Formation Of Inhomogeneities Research Articles

Study of the features of concentration inhomogeneities during the on ground-based processing of the space experiment of the Ge(Ga) crystals growth

The article presents the results of the preparation and ground testing of the space experiment for growing Ge (Ga) crystals, planned on board the multifunctional laboratory module as part of the ISS RS. Under the conditions simulating microgravity, the features of the formation of concentration inhomogeneity in the form of growth bands when growing crystals under various thermal conditions (in the presence or absence of a free melt surface (Marangoni convection)), as well as when changing technological parameters (variations in growth rate) were investigated. Based on the obtained results of metallographic and electrophysical studies, conclusions were made about the peculiarities of the influence of the technological parameters of the crystallization process on the structural perfection of the grown crystals under microgravity conditions

Effect of v-notch on impact toughness of fibre reinforced laminates produced by fff method

The rapid development of additive technology necessitates identifying opportunities for practical application. For this reason, many experimental measurements have focused on tensile or bending tests, resulting in numerous publications. Previously, the authors evaluated Charpy impact test results to assess the effect of various printing parameters on absorbed energy, using specimens without the notch. However, other studies focused on Charpy impact testing used notched specimens, raising questions about suitability of notch usage for testing of fibre reinforced composites produced by extrusion methods. This paper aims do deal with this question and to evaluate the influence of V-notch on the impact toughness of specimens. For specimens reinforced with chopped carbon fibres, the notch markedly affects impact toughness irrespective of the direction of load orientation (flatwise or edgewise). Conversely, in the case of flatwise loading of specimens reinforced with long HSHT glass fibres, we observed that the notch does not impact the absorbed energy values. However, edgewise impact loading led to decrease of absorbed energy up to 50%. This decrease in absorbed energy can be attributed to the material arrangement in the lamina, as the filament follows the notch, resulting in the formation of inhomogeneities and stress concentrators. In the case of flatwise loading, the notches were created by the lamina layering, so the arrangement of the matrix and fibres in the layer was not affected.

Deformation inhomogeneity evolution and crack formation mechanism analysis in ultra-high strength steel by crystal plasticity simulations

Understanding deformation inhomogeneity and the formation mechanism of crack are crucial for fully exploiting the potential of ultra-high strength steel (UHSS). In this paper, the deformation inhomogeneity and microscopic crack formation mechanism of UHSS were investigated by combining high-fidelity crystal plasticity models with microscopic experiments. The simulation results at grain level show that the deformation strain of the UHSS is non-uniform, characterized by distinct deformation bands. A broad deformation band extends between multiple grains at an angle of approximately 40 degrees to the rolling direction, while a sharp deformation band is observed within a single grain. These features are intricately linked to the initial orientation (Taylor factor) distribution of the grains and their rotational behavior. The locations with greater Taylor factor deviations become potential crack initiation sites. In addition, as the deformation proceeds, the α-fiber reinforcement exacerbates the deformation inhomogeneity of the UHSS.

Exploring the use of graphene lubricant and TiO2 nanolubricants in micro deep drawing of stainless steel SUS301

This study investigates the effects of different lubrication conditions on drawing force and microcup formation during micro deep drawing (MDD). Results show that graphene lubricant, in combination with TiO2 nanolubricants, has the potential to reduce friction during MDD. The peak drawing force was reduced by 15.39% when both lubricants were used together, while the use of TiO2 nanolubricant and 10.0 mg/ml graphene lubricant reduced it by 6.03% and 14.52%, respectively. The study also reveals that lubricants reduce wrinkling during the formation of microcups by minimising energy consumption during the primary formation. However, the combination of TiO2 nanolubricant and graphene lubricant can cause inhomogeneous formation on the upper part of the blank, leading to more apparent wrinkling. Overall, the study highlights the potential of TiO2 nanolubricant and graphene lubricant in reducing friction and improving microcup formation during MDD.

