Wave Dispersive Spectroscopy Research Articles

Microstructure and Nanoindentation Studies of Hydridated Zircaloy-4 Claddings After High Temperature Oxidation

Abstract Zirconium-based alloys are one of the most significant materials in thermal-neutron reactor systems. With very low neutron capture cross section, good corrosion resistance, mechanical strength and resistance to neutron radiation damage, zirconium alloys are used for fuel claddings. Cladding materials are still improved and tested in normal as well as critical reactor conditions. Zircaloy-4 (Zr-1.5Sn-0.2Fe-0.1Cr) is used for west types of light-water reactors, Pressurized Water Reactors (PWR). In our study, Zircaloy-4 cladding tubes were high-temperature oxidized in steam at the series of temperatures from 950 up to 1425 °C to simulate PWR reaching severe accident conditions. To observe the influence of hydrogen (H) diffusing from the coolant water on oxidation process, the specimens with ∼1000 ppm H were compared to the specimens with almost no hydrogen content. Wave Dispersive Spectroscopy (WDS) and nanoindentation were performed in line profiles across the cladding wall. Both methods contributed to verify the pseudobinary Zircaloy-4/oxygen phase diagram with focus on determination of phase boundaries. The increase of oxygen concentration with increasing temperature was observed. Moreover, oxygen concentration profiles and related change in nanohardness and Young's modulus showed the effect of hydrogen on the cladding microstructure. Hydrogen dissolved in metallic matrix increases the oxygen solubility in prior β-phase, the specimens with 1000 ppm H showed the higher oxygen content at almost all temperatures. As well, material hardening was observed on specimens with 1000 ppm H with significant difference in β-phase, measured on specimens exposed to lowest and highest oxidation temperature. Thus, with increasing temperature and hydrogen content, increased oxygen solubility affects the cladding ductility.

Experimental Verification of Phase Diagram Calculations of Zr-Based Alloys after High-Temperature Oxidation

Zirconium-based alloys are commonly used as a material for nuclear fuel claddings in the light water reactors. The cladding material must function to fix a huge number of pellets, while conducting heat into the coolant that flows turbulently around the fuel rods. Cladding tubes can contain gaseous fission products that escape the fuel. Thus, by functioning as a sealed unit, it prevents a contamination of the coolant water with high-radioactive fission products. The integrity of claddings is always a critical issue during reactor operation and wet or dry storage and transport of the spent fuel rods. Moreover, the role gains importance at Loss of Coolant Accidents (LOCA). After Fukushima accident, cladding materials are widely studied with the purpose to reduce the high-temperature oxidation rate and enhance accident tolerance. In our contribution, we introduce the studies on Zr-1Nb (E110) cladding tubes after high-temperature steam oxidation at 1350 °C. During the testing of claddings, microscopy analytical methods play an important role in experimental verification of pseudo-binary phase diagram Zr1Nb-O, i. e. particularly in oxygen content determination at phase transitions. Wave Dispersive Spectroscopy (WDS) with complementary nano-indentation method were used to characterize the Zr1Nb microstructure formed after LOCA. It includes the regions from an oxide and oxygen-stabilized α-Zr(O) to the acicular prior β-Zr phase. The decrease of hardness and Young's modulus corresponds with oxygen content measured in line-profiles by WDS. The oxygen level at transition points was partly determined from Fe, Nb β-stabilizers and significant change in mechanical properties in fine-grained prior β-Zr. The slight fluctuation of oxygen values in adjacent grains can be caused by preferential oxidation through the favorably oriented α-Zr(O) grains studied by WDS+EBSD. As well, the non-uniform oxygen-rich α-Zr(O) phase adjacent to the oxide was characterized by EBSD & WDS. Increasing hydrogen content in specimens, 10, 700 and 1000 ppm H, caused increasing solubility of oxygen in prior β-Zr phase upon high-temperature and the cladding material hardening.

