of δ precipitates from the matrix or the interaction between slip traces and grain boundaries. When the intragranular MC carbides interact with the slip traces, microcracks can be formed by particle fracturing. The dense distribution of particles along the grain boundaries will result in a significantly higher critical stress required for microvoid nucleation, whereas the non-coherent particles inside the grains, particularly the large size MC carbides, can decrease the critical shear stress for microcrack formation to as low as 88.9 MPa, thereby contributing to alloy rupture. For the coherent precipitates, a comprehensive strengthening effect of 389.12 MPa is achievable by the synergistic precipitation of γ″ and γ', which primarily serve to enhance and coordinate intragranular deformation during creep.