Void Density Research Articles

WEDM machining of MoNbTaTiZr refractory high entropy alloy

Refractory high entropy alloys (RHEAs) have shown great promise for a multitude of advanced engineering applications due to their high mechanical stability from cryogenic temperatures to 1600 °C. However, the low ductility they exhibit at room temperature limits their machinability when traditional machining techniques are used. Studies on the nontraditional machining of RHEAs, on the other hand, are very limited. In the present work, MoNbTaTiZr RHEAs subjected to wire electrical discharge machining (WEDM) were examined using electron microscopy, contact profilometry, and nanoindentation. Voids, microcracks, and recast material were observed on the machined surfaces. A transition from roughing to finishing decreased the amount of recast material, but the density of observable voids and microcracks on the surface increased. Optimal results were obtained by finishing, where the surface quality was improved by the removal of recast material remaining from prior passes. The brass wire electrode provided a smoother surface while the copper-core electrode provided minor heat-affected zone in the MoNbTaTiZr samples. In the roughing cuts, a 7.00% improvement in surface roughness was achieved using the copper-core electrode compared to the brass electrode. In the semi-finishing and finishing cuts, the brass wire electrode provided improvements of 13.68% and 22.68%, respectively, compared to the copper-core electrode. On the other hand, the wear of the brass electrode was as much as 20.98% higher than that of the copper-core electrode.

The GIGANTES Data Set: Precision Cosmology from Voids in the Machine-learning Era

We present GIGANTES, the most extensive and realistic void catalog suite ever released—containing over 1 billion cosmic voids covering a volume larger than the observable universe, more than 20 TB of data, and created by running the void finder VIDE on QUIJOTE’s halo simulations. The GIGANTES suite, spanning thousands of cosmological models, opens up the study of voids, answering compelling questions: Do voids carry unique cosmological information? How is this information correlated with galaxy information? Leveraging the large number of voids in the GIGANTES suite, our Fisher constraints demonstrate voids contain additional information, critically tightening constraints on cosmological parameters. We use traditional void summary statistics (void size function, void density profile) and the void autocorrelation function, which independently yields an error of 0.13 eV on ∑ m ν for a 1 h −3 Gpc3 simulation, without cosmic microwave background priors. Combining halos and voids we forecast an error of 0.09 eV from the same volume, representing a gain of 60% compared to halos alone. Extrapolating to next generation multi-Gpc3 surveys such as the Dark Energy Spectroscopic Instrument, Euclid, the Spectro-Photometer for the History of the Universe and Ices Explorer, and the Roman Space Telescope, we expect voids should yield an independent determination of neutrino mass. Crucially, GIGANTES is the first void catalog suite expressly built for intensive machine-learning exploration. We illustrate this by training a neural network to perform likelihood-free inference on the void size function, giving a ∼20% constraint on Ωm. Cosmology problems provide an impetus to develop novel deep-learning techniques. With GIGANTES, machine learning gains an impressive data set, offering unique problems that will stimulate new techniques.

TEM characterization of irradiation-induced dislocation loops and voids in ion-irradiated pure chromium

Chromium (Cr) based coatings have been proposed for Zircaloy fuel rods to enhance the accident tolerance in water-cooled reactors. However, the response of Cr to irradiation has received limited attention in prior studies. To get a better understanding of radiation damage in Cr for future nuclear applications, in the present study, the irradiation-induced microstructure evolution of dislocation loops and voids was studied in pure Cr subjected to 2.8 MeV iron ions irradiation at 550 °C (belonging to stage III, intermediate-temperature). TEM observation results show that the distribution of dislocation loops extends the SRIM simulated irradiation depth to 3.5 µm, while voids were only formed in the irradiated region up to a depth of 1.3 µm. A rigorous method with combined consideration of edge-on view and inside-outside analysis was proposed to determine the habit plane. With this method, what has normally considered as an unsafe zone becomes a favored zone for determining the nature of dislocation loops. The nature of dislocation loops was determined including both interstitial and vacancy types with ½<111> Burgers vector in all regions. Within the irradiation region, the loops are approaching half interstitial and half vacancy, while beyond the irradiated region interstitial loops became dominant. The irradiation-induced swelling was quantified by the void size and density. The swellings are mostly corresponding well with the irradiation dose distribution which is simulated by SRIM. The swelling rate close to the peak region is around 0.3%/dpa. Results demonstrate that Cr tends to experience some similarities in irradiation loop evolution to W-based, Mo-based materials, as they are in the same group in the periodic table, despite the discrepancy in the characteristic of loops such as the irradiation temperature-dependent dislocation loop formation was observed as well. The present study is significant not only for supplementing the fundamental knowledge of irradiation damage in Cr but also for the application of Cr coating to the accident tolerant fuel claddings or other nuclear structure materials.

