Redistribution Of Elements Research Articles

The precipitates evolution with related element interaction and redistribution during long-term high-temperature aging of Alloy 617

The precipitates evolution with related element interaction and redistribution during long-term high-temperature aging of Alloy 617

Stress driving element redistribution and rafting of γ′ phase in Ni–Al–Mo superalloy

Stress driving element redistribution and rafting of γ′ phase in Ni–Al–Mo superalloy

Interaction of irradiation defects with precipitates in CuCrZr and Cu-1Fe alloys

In this work, we employ transmission electron microscopy and helium ion irradiation to study the interactions between the radiation-induced point defects and the incoherent/semi-coherent precipitates in CuCrZr and Cu-1Fe alloys. Both thin foil and bulk implantation were used to explore the interactions of radiation defects with interfaces. The irradiated defects show a strong interface character dependence in both implanted CuCrZr and Cu-1Fe alloys after similar level of radiation damage. Large-sized voids appear around the incoherent Cr precipitates, while no visible cavities are formed around precipitates in Cu-1Fe alloy. Interestingly, three types of semi-coherent Fe precipitates exhibit various irradiation damage mitigation mechanisms, such as twin boundaries migration, short range elements redistribution and precipitate abnormal growth, which are caused by radiation defect-mediated dislocation glide, element diffusion and mass transportation. The high sink efficiency of the incoherent precipitates trap vacancies and leads to the generation of submicron-sized voids. In contrast, the semi-coherent precipitates can regulate the motion of point defects and effectively enhance the recombination rate of vacancies and interstitials.

Irradiation damage reduces alloy corrosion rate via oxide space charge compensation effects

Radiation effects in materials often compound and accelerate other detrimental phenomena such as embrittlement, oxidation and creep. However, irradiation can also decrease the oxidation rate, for instance with ZrNb alloys nuclear fuel cladding. In this study, we rationalize this observation on Zr-0.5Nb alloy by introducing a mechanism based on oxide space charge modification, resulting from irradiation enhanced Nb clustering. This mechanism is investigated using a multiscale approach: from the macroscale, to determine post-irradiation oxidation kinetics, to the atomic scale, using in-situ atom probe tomography sample oxidation, to observe elemental solute redistribution across the oxide/metal interface. The mechanism is further supported by high resolution transmission electron microscopy characterization and density functional theory calculations. A point defect model is proposed to account for oxide space charge effects and their changes under irradiation. This integrated, multiscale experimental and modeling approach challenges the current paradigm on irradiation effects and how they can potentially improve materials performance in extreme environments.

Development of the application for determination of the optimal partitioning form of large-dimensional matrix’s elements for multiplication on three heterogeneous processors

The article presents the results of the development of a web application for finding the optimal form of splitting matrix elements between three abstract heterogeneous processors when performing the operation of their multiplication. The paper considers five classes of parallel matrix multiplication algorithms: serial communication with a barrier, parallel communication with a barrier, serial communication with overlapping, parallel communication with overlapping, parallel overlapping with alternation. The Hockney model is used to estimate the communication complexity of the algorithms. The work uses six non-rectangular candidate partitioning shapes identified by Ashley DeFlumere in her work [1] as a result of applying the «push» technology of redistribution of matrix elements between the processors: Square Corner, Rectangle Corner, Square Rectangle, Block Rectangle, L-Rectangle, Traditional 1D Rectangular. Determination of the optimality of the form is made on the basis of mathematical models presented in the works [2,3]. The programming languages Python and JavaScript, the Django framework, the pip package manager, and Ajax technology were used to develop a web application. Solving the problem of determining the optimal matrix shape will allow for efficient planning of computing power resources for various scientific fields using parallel matrix multiplication.

