Void Formation Research Articles

Interface homogenization control and microstructural analysis of ZrC0.85 joints diffusion bonded using Nb and Ti/Nb/Ti as the interlayer

Joint homogenization during transition metal carbides ceramic bonding has attracted much attention as a technique to increase the service temperature and relieve the residual stress for various high-temperature applications. In this work, homogeneous joints of ZrC0.85 ceramic were obtained by diffusion bonding using single Nb and multiple Ti/Nb/Ti as the interlayer. The effect of interlayer composition, bonding temperature and holding time on the microstructure of the joints was investigated. The effect of Nb and Ti on the composition homogeneity and the formation of Kirkendall voids in the ZrC0.85 joints was also discussed. When using single Nb as the interlayer, the homogenization of the joints can be achieved at a bonding temperature of ∼1500 °C and holding for 1 h and no Kirkendall voids were observed when further increasing the bonding temperature to 1600 °C because of the good mutual solubility of NbCx and ZrCx and the relative moderate diffusion rate of Nb. However, severe Kirkendall effects were observed at a higher temperature of 1700 °C, which would deteriorate the high-temperature performance of the joints. The adoption of Ti/Nb/Ti further minished the diffusion rate difference of the interfacial elements through the formation of TiCx phase. As a result, only a few Kirkendall voids were formed at 1700 °C. Nano-hardness of the resultant homogeneous joints was comparable to that of the ZrC0.85 ceramic due to their similar composition. This study shows that active diffusion bonding based on interlayer design for homogeneous joints could pave a new way to join transition metal carbides.

Interfacial characteristics, interfacial oxide evolution and bonding mechanism of 2219 aluminum alloy joints manufactured by hot-compression bonding

The bonding joints of 2219 aluminum alloy with different deformations of 30%, 45% and 55% were fabricated using hot-compression bonding, and subsequent subjected to homogenization treatment. The interfacial microstructure and interfacial oxide evolution of the bonding joints were systematically investigated. The results showed that increasing deformation can effectively reduce the formation of interfacial voids and promote the interfacial grain boundary migration (IGBM). As the deformation increased from 30% to 55%, the flat bonding interface transformed into curved grain boundaries, and ultimately being occupied by dynamically recrystallized (DRXed) grains. The development of IGBM and interfacial DRXed grains is crucial for ensuring high-quality bonding joints. At 55% deformation, the interface bonding strength reached 156.2 MPa, corresponding to 98.1% of the matrix bonding strength. In addition, the residual interfacial oxide film Al2O3 reacted with MgO and transformed into MgAl2O4 spinel. The final evolution products at the bonding interface were the mixture of MgO, Al2Cu, Al2O3, and MgAl2O4. The bonding interface at 55% deformation successfully achieved relatively clean atomic bonding after homogenization. Based on interfacial void closure, interfacial oxide film fragmentation and evolution, and interfacial recrystallization, the bonding mechanism of 2219 aluminum alloy joints was proposed. These findings contribute to our understanding of the interfacial bonding process in metal solid bonding.

Beyond nothingness in the formation and functional relevance of voids in polymer films

Voids—the nothingness—broadly exist within nanomaterials and impact properties ranging from catalysis to mechanical response. However, understanding nanovoids is challenging due to lack of imaging methods with the needed penetration depth and spatial resolution. Here, we integrate electron tomography, morphometry, graph theory and coarse-grained molecular dynamics simulation to study the formation of interconnected nanovoids in polymer films and their impacts on permeance and nanomechanical behaviour. Using polyamide membranes for molecular separation as a representative system, three-dimensional electron tomography at nanometre resolution reveals nanovoid formation from coalescence of oligomers, supported by coarse-grained molecular dynamics simulations. Void analysis provides otherwise inaccessible inputs for accurate fittings of methanol permeance for polyamide membranes. Three-dimensional structural graphs accounting for the tortuous nanovoids within, measure higher apparent moduli with polyamide membranes of higher graph rigidity. Our study elucidates the significance of nanovoids beyond the nothingness, impacting the synthesis‒morphology‒function relationships of complex nanomaterials.

