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The 45 mm thick plate of 9% Ni steel was successfully butt welded with NiCrMo-4 filler metal adopting the submerged arc welding (SAW) via a multi-layer and multi-pass process. After welding, the weld joints were tested in cryogenic and room temperature, respectively, to reveal the influence of microstructure evolution on fracture toughness. The microstructure of the heat-affected zone (HAZ) was characterized by reversed austenite and tempered martensite like the base metal (BM) after post-weld heat treatment, and the weld metal (WM) was presented by austenite in the form of layered columnar grain region (CGR) and fine equiaxed grain region (FGR). With the decrease in temperature, most of the reversed austenite in 9%Ni steel transformed into martensite, resulting in the plastic deformation ability of 9%Ni steel decreased significantly. Moreover, many microvoids formed in WM during the cryogenic fracture process due to the strength mismatch between precipitates and austenite. Compared to FGR, larger and more densely distributed microvoids in CGR were more likely to aggregate into macrocracks, making CGR the weak region in WM at cryogenic temperature. [ABSTRACT FROM AUTHOR]

Fiber Bragg gratings are key components for optical fiber sensing applications in harsh environments. This paper investigates the structural and chemical characteristics of femtosecond laser photo-inscribed microvoids. These voids are at the base of type III fs-gratings consisting of a periodic array of microvoids inscribed at the core of an optical fiber. Using high-resolution techniques such as quantitative phase microscopy, electron transmission microscopy, and scattering-type scanning near-field IR optical microscopy, we examined the structure of the microvoids and the densified shells around them. We also investigated the high-temperature behavior of the voids, revealing their evolution in size and shape under step isochronal annealing conditions up to 1250 °C. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) provides exceptional geometrical freedom to the architects and designers and enables the construction of architecturally exposed steel structures. However, the AM structural elements inherently possess microscale defects that can affect their ductility. This study aims to identify the fracture-initiating mechanism in AM 17-4 stainless steel that is popularly used owing to its excellent engineering properties. To this end, axisymmetric cylindrical notched and unnotched tension specimens are manufactured employing direct metal laser sintering from 17-4 stainless steel powder with established processing and build parameters. The test specimens were manufactured using a 90° build orientation with the build plate and a layer thickness of 40 μm. Postprocessing heat treatment was avoided as the study focused on understanding the failure mechanism in as-built AM test specimens. Detailed metallurgical analysis is performed employing scanning electron microscopy (SEM) and electron backscatter diffraction. Subsequently, micro–computed tomography (CT) studies are conducted on the tension specimens before and after mechanical testing. Although the SEM analyses of fracture surfaces are inconclusive, the micro-CT analysis revealed evidence of nucleation of new microvoids, growth of existing voids, and void coalescence in the vicinity of the fracture surface, which is unequivocal evidence for ductile fracture. Furthermore, the larger AM defects were found to play an important role in lowering the ductility in addition to stress concentration, and the fracture was initiated when the AM defects coalesced over a length of around 600 μm. The conclusions of this study emphasize the importance of controlling the maximum size of defects in AM structural elements to improve their performance. [ABSTRACT FROM AUTHOR]

Background: Polymerization shrinkage and microvoid formation has been a significant problem giving way to resin composite failure. The aim of this study was to evaluate the microvoid potential and microleakage of two bulk-fill and a microhybrid resin composite applied with different adhesive materials. Materials and Methods: MOD cavities were prepared in 60 endodontically treated maxillary premolars. The teeth were divided into six different groups (n = 10) according to adhesive systems (Gluma (Kulzer), OptiBond FL (Kerr) and resin composite materials EverX Posterior (GC) and Filtek One Bulk Fill (3M ESPE). An aging procedure with 5000 cycles of thermal cycling was applied. All teeth were individually scanned with micro-computed tomography. A Shapiro–Wilk test, two-way MANOVA, and Bonferroni analysis were used for statistical tests. Results: Self-etch groups showed more microleakage than total-etch groups. Minimum microleakage was observed in Filtek One Bulk Fill groups, whereas G-aenial Posterior groups showed maximum microleakage. Conclusions: Filtek One Bulk Fill (3M ESPE) resin composite was found to be more effective in reducing microvoid formation in MOD cavities when applied with total-etch adhesive systems. However, EverX Posterior (GC) and G-aenial Posterior (GC) showed less microvoid formation with self-etch adhesive systems. [ABSTRACT FROM AUTHOR]

The analysis method proposed by Ruland et al. is widely used to analyze the void lengths in carbon fibers, but it could not apply to mesophase pitch-based carbon fibers. We thought that the reason for the inability to analyze pitch-based carbon fibers was the length distribution of voids that Ruland neglected. We investigated an analytical method that considers the length distribution of voids in carbon fibers. The proposed new method could be applied to various carbon fibers from polyacrylonitrile and mesophase pitch. The analysis results revealed that the average length of voids in mesophase pitch-based carbon fibers is not only long but also widely distributed. On the other hand, the voids of carbon fibers tend to be longer as the crystallite length is longer in both polyacrylonitrile-based and mesophase-based carbon fibers. It suggests that the growth of void length is strongly influenced by the growth of crystallites in the plane direction.

