Microstructure Distribution Research Articles

Precipitation–Flotation Process for Molybdenum and Uranium Separation from Wastewater

The mining of molybdenum and uranium ores inevitably results in the generation of large volumes of wastewater containing low concentrations of metals, which poses significant threats to the environment. This study presents a novel precipitation–flotation process for the simultaneous separation of molybdenum and uranium from wastewater. A systematic investigation was conducted on the impacts of the type of precipitant, flotation reagent type, and flotation parameters on the experimental results. Ferric salt served better as a precipitant than aluminum salt and humic acid did, and sodium dodecyl sulfate (SDS) was more suitable than sodium dodecyl benzene sulfonate for acting as a surfactant and foaming agent. Under specific conditions, including a pH of 6.6, an Fe3+ dosage of 0.6 mmol·L−1, an SDS dosage of 40 mg·L−1, an air flow rate of 25 mL·min−1, and a flotation time of 10 min, the removal efficiencies of molybdenum and uranium reached 96.6% and 93.6%, respectively. After flotation, the molybdenum concentration, uranium concentration, chemical oxygen demand, and turbidity of the treated water all meet the emission standards. Furthermore, the metal removal mechanisms, including the particle size distribution, functional group structure, surface element composition, microstructure, and element distribution, were elucidated on the basis of characterization of the precipitation–flotation products.

Split Hopkinson bar and flash X-ray characterization of ultra high performance concrete reinforced by steel fibers subjected to dynamic compression

AbstractExcellent mechanical properties of ultra high performance concrete make it suitable for use in special applications, where the material is subjected to dynamic phenomena such as impacts, explosions, or earthquakes. This paper presents a novel experimental approach that integrates a Split Hopkinson Pressure Bar with a flash X-ray system and high-speed optical imaging to investigate the dynamic behavior of steel fiber reinforced UHPC under high strain rate uni-axial compression. In-situ Flash X-ray radiography emerges as a particularly effective tool, providing clear visualization of deformation response and overcoming challenges associated with flying debris encountered in optical inspection. Moreover, computed tomography and scanning electron microscopy appear as a vital technique for analyzing micro-structure and fiber distribution and orientation. The combined approach offers a promising method to study the dynamic behavior of steel fiber reinforced ultra high performance concrete and also holds promise for analyzing more complex modes of deformation and material interactions, providing valuable insights for enhancing the design and performance of critical infrastructure subjected to dynamic loading events.

Preparation of high‐strength Si3N4 ceramics via vat photopolymerization: A bi‐phase particle size gradation strategy

AbstractThis paper introduces an approach to preparing high‐strength Si3N4 ceramics using vat photopolymerization with a bi‐phase particle size gradation strategy. The influence of different ratios of coarse β‐Si3N4 powders (Cβ) and fine α‐Si3N4 powders (Fα) on the slurry performance, microstructure evolution, and final ceramic strength was systematically studied. It was found that an appropriate particle size gradation can significantly reduce the viscosity of the slurry. The curing depth of Si3N4 slurries decreases with increasing Fα content, while the stability increases. During sintering, dissolved Fα‐Si3N4 not only directly precipitates into small elongated β‐Si3N4 grains but also onto the neighboring Cβ‐Si3N4, promoting the development of large elongated β‐Si3N4 grains and resulting in a bimodal microstructure distribution. The highest strength of Si3N4 ceramics was achieved with a ratio of 6:4 Cβ to Fα Si3N4 powders. Under these conditions, the Si3N4 ceramics exhibited a flexural strength of 472 MPa, significantly higher than that of Si3N4 ceramics prepared using pure Cβ/Fα powders. The strength improvement is primarily due to the well‐designed bi‐phase particle size gradation strategy, which optimizes slurry performance, minimizes defects that may be introduced during the green part printing process while controlling the microstructure evolution during sintering, achieves the ideal bimodal microstructure distribution. The outcomes of this research demonstrate the feasibility of using vat photopolymerization with bi‐phase particle size gradation for the preparation of high‐strength Si3N4 ceramics, which has great potential for application in the manufacturing of various ceramic products.

Effect of Dual Shot Peening on Microstructure and Wear Performance of CNT/Al-Cu-Mg Composites.

