Void Formation Research Articles

Micro‐mesoscopic analysis of 3D void formation and evolution in CFRP composite using high‐resolution x‐ray microtomography

AbstractVoid defect is prevalent during the composite manufacturing process and may reduce the mechanical properties of composite structures, while limited information about three‐dimensional void distribution and evolution can be found due to the difficulties in void observation. In this work, void defects at different positions were detected and analyzed using x‐ray microtomography (XRM), and the random forest algorithm was implemented for segmenting components of CFRP samples. Results showed a trend of gradual rising porosity in the axial direction, with an increase of ~250% of porosity at the outlet of resin injection compared to the one at the inlet during the composite manufacturing process. The voids mainly featured with microscale between carbon fibers, with less distribution between fiber bundles and resin‐rich zones. Void defects achieved aggregation at the middle position of manufactured laminate, which is probably related to pressure interception. In the axial direction, the proportion of large‐diameter voids gradually increased, and a large volume of connected voids appeared near the outlet. Due to the shear deformation of resin and fiber and the pressure gradient effect, most of the voids showed stripe shape. The spatial orientation of voids was predominantly along the direction of resin flow and fluctuated due to fiber curl.Highlights 3D void characteristics in CFRP were studied using the XRM technique. Void formation and the effects of fibers on void morphology were analyzed. Dynamic void transport mechanisms during CFRP manufacturing were studied. Location and morphology of voids are helpful for CFRP damage modeling. The effective partitioning of CFRP was achieved using a random forest algorithm.

Phase field crystal study on the size and strain rate dependent evolution of Kirkendall voids in binary alloy

The evolution of Kirkendall voids in binary alloy under a uniaxial strain rate loading is investigated by the phase field crystal (PFC) model. The simulation results show that model size and the applied strain rate greatly affect the formation and growth of Kirkendall voids. It is found that the grains are prone to rotate when the model size is smaller than 34.7a×34.7a (a is the lattice constant) and the initially set grain boundaries will disappear after relaxation, no Kirkendall voids form in this case. As the model size increases, Kirkendall voids arise and interconnect with each other, and large voids will dissociate to produce small voids. Moreover, the applied strain rate also affects the formation and growth path of Kirkendall voids. Voids only form at the grain boundaries in the absence of strain rate loading, whereas voids form both inside the grains and at the grain boundaries under strain rate loading. The growth of voids can easily form oblique structures caused by dislocation slip, and they tend to grow perpendicular to the direction of applied strain rate.

The Effect of the Chemical Composition on Mechanical Properties of CMAS Diopside Glass Ceramics

Molecular dynamics simulations were performed on CaO-MgO-Al2O3-SiO2 (CMAS) diopside glass ceramics (GCs) to study the effect of nanocrystal on glass and the effect of chemical composition on mechanical properties. Under tensile loading, the GCs demonstrated that the strength lay between its glass and ceramic counterparts and maintained considerable ductility. Moreover, high Mg/Ca ion ratios are conductive to both the strength and ductility of GCs. In addition, Al ions should be avoided as far as possible since they would promote fracture. After analyzing the shear strain and displacement vector map for ion structures, we found that the presence of nanocrystal in glass changes the original deformation pattern and led to the deformation concentration surrounding the nanocrystal. A high Mg/Ca ion ratio would make the deformation more homogeneous, while a high Ca/Mg ion ratio would aggregate the deformation in the glass region near the nanocrystal. The existence of Al ions near the interface between glass and crystal would promote the formation of voids.