The adiabatic shear sensitivity of AZ31 magnesium alloys with different grain sizes under high-strain-rate deformation was investigated using a split Hopkinson pressure bar at 2000s−1 and a hat-shaped specimen at 150 °C. The microstructure of the forced shear regions was characterized via optical microscopy, scanning electron microscopy, electron back-scattered diffraction, and transmission electron microscopy. The microhardness across the forced shear region after high-strain-rate deformation was investigated through Vickers hardness testing. The results show that the adiabatic shear sensitivity of AZ31 magnesium alloys decreases with decreasing grain size, while the width of the adiabatic shear band (ASB) increases with decreasing grain size, and a diffused shear band is formed in the forced shear region when the grain size is reduced to 3 µm. From the center to the edge of the forced shear region, the microstructure changes from equiaxed grains, to fine grains, and eventually to the matrix, which reflects a gradual variation in the grain size. The fine grains in the ASB cause its microhardness to be significantly higher than that of the surrounding microstructure. The microvoids in the ASB grow and connect with each other along the shear direction, finally resulting in macrofractures. [ABSTRACT FROM AUTHOR]

Fiber Bragg gratings are key components for optical fiber sensing applications in harsh environments. This paper investigates the structural and chemical characteristics of femtosecond laser photo-inscribed microvoids. These voids are at the base of type III fs-gratings consisting of a periodic array of microvoids inscribed at the core of an optical fiber. Using high-resolution techniques such as quantitative phase microscopy, electron transmission microscopy, and scattering-type scanning near-field IR optical microscopy, we examined the structure of the microvoids and the densified shells around them. We also investigated the high-temperature behavior of the voids, revealing their evolution in size and shape under step isochronal annealing conditions up to 1250 °C.

Non-traditional polyesters from low molecular weight Poly (ethylene glycol) (PEG, Mn 4000) and biocompatible Trimesic acid (TMA) were synthesised through stoichiometric feeding of PEG and TMA in the mole ratios starting from 1:0.5 to 1:5. The melt condensation was carried out under catalytic condition for a limited period of 6 h to prohibit gelation of the entire mass due to over-abundance of the functional groups. The polyesters were formed with substantial soluble yield; at lower acid concentration in the feed e.g. 1:0.5, 1:1 and 1:2-they were mostly branched while at higher concentration e.g. 1:3 and 1:5-they were significantly crosslinked. Nearly all the specimens contained partially reacted TMA molecules in the branch ends which made them pH responsive (the hydrodynamic sizes altered with change in pH). The polymers were characterized using solubility, spectroscopy, viscometry and particle size measurements to establish the microstructure, formation kinetics and branched topology. Nuclear magnetic resonance (1H NMR) established the maximum extent of branching (65%) at 1:5 mol composition. Suitability for bioapplication of the polyesters was examined from surface texture study and cell cytotoxicity analysis. The scanning electron microscopic (SEM) images portrayed adequate micro voids on the surface, on the other hand, the cytotoxicity study depicted those surfaces could adhere and support the growth of mammalian cells and also successfully survive the MTT assay. [ABSTRACT FROM AUTHOR]

The fracture surface characteristics and the associated micromechanisms governing the fish-eye crack initiation of a Ti-6Al-4V alloy under very high cycle fatigue (VHCF) loading are investigated. Microscopic observation revealed that the crack initiation area of fish-eye center is covered by ragged-like mountains and dimples containing various irregular rods/particles, grooves and microvoids. These micro-ductile characteristics primarily result from the nucleation and coalescence of microvoids and grooves at αs/βr interface inside βtrans. This could be due to the incompatibility of both micro-plastic deformation and slips in αs and βr. The βtrans plays a dominant role in the fish-eye crack initiation and early propagation process of the Ti-6Al-4V alloy in the VHCF regime.

The dynamic growth process of intermetallic compounds (IMCs) at the interface of copper–tin coating and the process of microvoid formation were studied using the phase field method combined with thermal–mechanical–electrical diffusion coupling theory. Numerical results show that the thickness of IMCs in the copper–tin coating increased rapidly and then slowly. Current density had a significant effect on the growth of IMCs at the interface. Under the action of electromigration, the thickness of IMCs at the anode was much greater than that at the cathode, which was consistent with the experimental results. The thickness of IMCs increased with the increase in current density. The influence of a rough interface on IMCs was also studied. Uneven diffusion occurred in the rough interface, resulting in microvoids, and the electromigration effect was one of the reasons for the unbalanced diffusion. [ABSTRACT FROM AUTHOR]

Dense non-aqueous phase liquids(DNAPLs) with a density greater than water have a tendency to migrate to the depth of the underground medium under natural conditions and under the action of gravity in the process of artificial remediation, thus increasing the risk of contamination.Previous experiments on one-dimensional sand column and two-dimensional sand box have found that the density-modified displacement(DMD) could reduce the risk of downward migration of DNAPLs, but there is a lack of quantitative observation on the effect of DMD on DNAPLs migration at the pore scale.In this study, simulated n-BuOH injection into microvoids was used to achieve PCE density conversion.By establishing the quantitative relationship between the PCE concentration, density and grayscale of dyeing PCE in non-aqueous phase(NAPL), the dynamic change of PCE-butanol density in microvoids after n-BuOH injection was quantitatively monitored.The migration state was analyzed based on the stress of representative PCE-butanol blobs in voids.The influence of the properties of void-scale media and density regulation on DNAPLs migration was revealed.The experimental results show that after n-BuOH injection, the concentration and density of PCE decreased rapidly, resulting in the reduction of the combined force of buoyancy and gravity and the friction of tube wall in the PCE-butanol blobs.The effective contact area between discrete PCE and n-BuOH is large and the effect is fast.When the density of PCE-butanol blobs decreases to slightly higher than that of water phase, the PCE-butanol blobs stop migrating downward under the influence of capillary force and friction.When the density of PCE-butanol blobs is less than that of water phase, the PCE-butanol blobs migrates upward, overcoming the capillary force, gravity and friction under the action of injection pressure and buoyancy.Injection pressure, friction, capillary force, buoyancy and gravity influence the migration behavior of PCE-butanol blobs in microvoid.The larger the microvoid radius, is the less influence the capillary force has on regulating the upward migration of PCE.n-BuOH with lower density than water migrates upward after being injected into the microvoids, so the n-BuOH injection from the lower end could improve the repair efficiency.The experiment confirmed that the injection of n-BuOH into the porous medium could significantly reduce the density of the DNAPLs and the risk of downward migration, providing information on the microscopic mechanism for the DNAPLs remediation program in the actual site.