Study of the creep cavitation behavior of P91 steel under different stress states and its effect on high-temperature creep properties

In this study, circumferential U-notches of different depths were machined on a plain cylindrical creep specimen to simulate different stress states during steam pipe operation. The effects of stress concentration on the creep cavitation behavior and high-temperature creep properties of P91 steel were investigated through creep experiments and microstructure analysis, as well as measurement and analysis of scanning electron microscopy (SEM) micrographs using ImageJ to obtain the equivalent diameter, circularity, area and distribution of the voids after high-temperature creep of P91 steel. In the analysis of 98 notched samples of 14 bars, it was found that a large number of voids with diameters of 0.78–3.56 μm existed at the notch root, the voids were distributed in a fan shape near the notch root, the size of the distribution area was related to the stress, and the larger the stress was, the larger the area. The number, density and average area of voids increased with stress and time. The stress level at the notch root was found to be positively correlated with the area of damage caused by the voids in the region and negatively correlated with the number of voids based on the FE analysis. By analyzing the experimental data, it is found that the circularity is closely related to the void diameter, and the void coalescence occurs when the void diameter reaches a critical value, which varies with temperature, stress and time.

A Novel Microshear Geometry for Exploring the Influence of Void Swelling on the Mechanical Properties Induced by MeV Heavy Ion Irradiation.

Small disks are often the specimen of choice for exposure in nuclear reactor environments, and this geometry invariably limits the types of mechanical testing that can be performed on the specimen. Recently, shear punch testing has been utilized to evaluate changes arising from neutron irradiation in test reactor environments on these small disk specimens. As part of a broader effort to link accelerated testing using ion irradiation and conventional neutron irradiation techniques, a novel microshear specimen geometry was developed for use with heavy-ion irradiated specimens. The technique was demonstrated in pure Cu irradiated to 11 and 110 peak dpa with 10 MeV Cu ions. At 11 peak dpa, the Cu specimen had a high density of small voids in the irradiated region, while at 110 peak dpa, larger voids with an average void swelling of ~20% were observed. Micropillar and microshear specimens both exhibited hardening at 11 dpa, followed by softening at 110 dpa. The close alignment of the new microshear technique and more conventional micropillar testing, and the fact that both follow intuition, is a good first step towards applying microshear testing to a wider range of irradiated materials.

TEM investigation of neutron irradiated and post irradiation annealed tungsten materials

In this paper, we present a transmission electron microscopy study of three tungsten grades subjected to neutron irradiation and post-irradiation annealing. The irradiation was performed at 600 °C up to 0.2 dpa and the microstructure was investigated after the irradiation, reported in a previous publication, as well as after the annealing at 800 °C and 1000 °C. The evolution of the radiation induced defects is characterized and the overall microstructural features are compared in three states: virgin-as irradiated – as annealed after irradiation. The annealing at 800 °C causes an increase in the loop and void densities and moderate increase in the mean sizes. An increase of the annealing temperature to 1000 °C causes a reduction of the loop density, while the loop size increases. Also the void density reduces, but not necessarily the void fraction. The peak of the void volume fraction is found around 800 °C, which coincides with the earlier reported experimental data on the void swelling peak under neutron irradiation.