This work systematically investigated the effect of dual shot peening (DSP) and conventional shot peening (CSP) on the microstructure, residual stress and wear performance of the CNT/Al-Cu-Mg composites. The results indicated that compared with CSP, DSP effectively reduced surface roughness (Rz) from 31.30 to 12.04 μm. In parallel, DSP introduced a smaller domain size (33.1 nm) and more dislocations, higher levels compressive residual stress and a stiffer deformation layer with deeper affected zones. Moreover, DSP effectively improved the uniformity of the surface layer's microstructure and residual stress distribution. The improvement is mainly due to secondary impact deformation by microshots and fine grain strengthening. In addition, the transformation of the hard second phases such as Al4C3 and CNT and its effects on improving the surface strength and deformation uniformity were discussed. Significantly, DSP improved the wear resistance by 31.8% under the load of 6 N, which is attributed to the synergistic influence of factors including hardness, compressive residual stress, surface roughness, and grain size. In summary, it can be concluded that DSP is an effective strategy to promote the surface layer characteristics for CNT/Al-Cu-Mg composites.

Microstructure, thermal, and mechanical properties of hierarchical porous silicon carbide made by direct ink writing

AbstractHierarchical porous silicon carbide (SiC) ceramics were fabricated by combining particle‐stabilized emulsions and three‐dimensional (3D) printing. Direct ink writing (DIW) was used as the 3D printing technique. The formulation for successful printing is discussed in relation to the rheology of the emulsions. The SiC emulsions were able to be printed with a lower storage modulus (G′) and apparent yield shear stress (τy) than previously reported SiC ink pastes. The printed and sintered porous SiC ceramics possess a total porosity of 73.7% with an average pore size within the filaments of 2.2 µm in diameter. A hierarchical pore structure that contains pore sizes of about 250 µm, around 1–10 µm and smaller than 0.5 µm can be observed in the microstructure and pore size distribution. The mechanical properties showed a good strength‐to‐density ratio, and the thermal conductivity was reduced to 4.9 W/m·K. This study provides a new reliable approach for fabricating hierarchical porous SiC ceramics with low thermal conductivity.

Observation and Analysis of In Vitro Digestibility of Different Breads Using a Human Gastric Digestion Simulator.

The digestion behavior of a food bolus comprising bread particles in the presence of gastric peristalsis remains poorly understood. This study systematically investigated the effect of bread type on in vitro gastric digestion behavior using a human gastric digestion simulator (GDS) that is capable of quantitatively simulating gastric peristalsis. A food bolus consisting of 60 g of bread (white bread, bagel, German bread, French bread, or croissant), 15 mL of a simulated salivary fluid, and 240 mL of a simulated gastric fluid was used for gastric digestion in vitro using the GDS for 3 h at 37 °C. Direct observation of the gastric digestion behavior in the GDS vessel demonstrated that the structure and composition of breads considerably influenced the physical digestion processes of bread particles. These processes include their fracture, rubbing, disintegration, swelling owing to the penetration of gastric fluid, and release of fat from their surface. Fluorescence microscopy enabled an improved understanding of the variations in the microstructure and major component distribution of the breads during the gastric digestion in vitro. The results showed how the different breads influenced gastric digestibility in vitro through quantitative gastric peristalsis. The GDS can also be applicable to studying gastric digestibility in vitro of other types of bread.

Microstructure and mechanical properties of Ti60–Ti2AlNb functionally graded materials fabricated by laser directed energy deposition

The increasing demands for materials that service under high temperature environments in advanced aero-engines with high thrust-to-weight ratios have led to the exploration of functionally graded materials, which can offer unique advantages for addressing these challenges, such as the ability to achieve multiple properties at different positions of the components. In this study, Ti60–Ti2AlNb functionally graded materials were fabricated via laser directed energy deposition (L-DED) with 20% compositional step and various step widths in the transition zone. The distribution of chemical composition, microstructure, and microhardness in the transition zone of functionally graded materials with different compositional paths along the deposition direction were investigated. Meanwhile, the mechanical properties and fracture mechanisms were also evaluated. Smooth composition transition has been achieved in the joint zone between Ti60 and Ti2AlNb. By decreasing the width of each composition zone in the transition area or removing the Ti60-60% Ti2AlNb zone, the precipitation of the hard and brittle α2 phase can be effectively suppressed, thereby enhancing the tensile strength of the graded material. Through this approach, Ti60–Ti2AlNb functionally graded material with a tensile strength of 1030.9 MPa and elongation of 2.0% was fabricated.