Herein, the effect of heat treatment with die quenching on Zn‐coated hot stamping steel is analyzed. Heating temperatures are 850, 880, 900, and 930 °C, and soaking times are 4 and 8 min. Then, microstructure, hardness, coating layer morphology, element diffusion and distribution, formation of microcrack and microvoid, and oxidation are analyzed. Results reveal that as heating temperature increases, the Vickers hardness of Zn‐coated hot stamping steel increases when soaking time is 4 min, while it decreases when soaking time is 8 min. The least average hardness value is still larger than 460, resulting from the formation of the martensitic phase. The diffusion tends to be significant as heating temperature and soaking time increase. Both the diffusion and the evaporation affect the thickness of the coating layer remarkably. The average layer thickness is at least 18.2 μm. Microcrack generates in the coating layer due to different thermal expansions between substrate and coating layer and the melting of Zn or Zn–Fe binary phase with high content of Zn. Microvoid forms in the coating layer, resulting from the Kirkendall effect and oxidation of the Zn element. Moreover, with the increase in heating temperature and soaking time, Fe2O3 is also generated on the coating surface along with ZnO. [ABSTRACT FROM AUTHOR]

The effects of different vibration frequencies on the microstructure, laves phases and microvoids of Inconel 718 weld joints were investigated in this research by using the laser welding combined with mechanical vibration. The results demonstrated that the application of vibration significantly suppressed the growth of columnar crystals, reduced the formation of carbides, and refined the microstructure. With the increase of the vibration frequency, the mechanical vibration stayed prominent. The molten pool was subjected to the pressure and vibration of the metal liquid, which expanded the depth and the width of the weld. Applying vibration could reduce the amount of Laves phase, and it is found that with the increase of vibration frequency, the morphology of Laves phase could change from granular to strips, as found during the experiment. The welds with 522 Hz vibration frequency had the smallest Laves phase size and the largest average microhardness value of 331 HV. At the vibration frequency of 1331 Hz, the amount of Laves phases was the least, and it was distributed in a miscellaneous manner in the form of granules and stripes. However, increasing the vibration frequency could not effectively reduce the number of microvoids in the weld. [ABSTRACT FROM AUTHOR]

One of the main challenges for fiber-reinforced polymers (FRP) is the difficulty to predict their mechanical behavior. At the microscale, the properties of the constituents, their spatial distribution and the defects arising from manufacturing affect the mechanical behavior. In this work, statistically representative volume elements (SRVEs) are proposed based on a micromechanical finite element model to determine the effect of content, distribution and size of microstructural defects and, material uncertainties on the elastic mesoscale properties of FRPs. To that end, different cylindrical void sizes are considered as well as irregular shaped voids between fiber tows (inter-fiber voids). Fibers and voids are randomly distributed in a SRVE. An uncertainty quantification and management analysis is employed to obtain statistical descriptors of the effective mesoscale mechanical properties of FRPs. The results obtained are compared with analytical models. It is demonstrated that, for carbon fiber/epoxy composites, SRVEs with lateral dimensions equivalent to 15 times the average fiber diameter and a length of 0.01 mm along the longitudinal direction remain statistically representative with or without the presence of voids. The results show that the presence of voids reduces the transverse and shear elastic properties of FRPs. The smaller the voids are, the bigger is the reduction. Regarding the presence of inter-fiber voids, the reduction is lower. This trend is well predicted by the Mori–Tanaka mean field theory. However, the relative difference between the numerical and the analytical predictions increases for high void volume fractions. Regarding the effective longitudinal Young's modulus, the rule of mixtures, the Mori–Tanaka mean field theory and the concentric cylinder assembly model provide similar predictions for the mean value, but the uncertainty is overestimated by the analytical models because the properties of the fibers take a single value for each calculation with the analytical model, while they more realistically change from fiber to fiber in the numerical SRVEs. [Display omitted] • Methodology to propagate uncertainties on the mesoscale properties. • Computational micro-mechanics applied to composites with microscale voids. • Voids induce a knock-down factor on the mean elastic mesoscale properties. • Constituents variability contributes more to the STDV on the predicted properties. [ABSTRACT FROM AUTHOR]

Microvoids, a common casting defect, have a significant effect on the mechanical properties of as-quenched aluminum alloys. In this study, low-pressure casting and quenching processes were conducted on an Al-Cu-Mn alloy to investigate the porosity variation, which was characterized by using a high-precision densimeter and x-ray microtomography. Mechanical properties were tested at elevated densities varying from 2.7828 to 2.8114 g/cm3. The Voce behavior and linear hypotheses were proposed on the relationship between the yield strength and density. A tensile constitutive model was established and validated with experimental data, and the difference between tension and compression was compared. With a decrease in density, the yield stress declined, and the tensile–compressive asymmetry increased. The ideal density, ρ 0 , and the ideal saturated stress, σ s , of the as-quenched alloy were predicted. A comparison between the quantity and volume of microvoids showed that larger pores were the main factor affecting the porosity of the as-quenched alloy. The growth of single microvoid and the coalescence of several microvoids caused an increase in porosity under tensile stress. [ABSTRACT FROM AUTHOR]