Effects of adding aluminium in zinc bath on Co-Zn interfacial reaction

Effects of adding 0.3 wt.% Al in Zn bath on the microstructure and reaction kinetics of intermetallic compounds have been studied using Co/Zn and Co/Zn-Al solid/liquid diffusion couples by means of scanning electron microscopy (SEM) and wave dispersive spectrometry (WDS). The intermetallic compounds in the Co-Zn interface have been identified and the diffusion process of Al in zinc bath has been analyzed. The diffusion constants of intermetallic compounds have been evaluated. The chemical potential of Al and standard Gibbs free energy of intermetallic compounds have been calculated using the Co content as a variable based on the calculation of phase diagram (CALPHAD) method. The results show that the chemical potential of Al decreases with increasing Co. At the solid/liquid interface, the Co content is high, the chemical potential of Al atoms is lower than that in other areas, uphill diffusion of Al atoms occurs, and an Al-rich metastable phase forms. The Gibbs free energy of the CoAl phase is lower than that of Co-Zn compounds; therefore, the Co atoms diffuse through the γ2 layer into the Al-rich area and nucleate to form a shape-stable CoAl layer at the solid/liquid interface and significantly inhibit the Co-Zn interfacial reaction.

Deposition and characterization of Ti-Al-C-N coatings

In the present work, Ti-Al-C-N coatings were deposited on cemented carbide substrates by lateral rotating cathodes (LARC®) process using Platit π80+DLC deposition unit. The effect of C2H2 gas flow rate on elemental and phase composition, deposition rate, cross-sectional and surface morphology, mechanical and tribological properties of the coatings was studied. Following analytical techniques, namely: scanning electron microscopy (SEM) with energy and wave dispersive X-ray spectroscopy (EDS and WDS), X-ray diffraction analysis (XRD), nanoindentation measurements, Rockwell C indentation test and tribological testing were used for Ti-Al-C-N coatings evaluation. From the EDS analysis, it was found that the carbon content in the coatings increased from 0 at.% to 22.3 at.% as the C2H2 gas flow rate increased from 0 sccm to 75 sccm. The increase in deposition rate of coatings from 0.029 μm/min to 0.052 μm/min was documented. From XRD results it was found that the coatings consist of a cubic B1-NaCl type Ti1N0.9 phase. The maximum hardness was observed at C2H2 gas flow rate of 25 sccm and the lowest friction coefficient (0.35) at the maximum C2H2 gas flow rate. The coatings deposited at C2H2 gas flow rates (25 sccm and 50 sccm) exhibited an excellent adhesion.

Phase Equilibria of the Zr-Si-Y Ternary System at 900 °C

The isothermal section of the Zr-Si-Y ternary system at 900 °C has been investigated using x-ray power diffraction, Scanning electron microscopy coupled with energy-/wave-dispersive x-ray spectroscopy. Nine three-phase equilibrium regions were determined experimentally. No ternary compound was observed in the present work. The 9 binary compounds Zr2Si, Zr3Si2, Zr5Si4, ZrSi, ZrSi2, Y5Si3, Y5Si4, YSi and Y3Si5 were confirmed to exist in the Zr-Si-Y ternary system at 900 °C. The solubility of the third component in the binary compound was determined experimentally.

Characterization of a Continuously Cooled Dual-Phase Steel Microstructure

Continuous-cooling transformation behavior of a DP steel was analyzed from dilation curves with cooling rates that range between 10 °C/s and 98 °C/s and data taken in 10 °C/s increments. For a precise understanding of the problem, several metallographic techniques were used in order to determine which phases and types of transformation are present, the grain structure and crystal defects generated for each cooling rate, among other characteristics. The local distribution of the main alloying elements was analyzed by wave dispersive spectroscopy. From the dilation curves, the relative amount of transformed phase was estimated, as well as the first derivatives as a function of both temperature and time to analyze the characteristics of the transformation and correlate these with a characteristic microstructure. To further understand these results, the mobility of suitable alloying elements such as Cr, Mn, Al, and P was evaluated. The analysis showed that at lower cooling rates, 10 °C/s to 20 °C/s, the transformation occurs at temperatures above 700 °C (at which the majority of alloying atoms have good mobility) in a relatively slow process producing polygonal ferrite. At cooling rates greater than 40 °C/s, the transformation occurs below 700 °C in a relatively short time, where massive transformation takes place. Finally, a cooling rate of 30 °C/s gives a mixed transformation, producing an appreciably smaller grain structure with a high density of crystal defects.