Analysis of macrosegregation during slab continuous casting using 3D-longitudinal 2D hybrid model

ABSTRACT To improve the computational efficiency of simulating the macrosegregation process that occurs during continuous casting of steel slabs, a new hybrid method combining three-dimensional and longitudinal two-dimensional models was developed to consider the turbulent flow, heat transfer, solidification, and solute transport phenomena. The reasonability of the performed computational domain division was determined, and the model accuracy was verified experimentally. Using this approach, the solute distribution characteristics and central segregation during continuous casting were examined in detail. The obtained results revealed that recirculation flows in the turbulent flow region play a critical role in the distribution of solute elements near the slab surface. Owing to the redistribution of solute elements at the solid–liquid interface and the movement of the solid–liquid interface towards the slab centre during continuous casting, the solute elements in the slab centre are continuously enriched, ultimately resulting in central segregation.

Bioceramics in the CaMgSi2O6–Li2O System: A Glass‐Ceramic Strategy for Excellent Mechanical Strength and Enhanced Bioactivity by Spontaneous Elemental Redistribution

AbstractA novel glass‐ceramic strategy for synthesizing mixed phase diopside (CaMgSi2O6)–lithium oxide (Li2O) bioceramics with excellent mechanical strength, superior biodegradation resistance, low environmental pH impact, enhanced bioactivity, and reasonable biocompatibility is developed for biomedical applications. The substitution of Li2O for MgO in CaMgSi2O6 stimulates the formation of secondary phases: CaSiO3, Li2Si2O5, SiO2, Li2SiO3, and Li2Ca2Si5O13. The evolution of CaSiO3 improves the surface hydroxyapatite (HAp) formation but lowers the mechanical strength and biological resistance, while the amorphous Li2Si2O5 phase tremendously reinforces the bioceramics by densifying the microstructure, indicating the simultaneous enhancement of bioactivity, mechanical strength, and durability. The promoted HAp formation is induced by the elemental redistribution where Mg elements are concentrated in large CaMgSi2O6 grains embedded in Li2Si2O5 amorphous matrix, which hinders the Mg2+ release and its readsorption by HAp. The cell viability is affected by Li2O substitution because of the high‐dose Li+. In the current work, Li0.25 (25 mol% Li2O) has the highest hardness (700 Hv as sintered and 197 Hv after simulated body fluid soaking), lowest weight loss (≈0.6 wt%), lowest pH variation (≈8.1), efficient HAp formation, and reasonable cell viability (70.5%), demonstrating its remarkable potential for bone implant applications due to the synergistic structural densification and biological improvement.

GEOCHEMICAL ASPECTS OF METAPSAMMIT FRICTIONAL MELTING DURING SEISMIC MOVEMENTS (BY THE EXAMPLE OF PSEUDOTACHYLYTES OF THE LADOGA REGION)

Based on geochemical analyses of tectonic pseudotachylytes and their host rocks the features of redistribution of major, rare and rare-earth elements during seismogenic frictional melting of arkose-type metaterrigenous rocks from different-temperature zones of regional metamorphism) of Northern Ladoga region are considered. Multidirectional trends in variations of the major elements oxides contents in the triad protolith-blastocataclasite-pseudotachylyte were revealed, but a unidirectional increase of the frictional melt basicity in comparison with the protolith was established. Geochemical evidence of partial selective melting of source rocks is considered. Peculiarities of rare and rare-earth elements fractionation during transition to the melt of protolithic material, as well as during its subsequent partial crystallization are shown. The appearance of positive europium anomaly in the melt matrix of all three sampling points is noted. By changes of these elements’ concentrations in zones of pseudotachylyte substrate generation and in areas of its injection their differential mobility during frictional melting in a zone of dynamic movement is estimated.

A combined X-ray fluorescence and infrared microspectroscopy study for new insights into elemental-biomolecular obesity-induced changes in rat brain structures