Abstract It is well known that Cu precipitates are formed by neutron irradiation of Fe Cu alloys, which are the model alloys of reactor pressure vessels (RPVs), and Cu precipitates increase the yield stress and decrease the total elongation of Fe Cu alloys. However, the correlation between the formation of Cu precipitates and the mechanical properties of Fe Cu alloys is not clear. In this study, two model alloys, Fe-0.3Cu and Fe-0.6Cu were irradiated with neutrons at 573 K with up to 6.2 × 1022 neutrons/m2 (E > 0.1 MeV), corresponding to 9.5 × 10−3 dpa (displacement per atom). Cu precipitates were formed in both FeCu alloys even after an irradiation of 1.1 × 10−5 dpa. The Vickers microhardness, 0.2% yield stress, and tensile stress increased, but the total elongation decreased with an increased irradiation dose up to about 4.7 × 10−4 ∼ 2.4 × 10−3 dpa for both alloys. After that, the Vickers microhardness, 0.2% yield stress, and tensile stress decreased with an increased irradiation dose. These changes in the mechanical properties of the alloys are related to the growth of microvoids. [ABSTRACT FROM AUTHOR]

In the present study, impulse pressure-assisted diffusion bonding of ferritic stainless steel was investigated. The effect of pressure pulsation and surface roughness on the tensile shear load-carrying capacity of the diffusion bonds was studied by evaluating the shear load and bond interface characteristics, and the optimum bonding parameters were determined. It was found that bond strength increases with the increase in maximum pulse pressure, and under optimum conditions, the failure occurred from the base metal in tensile shear testing. The void distribution analysis at the bond interface for some selected specimens was also done to study the effect of pressure pulsation. From FE-SEM observation, it was found that pressure pulsation helps in two ways: (a) it breaks the oxide film and (b) it fills the voids at the interface by plastic flow of the metal in the overlapped area. Also, pressure pulsation resulted in grain refinement at the interface owing to the compressive deformation, which led to the grain boundary diffusion. [ABSTRACT FROM AUTHOR]

Both theoretical and applied studies on microstructure of cheese immediately after a technological cycle and dry cheese obtained by vacuum drying are described. The aim of the microstructure studies is a more comprehensive evaluation of the product quality. Images of cheese upon high- and low-temperature secondary heating at different magnification were studied. The effect of drying on cheese microstructure was investigated. Analysis and identification of various components in the cheese mass using microstructure studies were performed. Calcium phosphate depositions were detected with electron microscopy. Calcium lactate was detected in mature cheese.

A diffuse interface model is developed to simulate the effect of electric field on the morphological evolution and migration behavior of the microvoid in the solder interconnect consisting of the Sn based solder and Cu substrate (i.e., Sn/Cu system). The model takes into account the coupled effect of surface diffusion and electric field, and the validity of the model is confirmed by good agreement between the simulation and theoretical predictions in terms of evolution behavior of the noncircular microvoid driven by surface energy. The results show that the coalescence of microvoids driven only by surface energy occurs when the microvoids contact each other. The evolution and migration of the microvoid under electric field are governed by the magnitude of electric field and the initial size of the microvoid. The microvoid migrates at a constant velocity under a weak electric field, while the strong electric field results in the shape change of the microvoid from circular to narrow crack-like. In addition, the migration velocity of the microvoid increases linearly with the voltage and is inversely proportional to the size of the microvoid; a small microvoid can catch up with a large one, and finally they merge to form a larger microvoid, which may promote the open circuit failure near the solder/Cu interface in solder interconnects. [ABSTRACT FROM AUTHOR]

Structural materials for commercial reactor are usually used under conditions of stress. However, the evaluation of the microstructural evolution and the changes in the mechanical property induced by the neutron irradiation in structural materials does not typically consider the effect of stress since it is difficult to carry out neutron irradiation testing under conditions of stress. In this study, a model alloy (Fe–0.6Cu) of reactor pressure vessels was irradiated by neutrons at 573 K with a dose of about 3.2 × 1021 neutrons/m2(E > 0.1 MeV), corresponding to 5.2 × 10−4 dpa (displacement per atom), with and without tension stress. The tension stress caused elastic deformation in the specimens. The size of microvoids in the irradiated sample with tension stress was larger than that in the sample without tension stress. However, the effects of stress on the formation of Cu precipitates and the changes in the mechanical property were not clear. [ABSTRACT FROM AUTHOR]

Zn is a promising biodegradable metal that shows huge potential as bioresorbable implant material as it possesses outstanding biocompatibility and high corrosion resistance than Mg. However, the low value of mechanical strength and hardness has hugely restricted its application. Moreover, incorporating alloying elements have typically magnified its mechanical properties. In the current study, the effect of the alloying component Mn and HA on the Zn–Mg composite and also the effect of polymer-ceramics nanofiber coating on the composite sample was studied. The result shows that the current studied samples were mainly comprised of a primary Zn matrix and a secondary phase of Mg 2 Zn 11. The prepared sample shows very high compressive yield strength (CYS 228 MPa) and hardness (83 HV). The value of corrosion rates of the as-cast Zn–1Mg–1Mn-1HA sample was higher in comparison to that of the as-cast Zn–1Mg–1Mn sample, but after the polymer-ceramics nanofiber coating formation of PLA/HA/TiO 2 , the values were reduced to a more significant extent and achieved values of 0.01484 mm/year from 0.01892 mm/year in electrochemical tests. Moreover, the coated and uncoated sample shows outstanding hemocompatibility for both samples, but the minimum value is obtained for coated Zn–1Mg–1Mn-1HA sample (2.251%). The viability of MG63 cells cultured in different diluted extracts (25% and 50% extract) of the coated Zn–1Mg–1Mn-1HA sample reached a value greater than 90%, which displayed no possible cytotoxicity for biomedical applications. [Display omitted] • Magnesium, Manganese and HA (Hydroxyapatite) is successfully reinforced in the Zinc matrix through Stir Casting method. • A fiber coating of PLA/HA/TiO 2 composite is successfully formed on the Zinc composite sample by Electrospinning technique. • As cast Zinc composite sample shows enhanced mechanical strength and reduced corrosion rate. • Formation of coating on Zinc composite sample displayed suitable cytocompatibility and hemocompatibility. [ABSTRACT FROM AUTHOR]