Neutron Reflectivity for Testing Graphene Oxide Films Sorption of EuCl3 in Ethanol Solution

Neutron reflectivity (NR) was used to study the sorption of Eu(III) by graphene oxide (GO) films exposed to ethanol solution of EuCl3. Most of the earlier sorption studies have been performed using GO dispersed in solution. In contrast, layered structure of GO films imposes limitations for penetration of ions between individual sheets. The analysis of NR data recorded before and after sorption under vacuum demonstrates an increase of GO film thickness due to sorption by 35–40%. The characterization of chemical state of Eu(III) sorbed by GO films by X‐ray absorption near‐edge structure (XANES) in high‐energy resolution fluorescence detection (HERFD) method at the Eu L3 edge reveals that it remains the same as in anhydrous EuCl3. Analysis of all collected data including reference experiments with bulk GO samples allows to conclude that EuCl3 penetrates into GO interlayers with ethanol solution and remains trapped in interlayers after evaporation of ethanol. Sorption of EuCl3 results in nearly complete amorphization of film and likely formation of voids, thus making NR models based on specific volume of unit cell not valid for quantitative evaluation of Eu sorption. Limitations of NR method must be taken into account in future studies of sorption by thin films.

Results of experimental research of the process of forming reinforced concrete products by the centrifugation method

The method of conducting an experimental study of the process of forming reinforced concrete products is disclosed. The key factors influencing the quality indicators of the product being formed are defined and considered. On the basis of the conducted active, factorial experiment, a regression equation was compiled, graphical dependences of the influence of these factors on the process were obtained, rational parameters of the centrifugation process were determined, which are decisive in the manufacture of reinforced concrete products by the centrifugation method. Based on the results of laboratory experiment data processing, recommendations were developed for optimizing the operating parameters of industrial equipment for forming reinforced concrete products by the centrifugation method. Problem. When forming reinforced concrete products by the centrifugation method, some problems may arise, uneven distribution of the mixture in the mold body and of reinforcement, formation of voids or cracks, insufficient compaction of the mixture. If the parameters of the centrifugation process are not properly controlled, the quality of the products may vary, which may lead to deviations from specifications and standards. Problems with the deformation of the molds after forming the product can lead to damage to the product or difficulties in its removal. Goal. Based on the results of the conducted factorial experiment, recommendations are developed regarding the rational parameters of the process of forming columns of reinforced concrete supports for power transmission lines by the centrifugation method in the conditions of an operating technological line. Methodology. The basis of the research is the method of conducting a planned factorial experiment with further statistical processing of the obtained results using a computer program. Results. Based on the processing of the obtained results of the conducted factorial experiment, the following recommendations are suggested regarding the rational parameters of the process of forming reinforced concrete pillars for power lines by the centrifugation method in the conditions of an operating technological line.

Physically simulating the dispersion of chopped carbon fibres in mortar

Carbon fibre dispersion exerts a critical influence on the characteristics of carbon fibre-reinforced cement mortars (CFRCMs). This study accordingly investigated the dispersion of chopped carbon fibres (CCFs) in mortar using physical experiments with a transparent simulated mortar system comprising colloidal silica and silica sand as replacements for cement and aggregate, respectively, and evaluated the microstructures and conductive performances of corresponding CFRCM specimens. In the simulated solutions, bundled CCFs in order were more prone to disperse into single fibres than clustered ones in disorder due to no physical fixation, colloidal silica prevented the formation of CCF clusters during stirring, and the shear force of moving sand dispersed but also broke CCFs. In the CFRCMs, sand aggregates reaggregated dispersed CCFs while larger sand particles increased CCF dispersion and improved specimen conductivity. Thus, decreasing the amount of CCFs clusters before dispersion, and a short stirring time in a single direction should be provided to prepare CFRCMs with well-dispersed CCFs. Meanwhile, a more dispersible aggregate and less formation of void should be also essential.

Mulberry (Morus alba L.) leaf powder modified the processing of meat alternatives: Principal component analysis from apparent properties to chemical bonds

For texture control in plant-meat alternatives, the interrelationship between apparent characteristics and chemical bonds in high-fiber formulations remains unclear. The influence of mulberry leaf powder on apparent characteristics and chemical bonds of raw materials, block and strip products at addition amounts of 0.5–25% was analyzed. The results showed that 8% addition significantly increased the chewiness of the block by 98.12%. The strips' texture shows a downward trend, and the processing produced more redness and color difference. Additives promoted the formation of voids, lamellar and filamentous structures, and the strip produced more striped structures. Disulfide bonds significantly increased in the block, and the β-turn in the secondary structure enhanced by 12.20%. The β-turn transformed into a β-sheet in strips. Principal component analysis revealed that the texture improvement was associated with producing disulfide bonds and β-turn, providing a basis for high-fiber components to improve products' apparent characteristics by chemical bonds.