Ion imaging of spatially inhomogeneous nanoplasmas in NaCl particles.

Studying photoemission from free, unsupported aerosol particles is a powerful method for gaining insight into light-matter interactions at the nanoscale. We used single-shot velocity map imaging to experimentally measure kinetic energy and angular distributions of ions emitted following interaction of sub-micrometer NaCl particles with femtosecond pulses of near infrared (NIR, 800 nm) and ultraviolet (UV, 266 nm) light. We combined this with time-dependent simulations of light propagation through the particles and a rate equation approach to computationally address the origin of the observed ion emission. For both NIR and UV pulses, ion emission is caused by the formation of an under-dense nanoplasma with similar densities, although using an order of magnitude weaker UV intensities. Such conditions result in remarkably similar ion fragments with similar kinetic energies, and no obvious influence of the plasma formation mechanism (photoionization or collisional ionization). Our data suggests that Coulomb explosion does not play a significant role for ion emission, and we discuss alternative mechanisms that can lead to material ablation from under-dense nanoplasma. Finally, we show how finite size effects play an important role in photoemission through generation of spatially inhomogeneous nanoplasmas, which result in asymmetric ion emission that depends on particle size and laser wavelength. By utilizing the single-particle information available from our experiments, we show how finite size effects and inhomogeneous nanoplasma formation can be exploited to retrieve the size and orientation of individual submicrometer aerosol particles.

A Direct Comparison between the Use of Double Gray and Multiwavelength Radiative Transfer in a General Circulation Model with and without Radiatively Active Clouds

Inhomogeneous cloud formation and wavelength-dependent phenomena are expected to shape hot Jupiter atmospheres. We present a general circulation model with multiwavelength “picket fence” radiative transfer and radiatively active, temperature-dependent clouds, and compare the results to those of a double gray routine. The double gray method inherently fails to model polychromatic effects in hot Jupiter atmospheres, while picket fence captures these non-gray aspects and performs well compared to fully wavelength-dependent methods. We compare both methods with radiatively active clouds and cloud-free models, assessing the limitations of the double gray method. Although there are broad similarities, the picket fence models have larger dayside–nightside temperature differences, nonisothermal upper atmospheres, and multiwavelength effects in the presence of radiatively active clouds. We model the well-known hot Jupiters HD 189733 b and HD 209458 b. For the hotter HD 209458 b, the picket fence method prevents clouds from thermostating dayside temperatures, resulting in hotter upper atmospheres and the dissipation of dayside clouds. Differences in the temperature structures are then associated with nuanced differences in the circulation patterns and clouds. Models of the cooler HD 189733 b have global cloud coverage, regardless of the radiative transfer scheme, whereas there are larger differences in the models of HD 209458 b, particularly in the extent of the partial cloud coverage on its dayside. This results in minor changes to the thermal and reflected light phase curves of HD 189733 b, but more significant differences for the picket fence and double gray versions of HD 209458 b.

Hydrophobicity as the key to understanding the nanostructural behavior of eutectic mixtures upon apolar cosolvent addition

The influence of the addition of the apolar n-hexane (HEX) cosolvent on the structural arrangement of eutectic mixtures with different degrees of hydrophobicity, namely butylated hydroxytoluene (BHT), L-menthol (MEN), thymol (TYM), and choline chloride (ChCl), has been studied with a combined approach using small- and wide-angle X-ray scattering and molecular dynamics simulations. The cosolvent introduction has a similar impact on the molecular scale-length aggregation in BHT:MEN:HEX, TYM:MEN:HEX, and ChCl:TYM:HEX mixtures at different 1:3:H, 1:2:H, and 1:7:H molar ratios, specifically a dramatic perturbation of the main interactions present in the pure eutectics where hydrogen-bonds dominate. On larger scale-lengths, HEX addition results in a homogeneous electron-density distribution in the BHT:MEN:HEX and TYM:MEN:HEX mixtures due to a high affinity of the cosolvent for the BHT, MEN, and TYM components. Conversely, the presence of the more hydrophilic ChCl compound in the ChCl:TYM 1:7 system is the driving force for the segregation mechanism of this component which causes the formation of nano-scale inhomogeneities at high HEX concentrations, before macroscopic phase separation. The different degree of hydrophobicity is therefore key to understanding the nanostructural behavior of these eutectics in the presence of an apolar cosolvent. These findings have important implications for the employment of deep eutectic solvent mixtures, as the formation of pseudo-phase aggregates can help explaining the macroscopic behavior of these alternative media in applications like extraction procedures.