Dynamic tensile characteristics of an artificial porous granite under various water saturation levels

Underground rocks are generally subjected to water erosion and dynamic disturbances. To exclude the effect of clay minerals on the water–rock interaction mechanism, clay-free artificial porous rock (APR) was used to investigate the coupling effect of water saturation and loading rate on tensile behavior. Dynamic Brazilian disc experiments were performed on APR with six water saturation levels (100, 80, 60, 40, 20, and 0%) using a split Hopkinson pressure bar (SHPB) combined with a high-speed camera. The results indicated that the number of cracks in the APR specimens increased with the water saturation level during the dynamic damage process, with more radial cracks at the water saturation of 80–100%. The dynamic tensile strength (DTS) and dissipated energy density exhibited different change trends with water saturation levels under different loading rates and the rate dependence was most significant in the fully saturated state (100%). At lower loading rates, DTS initially decreased rapidly and then more slowly with increasing water saturation. At higher loading rates, DTS exhibited a ‘decrease then increase’ trend. Moreover, the water-affecting factor exhibited an overall decreasing trend with the loading rate and gradually converged to 1.0. These phenomena can be attributed to the interplay between the weakening and strengthening water-effect mechanisms based on the microstructure and water distribution in the APR specimens.

Microstructure and residual stress gradient evolution mechanism of electronic copper strip for lead frame

The miniaturization of integrated circuits has led to a shift in lead frame fabrication methods from physical stamping to chemical etching. However, this process is highly sensitive to residual stress. We investigated the gradient distribution of residual stress, microstructure, and macroscopic texture in electronic copper foils using a layer-by-layer peeling method, and proposed a novel strategy for evaluating residual stress levels. Our findings reveal that the rolling-induced residual stress exhibits a gradient distribution along the thickness direction. Specifically, from the surface to the central layer, the stress transitions gradually from tensile to compressive, with the stress type primarily influenced by metal flow during rolling. Additionally, we observed gradient variations in the S and Cube texture. Tensile stress favors the formation of Cube-texture, while compressive stress promotes S-texture development. Notably, Cube-texture can lead to strain localization during rolling, directly impacting the local residual stress levels and distribution. Furthermore, quantitative analysis of dislocation density using peak profile methods revealed a consistent trend between {111} plane dislocation density and lateral residual stress. Further investigation highlighted that dislocations and precipitates associated with {111} planes in face-centered cubic metals significantly influence residual stress, with their combined effects determining the overall stress magnitude in relation to texture, dislocations, and precipitates.

Effect of sawdust fillers loaded on Cucumis sativus fiber‐reinforced polymer composite: a novel composite for lightweight static application

AbstractThis research investigates the impact of sawdust fillers on Cucumis sativus fiber‐reinforced polymer composites through a conventional hand layup process. The objective is to develop a novel material suitable for static applications that is both lightweight and environmentally sustainable. A range of analytical techniques including X‐ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, mechanical testing, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and energy‐dispersive X‐ray (EDX) analysis were employed to thoroughly characterize the resulting composite material. By integrating Cucumis sativus fibers and sawdust fillers into a polymer matrix, the study demonstrates the potential to create materials with improved mechanical properties due to addition of sawdust filler, including tensile strength (27.61 MPa), flexural strength (32.84 MPa), impact resistance (14.7 J cm−2) and hardness (42). These enhancements, averaging at 16.2%, are attributed to the addition of sawdust filler, which opens new avenues for environmentally conscious engineering solutions. XRD analysis reveals the composite's crystalline structure, indicating a crystallinity index of 64.5% and the orientation of crystalline planes. FTIR spectroscopy identifies chemical bonding and CO and CO functional groups present in the material with major peaks at 2123 and 2438 cm−1. TGA assesses the composite's thermal stability and decomposition behavior up to 380 °C. Additionally, SEM imaging elucidates the microstructural features and distribution of Cucumis sativus fibers and sawdust fillers within the epoxy matrix, while EDX analysis provides quantitative data on elemental composition. © 2024 Society of Chemical Industry.