Revealing the Void Formation Mechanism during Superplastic Deformation of a Fine-Grained Ni–Co-Base Superalloy

Revealing the Void Formation Mechanism during Superplastic Deformation of a Fine-Grained Ni–Co-Base Superalloy

Experimental Study on Mechanical, Chemical and Acoustical Properties of Waste Tea Leaf Fiber Reinforced Epoxy Composites

Fibre reinforced polymer composites are employed instead of metal and wood because they are stronger, more lightweight, have a favourable strength to weight ratio, and are noncorrosive. In the current research, sisal, carbon fibre, and industrial waste tea leaf fibre (WTLF) reinforced hybrid epoxy composites are being examined for their chemical, mechanical and acoustical properties with experimental study. The sisal and WTLF were chemically treated with 5% sodium hydroxide (NaOH) solution. By modifying the weight percentage of sisal and WTLF with a structure of 40 weight percent fibre and 60 weight percent matrix, five different compositions of natural fibre reinforced hybrid composites were fabricated using an automatic compression moulding technique. As per the ASTM standard the manufactured hybrid composites are tested for mechanical, chemical and acoustic characteristics. According to the experimental findings, sisal fibre with a 25 wt% and WTLF with a 5 wt% demonstrated superior mechanical properties, while these materials also demonstrated an excellent acoustic absorption coefficient (AAC) of 0.62 between the frequency range of 2000 to 6300 Hz. The morphology of failure samples revealed the matrix micro crack, void formation, fiber pullout and layers of fractured fibers which are being examined using Scanning Electron Microscopy (SEM). The superior bonding between fibre and matrix was seen in the FTIR study of 5% alkali treated composites.

Red-Mud, A Golden Waste for Radiation Shielding”: Red-Mud Polymer Composites for High-Performance Radiation-Shielding Components

Red mud (RM) is generated in huge quantities and holds the ability to form radiation shielding structures due to its metal oxide-rich composition. In this work, this metal oxide-rich waste is converted into X-ray shielding sheets via a solution-casting technique incorporating polyvinyl alcohol (PVA) as a binder which holds RM particles together. We show a successful fabrication of sheets employing varying wt.% of RM (60, 70, 80, and 90 wt.%). The linear attenuation coefficient (LAC) values have been compared to analyze what maximum RM wt.% can effectively shield diagnostic X-rays at energies of 60 kVp, 90 kVp, and 120 kVp. Structural characterizations of the fabricated samples have been examined through SEM, XRD, RAMAN, and FTIR. The LAC analysis revealed that 70 wt.% of RM with PVA binder yields highest radiation shielding. However, with increased wt.% of RM there is a catastrophic decrease in strength and shielding capability of the composite due to the formation of voids due to decreased wt.% of polymer binder. So, an innovative polymer-rich coating has been applied to RM composite having 90 wt.% of RM, which boosted the LAC and strength, but not more than RM composite having 70 or 80 wt.% of RM. The UV shielding analysis of best samples having 70 and 80 wt.% of RM was also analyzed to show the capability of RM in shielding UV along with X-ray.

The enhancement of energy storage performance of BaTiO3–Bi(Mg0·5Ti0.5)O3 Pb-free ceramics via an optimized viscous polymer process route

In this study, the viscous polymer processing (VPP) technique is implemented to optimize the characteristics of bulk (1-x)BaTiO3-xBi(Mg0·5Ti0.5)O3 (BT-xBMT) lead-free relaxor ferroelectric ceramics, with a focus on enhancing the recoverable energy storage density (Wrec), improving breakdown strength resistance (Eb), and increasing storage efficiency (η). The influence of polyvinyl alcohol (PVA) inclusion in the VPP process on the resulting dielectric ceramics is thoroughly investigated, covering rheological, dielectric, and ferroelectric properties. The results reveal that a gradual increase in PVA quantity during the VPP process effectively improves the density of ceramic blanks. However, an excess of PVA leads to void formation in the ceramic blanks post-debinding, hindering the achievement of a dense structure in the final ceramics and causing performance degradation. The resulting BT-0.405BMT-40 wt% PVA ceramic showed excellent storage performance, with Wrec, η, and Eb of 6.55 J/cm3 81.45 %, and 480 kV/cm, respectively. In comparison to bulk BT-0.405BMT ceramics, there is a notable 2.47-fold increase in Wrec and a 1.92-fold increase in Eb, accompanied by a substantial improvement in η. Moreover, the BT-BMT-40 wt% PVA ceramic exhibits favorable temperature stability (30–150 °C), frequency stability (1–50 Hz), and commendable charge/discharge performance.