Formation of Defects and Inhomogeneities in the Structure of Composite Materials Based on Aluminum-Manganese Bronze with an In Situ Introduction of Nickel and Titanium Alloys or Steel During Wire-Feed Electron Beam Additive Manufacturing

Formation of Defects and Inhomogeneities in the Structure of Composite Materials Based on Aluminum-Manganese Bronze with an In Situ Introduction of Nickel and Titanium Alloys or Steel During Wire-Feed Electron Beam Additive Manufacturing

Formation of Structure Inhomogeneities and Defects During Production of Composite Materials Based on Grade2 Titanium Alloy by Friction Stir Processing

Formation of Structure Inhomogeneities and Defects During Production of Composite Materials Based on Grade2 Titanium Alloy by Friction Stir Processing

The homogeneity effects of magnetic flux density distribution on the detection of railhead surface defects via the magnetic flux leakage method

Magnetic flux leakage (MFL) is a non-destructive testing method used to detect railhead surface defects. For effective MFL testing, the homogeneity of the magnetic flux density distribution (MFDD) within the railhead is crucial. Inhomogeneous formation of the MFDD within the railhead reduces the efficiency of the MFL testing. The homogeneity of the MFDD depends on the distance between poles (DBP) of the MFL testing system. According to the literature, as the DBP parameter increases, the MFDD becomes more homogeneous. In this study, four different homogeneity levels of the MFDD are introduced based on the DBP parameter. 3D finite element method (FEM) modelling simulation is conducted to obtain MFL testing analyses. The analyses are performed on a rail that contains rectangular surface defects of varying depth and length. The results of this study are evaluated using characteristic features of the MFL signal BX component, namely the slope of the baseline, the bottom value and the peak-to-peak value. The results show that if the homogeneity level of the MFDD within the railhead is higher, the bottom value and slope of the baseline decrease and the peak-to-peak value increases. This indicates that higher homogeneity of the MFDD enhances the detection efficiency of the MFL testing. Eventually, it is found that with the formation of nearly 100% homogeneous MFDD in the railhead, the slope of the baseline, the bottom value and the peak-to-peak value are enhanced by up to 83%, 77% and 12%, respectively.

Structuring step dependent characteristics in joining using pin-like structures in the vibration welding process

Abstract With this study, correlations in the structuring step of pin-like joining were derived. Increased friction energy due to higher amplitude or force leads to a reduction in structuring time. Changes in thermo-mechanical properties for humid specimens result in increased process times. The theoretical geometry of the pin-like structures is well reproduced in the lower pin area, regardless of the process control. In the upper pin area, increased force and amplitude results in increased defects and air inclusions as a result of an accelerate and more inhomogeneous pin formation. Humidity does not affect the general pin geometry, but should be avoided due to increased air inclusions that can weaken the structure. For the multi-material joints, high bond strengths of up to 30 % of the base material (max. 50 % possible with the geometry used) can be achieved. Therefore, a minimum undercut is required. Once this is reached, the pin defects and the corresponding pin-foot ratio are decisive for the resulting bond quality.