Characteristics and distribution of microstructures in high pressure die cast alloys with X-ray microtomography: A review

Characteristics and distribution of microstructures in high pressure die cast alloys with X-ray microtomography: A review

Nanoscale stress and microstructure gradients across a buckled Mo-Cu bilayer: Cu self-annealing triggered by interface delamination

Residual stresses in thin film structures significantly impact their mechanical properties and affect interface delamination. Highly compressively stressed thin films buckling is the predominant interfacial failure mode due to strain energy release. In the present study the effect of cross-sectional stress and microstructural gradients of thin films on the buckling behavior are explored in a model material system consisting of a thin Cu film sputtered onto glass and a highly compressively stressed 500 nm thick Mo overlayer causing buckling delamination at the Cu-glass interface. Employing synchrotron cross-sectional X-ray nano-diffraction, multiaxial X-ray elastic strain and microstructure distributions were explored across the cross-section of the adhering and buckled bilayer, respectively. In the adhering state, a gradual thickness evolution of columnar microstructure and residual stress was found for Mo, while in Cu, no microstructure changes and only minimal stress variations were detected along the film thickness. After delamination, diffraction peak broadening and changes in unstrained lattice parameters in the Cu sublayer indicated structural defect annihilation and grain coarsening. These microstructural changes were further validated via cross-sectional transmission electron microscopy. The evaluated residual stress distributions across the two sublayers of the pristine and buckled bilayer were used to quantify the released strain energy per unit area due to buckling, amounting to 0.61 J/m². Further cross-validation of experimental stress results with finite element simulations strengthened the experimental findings, providing a comprehensive understanding of the stress distribution across the buckled bilayer.

Layout optimization of pore microstructure in fluid-saturated porous media using Galerkin decoupling technology and independent continuous mapping method (GDT-ICM)

A layout optimal design method combining Galerkin decoupling technology and independent continuous mapping method (GDT-ICM) is proposed to rearrange the layout of pore microstructure. Firstly, the Galerkin decoupling technology (GDT) is employed to solve the Brinkman equation for fluid flow in fluid-saturated porous media, which integrates the Stokes equation and Darcy's law. Within this framework a self-programmable element balance equation is developed. Secondly, a permeability interpolation function is defined for each element, incorporating the permeability of the fluid and pore microstructure. This function distinguishes strictly between the fluid domain and the pore domain. Pore microstructures with arbitrary shape including permeability information are established in an Euler mesh by introducing the Carman-Kozeny equation, shape functions, the Joukowski mapping and filter functions (the modified arctan mapping function and the ‘inpolygon’ function) based on the ICM method. Thirdly, a layout optimization model aiming at minimizing energy dissipation is established to accomplish the optimal distribution of pore microstructures. A sensitivity analysis is calculated with respect to design variables and the optimal model is solved by a genetic algorithm. Numerical results demonstrate that the proposed method is effective and feasible in 2D-space. The maximum velocity within the fluid field is reduced by 45%, and the issue of localized high pressure occurring around the pore is solved. This paper provides guidance for solving the Brinkman coupled equation and the layout optimization of the microstructure in porous media.

Effect of wall microstructure on conical hypersonic boundary layer flow

As an effective boundary layer flow control method, wall microstructure has an important application prospect in heat and drag reduction of hypersonic. In this paper, based on experimental techniques such as high-frequency pressure fluctuation testing, the effects of different microstructure configurations (V-shaped and rectangular) and distribution modes (streamwise and transverse) on the flow of hypersonic conic boundary layer under the condition of Mach 6 hypersonic incoming flow are studied. The experimental results show that compared with the flow of the smooth wall boundary layer, the wall microstructure has a greater influence on the eigenfrequency of the second-mode wave in the boundary layer, and the streamwise increases by about 20 kHz to the rectangular microstructure and decreases by about 30 kHz to the transverse rectangular microstructure. At the same time, the transverse V-shaped microstructure can increase the amplitude of the second mode in the boundary layer by 5.5 times compared with the smooth wall. For the evolution of boundary layer flow, the microstructure arranged along the flow direction will accelerate the linear development of the disturbance wave during the transition, so that the laminar flow will be transformed into turbulent flow in a shorter distance. The microstructure arranged along the transverse direction prolongs the linear development stage of the disturbance wave during the transition, so that the laminar flow turns into turbulent flow over a longer distance. Downstream of different structures, it is shown that transverse rectangular microstructure has lowest temperatures.