The effect of boron carbide doping content on the mechanical properties of polyethylene

ABSTRACT This paper presents Martin Buber‘s unpublished manuscript ‘Fragen und Antworten. Die jüdische Besiedlung Palästinas’ in the original German with English translation and contextualizes it within the main stations of Buber‘s Zionist thinking: cultural Zionism, religious Zionism, and Zionism of realization. It problematizes Buber‘s reflection on Jewish settlements in Palestine with reference to the significance of Zionism for humanity as well as the possibility of reconciliation between Jews and Arabs in the Middle East. It also addresses the problem of Jewish terror, framing it in correlation with the restrictions on Jewish migration to Palestine and the catastrophe of the Shoah.

Chemo-mechanical failure mechanisms of the silicon anode in solid-state batteries.

Silicon is a promising anode material due to its high theoretical specific capacity, low lithiation potential and low lithium dendrite risk. Yet, the electrochemical performance of silicon anodes in solid-state batteries is still poor (for example, low actual specific capacity and fast capacity decay), hindering practical applications. Here the chemo-mechanical failure mechanisms of composite Si/Li6PS5Cl and solid-electrolyte-free silicon anodes are revealed by combining structural and chemical characterizations with theoretical simulations. The growth of the solid electrolyte interphase at the Si|Li6PS5Cl interface causes severe resistance increase in composite anodes, explaining their fast capacity decay. Solid-electrolyte-free silicon anodes show sufficient ionic and electronic conductivities, enabling a high specific capacity. However, microscale void formation during delithiation causes larger mechanical stress at the two-dimensional interfaces of these anodes than in composite anodes. Understanding these chemo-mechanical failure mechanisms of different anode architectures and the role of interphase formation helps to provide guidelines for the design of improved electrode materials.

Minimizing the diffusivity difference between vacancies and interstitials in multi-principal element alloys

Interstitial atoms usually diffuse much faster than vacancies, which is often the root cause for the ineffective recombination of point defects in metals under irradiation. Here, via ab initio modeling of single-defect diffusion behavior in the equiatomic NiCoCrFe(Pd) alloy, we demonstrate an alloy design strategy that can reduce the diffusivity difference between the two types of point defects. The two diffusivities become almost equal after substituting the NiCoCrFe base alloy with Pd. The underlying mechanism is that Pd, with a much larger atomic size (hence larger compressibility) than the rest of the constituents, not only heightens the activation energy barrier (Ea) for interstitial motion by narrowing the diffusion channels but simultaneously also reduces Ea for vacancies due to less energy penalty required for bond length change between the initial and the saddle states. Our findings have a broad implication that the dynamics of point defects can be manipulated by taking advantage of the atomic size disparity, to facilitate point-defect annihilation that suppresses void formation and swelling, thereby improving radiation tolerance.

Porous rGO/networked cellulose composite membranes: Towards enhanced nanofiltration performance of rGO-based membranes

Graphene-based materials have been widely used for the fabrication of superior separation membranes for water treatment and purification. In particular, reduced graphene oxide (rGO), which has better water stability than graphene oxide (GO), has been demonstrated to be a good building block. However, rGO laminates are characterized by narrow interlayer spacing leading to dense packing and consequently lower flux limiting their direct utilization for membrane development. In this study, we report the fabrication of networked cellulose (NC)/porous rGO composite membranes with enhanced separation performance. We observed a synergistic effect due to the incorporation of NC and the presence of nano-pores on the rGO sheets. Firstly, in addition to the enhanced hydrophilicity and mechanical stability, the presence of NC with networked fibers reduced the horizontal transport resistance within the interlayer channels due to the formation of voids and wrinkles. Secondly, in-plane pores created by H2O2 oxidation of GO effectively contributed to additional transport channels providing shortened transport length for water molecules. Results showed that composite membranes maintained stable long-term performance with a pure water permeance up to 25.1 ± 2.2 Lm−2h−1bar−1 and salt rejection of 70.2 %, 63.08 %, 17.13 % and 25.62 %, for Na2SO4, MgSO4, MgCl2 and NaCl respectively. Unlike many previously reported rGO membranes that rely on ultra-thin selective layers, this work demonstrates an effective strategy for fabricating superior rGO membranes for water treatment and desalination.