Microstructures of voids in a-Si:H layers on the surface of c-Si wafers were quantitatively analyzed by combining spectroscopic ellipsometry and Fourier transform infrared spectroscopy. A diameter ( D ) from 0.52 to 2.11 nm and a number density ( N voids ) from 8.4 × 10 18 to 5.4 × 10 20 cm −3 were estimated. It was demonstrated large-size voids were formed owing to the network relaxation caused by H + etching. Measurements of the minority carrier lifetime revealed both D and N voids affect the passivation performance for a c-Si surface. [ABSTRACT FROM AUTHOR]

A series of rigid-rod co-polyimides (co-PI) containing benzimidazole and benzoxazole moieties were synthesized by the reaction of 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) and 5-amino-2-(4-aminobenzene)benzoxazole (BOA) with 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA). The corresponding co-PI fibers with various diamine ratios were prepared by the two-step wet-spinning process. The small chemical structure difference between benzimidazole and benzoxazole moieties leads to unexpected great changes on the aggregation structures and properties of the obtained fibers. The two-dimensional wide-angle X-ray diffraction (WAXD) spectra imply that the co-PI fibers containing more than 70% molar ratio of BIA show better-defined ordered crystal structures, while for those samples with more BOA contents, a new ordered lateral packing occurs. Meanwhile, the equatorial scattering streaks in the small-angle X-ray scattering (SAXS) patterns for the co-PI fibers suggest the presence of microvoids, whose sizes were evaluated by means of Guinier and Ruland’s method. The optimum tensile strength and modulus of co-PI fibers are as high as 1.74 and 74.4 GPa, respectively, at the BIA/BOA molar ratio of 7/3. Besides, the co-PI fibers exhibit excellent thermal and thermo-oxidative stabilities due to the rigid molecular chains. The introduction of BOA units in the polymer backbones have apparently improved the hydrophobic properties of PI fibers. [ABSTRACT FROM AUTHOR]

Zn is a promising biodegradable metal that shows huge potential as bioresorbable implant material as it possesses outstanding biocompatibility and high corrosion resistance than Mg. However, the low value of mechanical strength and hardness has hugely restricted its application. Moreover, incorporating alloying elements have typically magnified its mechanical properties. In the current study, the effect of the alloying component Mn and HA on the Zn-Mg composite and also the effect of polymer-ceramics nanofiber coating on the composite sample was studied. The result shows that the current studied samples were mainly comprised of a primary Zn matrix and a secondary phase of Mg 2 Zn 11 . The prepared sample shows very high compressive yield strength (CYS 228 MPa) and hardness (83 HV). The value of corrosion rates of the as-cast Zn-1Mg-1Mn-1HA sample was higher in comparison to that of the as-cast Zn-1Mg-1Mn sample, but after the polymer-ceramics nanofiber coating formation of PLA/HA/TiO 2 , the values were reduced to a more significant extent and achieved values of 0.01484 mm/year from 0.01892 mm/year in electrochemical tests. Moreover, the coated and uncoated sample shows outstanding hemocompatibility for both samples, but the minimum value is obtained for coated Zn-1Mg-1Mn-1HA sample (2.251%). The viability of MG63 cells cultured in different diluted extracts (25% and 50% extract) of the coated Zn-1Mg-1Mn-1HA sample reached a value greater than 90%, which displayed no possible cytotoxicity for biomedical applications., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

In this paper a selection of modern, commercial steels for automotive and pipeline applications, in different grades, microstructures and delivery conditions has been characterized, quantifying the void distribution on virgin materials and on several deformed and fractured specimens, including tensile tests at different triaxiality and torsion tests. The results described in the paper show that in such class of material the measured void fraction is fully negligible and not related to the plastic strain applied, even at the fracture proximity. The consequence is that also the matrix softening hypothesis may be dropped in the plastic behavior and that damage due to void evolution hypothesis is not adequate. [ABSTRACT FROM AUTHOR]

Abstract: The corrosion effects of 3.5% NaCl aqueous solution on the tensile mechanical, micromagnetic Barkhausen emission (MBE) and microfailure behavior of low carbon steel were investigated. At first it was found that this steel shows a dramatic and consistent decrease of its ductility with time of corrosion. The ductility reduction as well as microfailure features obtained by Scanning Electron Microscopy (SEM)-fractographic analysis yields an acceptable evidence for the occurrence of the Hydrogen Environmental Embrittlement (HEE) phenomenon during the corrosion process. During tensile straining the MBE-signal increases monotically at an average constant rate towards necking point. This rate shows tendency to increase with corrosion time fact which helped to establish the existence of a corrosion-induced micromagnetic hardening rate effect. It was shown that the main contribution to this effect should be attributed primarily to the combined effect of the HEE and dislocation multiplication and to a lower extent to the formed magnetite surface layers. Necking plasticity and MBE were correlated on the basis of combined stress bias and microvoid/microcracking-induced creation and rearangement of magnetic domains. [Copyright &y& Elsevier]

Highlights: [•] Sub-micron solder thickness Cu/Sn/Cu sandwich structure and Sn/Cu binary samples were studied by reflow and aging, to explore the unique “solder-depletion” phenomenon. [•] The “Cu6Sn5 consumption based” Cu3Sn growth was also studied, and it showed very different growth rate and characteristics. [•] Optimized thickness for ultra-thin solder layer interconnection were studied by experiments. Formation of micro-voids was observed and discussed. [•] Effects of acid cleaning (before electroplating) on the microstructures was also discussed. [Copyright &y& Elsevier]