Relationship between oxidation, stresses, morphology, local resistivity, and optical properties of TiO2, Gd2O3, Er2O3, SiO2 thin films on SiC

The relationship between internal mechanical stresses, surface morphology, nanoscale electrical properties, and optical characteristics in TiO2, Gd2O3, Er2O3, and SiO2 thin films on SiC substrates was investigated. The oxide films were synthesized using the rapid thermal annealing and analyzed through scanning spreading resistance microscopy, photoluminescence, and absorption spectroscopy. Tensile stresses were found in the films, they are attributed to thermal and lattice mismatch, oxidation, and grain boundaries. These stresses influence on surface morphology, resistivity variations, and photoluminescence intensity. Surface roughness and grain structure were found to correlate with variations in resistivity, which were attributed to conductive pathways along grain boundaries and possible metallic phases. Photoluminescence intensity was also observed to correlate with estimated lattice mismatch strain. Gd2O3/SiC exhibited the fewest defects, while Er2O3 and TiO2 showed more, with Er2O3 being the most mismatched and roughest. The results indicate that internal strains in oxide thin films on SiC substrates can influence on surface morphology, leading to formation of defects and spatial inhomogeneity. These fluctuations in local conductivity and luminescence center density have significant implications for dielectric and optical applications. The study provides insights for future processing refinements to mitigate internal strains and enhance the performance of oxide thin films in semiconductor and optical technologies.

Experimental study of turbulent thermal diffusion of particles in an inhomogeneous forced convective turbulence

We investigate experimentally the phenomenon of turbulent thermal diffusion of micrometer-size solid particles in an inhomogeneous convective turbulence forced by one vertically oriented oscillating grid in an air flow. This effect causes the formation of large-scale inhomogeneities in particle spatial distributions in a temperature-stratified turbulence. We perform detailed comparisons of the experimental results with those obtained in our previous experiments with an inhomogeneous and anisotropic stably stratified turbulence produced by a one oscillating grid in the air flow. Since the buoyancy increases the turbulent kinetic energy for convective turbulence and decreases it for stably stratified turbulence, the measured turbulent velocities for convective turbulence are larger than those for stably stratified turbulence. This tendency is also seen in the measured vertical integral turbulent length scales. Measurements of temperature and particle number density spatial distributions show that particles are accumulated in the vicinity of the minimum of the mean temperature due to the phenomenon of turbulent thermal diffusion. This effect is observed in both convective and stably stratified turbulence, where we find the effective turbulent thermal diffusion coefficient for micrometer-size particles. The obtained experimental results are in agreement with theoretical predictions.

Effect of Contact Pressure on Strain Distribution during Compression-Type Bulk Forming Processes.

Inhomogeneity of the material properties of workpieces developed during compression-type bulk forming processes (CBFPs) is an important issue. The effect of contact pressure on the workpiece surface on the strain inhomogeneity in the workpiece was investigated to understand and reduce the formation of strain inhomogeneity during CBFPs. Workpieces fabricated via rod caliber rolling, rod flat rolling, plate flat rolling, and rod compression were analyzed and compared. The extent of strain inhomogeneity in a workpiece differs with the forming process, because the occurrence of macroscopic shear bands (MSBs) is dependent on the workpiece shape and tool design. A flat-rolled rod exhibits the maximum strain inhomogeneity, whereas a flat-rolled plate shows the minimum strain inhomogeneity. The occurrence of MSBs was influenced by the distribution of the normal contact pressure or compression stress. The MSBs were stronger when the contact pressure was higher in the edge region of the surface. For example, the flat-rolled plate exhibited weak MSBs due to the relatively uniform or higher contact pressure on the central region. In contrast, strong MSBs appeared in the flat-rolled rod and compressed rod, because the contact pressure in the edge region of these two processes was high. Thus, the strain inhomogeneity in a workpiece fabricated via CBFPs can be reduced by controlling the contact pressure distribution on the workpiece surface.