Mg2Al4Si5O18 as a novel bond coat material for advanced thermal/environmental barrier coatings on SiCf/SiC composites

This study proposes cordierite (Mg2Al4Si5O18, MAS) as a novel bond coat material for thermal/environmental barrier coatings (T/EBC), deposited using atmospheric plasma spray on SiC fiber reinforced SiC matrix composites (SiCf/SiC-CMCs) coupons, forming a Mg2Al4Si5O18/Yb2Si2O7/Yb2SiO5/LaMgAl11O19 coating system. The phase composition and thermal properties of the as-sprayed MAS coating were investigated, revealing cordierite as the primary phase in the as-sprayed coating with minor amounts of spinel and quartz phases which disappeared after heat treatment. Additionally, the as-sprayed MAS coating exhibited a low thermal expansion coefficient (3.19 × 10−6 K−1). The thermal cycling behavior and steam corrosion performance of the T/EBC coating system with cordierite as the bond coat were studied. Detailed analysis revealed that during thermal cycling tests, the coating failure was primarily related to liquid-phase sintering caused by eutectic reactions. In steam corrosion tests, the coating delamination was linked to the formation and growth of cracks and corrosion voids due to the residual stress release.

Effect of long-term aging on the microstructure evolution and fracture mechanism of 9% Cr steels

The fracture toughness of pressure pipe steels is vital for their design and safe operation. Understanding the deterioration of the fracture toughness and the corresponding fracture mechanisms is instructive and meaningful for material selection and development. The elastic–plastic fracture toughness of 9% Cr steels aged at 873 K and 923 K from the initial state to 20000 h was investigated at ambient temperature and 873 K. The deterioration of the fracture toughness and the corresponding fracture mechanisms are discussed in detail. For 9% Cr steels, voids mainly initiated from primary inclusions such as silicides, sulfides, alumina and manganides in as-received state, while voids initiated from both primary inclusions and secondary particles such as the Laves phase after long-term aging. These voids grew and coalesced with neighboring voids and crack tips subsequently until ultimately fracture. After aging at 873 K, the fracture toughness values tested at 873 K decreased from the initial state to 3000 h and then increased to 10000 h. The peculiar deterioration of the fracture properties after 3000 h of aging at 873 K can be attributed to the high number density of Laves phase particles in the steels. It was found that the densely distributed hard Laves phase particles induced strain concentration at the interface between the Laves phase and the matrix under plane-strain tension condition and promoted nucleation of voids. It was suggested that the spatial distribution of the Laves phase played a significant role on the void formation. 9% Cr steels with a denser distribution of Laves phases brings about voids with shorter interspaces, which are more susceptible to coalesce into crack tip, resulting in lower fracture resistance. After aging at 923 K from 10000 h to 20000 h, the number density, size and volume fraction of precipitates, block size, misorientation angle and dislocation density remained almost constant. The slight increase in the fracture toughness from 10000 h to 20000 h can be mainly ascribed to the coarsening of the martensite lath in this stage.