Effect of helium ion irradiation on the microstructure, mechanical properties and surface morphology of Inconel 625 alloy

Inconel 625 alloy is mainly used for reactor pressure vessel, fuel cladding, nuclear fuel elements and cryogenic channels for cooling high temperature superconductors in Tokamaks. This study focuses on deciphering the impact of helium ion irradiation on the properties of Inconel 625 alloy. Helium-ions interaction with material leads to blistering, void formation, swelling, and degradation of mechanical properties. To understand these effects, the samples of Inconel 625 alloy were irradiated by helium-ion fluence beams at three different helium-ion beam fluence (1 × 1013, 1 × 1014, 1 × 1015 He/cm2). A decrease in grain size was observed from 34.4 to 19.0 nm with an increase in the ion fluence. According to the results, the residual strain is increased, from 1.8 to 43.0 micro-strain with the increase in helium-ion fluence, however structure is relaxed with decrease in micro-strain at higher helium-ion fluence (1 × 1015 He/cm2) and also there is a prominent increase in grain size. The surface morphology as observed by scanning electron microscope (SEM) illustrates the fuzz formation at low fluence (1 × 1013 He/cm2), while samples irradiated with high helium ion fluence (1 × 1015 He/cm2) showed grain growth, voids and surface blistering (deep valleys). An increase in hardness value at low helium-ion beam fluence is observed due to the presence of large population of defects. However, at higher helium-ion beam fluence, a decrease in hardness value is observed. This decrease might be attributed to the dislocation clustering and grain growth.

Li Stripping Behavior of Anode‐Free Solid‐State Batteries Under Intermittent‐Current Discharge Conditions

AbstractAnode‐free manufacturing holds promise to enable high energy densities and lower Lithium (Li)‐metal solid‐state batteries (LMSSBs). Nevertheless, in contrast to thick Li foil (>50 µm), the stripping capacity of in situ‐formed Li (10–30 µm) is limited due to diminished creep flow, resulting in reduced accessible capacity. This study explores the correlation between stripping capacity and surface roughness of garnet Li7La3Zr2O12 (LLZO) solid electrolyte. The results reveal that stripping capacity can be enhanced through the surface modification of solid electrolytes. Additionally, this study scrutinizes the stripping behavior of in situ Li under intermittent‐current discharge conditions, which are more relevant to the operational conditions of electric vehicles (EVs). It is demonstrated that, when compared to constant‐current stripping, intermittent‐current stripping effectively suppresses void formation and enhances the stripping capacity of in situ Li by 40%. It is considered that the intermittent current inhibits the accumulation of Li vacancies, thereby delaying the void formation. These findings provide valuable insights into the development of high‐performance anode‐free LMSSBs for EVs.

Constructing a cut-off dam inside a water-filled circular tunnel with backfill grouting

This study employs laboratory model tests for backfill grouting and numerical analyses (coupled analysis of the discrete element method and computational fluid dynamics, DEM-CFD coupling analysis) to investigate the feasibility of constructing a cut-off dam inside a water-filled circular tunnel using the backfill grouting method from the ground surface. Several improved backfill methods were studied to enhance the effectiveness of the cut-off dam. These methods include: (a) adding an additional backfill grouting hole between the double-row cut-off dam and applying pressurized grouting; (b) adjusting the number of backfill grouting holes per row of the cut-off dam; (c) simultaneously grouting the double-row cut-off dams to minimize the formation of interface fissures and voids; (d) adjusting the grout hole spacing of the double-row cut-off dams to reduce the volume of backfill material. Additionally, pressurized mortar grouting is a critical mass to ensure the water tightness of the cut-off dam. The implementation of these backfilling arrangements improves the effectiveness and watertight of the cut-off dam, thereby reducing the construction time and cost. The findings of this study can serve as a reference for water-filled tunnels and subsequent rehabilitation works in the future.

Thermal stability and strength degradation of lithium slag geopolymer containing fly ash and silica fume

This paper investigates the thermal stability of lithium slag geopolymer (LSG) containing fly ash (FA) and silica fume (SF) exposed up to 900˚C. The effects of elevated temperatures on the microstructural evolution were investigated by thermogravimetric analysis (TGA), X-ray Diffraction (XRD), mineral analysis, surface porosity, and compressive strength of LSG modified by optimum incorporation of fly ash and silica fume. The results indicated that elevated temperature exposure significantly affects compressive strength, surface porosity, void size, weight loss, and phase transformation of fly ash incorporated lithium slag geopolymer (LSGFA) and silica fume incorporated geopolymer (LSGSF). The maximum loss in compressive strength of 44.07% was observed in LSGFA compared to 31.50% loss in LSGSF after exposure at 900˚C. The weight loss of LSGSF was higher than that of LSGFA between 500 and 800˚C and 800–1000˚C indicating a higher degree of dehydroxylation, crystal phase transformation, and viscous sintering observed in the former mix. A larger shrinkage cracking was observed in LSGSF by self-desiccation of the aluminosilicate paste matrix by dehydroxylation of mordenite molecules. Therefore, the degradation of compressive strength is governed by the combination of the crystallization of aluminosilicate gel and the formation of voids.