The objective of our research was to determine the brain changes at the molecular and elemental levels typical of early-stage obesity. Therefore a combined approach using Fourier transform infrared micro-spectroscopy (FTIR-MS) and synchrotron radiation induced X-ray fluorescence (SRXRF) was introduced to evaluate some brain macromolecular and elemental parameters in high-calorie diet (HCD)- induced obese rats (OB, n = 6) and in their lean counterparts (L, n = 6). A HCD was found to alter the lipid- and protein- related structure and elemental composition of the certain brain areas important for energy homeostasis. The increased lipid unsaturation in the frontal cortex and ventral tegmental area, the increased fatty acyl chain length in the lateral hypothalamus and substantia nigra as well as the decreased both protein α helix to protein β- sheet ratio and the percentage fraction of β-turns and β-sheets in the nucleus accumbens were revealed in the OB group reflecting obesity-related brain biomolecular aberrations. In addition, the certain brain elements including P, K and Ca were found to differentiate the lean and obese groups at the best extent. We can conclude that HCD-induced obesity triggers lipid- and protein- related structural changes as well as elemental redistribution within various brain structures important for energy homeostasis. In addition, an approach applying combined X-ray and infrared spectroscopy was shown to be a reliable tool for identifying elemental-biomolecular rat brain changes for better understanding the interplay between the chemical and structural processes involved in appetite control.

Resolving Diverse Oxygen Transport Pathways Across Sr‐Doped Lanthanum Ferrite and Metal‐Perovskite Heterostructures

AbstractPerovskite structured transition metal oxides are important technological materials for catalysis and solid oxide fuel cell applications. Their functionality often depends on oxygen diffusivity and mobility through complex oxide heterostructures, which can be significantly impacted by structural and chemical modifications, such as doping. Further, when utilized within electrochemical cells, interfacial reactions with other components (e.g., Ni‐ and Cr‐based alloy electrodes and interconnects) can influence the perovskite's reactivity and ion transport, leading to complex dependencies that are difficult to control in real‐world environments. Here, this work uses isotopic tracers and atom probe tomography to directly visualize oxygen diffusion and transport pathways across perovskite and metal‐perovskite heterostructures, that is, (Ni‐Cr coated) Sr‐doped lanthanum ferrite (La0.5Sr0.5FeO3; LSFO). Annealing in 18O2(g) results in elemental and isotopic redistributions through oxygen exchange (OE) in the LSFO while Ni‐Cr undergoes oxidation via multiple mechanisms and transport pathways. Complementary density functional theory calculations at experimental conditions provide rationale for OE reaction mechanisms and reveal a complex interplay of different thermodynamic and kinetic drivers. These results shed light on the fundamental coupling of defects and oxygen transport in an important class of catalytic materials.

Correlative Imaging of the Rhizosphere─A Multimethod Workflow for Targeted Mapping of Chemical Gradients.

Examining in situ processes in the soil rhizosphere requires spatial information on physical and chemical properties under undisturbed conditions. We developed a correlative imaging workflow for targeted sampling of roots in their three-dimensional (3D) context and assessed the imprint of roots on chemical properties of the root-soil contact zone at micrometer to millimeter scale. Maize (Zea mays) was grown in 15N-labeled soil columns and pulse-labeled with 13CO2 to visualize the spatial distribution of carbon inputs and nitrogen uptake together with the redistribution of other elements. Soil columns were scanned by X-ray computed tomography (X-ray CT) at low resolution (45 μm) to enable image-guided subsampling of specific root segments. Resin-embedded subsamples were then analyzed by X-ray CT at high resolution (10 μm) for their 3D structure and chemical gradients around roots using micro-X-ray fluorescence spectroscopy (μXRF), nanoscale secondary ion mass spectrometry (NanoSIMS), and laser-ablation isotope ratio mass spectrometry (LA-IRMS). Concentration gradients, particularly of calcium and sulfur, with different spatial extents could be identified by μXRF. NanoSIMS and LA-IRMS detected the release of 13C into soil up to a distance of 100 μm from the root surface, whereas 15N accumulated preferentially in the root cells. We conclude that combining targeted sampling of the soil-root system and correlative microscopy opens new avenues for unraveling rhizosphere processes in situ.