Exploring the effect of Cr and Mn on the intrinsic strength of the tensile properties of FeCoNi, FeCoNiMn, FeCoNiCr, and FeCoNiCrMn multi-principal element alloys using in-situ EBSD

As the composition elements in multi-principal element alloys increase, it can bring excellent mechanical properties. However, the strengthening mechanism of the additional element is still unclear. In this work, we establish a method based on the in-situ EBSD technology to explore the possible effect of additional elements on the intrinsic strength of tensile properties. We prepared four different multi-principal element alloys, including FeCoNi, FeCoNiMn, FeCoNiCr, and FeCoNiCrMn with similar initial status. We systematically investigated the evolution of the microstructure, dislocation density, twin boundary, grain size, and element distribution during the tensile process by in-situ EBSD and EDS. By carefully analyzing the results of four different multi-principal element alloys, the strength effects of the solid-solution hardening, grain-boundary hardening, twin boundary hardening, precipitate hardening, and dislocation hardening were peeled. The effect of the Cr and Mn element addition on the intrinsic strength can be explored. It is found that the element addition indeed increases the intrinsic strength from quaternary to quinary but not very clear from ternary to quaternary no matter Cr or Mn, which indicated that the intrinsic strength was more related to the number of elements in the alloy than to which element was present. This can be explained using the mixing entropy theory, which states that the intrinsic strength is enhanced when the mixing entropy is over a threshold between the MEA and HEA. This paper presents a method to study the individual factors affecting the tensile properties, which can help other researchers to better investigate HEA.

Enhancing oxidation resistance of silicon nitride using a Ca2+ stabilizer

Silicon nitrides are widely used in ceramic heaters for combustion engines due to their high strength and wear resistance. However, their poor oxidation resistance at elevated temperatures limits their reliability. Oxidation products, such as silica and intermediate compounds from sintering additives, often suffer from microcracks due to phase transformation and volume expansion mismatch during thermo-mechanical cycles. Use of cation dopants to chemically stabilize the transformation of the oxidation front is proposed. This study investigated the effect of Ca2+ treatment on Si3N4 with MgO and Y2O3 sintering aids. The Si3N4 samples were coated with CaO and the phase composition, microstructure, and chemical distribution of the oxidation products were analyzed using XRD, SEM, TEM, STEM, and EDS. The oxidation coupon tests revealed that the CaO coating effectively protected Si3N4 from oxidation at 1300 ºC for 40h. Moreover, the microstructure analysis showed that CaO coating created more favorable microstructures which reduced oxidation reactions.

Effects of temperature and stress evolution on microstructural change and mechanical properties during friction element welding

Dissimilar material joining is essential for improving the strength-to-weight ratio of materials for various applications. Friction element welding (FEW) is a promising solution for joining highly dissimilar materials that vary in strength and thickness. However, the influence of the process parameters on the material’s resultant microstructure and mechanical properties remains unclear. In this study, the relationship between microstructure and microhardness distribution of the welded specimen is experimentally studied, and the effects of temperature and stress evolution are revealed by a thermal–mechanical finite element model. It is found that the microhardness can be improved by over 50% in the central region due to microstructural change and grain refinement. The beneficial microstructural change can be achieved by inducing either a high peak temperature (over the austenitization temperature) or a high peak stress (over the hardening factor) during the FEW process, which can be obtained by controlling the endload and rotational speed of the friction element. The size of the region with improved hardness is observed to vary with the depth of deformation in the steel layer. For the transverse shear strength (TSS), it is observed that irrespective of the temperature levels reached, TSS increases with increasing stress in the steel layer. Temperature plays a crucial role when the steel layer’s temperature is higher than the austenitization start temperature wherein TSS increases with the temperature.