Determination and estimation of magnesium content in the single phase magnesium-calcite [Ca(1−x)MgxCO3(s)] using electron probe micro-analysis (EPMA) and X-ray diffraction (XRD)

Mg-calcite (MgCc) is the term used for calcite containing variable magnesium content. The correct determination of the Mg-content in the calcite is of great interest for many fields of research. This study presents the potential, accuracy and the limitations of determining Mg-content in MgCc by means of electron probe micro-analysis (EPMA) coupled with the energy dispersive and wave dispersive spectrometry (EDS/WDS), and X-ray diffractometry (XRD). These techniques were used to examine the distribution of Mg (in mol% MgCO3) in six calcite marble samples from different locations of Peshawar basin (Pakistan), a part of Lesser Himalayas. Results showed variable Mg-content averaging 0.944–1.740 mol% from the chemical analysis with EPMA/EDS of the whole rock sample. This was almost consistent with the XRD findings of 0.750–1.690 mol%. The sample NO13 with heteroblastic grain structure showed disequilibrium geometry due to the contact metamorphism, characterized by the relatively high temperature and low pressure. This caused predominantly quick re-crystallization of the carbonate phase, thus showing lower Mg-content in the sample. It was assumed that the observed small variability in the Mg-content of the investigated calcites even with in the sample is due to the temperature dependency of the Mg incorporation into the calcites. The highest degree of accuracy in Mg-content determination was observed based on the lattice parameter a and cell volume V. For the Mg-content obtained by XRD, best correlation was observed between the lattice parameter a, cell volume V and Mg-content, with r2 = 0.991 and 0.990 respectively. The difference between the d104 values from the Rietveld refinement and the observed XRD patterns were generally < 0.002 A.

Evolution of Microstructure and Microsegregation of Ti‐45Al‐8Nb Alloy during Directional Solidification

High Nb‐containing TiAl alloys have good oxidation resistance and mechanical properties, but the microstructure and the properties are substantially affected by the segregation. To quantitatively investigate the segregation behavior of Al during solidification, microstructures of directionally solidified (DS) Ti‐45Al‐8Nb (in atomic percent) alloy prepared at withdrawing rates of 30 μm/s and 200 μm/s and a temperature gradient of 4200 K/m were observed by optical microscope and electronic probe microanalyzer. The microsegregations were characterized by wave dispersive spectroscopy. The results show that the DS ingots include the no melting zone, directionally solidified zone with columnar grains, mushy zone, and quenched liquid zone. The primary dendritic arm spacings are 353 μm and 144 μm, respectively, for the two ingots. But the solidified microstructures of the ingots are large lamellar colonies, which contain a few B2 patches and γ bands induced by microsegregation. From dendritic zone to columnar zone, the volume fractions of B2 patches and γ bands decrease. The segregation extents of Al and Nb decrease with the increase of solidification rate. There exists an obvious back diffusion process of Al during solidification and cooling after solidification. According to evolution of Al concentration profiles from mushy zone to columnar grain zone, interdiffusion coefficient for Al in β‐Ti at near solidus temperature is semiquantitatively calculated, and the value is (6 – 11) × 10−11 m2/s.

Microstructure, chemical composition, wear, and corrosion resistance of FeB\u2013Fe2B\u2013Fe3B surface layers produced on Vanadis-6 steel using CO2 laser

The paper presents the study results of laser modification of FeB–Fe2B surface layers produced on Vanadis-6 steel using pack cementation method. Microstructure, x-ray phase analysis, chemical composition study using wave dispersive spectrometry method, microhardness, corrosion resistance as well as surface condition, roughness, and wear resistance were investigated. The diffusion boronizing processes were performed at 900 °C for 5 h in the EKabor® powder mixture. The boronized layers had a dual-phase microstructure composed of two types of iron borides, FeB and Fe2B, and their microhardness ranged from 1800 to 1400 HV. The laser surface modification was carried out on specimens after diffusion boronizing process using CO2 laser with a nominal power of 2600 W. Laser beam power used in this experiment was equal to 1040 W and was constant. While the three values of scanning speed were used: 19, 48, and 75 mm/s. During laser modification, the multiple tracks were made where distance between of axis tracks was equal to 0.5 mm. As a result of this process, microstructure consisted of remelted zone, heat-affected zone, and substrate was obtained. In remelted zone, the boron-martensite eutectic was observed. Boronized layers after laser modification were characterized by the mild gradient of microhardness from surface to the substrate and their value was dependent on the scanning speed used and was between 1700 and 1100 HV. Corrosion resistance tests revealed reducing the current of corrosion in case of laser modification process. Wear resistance of laser modified specimens was improved in comparison to diffusion boronized layers.