Boron-10 stimulated helium production and accelerated radiation displacements for rapid development of fusion structural materials

Boron doping, combined with neutron capture in fission reactors, has been used to simulate the helium effect on fusion structural materials. However, inhomogeneous helium bubble formation was often observed due to boron segregation to grain boundaries. The excess radiation displacements due to 10B(n, α)7Li reaction, the high-energy lithium and helium ions, also were not accounted for, which can significantly accelerate the displacements-per-atom (dpa) accumulation alongside helium production (appm). Hereby an isotopically pure 10B doping approach is proposed to simulate the extreme environment inside fusion reactors with a high He appm-to-dpa ratio of about 10, which is about 102 × larger than in fission reactors. Computational modeling showed that ∼13% of total radiation displacement was induced by 10B(n, α)7 Li in the case of 1 000 appm 10B doped Fe samples, which becomes even greater with increasing 10B loading. Spatially homogenous radiation damage and helium generation are predicted for grain sizes less than 1 μm, even if the boron partially formed precipitates or segregates on grain boundaries. Feasibility studies with various 10B doping (and 235U-codoping) levels in research reactors showed the estimated helium generation and radiation damage would significantly mimic fusion conditions and greatly expedite fusion materials testing, from many years down to months.

P75 MULTIDISCIPLINARY MANAGEMENT OF INTRACARDIAC LEIOMYOMATOSIS: A CASE REPORT

Abstract A 60–year–old woman with no cardiological history came to our attention for exertional dyspnea since few months. The electrocardiogram and chest radiograph were normal. Trans–thoracic echocardiogram revealed the presence of a floating parenchymatous formation measuring 12 x 2 cm starting from the inferior vena cava (IVC) and jutting into the right chambers, without obstruction to inflow. Chest CT and cardiac MRI described a nonvascularized inhomogeneous formation suggestive of thrombotic apposition in VCI, so the patient was treated with unfractionated heparin. Total body CT/PET scan excluded hypercaptant lesions. After two weeks of anticoagulant therapy, on echocardiogram the mass appeared unchanged in morphology and size. On reevaluation of the CT images, a probable origin of the formation at the level of the right ovarian vein was identified. In light of the positive history of bilateral hysteroannessiectomy for uterine myomas and the lack of response to anticoagulant treatment, the suspicion of intravascular and intracardiac leiomyomatosis was raised. After collegial discussion, given the high risk of an eventual thoraco–abdominal surgery, it was decided to remove only the portion of the mass adherent to the VCI jutting into the right heart chambers. The patient underwent cardiac surgery: a polypoid, capsular, hard–elastic mass, 12 x 2 cm in size, jutting into the right chambers and with the base of implantation located in the anterior wall of the VCI, was removed. The final histologic diagnosis was sclero–jalin leiomyoma. The surgery and postoperative course proceeded without complications. At follow–up at 20 months, the patient is asymptomatic and no mass is detectable on echocardiogram. Intracardiac leiomyomatosis is a rare condition characterized by benign smooth muscle tumors of extracardiac origin reaching the right heart by direct extension into the venous canal, described predominantly in women with a history of uterine myomas. Although histologically benign, intracardiac leiomyomatosis can result in sudden death if there is total obstruction to the outflow tract. In our case, the multimodality imaging approach and serial monitoring by echocardiography were essential to guide treatment choices and for the follow up.

Peculiarities in the Radiolysis of β-Diketones

Intramolecular hydrogen bonding has a significant effect on the radiolytic transformations of β- diketones. Using the radiolysis of acetylacetone as an example, it has been shown that a hydrogen bond between the hydroxyl and carbonyl in an enol prevents proton transfer from the primary radical cation to the neighboring molecule. As a result, the radiolytic formation of a keto alcohol (4-hydroxy-2-pentanone) was not observed at room temperature, but it was effective under boiling conditions. The intramolecular hydrogenbond contributed to a significant structural stress in the radical cation, which increased the yield of C–OH bond cleavage and the inhomogeneous formation of acetate (4-oxopent-2-en-2-yl acetate) under normal conditions