Bicomponent melt-spinning of filaments for material extrusion 3D printing

In material extrusion (MEX) 3D printing, the layer-by-layer structure often presents challenges such as poor adhesion, void formation and rough surfaces, which can compromise the mechanical properties of printed parts and limit their applications. This study investigates whether 3D printing from bicomponent core-sheath filaments instead of printing from conventional monofilaments provides a potential solution to some of the described issues. Based on different material selections, various bicomponent filaments, comprising a rigid core and a soft sheath, were produced through co-extrusion and overcoating extrusion techniques. Tensile properties of 3D-printed specimens with different raster angles (0° vs 45°) from bicomponent filaments are compared to the properties of reference specimens printed from conventional monofilaments. While similar mechanical properties were observed for some 3D-printed specimens from bicomponent filaments (e.g., polylactic acid (PLA)-based), as compared to reference specimens, some core-sheath combinations of polyamide (PA) demonstrated a noticeable improvement of the mechanical properties of 3D-printed specimens, particularly for 45° raster angles. In particular, bicomponent filaments comprising a carbon fiber reinforced PA (PACF) core and a pure PA sheath exhibited improved processability and enhanced structural strength. Moreover, two overcoated filaments consisting of polyethylene terephthalate (PET) and polyphenylene sulfide (PPS) monofilament cores with a copolyester (CoPES) sheath were prepared for 3D printing. 3D-printed parts made from PET/CoPES overcoated filaments exhibited good compatibility and satisfactory results when printed at temperatures above the melting point of PET. These findings demonstrate the potential of bicomponent filaments to enhance both printability and mechanical performance of 3D-printed parts, offering new avenues for material selection and design optimization in various 3D printing applications.

Impact of molten salts composition on the corrosion behavior of NiMoCr and CoNiCrAl coatings on L-PBF 316L stainless steel for CSP plants

The high-temperature corrosion performance of NiMoCr and CoNiCrAl coatings produced by high velocity oxy-fuel (HVOF) on laser powder bed fusion (L-PBF) 316L stainless steel substate has been evaluated in presence of three different molten salts used as thermal energy storage (TES) materials for concentrated solar power (CSP) plants. The coatings have an excellent oxidation resistance at 700 °C, showing a percentage of affected thickness lower than 2 %, due to the formation of a protective layer of Cr2O3 and Al2O3 in both NiMoCr and CoNiCrAl coatings, respectively. The carbonates-based molten salt accelerates the corrosion of the NiMoCr coating, affecting around 43 % of the coating thickness, due to the formation of chromates and the high depletion of Mo in the coating. In contrast, the effective protection shown by the CoNiCrAl coating is explained because the grown LiAlO2 after the lithiation process has a high capacity to act as a strong diffusion barrier for metal ions and inhibited the formation of chromates. In the presence of two different ZnCl2 and MgCl2-rich molten salts, the CoNiCrAl coating behaved worse than NiMoCr coating due to the breakage of the (Al,Cr)-rich oxide layer as a consequence of an active oxidation mechanism and due to the formation of voids along the entire thickness, which were identified in 100 % of the coating thickness. The superior corrosion resistance of the NiMoCr coating in presence of the chloride rich molten salts was attributed to the presence of Mo, which fixed the Cr and inhibited the diffusion of oxygen.

Exploring mechanism of suppressing void formation at Interface of Sn–9Zn and Cu

Exploring mechanism of suppressing void formation at Interface of Sn–9Zn and Cu

Three-Dimensional Epitaxy of Low-Defect 3C-SiC on a Geometrically Modified Silicon Substrate.

We demonstrate the growth of 3C-SiC with reduced planar defects on a micro-scale compliant substrate. Heteroepitaxial growth of 3C-SiC on trenches with a width and separation of 2 µm, etched into a Si(001) substrate, is found to suppress defect propagation through the epilayer. Stacking faults and other planar defects are channeled away from the center of the patterned structures, which are rounded through the use of H2 annealing at 1100 °C. Void formation between the columns of 3C-SiC growth acts as a termination point for defects, and coalescence of these columns into a continuous epilayer is promoted through the addition of HCl in the growth phase. The process of fabricating these compliant substrates utilizes standard processing techniques found within the semiconductor industry and is independent of the substrate orientation and offcut.