In this work, the impact of microvoids on the microstructural evolution of η-CuSn and ɛ-CuSn in the Cu-Sn system is evaluated numerically. Through the use of the multiphase-field method, the systems of interest are allowed to evolve using a solid-state aging temperature of 453 K in conjunction with material parameters and reaction conditions adopted from previous research. The simulation results are then analyzed and compared with previous experiments in terms of the morphological evolution of the intermetallic compounds (IMCs), the IMC layer thicknesses, and the corresponding interfacial roughness. It is shown that the presence of microvoids at the ɛ/Cu interface interferes with the flow of mass throughout the phases, impeding phase transformations and grain coarsening. This ultimately affects the IMC coarsening rate and overall IMC layer thicknesses. Additionally, it was observed that the presence of microvoids at the ɛ/Cu interface affects the formation of both IMC layers and their corresponding interfaces, and the changes in roughness for the interfaces are quantitatively provided. Overall, the simulations are found to be within the range of accepted experimental values for the morphology of the IMC grains, the evolution of IMC layer thicknesses, and the evolution of interface roughness. [ABSTRACT FROM AUTHOR]

Abstract: A defect study of ultra-fine grained (UFG) Cu prepared by high-pressure torsion (HPT) will be reported. Conventional positron annihilation spectroscopy (PAS) including positron lifetime (PLT) and Doppler broadening (DB) techniques was employed as the main experimental tool. PAS was combined with transmission electron microscopy, X-ray diffraction and Vickers microhardness (HV) measurements. First, lattice defects introduced by HPT were characterized. A very high concentration of defects created during HPT deformation was observed and the two kinds of defects could be identified: dislocations and small vacancy clusters (microvoids). Further investigations were focused on (i) the radial distributions of defects and (ii) the evolution of microstructure during HPT processing. The results of the present study are consistent with an increase of shear strain from the sample centre toward its periphery. Extended lateral mapping of microstructure was performed using HV and DB techniques. The latter one reveals a significant non-uniformity of defect distribution which was less pronounced in the HV measurements. [Copyright &y& Elsevier]

Numerical simulation is used to study patented high-C steel flat-rolled wire cold forming processes. An elasto-plastic power law, identified from mechanical tests, is used into Forge2005® finite element (FEM) package in order to describe the material behaviour during wire drawing followed by cold rolling. A through-process approach has been favoured, transferring residual wire-drawing stresses and strain into the flat-rolling preform. This mechanical analysis, associated with a triaxiality study, points to dangerous areas where fracture may initiate due to high tensile stresses. Lemaître's isotropic damage criterion, including crack closure effect, a -1/3 cut-off value of stress triaxiality, and tension/compression damage asymmetry, has been used and has confirmed the previous analysis. A number of non-coalesced voids nucleated on inclusions have been observed in the Scanning Electron Microscopy (SEM), especially in high-deformation zones ('blacksmith's cross'). Their evolution has been simulated in the FEM model using spherical numerical markers, which deform into oblate or prolate ellipsoids. The deformation-induced morphological evolution of voids observed in the SEM compares well with the geometrical evolution of the markers, which suggests that the morphologies observed do not result from micro-crack propagation, but from material transport of the nucleated voids. [ABSTRACT FROM AUTHOR]

Abstract: The structure of soil organic matter (SOM) and humic substances (HS) has been discussed from different viewpoints including molecular conformation, molecular aggregation, macromolecularity, supramolecular characteristics, domain mobility, and many others. Until now, the individual models appear partly contradictory, although each viewpoint provides important information on the structural and functional properties of SOM. This is most probably due to the huge heterogeneity of SOM. Therefore, the question: “How can molecular modeling help to further understand structure and functioning of soil organic matter?” needs to be addressed with care. This contribution reviews and discusses the potential of important molecular modeling approaches currently applied in soil organic matter science. Computer models are useful in giving a visualization of the general structure and of the possible effects on soil chemistry and soil physics. Computational chemistry in this context aims to estimate a lowest energy conformation for a molecule or an assembly of molecules specified by the programmer. On the basis of the calculated conformation, physicochemical characteristics like surface area, polarity and other can be estimated and information on the stability of molecular assemblies can be derived. The significance of the obtained conformation and physicochemical information strongly depends on the initial hypothesis of the molecular structure of each involved molecule. Recent computer models have been developed on the base of computer assisted structure elucidation (CASE). In this procedure, all possible isomers or a statistically representative set of isomers consistent with the experimental input data are processed. Further interesting fields of computational chemistry in soil research follow a different conception, where specific processes of interest are elucidated with the help of computational models which simplify the humic molecules with respect to the individual modeling problem. This way helps to understand the relevance of principal processes expected to occur in soil. In this context, complexes of Al with organic acids, clay mineral sorption sites, interactions of pesticides with organic functional groups or organic soil constituents as well as cross-linking of molecule segments by water molecules were modeled in targeted process-orientated models. The act of simplification is the crucial process in these kinds of models, and if the models are based on good conceptions, they allow to learn about potential SOM functioning. The transfer to more complex situations, however, needs special care and the predictive character of these models needs to be judged with care. Still, any computer model is only as good as its initial hypothesis. [Copyright &y& Elsevier]