High-temperature oxidation behavior of Nb–Si-based alloy with separate vanadium, tantalum, tungsten and zirconium addition

The microstructure and oxidation behavior of directionally solidified (DS) Nb–15Si–24Ti–4Cr–2Al–2Hf alloys with separate vanadium, tantalum, tungsten and zirconium additions were investigated by X-ray diffraction (XRD), electron probe microanalyzer (EPMA) equipped with wave-dispersive spectroscopy (WDS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) equipped with an energy-dispersive spectroscopy (EDS). Results show that the five alloys are all composed of primary (Nb,Ti) solid solution ((Nb,Ti)SS) phase and eutectic (Nb,Ti)SS/(Nb,Ti)5Si3 structure. After oxidation at 1250 °C for 100 h in air, the surfaces of the five alloys are covered by the oxides of Nb2O5, TiNb2O7, Ti2Nb10O29, TiO2 and amorphous SiO2. It is found that the alloying elements of V and W are detrimental for oxidation resistance and the addition of Ta has no obvious effect. Zr addition obviously benefits the oxidation resistance at high temperature, by decreasing the weight gain from 242.75 to 184.83 mg·cm−2. The oxidation mechanism of Nb–Si-based alloys and the effects of different alloying elements on the oxidation resistance of Nb–Si-based alloys were discussed.

Mechanical properties and microstructure of removable partial denture clasps manufactured using selective laser melting

This study compares the mechanical response and microstructure of Co–Cr–Mo removable partial denture models made through conventional lost-wax casting and the selective laser melting additive manufacturing process. Co–Cr–Mo clasps for removal partial dentures, based on a wax model (BEGO USA), were fabricated through lost-wax technique and selective laser melting, and subjected to mechanical bending experiments to determine their yield strength and maximum reversible deformation. Single-Factor Analysis of Variance (ANOVA) was used to compare data from the two populations. Microstructure and chemical composition of the clasps were determined through scanning electron microscopy and wave-dispersive spectroscopy to rationalize the differences and similarities in the mechanical testing results from the two groups.It was found that the clasps made using lost-wax technique and selective laser melting exhibit comparable mean yield strengths and maximum elastic deformations, however the underlying microstructure of the cast clasps vastly differs from the laser-melted counterparts. Furthermore, the laser melted clasps exhibit larger variability in their mechanical response. While selective laser melting is capable of producing removable partial denture clasps with similar average mechanical responses to those of lost-wax cast counterparts, additional studies should be conducted to minimize the variability in the laser melted clasps in order to minimize unexpected failures.

Crystal-chemical study of wavellite from Zbirov, Czech Republic

AbstractThe crystal chemistry of wavellite from Zbirov (Czech Republic), ideally Al3(PO4)2(OH,F)3·5H2O, was addressed by means of a multi-methodological approach based on electron microprobe analysis (EMPA) using wave-dispersive spectroscopy, single-crystal X-ray diffraction, powder and singlecrystal infrared spectroscopy and Raman spectroscopy. The EMPA data showed the presence of significant F replacing OH in the sample studied. The structure was solved in thePcmnorthorhombic space group, with the following unit-cell constants:a= 9.6422(7),b= 17.4146(15),c= 7.0094(2) Å,V= 1176.98(10) Å3. Phosphorus atoms display tetrahedral (PO4) coordination, while Al cations display octahedral coordination. The mineral framework can be viewed as the repetition of cationic arrays made up of AlO6polyhedra, bridged by PO4groups and further joined by O–H⋯O hydrogen bonds. The single-crystal unpolarized Fourier transform infrared (FTIR) spectrum shows combination bands indicating the presence of both OH and H2O in the structure. Both FTIR and Raman spectra show a broad absorption extending from 3600 to 2800 cm−1resulting from the overlapping of several components due to the water molecules and the OH group. The frequencies observed are comparable to those expected on the basis of the Libowitzky relationship for the range ofD–H⋯Abond systems in the structure.