Elemental partitioning as a route to decrease HAZ hardness

In the present study, in order to find out a valuable method to decrease the hardness of heat-affected zone (HAZ), elemental partitioning was introduced before welding simulation to realize elemental redistribution. The results demonstrate that about 10% reduction of HAZ hardness can be achieved by introduction of elemental partitioning. During elemental partitioning, the content of retained austenite increases with increasing of elemental partitioned time. Further research reveals that the value of geometrically necessary dislocation density decreases with elemental partitioning. It is found that the alloying elemental contents in the matrix after elemental partitioning are lower than that without elemental partitioning. In addition, the differences of grain size distribution and elemental distribution resulted in elemental partitioning are studied and compared to explain the reason for the reduction in hardness.

Reactive interaction between migmatite-related melt and mafic rocks: clues from the Variscan lower crust of Palmi (southwestern Calabria, Italy)

Abstract. In the Variscan lower–intermediate crust exposed in the Palmi area (southwestern Calabria, Italy), amphibolites occur as foliated, decimeter-thick layers within migmatitic paragneiss and as a decametric main body adjacent to the migmatites. The main body is mostly fine-grained and weakly to moderately foliated; unfoliated medium-grained portions rarely occur. Amphibolites are mainly composed of plagioclase (An80−91) frequently developing triple junctions, amphibole consisting of cummingtonite rimmed by hornblende and variable amounts of biotite. Minor quartz is present in amphibolite layers within paragneiss. Accessory allanite occurs in amphibolite layers within migmatites and in foliated, fine-grained portions from the main body. This study mainly aims to achieve information about the effects triggered by the migration of migmatite-related melts into associated mafic rocks and its role in the re-distribution of major and trace elements out of the anatectic source. On the basis of whole-rock major- and trace-element compositions, the protolith of amphibolite is recognized as of cumulus origin, likely derived from basic melt emplaced in the framework of the late-Variscan lithospheric extension. The rocks experienced high-temperature subsolidus re-equilibration (∼800 ∘C) in conjunction with the development of amphibole. The origin of amphibole is attributed to a coupled dissolution–precipitation process related to the reaction between migrating SiO2-rich hydrous melt and precursor orthopyroxene (± plagioclase). Reactive melt migration also caused the crystallization of biotite ± allanite ± quartz ± plagioclase. SiO2-rich hydrous melt had REE (rare earth element) compositions similar to late-Variscan peraluminous granites and could have been derived by partial melting of metasediments akin to neighboring migmatitic paragneisses. Both whole-rock and amphibole analyses reveal a decrease in Mg# (Mg/(Mg+Fe2+)) from amphibolite layers within paragneiss to fine- and medium-grained rocks of the main body. Hornblende shows an increase in SiO2 and a decrease in Al2O3 and K2O with increasing Mg#. Amphibolites interlayered with paragneiss have higher K2O, Rb, Ba, Th, U and Zr relative to those from the main body. Furthermore, amphibole from amphibolites interlayered with paragneiss is distinct for relatively high Rb, Ba, MREE (middle rare earth element) and HREE (heavy rare earth element) concentrations. Within the main body, foliated, fine-grained rock has both the whole rock and amphibole enriched in Rb and Ba and high Zr bulk-rock contents. Whole-rock and mineral chemistry heterogeneity most likely reflects (i) variation of the composition of the melt during its reactive migration, in response to dissolution of pre-existing minerals and crystallization of new phases, and (ii) variable modification of the original compositions. Foliated and fine-grained amphibolites record the strongest modification, thereby suggesting that they represent permeable pathway enabling effective interaction of the reacting melt with precursor minerals and nucleation of new mineral phases.

Excellent corrosion resistance of electron beam welded joint and remelted layer of eutectic high-entropy alloy AlCoCrFeNi2.1

Electron beam welding (EBW) and electron beam remelting (EBR) experiments were performed on the eutectic high-entropy alloy (EHEA) AlCoCrFeNi2.1. Electrochemical corrosion experiments of different regions of the joint and the remelted layer were carried out, the subsequent corrosion behavior, the corresponding microscopic morphology, structural characteristics were compared and analyzed in detail. The results show that the corrosion resistance of both the welded joint and the remelted layer is better than that of the cast EHEA. Additionally, the corrosion resistance of the weld center area and the core area of the remelting layer is significantly enhanced. This is mainly because the grain refinement of the weld and the remelted layer, and the redistribution of elements play a key role. Moreover, the effect of large and small angle grain boundaries and the change of dislocation density on the corrosion resistance of different regions cannot be ignored.