Size Dependent Properties of Reactive Materials

The nature of the self-sustained reaction of reactive materials is dependent on the physical, thermal, and mechanical properties of the reacting materials. These properties behave differently at the nano scale. Low-dimensional nanomaterials have various unusual size dependent transport properties. In this review, we summarize the theoretical and experimental reports on the size effect on melting temperature, heat capacity, reaction enthalpy, and surface energy of the materials at nano scale because nanomaterials possess a significant change in large specific surface area and surface effect than the bulk materials. According to the theoretical analysis of size dependent thermodynamic properties, such as melting temperature, cohesive energy, thermal conductivity and specific heat capacity of metallic nanoparticles and ultra-thin layers varies linearly with the reciprocal of the critical dimension. The result of this scaling relation on the material properties can affect the self-sustained reaction behavior in reactive materials. Resultant, powder compacts show lower reaction propagation velocities than bilayer system, if the particle size of the reactants and the void density is decreased an increase of the reaction propagation velocity due to an enhanced heat transfer in reactive materials can be achieved. Standard theories describing the properties of reactive material systems do not include size effects.

Type IV creep crack initiation and propagation in mod.9Cr-1Mo steel welds

ABSTRACT The ratio of crack initiation and crack propagation life is important from the viewpoint of residual life prediction of mod. 9Cr-1Mo steel welds under Type IV creep damage. Both the creep void density distribution and the failure process with crack initiation/propagation/final failure are predicted for three types of welds in pipes and nozzles, which are compared with experimental results at 650°C. The ratio of crack initiation and final failure life depends on weld type and loading conditions; the ratio is about 0.95 in the cases where redistribution of stress occurs only in the thickness; the ratio is 0.59 ~ 0.65 in the cases where redistribution of stress occurs in both the thickness and circumferential directions of the pipe. Influence of stress ratio (axial vs. circumferential stress) is also predicted for circumferential welds subject to internal pressure/axial load and is compared with experimental results at 650°C.

Positron annihilation spectroscopy investigation of defects in neutron irradiated tungsten materials

The identification of defects in neutron damaged materials is essential for elucidating the correlation between the microstructure and the properties of a material. Positron annihilation spectroscopy (PAS) is very sensitive in open volume defects and thus a useful tool for the investigation of the radiation damage in matter. Tungsten is a critical material for the first wall and divertor of fusion reactors. In the current work, the evolution of the open volume defects in tungsten (W) materials neutron irradiated to 0.12 displacements per atom (dpa) and in the temperature range from 600 to 1200 °C in the Belgian Material Test Reactor BR2 is investigated by positron annihilation lifetime and coincidence Doppler broadening spectroscopy. Three tungsten grades were studied: W(100) single crystal, ITER grade forger bar and heavily deformed “cold”-rolled sheet. PAS results show that the neutron irradiation results in the formation of dislocations and voids of size larger 1 nm at all irradiation temperatures and in all W grades. The dislocation and void density decreases with increasing irradiation temperature. Moreover, the void size increases with the increase of the irradiation temperature.

Cosmic Voids and BAO with relative baryon-CDM perturbations

ABSTRACT We study the statistics of various large-scale structure tracers in gravity-only cosmological simulations including baryons and cold dark matter (CDM) initialized with two different transfer functions, and simulated as two distinct fluids. This allows us to study the impact of baryon-CDM relative perturbations on these statistics. In particular, we focus on the statistics of cosmic voids, as well as on the matter and halo real-space 2-point correlation function and baryon acoustic oscillations (BAO) peak. We find that the void size function is affected at the 1–2 per cent level at maximum, and that the impact is more important at higher redshift, while the void density profile and void bias are roughly unaffected. We do not detect a sizeable impact of relative baryon-CDM perturbations on the real-space correlation functions of matter and haloes or the BAO peak, which is in line with results from previous works. Our results imply that it would be hard to use voids or real-space correlation functions to constrain baryon-CDM relative perturbations, but also that we might not have to include them in models for the analysis of future cosmological surveys data.