High-temperature annealing effects on epitaxial TiN films on 4H-SiC

To gain deeper insights into the impact of very high-temperature annealing on TiN film quality and thermal diffusion phenomena, the deposited TiN films underwent annealing in an induction heating furnace across a temperature range from 1150 °C to 1700 °C. Our findings indicate that TiN films remain stable, and the full-width at half-maximum (FWHM) of TiN (111) noticeably reduced by about 30 % when annealed at 1250 °C. However, as the annealing temperature rises to 1400 °C, the film composition gradually enriches with carbon as TiCxN1-x with x up to 0.5. After annealing at 1700 °C, the film is further enriched with x larger than 0.5. For a long time annealing at 1700 °C, the decomposition of SiC substrate with void formation is verified from observations by cross-sectional transmission electron microscopy.

The effect of spent coffee ground (SCG) loading, matrix ratio and biological treatment of SCG on poly(hydroxybutyrate) (PHB)/poly(lactic acid) (PLA) polymer blend

This study investigates the effects of SCG embedded into biodegradable polymer blends and aimed to formulate and characterise biomass-reinforced biocomposites using spent coffee ground (SCG) as reinforcement in PHB/PLA polymer blend. The effect of SCG filler loading and varying PHB/PLA ratios on the tensile properties and morphological characteristics of the biocomposites were examined. The results indicated that tensile properties reduction could be due to its incompatibility with the PHB/PLA matrixSCG aggregation at 40 wt% content resulted in higher void formation compared to lower content at 10 wt%. A PHB/PLA ratio of 50/50 with SCG loading 20 wt% was chosen for biocomposites with treated SCG. Biological treatment of SCG using Phanerochaete chrysosporium CK01 and Aspergillus niger DWA8 indicated P. chrysosporium CK01 necessitated a higher moisture content for optimum growth and enzyme production, whereas the optimal conditions for enzyme production (50–55 %, w/w) differed from those promoting A. niger DWA8 growth (40 %, w/w). SEM micrographs highlighted uniform distribution and effective wetting of treated SCG, resulting in improvements of tensile strength and modulus of biocomposites, respectively. The study demonstrated the effectiveness of sustainable fungal treatment in enhancing the interfacial adhesion between treated SCG and the PHB/PLA matrix.

Void Formation and Radiation‐Induced Ion Migration in Perovskite Solar Cells under 10 MeV Proton Radiation

Perovskite solar cell (PSC) technology is a promising candidate for space applications because of its high power‐to‐weight ratio, low‐cost fabrication process, and good tolerance to high‐energy particle radiation. In this work, perovskite films and resultant high‐efficiency PSCs are assessed under 10 MeV proton radiation at fluences in the range 1e12–1e14 p cm−2, which are equivalent to 1 to 100 years in geostationary orbit (GEO) without any shielding or cover. For the first time, void formation and material ablation are detected on perovskite films, indicating structural damage of the materials under the proton radiation. Furthermore, ions inside the devices especially Au and Pb ions are displaced to underlying layers under the proton bombardment. These lead to the degradation of PSCs to ≈89% of the initial performance (from 24.1% to 21.4%) at the highest dose. The experimental results are supported by previous simulation works with a good fit in all optoelectronic parameters. This study provides insights into the degradation mechanism of PSCs under proton radiation and paves the way for the utilization of PSCs in space applications.

Demonstration of computer vision for void characterisation of 3D-printed continuous carbon fibre composites

Microstructural void formation during the processing of continuous fibre-reinforced polymer composites are a significant limitation of processes such as 3D printing, as voids inhibit resultant mechanical properties. Traditional optical microscopy approaches to void characterisation are tedious and are prone to errors due to non-ideal but realistic image conditions, including low contrast typical of microscopic images. This paper proposes a novel application of automated computer vision image processing techniques (i.e. a contrast-limited adaptive histogram equalisation (CLAHE) algorithm and Otsu's method) for detailed void characterisation of continuous fibre-reinforced composites. Microstructural void fraction was determined for both unidirectional and bi-axial laminates of a variety of thicknesses. The void characterisation by computer vision was shown to produce comparable results with manual contrast/brightness control, but with significantly less standard deviation. The computer vision software used in void characterisation is made freely available online at https://github.com/Xiao-ying/VoidDetector.

Influence of intermediate carbon content on the microstructure and high-temperature mechanical properties of cast and wrought Ni-based superalloy nimonic 105

NIMONIC® 105 variants with three different carbon concentrations were manufactured. The medium carbon content variant shows inferior creep properties due to a bimodal grain size distribution and non-uniform carbides repartition leading to plastic strain accumulation between the two domains. This eventually facilitated facile cracking and void formation during high-temperature creep.