Mass transfer and element redistribution during chloritization of metamorphic biotite in a metapelite: insights from compositional mapping

Abstract Fluid-driven reactions are common in the upper crust, leading to mineral replacement and element redistribution on a kilometer to a micron scale. One common fluid-induced reaction is the chloritization of biotite. Chloritization can lead to the production of multiple phases, such as K-feldspar, titanite, and rutile, depending on local chemistry and fluid composition. Here, we compare different approaches to mass balance calculations using an altered garnet-bearing metapelite collected from Ny Friesland, Svalbard Archipelago, Norway. In the outcrop, amphibolite facies schists are cut by joints that acted as fluid pathways that led to the development of a narrow (~5 cm) alteration zone. Alteration involved the replacement of biotite by chlorite + K-feldspar ± rutile ± titanite. Mass balance calculations based on whole-rock composition and assuming immobile Zr indicate the addition of H2O, Si, Ti, Fe, or Mg and the removal of K or Ca. In contrast, mass balance calculated for the pseudomorphic replacement of Bt by Chl + Kfs ± Rt ± Ttn using X-Ray maps for three focused areas indicates the removal of Si or Ti rather than addition. Moles of product phase and elements gained or lost during this reaction varies between individual areas. This variation suggests that fluid heterogeneity and local chemistry governed the progression of the replacement reaction. All the product phases involved in the biotite breakdown are geochronometers and/or geothermometers, providing new opportunities for the petrochronology of fluid-induced reactions.

Влияние послерадиационной термической обработки на микроструктуру и механические свойства сплава Э635

The mechanical properties, morphology of zirconium hydrides, dislocation structure and characteristics of phase precipitates in the fuel cladding material and guide channels made of the E635 alloy, which had been used as part of VVER-1000 fuel assemblies, were studied. The effect of post-radiation temperature exposure on the mechanical properties of these products, due to a change in microstructural characteristics and redistribution of elements between the solid solution and phase precipitation, was established.

Elemental Redistribution During the Crystallization of Ge–Cu–Te Thin Films for Phase-Change Memory

Herein, a GeCu2Te2 alloy is proposed as a phase-change material for application in nonvolatile phase-change random access memory (PRAM). The crystallization kinetics and microchemical changes during phase transformation are investigated, and their correlation with the electrical behaviors of the GeCu2Te2 thin films are examined. The key findings are as follows: (ⅰ) the GeCu2Te2 alloy shows a higher crystallization temperature (∼185 °C) than the classic Ge2Sb2Te5 (GST) thin films, thus demonstrating superior thermal stability; (ⅱ) the crystallization kinetics demonstrate a decreasing in the Avrami exponent n from 4, which is related to the growth-dominated crystallization process evidenced by the micromorphology; (ⅲ) a massive redistribution of the chemical elements along the depth of the thin films during crystallization is considered to be driven by selective surface oxidation at amorphous state, and stress buildup during crystallization. In addition, the crystallization-induced stress is determined as ∼168 MPa by utilizing the wafer curvature and X-ray diffraction methods for the GeCu2Te2 thin films. Finally, the lower threshold switching voltage ∼1.72 V for amorphous GeCu2Te2 thin films is beneficial for reducing the SET operating power consumption. The authors believe that these results are valuable for the optimal phase change material design.

Recrystallization of nanosized boehmite in an aqueous medium

The formation and subsequent recrystallization of nanoboehmite under hydrothermal treatment of γ-Al 2 O 3 nanopowder at a temperature of 150 °C in a 1.5% HCl solution have been studied. It has been found that boehmite nanowhiskers up to 2–3 μm in length and no more than 50 nm in diameter are formed from the crystals with a size of 10–20 nm, when kept them under synthesis conditions for up to 96 h. In the course of recrystallization, it was found that unit cell parameters of boehmite depend on time of thermal processing of samples. It has been concluded the solid-phase mechanism of recrystallization and the important role of the hydrothermal medium in the redistribution of elements of the crystal structure. • Nanopowder γ-Al 2 O 3 was hydrothermally treated • Boehmite crystals (2–3 μm in length, 50 nm in diameter) were synthesized • Solid-phase mechanism for improving the structure of boehmite crystals is proposed • Mass transfer and growth of needles define microregions of an ordered structure