Synergistic and competitive mechanisms of plastic anisotropy in high-efficiency laser melting deposited TC11 alloy

The layer-by-layer processing features of laser melting deposited (LMD) TC11 titanium alloy inevitably lead to microstructural inhomogeneity, and the grain morphology associated with micro-orientations induces plastic anisotropy, which causes uneven deformation and further performance deterioration. Understanding the main causes of these characteristics and how to distinguish their relative roles in inducing plastic anisotropy is critical. In this work, a high-efficiency LMD process is developed. Then, the individual factors causing the formation of elongated grains, microstructural inhomogeneity and micro-orientations are isolated to investigate the synergistic and competitive mechanisms of plastic anisotropy for high-efficiency LMD TC11 titanium alloy before and after various heat treatments. Initially, the TC11 titanium alloy is prepared by the LMD technique under high laser power and then heat-treated via three methods of double annealing in the α+β phase zone. Subsequently, the macro- and microscopic morphology, microstructure, and micro-orientations are characterized by optical microscopy (OM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The individual effects of grain shape, α grain boundary (αGB) and micro-orientations on tensile plastic anisotropy are systematically and thoroughly investigated via a hybrid method consisting of experimental and crystal plasticity finite element simulation methods. By introducing a redefined evaluation indicator of dislocation plugging coefficients, elongated grains are found to be the main source affecting the tensile strength in different loading directions. In addition, with increasing primary annealing temperature, the breakage degree of αGB parallel to the building direction (BD) is significantly higher than that perpendicular to the BD, which leads to an increase in tensile strength and elongation. Moreover, the preferred <0 0 0 1> orientation leads to different tensile strengths perpendicular and parallel to the BD, which is caused by the transformation between easy-to-slip and hard-to-slip orientations. The micro-orientations mainly affect the yield strength and elongation, while the tensile strength and elongation are simultaneously controlled by the grain morphology and αGB.

FORMATION OF INHOMOGENEITIES AND DEFECTS IN THE STRUCTURE OF COMPOSITE MATERIALS AND FUNCTIONAL-GRADIENT BIMETALLIC COMPONENTS PRODUCED BY WIRE-BASED ELECTRON-BEAM ADDITIVE MANUFACTURING

The paper presents the results of studies of the formation of defects and inhomogeneities in composites with a metal matrix and bimetallic products based on dissimilar metals and alloys when obtained by wire additive electron-beam technology. The main defects in the production of composites and bimetallic elements are pores, micro- and macro-cracks, as well as stratifications of different types. From the inhomogeneities of the structure, it is mainly possible to distinguish the resulting agglomerates of powder particles introduced simultaneously with the wire feed, large fragments of different components of the structure and the resulting large intermetallic structures. These structural elements can have a negative influence on the strength properties of materials, cause a sharp drop in mechanical properties. The main reasons for the formation of defects of different types are non-compliance with the optimal values of the process parameters, excess of the optimal concentration of components, significant differences in the density and melting temperature of the structural components. Despite the presence of defects, the modification of the process of feeding the material into the printing zone makes it possible to achieve a relatively homogeneous structure of different composite materials and high values of mechanical properties.

Periodic nanostructures induced by point defects in Pb1-xSnxTe

Lead tin telluride solid solutions are excellent candidates for the p-type conduction legs of the thermoelectric generator modules. The investigation of their microstructure properties is an important issue, that can effectively modify their electronic and thermal transport properties. In this work, we show the experimental dependences of the Pb1-xSnxTe component distribution, which were identified as periodic nanostructures with an amplitude of λ ≈ 50-500 nm. The observed periodicity is explained by the generation and recombination of point defects due to diffusion processes during the synthesis, sintering, and annealing of samples. A model describing the formation of such inhomogeneities in Pb1-xSnxTe ternary alloys during isothermal annealing is proposed.