Control of fatigue failure mechanisms in multilayer coatings by varying the architectural parameters of an intermetallic interlayer

AbstractA multilayer overlay coating system containing an intermediate intermetallic layer is an architecture expected to show good fatigue resistance. Experimental characterization and modeling simulations were carried out to classify the different crack initiation mechanisms occurring during fatigue of this coating system (2IML coating system) and to reveal how changes in the layer architecture lead to fatigue improvement. Surface crack initiation seems to play the dominated role in the fatigue failure of this coating system as over 55% of observed cracks were surface cracks. Fatigue improvement is achieved by increasing surface initiation resistance via decreasing the IML‐Top layer thickness. However, subsurface initiation mechanisms inhibit the improvement (dominated by surface initiation mechanism) achieved by locating the IML‐Top layer closer to the top surface. Optimizing the design of 2IML multilayer coatings based on the fatigue performance should eliminate the unreacted nickel layer in the intermediate IML‐Top layer, increase the subsurface interface strength, and decrease the density of voids occurring in the annealing process.

A-Site Substitute for Fabricating All-Inorganic Perovskite CsPbCl3 with Application in Self-Powered Ultraviolet Photodetectors.

Because of its stable chemical properties and wide band gap, CsPbCl3 perovskite has shown great application prospects in ultraviolet photodetectors (UPDs). However, the poor solubility of CsCl in organic solvents impedes the fabrication of high-quality CsPbCl3 films. Herein, we introduced an A-site substitute route for fabricating a high-quality CsPbCl3 microcrystalline (MC) film by spin-coating cesium acetate on a MAPbCl3 MC film followed by a high-temperature annealing process. To enhance the device performance of the FTO/SnO2/CsPbCl3 MCs/carbon structure UPD, a pressure-assisted annealing strategy was carried out, which reduced the void density and surface roughness of the microcrystal film. Finally, our optimized PDs showed high device performances with an on/off ratio of 6 × 104, a responsivity of 0.13 A W-1, a detectivity of as high as 1.07 × 1012 Jones, and a rise/fall time of 10/24 μs. Moreover, our unpacked PDs showed good storage and light stability. Our results lay a foundation for the application of all inorganic perovskite in the ultraviolet region.

Exploring the suitability of using Foam concrete as pore pressure dissipation measure for slope Stability: A state of art review

Landslides are one of the major factors leading to disruption of transportation and urbanization of north-eastern India (NEI). The primary reasons are continuous precipitation and alarming seismicity at frequent intervals. Among various factors which can trigger landslide, most common is the increase of pore water pressure (PWP). This in turn increases the weight of the backfill and subsequently contribute to the overturning moment. Hence, measures to extract the pore water (PW) from the backfill through provision of drainage path is an efficient and widely followed approach to mitigate landslides. This paper presents a detailed overview on various landslides which have happened in the NEI during rainfalls and earthquake events, confirming these as two main triggering factors. Later, the limitations of various conventional landslide prevention techniques is also discussed. Though RWs are commonly adopted slope stabilization techniques, many case studies exist in where even RWs had failed to stabilize the slopes particularly where the slopes with higher groundwater table were subjected to heavy precipitation. The primary reason of failure was development of excess PWP behind RWs. While weep-holes in the RW play a critical role in dissipating PWP of the backfill, these are clogged resulting in the failure of the RWs. The fact cannot be denied that the effectiveness of the weep-hole depends upon its design, construction as well as its maintenance.Recently few researchers have shown that the Foam concrete (FC), a type of lightweight concrete, act as an excellent draining material to facilitate PW discharge for slope stabilization owing to its high permeability. Further, as the density of air voids in FC is more, rate of clogging is expected to be lesser, thus demanding lesser maintenance when compared to conventional weep-holes. This way, the need of regular maintenance of weep-holes can be minimized by use of FC. It should be highlighted here that though FC has lot of potential to be use in aforementioned application, there is not much of research exist in the literature on use of FC for PWP dissipation application. In this light, the present work also presents an in-depth review on permeation characteristics of FC, enumerating the PWP dissipation mechanism with the help of case studies from the literature.

A micromechanical approach to the mechanical characterization of 3D-printed composites

Aiming for the development of experimentally validated computational models to predict the mechanical properties of 3D-printed composites, the present study proposes a micromechanical approach by using a simplified unit cell model to characterize the material properties and behavior of 3D-printed composites manufactured through fused deposition modeling. The effective properties of the voided polymer matrix phase of the material are computed by calculating the void density as a tensorial meso-structural variable. These effective properties along with those of the fiber are input into a simplified micromechanical model to predict the material properties of the 3D-printed composite. The predictions are seen to be in very good agreement with the experimental values. The present approach is much simpler and less computationally costly compared to the finite element homogenization method. In addition, the present approach has the potential to simulate the response of the 3D-printed composite under different loading conditions.