Quantifying chemical fluctuations around medium-range orders and its impact on dislocation interactions in equiatomic CrCoNi medium entropy alloy

Equiatomic multi-principal element alloys manifest unique mechanical properties derived from the single-phase solid solutions with compositional disorders. Recently discovered medium-range orders (MROs) with a size of 1–5 nm in CrCoNi medium entropy alloy acclaimed measurable impact on mechanical properties, which, however has been questioned by density functional theory calculations. Here we report that the formation of MROs is accompanied by the redistribution of constituent elements, and the subtle chemical composition fluctuations could by directly probed and quantified by using a state-of-the-art aberration-corrected transmission electron microscope. The presence of such MROs contributes to an appreciable increase in yield strength (∼40 MPa) with a higher work hardening rate, originating from the strong dislocation interactions with MROs at the incipient plastic deformation. These findings demonstrate that MROs have a significant impact on reducing the mean free path of full/partial dislocations along a specific slipping plane, offering a new avenue for strengthening of equiatomic element alloys by tuning local composition and atomic configurations.

Redistribution and fractionation of trace and rare earth elements during weathering and lateritization of orthogneiss in Ndokayo (Bétaré-Oya Gold District, South East Cameroon)

Ferralsols in the transitional zone between the Adamaoua and the South Cameroonian plateaus provided evidence of significant economical and scientific interests, but they have received very little attention over the last decades. Thus, macroscopic, mineral and geochemical investigations of two residual soil profiles from orthogneiss in the Bétaré-Oya Gold District (BOGD) with significant morphological differences were conducted in order to assess weathering and lateritization processes and their significance to the occurrence of mineralized trace and rare earth elements. Macroscopically, soil profile in upslope is deep weathered and thick (> 8.0 m thick), exhibiting a 5.1 m thick encrusted mineral level. Inversely, the downslope soil profile is moderately weathered and marked by a near surface water table that partly affects the mineral horizon B. These studied ferralsols result from an intense weathering but weak to moderate lateritization as revealed by the Chemical Index of Alteration (CIA: 87 to 99%), the Plagioclase Index of Alteration (PIA: 98 to 100%) and the Index of Lateritization (IOL: 31.48 to 60.83%). The two soil profiles have a similar mineralogical content characterized by the predominance of newly-formed secondary minerals such as kaolinite (12–40%), gibbsite (12–27%), goethite (7–15%), hematite (2–15%), maghemite (6–10%) and anatase (1–2%). However, a considerable amount of residual quartz (16–56%) and muscovite (3–15%) is evidenced in the weathering products. Geochemically, the weathering products of Ndokayo show weak to moderate depletion of SiO2 (77.26–31.82%), strong depletion of alkali and alkaline earths (Weathering Index of Parker or WIP: 56.73 to 1.56), and moderate enrichment of Al2O3 (12.43–29.20%), Fe2O3 (1.26–23.45%) and TiO2 (0.11–1.77%). V (64.67–210 ppm) and Cr (25.81–720 ppm) are the most enriched trace elements in this area, with their respective maximum enrichment factor of 2 and 7, and display similar geochemical patterns with Fe2O3, suggesting their adsorption or incorporation into the crystalline structure of Fe-oxides. Some others mineralized trace elements (Sc, Ga, As, Mo, Sn, Cs, Pb, Bi, Th and U) exhibit low to moderate contents, even if their mineralization indices range between 1 and 81. This is indicative of low mining potential of the Ndokayo weathering products. Finally, the deep and intense weathering of orthogneiss, coupled with weak to moderate lateritization of the weathering products in the study area is controlled by rock type involving the formation of kaolinitic laterites and bauxitious kaolins with weak mineralization indices of some trace and rare earth elements.