Rim nucleation and step-train orientation effects in SOI(111) dewetting

We demonstrate that the step-train orientation of a vicinal surface plays an important role in solid-state dewetting. Focusing on SOI(111), we observe the formation of hexagonal voids in the silicon film due to dewetting. These voids are surrounded by an asymmetric rim, which is wider on the higher-terrace side compared to the lower-terrace side. Our findings also reveal a layer-by-layer growth of the rim around the dewetting voids during the early stages, before the formation of branched structures. Dewetting fingers develop faster and are thinner in the step-down direction compared to the step-up direction. Kinetic Monte Carlo (KMC) simulations confirm our experimental observations and provide insights into the atomic details underlying rim and finger formation. During the initial stages of dewetting, the nucleation of a new rim layer is not required: Atoms leaving the dewetting void are captured by the adjacent upper step, leading to the growth of the upper terrace that thus surrounds the dewetting void. The nucleation of a new rim layer only becomes necessary when the distance between the edge of the void and the upper terrace increases. The energetics involved in the dewetting kinetics of SOI(111) are consistent with those of SOI(100).

Characterization of the microstructure, texture, and tensile behavior of additively manufactured Hastelloy X superalloy: Insights into heat treatment at 900 °C

This research aimed at the microstructural characterization and elucidation of room- and high-temperature tensile properties of additively manufactured Hastelloy X Ni-based superalloy heat-treated at 900 °C. The samples were fabricated via the laser powder bed fusion method utilizing two scan strategies known as island and meander types. The results indicated that the cellular structure embedded in the columnar grains of the as-built microstructure disappeared after applying the heat treatment, linking to the reduction in dislocation density while keeping the former morphology of the grains unchanged. However, the intensities of the Brass, Goss, Goss-Brass, and rotated Goss texture components were reduced, leading to the generation of more homogenous fibers in the heat-treated microstructure. Additionally, it caused the formation of a Mo-rich phase on the grain boundaries, which improved the room temperature's ultimate tensile strength. However, it was elucidated that the Mo-rich phase-induced void formation and intergranular cracking failure caused a slight decrease in hot ductility. Overall, the obtained results revealed that the heat-treated island samples showed superior hot tensile behavior than the meander sample due to having a larger grain size.

Reliability of FET-type gas sensor with asymmetric air-gap micro-heater structure considering thermoelectric effect

Poly-silicon has a wide range of applications because of its interesting properties in the thermoelectric effect. We propose an optimal field-effect transistor-type (FET-type) gas sensor platform with an embedded poly-silicon micro-heater designed considering both power consumption and reliability. Since the poly-silicon micro-heater has a thermoelectric effect, the reliability of the micro-heater can be improved without a significant increase in power consumption by adopting asymmetric etch-holes (finally asymmetric air-gap) along the heater electrode. The sensor with the shorter etch-hole (10 µm) around one electrode of the heater electrode increases power consumption by only 1.22 times but can increase lifetime by 14.2 times. The heat distribution and contact temperature of symmetric and asymmetric air-gap heaters are compared using COMSOL Multiphysics. Sensors with different lengths of etch-holes are fabricated, and the thermal response and reliability of the fabricated sensors are measured and analyzed. In addition, in a sensor in which a thin film of indium oxide is deposited as a sensing material on the gas sensor platform, the effect of air-gap design change on the gas sensing characteristics is investigated. Depending on the polarity of the voltage applied between the two terminals of the heater, the difference in void formation and damage at the heater contacts is confirmed by TEM and EDS analysis.

The effects of twist angle and loading mode on the deformation behavior of bicrystal copper

The effects of twist angle and loading mode on deformation behavior of bicrystal Cu containing symmetric twist grain boundary are investigated by molecular dynamics. Grain boundary dislocation network changes from square-like to ring-like with increasing twist angle. Tensile strength under loading parallel to grain boundary is higher than that under perpendicular loading to grain boundary for the same model, and the larger twist angle is, the larger difference under two loading modes is. Under perpendicular and parallel loadings, initial plastic yield of bicrystal Cu with low angle is triggered by slipping of grain boundary partial dislocations, which results in almost complete dissociation of grain boundary and formation of pillar-like voids inside grains. However, initial plastic yields of bicrystal Cu with higher angle are triggered by explosive collective slipping of short grain boundary partial dislocation and nucleating of new lattice dislocations on grain boundary, respectively, which result in direct splitting of grain boundary and formation of sphere-like voids, respectively. The calculated increase rates of partial dislocation number increase with increasing twist angle, but the increase amplitude is significantly larger under parallel loading. In later stage, void volume of each model is almost the same, but void surface area is significantly different.