Internal hydrophobic treatment for mortar containing supplementary cementitious materials: thermal analysis of kinetics and products of hydration

AbstractThe presented research investigates the application of the organosilicon admixtures based on triethoxyoctylsilane (OTES) on the hydration of the cement-based material with addition of supplementary cementitious materials (SCM) such as blast furnace slag and microsilica. The influence of silane-based admixtures on the kinetics of hydration was investigated by isothermal calorimetry. The calorimetric results disclosed that applied admixtures affect the hydration process of cement paste with SCM. The DTA/TG analysis provided the information about impact of triethoxyoctylsilane on the composition and formation of the mineral phases. The DTA/TG measurements showed noticeable changes in the thermal decomposition of the tested materials and amount of bounded water. The impact of OTES on the microstructure and pore size distribution of pastes was examined by mercury intrusion porosimetry. The result showed significant changes in the range of pore diameters. The influence of organosilicon admixtures on the compressive strength of mortars after 2, 7, 28, 56 and 90 days was also investigated. The effect depended on the mineral additive used. In case of blast furnace slag, the development of compressive strength was only delayed, however, in the case of microsilica, it was stopped.

Correlation between shot peening coverage and surface microstructural evolution in AISI 9310 steel: An EBSD and surface morphology analysis

In this study, martensitic high-strength steel serves as the subject of investigation, with both conventional and severe shot peening experiments being conducted. The coverage levels for conventional shot peening (CSP) are set at 100 % and 200 %, while severe shot peening (SSP) sees levels of 800 % and 1200 %. For the first time, the use of kernel average misorientation (KAM) enables the calculation of geometrically necessary dislocation (GND) density after peening, facilitating the study of GND density distribution across different coverage and offering a method for the visual assessment of peening degree. Results reveal that, under CSP, the gradient distribution of grain size is relatively uniform, whereas SSP leads to a pronounced gradient in grain size distribution. Taking into account the heterogeneous distribution of the initial material microstructure, a gradient in grain size from the surface to the interior of the material will appear after the coverage reaches a certain value, which is 400 % for AISI 9310 steel. Compared with CSP, SSP will further reduce the surface roughness Sa and improve the surface quality. The research presented further understands the relationship between shot peening process parameters and martensitic steel microstructure, providing an important reference for revealing the strengthening mechanism and selecting reasonable process parameters.

Study on the Influence of Laser Power on the Heat–Flow Multi-Field Coupling of Laser Cladding Incoloy 926 on Stainless Steel Surface

In order to explore the influence of laser power on the evolution of molten pool and convective heat transfer of laser cladding Incoloy 926 on stainless steel surface, a three-dimensional thermal fluid multi-field coupled laser cladding numerical model was established in this paper. The variation of latent heat during solid-liquid phase transformation was treated by apparent heat capacity method. The change in the gas–liquid interface was tracked using the mesh growth method in real time. The instantaneous evolution of temperature field and velocity flow field of laser cladding Incoloy 926 on a stainless steel surface under different laser power was discussed. The solidification characteristic parameters of the cladding layer were calculated based on the temperature-time variation curves at different nodes. The mechanism of the impact of laser power on the microstructure of the cladding layer was revealed. The experiment of laser cladding Incoloy 926 on 316L surface was carried out under different laser power. Combined with the numerical simulation results, the effects of laser power on the geometrical morphology, microstructure and element distribution of the cladding layer were compared and analyzed. The results show that with the increase in laser power, the peak temperature and flow velocity of the molten pool surface both increase significantly. The thermal influence of the molten pool center on the edge is enhanced. The temperature gradient, solidification rate, and cooling rate increased gradually. The microstructure parameters (G/R) are relatively small when the laser power is 1000 W. In the experimental range, the dilution rate and wetting angle of the cladding layer both increase with the increase in laser power. When the laser power is 1000 W, the alloying elements of the cladding layer are more evenly distributed and the microstructure is finer. The experimental results are in good agreement with the simulation results.