Experimental Investigation and Thermodynamic Calculation of the Co-Si-Zn System

Phase relations of the Co-Si-Zn ternary system were experimentally investigated and thermodynamically calculated. First, the isothermal sections of the Co-Si-Zn system at 1123 K and 1323 K (850 °C and 1050 °C) were investigated experimentally using scanning electron microscopy coupled with wave-dispersive X-ray spectroscopy and X-ray diffraction. Then the thermodynamic calculation for this system was carried out using the CALPHAD technique. The calculated results and the experimental data are reasonably self-consistent.

The Isothermal Section of the Fe-Si-Ti-93 at.% Zn Quaternary System at 450 °C

The 450 °C isothermal section of the Fe-Si-Ti-Zn quaternary system with Zn being fixed at 93 at.% was determined experimentally by means of scanning electron microscopy coupled with wave dispersive x-ray spectroscopy, and x-ray powder diffraction. Fourteen four-phase regions were confirmed experimentally in this isothermal section. The Fe-Ti-Zn ternary phase T-TiFe2Zn22 was found to be in equilibrium with the liquid, ζ-FeZn13, τ2-FeTiSi, and TiZn16 phases. The maximum solubility of Zn in τ2-FeTiSi is 2.74 at.%, but less than 1.08 at.% in τ1-FeTiSi2. Si solubility in T-TiFe2Zn22 is 0.31 at.%, but it is negligible in ζ-FeZn13. The solubility of Ti in the liquid phase is limited. The results of present work are consistent with the relevant ternary systems. No true quaternary compound was found in the isothermal section.

450°C isothermal section of the Zn-Fe-Co-Si quaternary system at the zinc-rich corner

AbstractThe Zn-rich corner of the 450°C isothermal section of the Zn-Fe-Co-Si quaternary system with the Zn content being fixed at 93 at.% was determined experimentally using the equilibrated alloy approach. The specimens were investigated by means of scanning electronic microscopy coupled with wave dispersive X-ray spectroscopy, and X-ray powder diffraction. It was found that 2 four-phase regions, i. e. L+(Fe,Co)Si+FeSi2+Si and L+(Fe,Co)Si+CoSi2+Si, exist in the section. The Si solubility in ζ-FeZn13 phase is rather limited, with Co dissolving in this compound, the solubility of Si is up to 0.82 at.%. The Fe solubility in CoSi2 is no more than 1.21 at.%, whereas the Co solubility in FeSi2 is high up to 7.81 at.%. The maximum solubility of Zn in (Fe,Co)Si, FeSi2, and CoSi2 is 1.92, 1.49, 2.93 at.%, respectively. No true quaternary compound was found in the present study.

Nanochemomechanical assessment of shale: a coupled WDS-indentation analysis

Establishing the links between the composition, microstructure and mechanics of shale continues to be a formidable challenge for the geomechanics community. In this study, a robust methodology is implemented to access the in situ chemomechanics of this sedimentary rock at micrometer length scales. Massive grids of coupled wave dispersive spectroscopy (WDS) and instrumented indentation experiments were performed over representative material surfaces to accommodate the highly heterogeneous composition and microstructure of shale. The extensive datasets of compositional and mechanical properties were analyzed using multi-variate clustering statistics to determine the attributes of active phases present in shale at microscales. Our chemomechanical analysis confirmed that the porous clay (PC) mechanical phase inferred by statistical indentation corresponds to the clay mineral phase defined strictly on chemical grounds. The characteristic stiffness and hardness behaviors of the PC are realized spatially in regions removed from silt inclusions of quartz and feldspar. At the microscale shared by indentation and WDS experiments, a consistent chemomechanical signature for shale emerges in which the heterogeneities of the PC are captured by the standard deviations of indentation properties and concentrations of chemical elements. However, these local behaviors are of second order compared to the global trend observed for mean mechanical properties and the clay packing density, which synthesizes the relative volumes of clay and nanoporosity in the material. The coupled statistical indentation and WDS technique represents a viable approach to characterize the chemomechanics of shale and other natural porous composites at a consistent scale below the macroscopic level.