A novel approach to producing architectured ultra-high strength dual phase steels

An ultrafine-grained dual phase (DP) microstructure has been produced in a steel that contains a combination of composition and deformation gradients. A carbon gradient was created by controlled decarburization of the steel. The compositionally graded steel was cold rolled to produce a large number of shear bands prior to recrystallization annealing at 650 °C for 5 h followed by intercritical annealing at 740 °C for 10 min. Microstructural characterization reveals a very fine heterogeneous dual phase microstructure with submicron grains appearing along the traces of the prior shear bands that had developed during rolling. Martensite volume fraction changes from the surface to the center and also within these shear band traces. Tensile tests of the new dual phase structure reveal that the work hardening rate changes spatially with martensite volume fraction. Detailed fractography using ex-situ X-ray computed tomography (XCT) reveals a unique form of multiple cup and cone fracture features that can be related to the evolution of damage along the shear band traces with a gradient of void density from the surface to the center. This strategy for fabricating dual phase steels enables the development of architectured ultra-high strength DP steels with different properties that can be tailored by controlling the composition and deformation gradients and subsequent annealing treatments.

Boron nitride nanosheets incorporated polyvinylidene fluoride mixed matrix membranes for removal of methylene blue from aqueous stream

This study aims to synthesize boron nitride nanosheets (BNNS) incorporated polyvinylidene fluoride (PVDF)-based membranes using phase inversion method for removal of methylene blue (MB) from water. We start with density functional theory (DFT) calculations to get a first order estimate of absorption capacity of PVDF and BNNS-PVDF for MB, which reveal the probability of attaining higher adsorption capacity of MB for BNNS-PVDF than PVDF. Experimentally, the loading of the BNNS has been optimized by varying it from 0.5 to 2.0 wt%. The morphological characterization shows higher roughness with increased loading and highest void density for PVDF + 1 wt% BNNS. The corresponding SBET obtained is 28 m2/g. Further, the highest pure water flux (1160 l m-2 h-1), porosity (87.68%) and mechanical strength (1.8 MPa) also confirm that the membrane loaded with 1.0 wt% BNNS is optimum. The maximum adsorption capacity of the optimized BNNS-PVDF membrane has been found to be (142.86 mg g-1) that is 2.2 times higher than the PVDF membrane (65.36 mg g-1) and is largely in line with our DFT simulations. Moreover, the thermodynamic studies reveal that the adsorption is favorable at high temperatures and the reaction is endothermic in nature. The membrane exhibits good separation and regeneration behavior. Additionally, the optimized membrane shows excellent continuous flow adsorption of simulated MB contaminated aqueous stream and 100% removal of 10 ppm MB solution is achieved. These results reveal that the synthesized membrane loaded with 1.0 wt%. BNNS is a potential candidate for MB remediation from the aqueous stream.

Experiment and modeling based studies of the mesoscaled deformation and forming limit of Cu/Ni clad foils using a newly developed damage model

Lack of systematic researches on mesoscaled deformation and damage criteria would obstruct the development of optimal microforming of clad foils. In this paper, a newly developed damage model, inspired by fracture mechanism, was developed to determine the forming limit of Cu/Ni clad foils via considering size effect and its influences on deformation and fracture behavior. The newly developed model integrates the interface separation model based on GTN-Thomason model and the Marciniak-Kuczynski (M-K) model to represent the two stages of ultimate strain before instability in the fracture process of Cu/Ni clad foils. In addition, the former model describes the first-stage strain of the interface separation dominated by void evolution; while the latter one models the second-stage strain of the localized instability of clad foils at interface separation locations via introducing the effects of surface roughness and interface separation on thickness. The results of the synchrotron radiation experiments indicate that void nucleation, growth and coalescence occurring in the interface layer are mainly located in the Cu layer grain boundary region. The localized high density of the nucleated voids is the direct cause of the localized instability. The results of surface roughness experiments demonstrate that surface roughness increases rapidly with strain and saturates at a low strain condition. The surface roughening becomes severe with the increase of grain size. The experimental results of the forming limit show that forming limit curves (FLCs) shift down and strain concentration occurs prematurely with the increasing grain size. The FLCs of Cu/Ni clad foils influenced by grain size are predicted by the newly developed model successfully. This study reveals the interfacial void evolution and surface roughening behavior and their influences on the forming limit of clad foils, in such a way to provide a theoretical basis for microforming of clad foils.