Toward High‐Performance All‐Solid‐State Thin Film FeOxSy/LiPON/Li Microbatteries via Dual‐Interface Modification

AbstractFeaturing high theoretical capacity, low cost, and low preparation temperature, Li‐free cathodes are considered promising for all‐solid‐state thin‐film lithium microbatteries (TFBs). In this work, a Li‐free cathode of amorphous FeOxSy film is prepared, followed by the fabrication and investigation of FeOxSy/LiPON/Li TFBs. It is found that the structural degradation at both the LiPON/Li and FeOxSy/LiPON interfaces results in a rapid capacity loss for the TFB during electrochemical cycling. To achieve both high rate capability and long cycle life for the TFB, a dual‐interface modification approach using amorphous Al2O3 as an interlayer is proposed. During the TFB cycling, the Al2O3 interlayer not only enables robust LiPON/Li contact by preventing the formation of Li voids but also blocks the diffusion of Fe element from FeOxSy to LiPON electrolyte, effectively suppressing the interfacial resistance growth. Consequently, the dual‐interface modified TFB achieves greatly improved rate capability (194.3 mAh g−1 at 5 A g−1) and cycle performance (71% capacity retention after 800 cycles), which are superior to the pristine TFB and single‐interface modified TFB. This work advances the fundamental understanding of the failure mechanisms at the solid‐solid electrode/electrolyte interfaces, offering a feasible interfacial modulation strategy to develop advanced all‐solid‐state lithium batteries.

Elimination of buried interfacial voids for efficient perovskite solar cells

Establishing optimal interfacial contact is crucial for enhancing the efficiency of perovskite solar cells (PSCs). However, formation of voids at buried interface of perovskite films often hinders this critical objective. Our investigation reveals that these buried interfacial voids predominantly manifest at sites characterized by large-angle pits on rough substrate, due to their elevated nucleation barriers compared to their small-angle counterparts. To address this challenge and promote uniform nucleation and growth across all sites, regardless of their angles, we develop an innovative precursor regulation strategy to reduce the nucleation barrier discrepancy between different sites by introducing nonstoichiometric homologous ions or by facilitating the formation of intermediate phases. Notably, the incorporation of FACl additive into the FAPbI3 precursor combines the dual benefits of this approach, yielding high-quality perovskite film with intimate contact and reduced defect density. Consequently, this leads to a significant enhancement in the photovoltaic performance of PSCs.

Advancements in emerging MXene-integrated nanocomposite coatings: Unraveling defect-free microstructure for superior tribological, mechanical, and anti-aging features

This study explored the enhancement potential of MXene, a novel two-dimensional material, in epoxy-based nanocomposites; which comprehensively examined the influence of MXene on epoxy's viscosity, void formation, aging resistance, mechanical properties, and anti-wear properties. MXene nanofillers, labeled as 25C and 80C, fabricated via different acid-etching methods, were incorporated into epoxy resin at varying weight percentages (0.1–2.0 wt%). Observations revealed that for both varieties of MXene, inclusion of 1.0 wt% MXene led to the mitigation of void content, whereas the incorporation of 2.0 wt% MXene yielded maximal enhancements in both tensile strength and abrasion resistance. Additionally, the integration of 1.0 and 2.0 wt% MXene displayed superior aging resistance, with around 80 % reduction in free radical formation compared to the unmodified epoxy, while maintaining its excellent mechanical properties after QUV exposure. Therefore, both MXene types significantly enhanced the performance of epoxy composites, with the 80C-MXene displaying marginally superior enhancement due to its smaller particle size and higher purity, as identified by SEM and TEM images.