Continuous flow synthesis of ceria nanoparticles using static T-mixers

Ceria nanoparticles are of interest owing to their interesting properties like photo-absorption and ability to absorb oxygen. Several batch synthesis routes exist however these methods often lack particle size control, result in agglomeration and typically require high temperature processing. In this paper, a continuous flow microchannel synthesis method based on precipitation is demonstrated with a static T-mixer, showing improved control over agglomeration through the manipulation of flow parameters. Three flow rates were chosen representing different mixing modes and computational fluid dynamics simulations were used to visualize flow conditions. The nanoparticles were characterized for composition, size and size distribution using transmission electron microscopy, wave dispersive spectroscopy and x-ray diffraction. The engulfment flow condition, corresponding to the highest Reynolds number in this study, gave the narrowest particle size distribution (15.0±4.7nm) and best compositional uniformity.

Study on calcination of bi-layered films produced by anodizing iron in dimethyl sulfoxide electrolyte

Research on well adherent, thick and nanoporous oxide film formation onto the metal substrates underwent a major burst throughout the last decade. In the current study, thick bi-layered films produced onto a pure iron surface by anodizing way in dimethyl sulfoxide (DMSO) electrolyte containing silica hexafluoride acid have been investigated upon the annealing in air. Compositional, phase and structural transformations of the film material to hematite, α-Fe2O3, were studied using Mössbauer spectroscopy at room to cryogenic temperatures, thermogravimetry (TG), differential thermal analysis (DTA), photoemission spectroscopy, scanning electron microscopy (SEM), and wave dispersive X-ray spectroscopy (WDX). Experimental findings indicated that much longer heating in air is required for these films to be fully transformed to hematite. This effect is linked here with the complex nature of DMSO films. Based on the combined WDX, photoemission and Mössbauer spectroscopy results, the transformations taken place during calcination of such amorphous films by heat-treatment in air to crystalline hematite have been determined. Investigations on the calcination effects of thick iron anodic films reported here offer opportunities for both fundamental research and practical applications.

Oxygen, Hydrogen and Main Alloying Chemical Elements Partitioning Upon Alpha←→Beta Phase Transformation in Zirconium Alloys

Due to their adequate properties, zirconium alloys are the reference materials for the nuclear fuel cladding tubes of Light Water Reactors (LWR). During some hypothetical accidental High Temperature (HT) transients, the materials should experience heavy steam oxidation and deep metallurgical evolutions. This promotes Alpha-Beta phase transformations and an associated strong partitioning of oxygen/hydrogen and of the main chemical alloying elements (Nb, Sn, Fe and Cr). Moreover, it has been shown quite recently that such chemical elements partitioning during on-cooling Beta-to-Alpha transformation can strongly impact the residual mechanical properties of HT oxidized materials. Thus, it appeared that it was important to better quantify and, if possible, to compute the quite complex phase equilibrium that occurs in multi-alloyed zirconium materials in the presence of both oxygen and hydrogen. For that, systematic studies have been performed on industrial alloys, charged with oxygen and/or hydrogen. After applying different heating/cooling scenarii, both Electron Microprobe using Wave Dispersive Spectrometry (WDS) and Nuclear Microprobe using Elastic Recoil Detection Analysis (ERDA) have been applied. Finally, to support the observed chemical elements partitioning between the Alpha and Beta allotropic phases, some thermodynamic calculations have been performed thanks to the development and the use of a specific thermodynamic database for zirconium alloys called “Zircobase".

Experimental investigation and thermodynamic calculation of the Zn–Al–Sb system

Abstract The 873 K isothermal section of the Zn–Al–Sb ternary system was experimentally determined using scanning electron microscopy coupled with wave and energy dispersive X-ray spectroscopy. No ternary compound was found in the present study. Based on the experiment results together with available information in the literature, the phase diagram calculation for Zn–Al–Sb was carried out by means of the CALPHAD technique. A consistent set of thermodynamic parameters for each phase was derived. The optimized results and the experimental data are in good agreement.