The electrodeposition conditions that contribute to microvoid formation during isothermal aging of Pb-free solder-electrodeposited copper were evaluated in a systematic series of processing experiments. The results of 2 full-factorial design of experiment are presented to show the effect of prescreened electroplating parameters such as brighteners, wetting agent, bath age, and current density on the propensity for microvoiding at solder-copper interfaces after annealing at 125°C for 40 days. It was found that the amount of microvoiding is greatly affected by bath age, wetting agent, brightener, and their interactions. Time-of-flight secondary-ion mass spectroscopy and glow discharge spectroscopy allowed us to establish a correlation between impurities incorporated in copper during electroplating and microvoiding at the solder-copper interface. [ABSTRACT FROM AUTHOR]

Abstract: The structure of soil organic matter (SOM) and humic substances (HS) has been discussed from different viewpoints including molecular conformation, molecular aggregation, macromolecularity, supramolecular characteristics, domain mobility, and many others. Until now, the individual models appear partly contradictory, although each viewpoint provides important information on the structural and functional properties of SOM. This is most probably due to the huge heterogeneity of SOM. Therefore, the question: “How can molecular modeling help to further understand structure and functioning of soil organic matter?” needs to be addressed with care. This contribution reviews and discusses the potential of important molecular modeling approaches currently applied in soil organic matter science. Computer models are useful in giving a visualization of the general structure and of the possible effects on soil chemistry and soil physics. Computational chemistry in this context aims to estimate a lowest energy conformation for a molecule or an assembly of molecules specified by the programmer. On the basis of the calculated conformation, physicochemical characteristics like surface area, polarity and other can be estimated and information on the stability of molecular assemblies can be derived. The significance of the obtained conformation and physicochemical information strongly depends on the initial hypothesis of the molecular structure of each involved molecule. Recent computer models have been developed on the base of computer assisted structure elucidation (CASE). In this procedure, all possible isomers or a statistically representative set of isomers consistent with the experimental input data are processed. Further interesting fields of computational chemistry in soil research follow a different conception, where specific processes of interest are elucidated with the help of computational models which simplify the humic molecules with respect to the individual modeling problem. This way helps to understand the relevance of principal processes expected to occur in soil. In this context, complexes of Al with organic acids, clay mineral sorption sites, interactions of pesticides with organic functional groups or organic soil constituents as well as cross-linking of molecule segments by water molecules were modeled in targeted process-orientated models. The act of simplification is the crucial process in these kinds of models, and if the models are based on good conceptions, they allow to learn about potential SOM functioning. The transfer to more complex situations, however, needs special care and the predictive character of these models needs to be judged with care. Still, any computer model is only as good as its initial hypothesis. [Copyright &y& Elsevier]

In reactions between solders and Cu, additions of minor alloying elements, such as Fe, Co or Ni, to solders often reduce the CuSn growth rate. Nevertheless, the mechanism for this effect remains unresolved. To provide more experimental observations that are essential for uncovering this mechanism, growth of CuSn in the reaction between Cu and high-lead solders with or without Ni additions has been studied. The solders used for this study were 10Sn-90Pb and 5Sn-95Pb doped with 0 wt.%, 0.03 wt.%, 0.06 wt.%, 0.1 wt.% or 0.2 wt.% Ni. Reaction conditions included one reflow at 350°C for 2 min and solid-state aging at 160°C for up to 2000 h. The effect of Ni on the growth of CuSn is discussed in detail based on the experimental results. [ABSTRACT FROM AUTHOR]

The growth kinetics of an intermetallic compound (IMC) layer formed between Sn-3.5Ag-0.5Cu (SAC) solders and Cu-Zn alloy substrates was investigated for samples aged at different temperatures. Scallop-shaped CuSn formed after soldering by dipping Cu or Cu-10 wt.%Zn wires into the molten solder at 260°C. Isothermal aging was performed at 120°C, 150°C, and 180°C for up to 2000 h. During the aging process, the morphology of CuSn changed to a planar type in both specimens. Typical bilayer of CuSn and CuSn and numerous microvoids were formed at the SAC/Cu interfaces after aging, while CuSn and microvoids were not observed at the SAC/Cu-Zn interfaces. IMC growth on the Cu substrate was controlled by volume diffusion in all conditions. In contrast, IMC growth on Cu-Zn specimens was controlled by interfacial reaction for a short aging time and volume diffusion kinetics for a long aging time. The growth rate of IMCs on Cu-Zn substrates was much slower due to the larger activation energy and the lower layer growth coefficient for the growth of Cu-Sn IMCs. This effect was more prominent at higher aging temperatures. [ABSTRACT FROM AUTHOR]

Abstract: The effect of strain rate on the inelastic properties of nanocrystalline Au films was quantified with 0.85 and 1.76μm free-standing microscale tension specimens tested over eight decades of strain rate, between 6×10−6 and 20s−1. The elastic modulus was independent of the strain rate, 66±4.5GPa, but the inelastic mechanical response was clearly rate sensitive. The yield strength and the ultimate tensile strength increased with the strain rate in the ranges 575–895 MPa and 675–940MPa, respectively, with the yield strength reaching the tensile strength at strain rates faster than 10−1 s−1. The activation volumes for the two film thicknesses were 4.5 and 8.1b3, at strain rates smaller than 10−4 s−1 and 12.5 and 14.6b3 at strain rates higher than 10−4 s−1, while the strain rate sensitivity factor and the ultimate tensile strain increased below 10−4 s−1. The latter trends indicated that the strain rate regime 10−5–10−4 s−1 is pivotal in the mechanical response of the particular nanocrystalline Au films. The increased rate sensitivity and the reduced activation volume at slow strain rates were attributed to grain boundary processes that also led to prolonged (5–6h) and significant primary creep with initial strain rate of the order of 10−7 s−1. [Copyright &y& Elsevier]