Intrinsic alignments of galaxies around cosmic voids

ABSTRACT The intrinsic alignments of galaxies, i.e. the correlation between galaxy shapes and their environment, are a major source of contamination for weak gravitational lensing surveys. Most studies of intrinsic alignments have so far focused on measuring and modelling the correlations of luminous red galaxies with galaxy positions or the filaments of the cosmic web. In this work, we investigate alignments around cosmic voids. We measure the intrinsic alignments of luminous red galaxies detected by the Sloan Digital Sky Survey around a sample of voids constructed from those same tracers and with radii in the ranges: [20–30; 30–40; 40–50] h−1 Mpc and in the redshift range z = 0.4−0.8. We present fits to the measurements based on a linear model at large scales, and on a new model based on the void density profile inside the void and in its neighbourhood. We constrain the free scaling amplitude of our model at small scales, finding no significant alignment at 1σ for either sample. We observe a deviation from the null hypothesis, at large scales, of 2σ for voids with radii between 20 and 30 h−1 Mpc, and 1.5σ for voids with radii between 30 and 40 h−1 Mpc and constrain the amplitude of the model on these scales. We find no significant deviation at 1σ for larger voids. Our work is a first attempt at detecting intrinsic alignments of galaxy shapes around voids and provides a useful framework for their mitigation in future void lensing studies.

Effect of annealing on the hardness and microstructure of Cr-Zr-O coatings

The hardness and microstructure of as-deposited and annealed Cr-Zr-O coatings have been comparatively investigated to clarify the effects of annealing treatment. The as-deposited coating comprises of nano-sized columnar grains of (Cr, Zr)2O3 that is formed due to the solution of Zr atoms in Cr2O3. Such a kind of structure is benefit for the hardness. The interface between the as-deposited coating and substrate is well-bonded and a sandwiched structure forms during the deposition process. After annealing at 800 °C, a high density of nano-sized voids were formed in the coating. The sandwiched structure at the interface is damaged and the bonding of interface becomes weak. As a result, the modulus and hardness of the Cr-Zr-O coating decrease significantly after annealing.

Mechanical Properties of Hybrid Carbonized Plant Fibers Reinforced Bio-Based Epoxy Laminates.

In this work, henequen and ixlte plant fibers were carbonized in a horizontal quartz tube furnace. Several carbonized and non-carbonized fiber fabric configurations were impregnated with a bio-based epoxy resin through the infuseon process. The infrared spectra revealed characteristic bands of styrene instead of organic compounds, representing that the carbonization procedure was adequate to carbonize the plant fibers. The porosity volume ratio for the non-carbonized henequen laminates showed the highest number of voids >1.9%, and the rest of the composites had a similar void density between 1.2–1.7%. The storage modulus of the non-carbonized and carbonized henequen laminates resulted in 2268.5 MPa and 2092.1 MPa, respectively. The storage modulus of the carbonized ixtle laminates was 1541.4 MPa, which is 37.8% higher than the non-carbonized ixtle laminates and 12% higher than henequen composites. The laminates were subject to thermal shock cycling, and tomography scans revealed no alterations on the porosity level or in the cracks after the cycling procedure. Thermal shock cycling promoted the post-curing effect by increasing the glass transition temperature. The viscoelastic results showed a variation in the storage modulus when the carbonized fiber fabrics were located between natural fiber fabrics, which was attributed to more excellent compaction during the infusion process. Variations in the viscoelastic behavior were observed between the different types of natural fibers, which influenced the mechanical properties.