Hydrogenated amorphous silicon (a-Si:H) films were deposited by reactive facing target sputtering (FTS) technique with a mixture of Ar and H reaction gas. Fourier transform infrared (FTIR) absorption, Raman scattering and ultraviolet-visible optical absorption are used to investigate the microstructure and optical properties of the deposited films. The decrease of the concentration of bonded hydrogen, especially that of (Si-H) with increasing substrate temperature ( Ts), was observed in FTIR spectra, suggesting the atomic density increases and the concentration of microvoids decrease in a-Si:H films. The increase of both the short range order and the intermediate range order of amorphous network for a-Si:H films were verified by Raman scattering spectra, in which increasing Ts decreasing the band width of TO and the scattering intensity ratio I / I were obtained. All above results clarify the effect of increasing Ts on the microstructure amelioration for a-Si:H films. The reduction of disordered domains is correlated with the film growing process, where the increased surface diffusion mobility and etching of weak bonds is induced by increasing Ts. Furthermore, analysis of optical absorption indicates that the films with a lower optical band gap and a narrower band edge can be obtained by this FTS technique. [ABSTRACT FROM AUTHOR]

Abstract: The interfacial reaction between Cu and SnxCu (x =0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8wt.%) solders were examined. Emphasis was placed on the effect of Cu composition on the formation of microvoids in the Cu3Sn phase. Reaction conditions included one reflows and subsequent aging at 160°C for up to 2000h. After aging, both Cu6Sn5 and Cu3Sn formed at interface, and Cu3Sn was void-free, and remained void-free after 500h of aging for all of the compositions. The microvoids appeared in Cu3Sn after 1000h of aging, but only in those solder joints with their apparent Cu concentrations that were 0.46wt.% and lower. After 2000h of aging, microvoids formed only in solder joints with their apparent Cu concentrations that were 0.50wt.% and lower. This observation suggests that the microvoids in Cu3Sn can be effectively inhibited by maintaining a high Cu concentration in solder (e.g. >0.58wt.%). Rationalization for this Cu concentration effect is presented. [Copyright &y& Elsevier]

An improved experimental methodology is developed and successfully evaluated to visualize deformation-induced microevents in ductile sheet metal. This easy-to-use methodology consists in a well-controlled brittle separation of samples previously deformed in a ductile manner, whereby a coupled-analysis of the two fracture surfaces permits three-dimensional features to be recombined from the ductile predeformation. The results obtained show a wealth of information regarding grain deformations, microvoid nucleation sites and growth mechanisms, and other microevents induced by ductile deformation. [Copyright &y& Elsevier]

Abstract: Crack instabilities and the phenomenon of crack speed saturation in a brittle material (PMMA) are studied with a meshfree cracking particle method. We reproduce the experimental observation that the computed terminal crack speeds attained in PMMA specimens are substantially lower than the Rayleigh wave speed; the computed crack speeds agree quite well with the reported experimental results. We also replicate repetitive microcrack branching along with the increased rate of energy dissipation after attainment of a critical crack speed, even in the absence of microstructural defects. We show that the presence of microdefects changes the response only a little. The computations reproduce many of the salient features of experimental observations. [Copyright &y& Elsevier]

Bimetallic welds (BMWs) play a critical and indispensable role in the primary heat transport piping system of nuclear reactors. The primary heat transport system itself is the critical part of a nuclear reactor. Any failure of this system can lead to very grave consequences, not only speaking of huge monetary losses resulting from non-utilization of the reactor setup, but also immensely valuable and irreparable loss of human life. This paper describes the experimental efforts towards estimation of Gurson material parameters of base metal and weld metal regions of a BMW so as to use the micromechanical modelling approach for addressing the structural integrity issues in BMWs. [ABSTRACT FROM AUTHOR]

The defect morphology in HgTe and CdHgTe was studied in (211)B-oriented layers grown in a 20°C temperature range around the optimal growth temperature. The density of defects varies strongly with the growth temperature. In HgTe, the shape of the microvoid defects is very sensitive to the growth temperature and can be used to determine the deviation from the optimal growth temperature. Using thermodynamical modeling, the optimal growth temperature for CdHgTe can then be calculated. We describe a mechanism for the formation of microvoids and needles which involves preferential surface diffusion of Te combined with an impurity or defect on the substrate. Microvoids on (111)B-oriented partially twinned HgTe layers were also studied. The microvoids in the twinned parts of the layer were found to be rotated 180 deg relative to the untwinned parts of the layer. [ABSTRACT FROM AUTHOR]

Two Fe-Cu binary model alloys, Fe-0.3Cu and Fe-0.6Cu, were irradiated with fission neutrons at doses ranging from 4 × 10-6 to 0.16 dpa (displacements per atom) at ∼573 K to investigate the formation of Cu precipitates and microstructural evolution. The Cu content only affected the formation of Cu precipitates and microvoids at low doses. In Fe-0.3Cu, the formation of microvoids and Cu precipitates initiated at doses of 1.2 × 10-4 and 4 × 10-5 dpa, respectively. On the other hand, the formation of microvoids started at a dose of 4 × 10-4 dpa in Fe-0.6Cu, and Cu precipitates were formed even after irradiation to 4 × 10-6 dpa. On further irradiation, the difference in the formation of Cu precipitates and microvoids was small. Microvoids grew with increasing irradiation dose up to 3 × 10-3 dpa in both alloys. Prominent aggregation of Cu atoms occurred upon irradiation from 3 × 10-3 to 1.6 × 10-2 dpa and the microvoids shrank. The Cu precipitates no longer grew, and microvoids nucleated and grew in the matrix above a dose of 1.6 × 10-2 dpa in both alloys. The present studies clearly reveal the relationships between the formation and growth of Cu precipitates and microvoids with irradiation dose. [ABSTRACT FROM AUTHOR]