•Li-Pb corrosion tests were conducted for multi-layer coatings using Er2O3 and ZrO2.•The outermost ZrO2 remained after Li-Pb exposure for up to 2000 h at 600 °C.•ZrO2 is more suitable as the ...outermost layer of multi-layer coatings than Er2O3.•Cracks and peelings formed on ZrO2 layer after Li-Pb exposure for 1000 h at 600 °C.•The difference in layer thickness may cause interlamellar peeling.
Tritium permeation through structural materials in fusion reactor blanket systems is a critical issue from the viewpoints of fuel loss and radiological safety. Ceramic coatings have been investigated to prevent tritium permeation; however, corrosion of the coatings by blanket materials, especially corrosive liquid tritium breeders such as lithium-lead is serious. In our previous study, the improvement of permeation reduction performance using an erbium oxide (Er2O3)-zirconium oxide (ZrO2) two-layer coating was confirmed, but it did not show substantial corrosion resistance. In this study, various multi-layer coatings were fabricated by metal organic decomposition and then exposed to lithium-lead under static conditions to investigate precise corrosion behaviors of multi-layer coatings. After lithium-lead exposure for 1000 h at 600 °C, the outermost Er2O3 layer almost disappeared, while the outermost ZrO2 layer remained, indicating that ZrO2 is more suitable as the outermost layer. However, many cracks and peelings were observed on the outermost ZrO2 layer in the cases of the samples having four coating interfaces. The optimization of layer combination and the control of adhesion between the coatings are required to reduce the degradation of multi-layer coatings.
The surface orientation of crystals has an influence on various material properties, like the oxidation. A method was developed to correlate the oxidation rate for individual single crystal grains ...with their surface orientation. The surface orientation of many grains of polycrystalline, recrystallized tungsten samples was determined using electron backscatter diffraction. Subsequently, the samples were oxidized in a thermobalance, measuring the time dependent weight increase. The grain dependent oxidation rates were determined by measuring the thickness of the oxide layer for many individual grains with confocal laser scanning microscopy and the scanning electron microscopy on focus ion beam prepared cross-sections. In the temperature range of 720 K to 870 K, tungsten grains with {100} surface orientation have the highest oxidation rate, which is two times higher than the lowest oxidation rate. The lowest oxidation rate belongs to the {111} surfaces orientation, while the {110} surfaces orientation has an intermediated rate. The derived oxidation rates are consistent with gravimetric measurements. They follow an Arrhenius behavior with an activation energy of 190 kJ/mol.
•Method to measure and evaluate orientation of many single crystal grains•Determine the fraction of the oxide layer above and below the original surface level•The oxidation rate vary by a factor of two in temperature range 720 to 870 K
•The interdiffusion coefficient between Iron and Tungsten is investigated.•For temperatures above 1000 K, the phase Fe2W was observed in Fe/W couples.•The growth rate of Fe2W was assesed.•The ...interdiffusion coefficient of Fe2W was quantified.
Low-activation steels are attractive candidates for wall materials in future nuclear-fusion power plants. Through a process called preferential sputtering, an enriched tungsten (W) layer is expected to develop on these steels, lowering erosion and thus increasing their lifetime and reducing contamination of the fusion plasma. However, the process of preferential sputtering may be counteracted by interdiffusion of W and iron (Fe). In this article, we investigate a simplified model system of such low-activation steels with a W-rich layer on the surface, by sputter depositing a thin W layer on top of pure Fe substrates. We investigate the processes that are activated when this model system is subject to temperatures relevant in the context of nuclear fusion reactors and assess the temperatures at which interdiffusion is expected to influence W surface concentrations. This is done by annealing a binary W-Fe system and analyzing the resulting concentration profiles by means of Rutherford backscattering spectrometry (RBS) and focused ion beam cross-sectioning (FIB). For annealing temperatures above 1000 K, an intermediate phase was observed to have formed, both between the Fe and W layer as well as on the surface of the W layer. This intermediate phase was determined to be Fe2W using Sputter X-ray photoelectron spectroscopy (XPS) and time-of-flight Rutherford backscattering spectrometry (ToF-RBS). The laterally averaged growth rate of this phase was determined to be (1.0±0.1)×10−18m2s at 1050 K and (2.8±0.2)×10−18m2s at 1100 K.
Most of spherical blisters formed by deuterium (D) bombardment (38
eV/D) up to 3
×
10
24
D/m
2 at 300
K on polycrystalline tungsten are fully elastic deformations. This has been proven by opening ...individual blisters with a focused ion beam and in situ observation of their complete relaxation by scanning electron microscopy. The D
2 gas filling is confirmed by observing simultaneously the D
2 puff. The gas pressure is causal for the stability of such spherical blisters after implantation and the gas release leads to sudden relaxation. The dilatation of the blister cap by trapped D can be excluded as cause for the blisters.
Studies of molten droplets emitted from cathode spots of vacuum arcs on copper, tungsten, and titanium have been carried out using a time-of-flight measurement procedure. In the arrangement, two ...light barriers at different distances from the cathode surface are used. When particles traverse the barriers, the appearance of scattered light can be used to establish the flight time and, thereby, the velocity of particles. Simultaneously, the intensity of scattered light provides a measure of the size of the particle by applying the Mie-scattering theory together with calibrations. By turning the cathode surface with respect to the drift tube axis, an angular resolution of the parameters was achieved. Algorithms were developed for automated processing of the measured data to identify particles arriving from the arc spot unobstructed. Distributions of the particle sizes, a statistical relation between the sizes and the emission velocities of particles, and other properties are discovered for all three cathode materials.
Various material properties, like oxidation, depend on the surface orientation of crystals. Most evaluations are focused on a few crystal orientations or using single crystals. A software tool ...written in python is introduced to correlate the thickness of the tungsten (W) oxide layer, i.e., the oxidation rate, and the individual single crystal grains with their surface orientation of polycrystalline W. The results are visualized in an inverse pole figure, which represent the oxidation rates for all crystal orientations. The use of polycrystalline W samples allows to analyze many different crystal orientations in a single experiment. Recrystallized, polished and polycrystalline W samples were pre-characterized using electron backscatter diffraction in a scanning electron microscope (SEM). Subsequently, the samples were oxidized in a thermobalance. A confocal laser scanning microscope was used for measuring the height of the oxide layer, which is scaled to thickness of the oxide layer by using SEM images from focused ion beam prepared cross-sections. Previous data of oxidation of W in the temperature range of 720 K to 870 K were reanalyzed with the new analysis tool. At grain boundaries, the oxidation is influenced by the neighboring grains. To evaluate the magnitude of this effect on the oxidation, samples with different textures were oxidized and evaluated. The results for the different textures agree within the estimated error bars, demonstrating the effectiveness of the automated analysis method. W grains with 〈100〉 surface orientation showed the highest oxidation rate.
•Method to measure and evaluate orientation of many single crystal grains with a python tool•Visualize the oxidation rate in an inverse pole figure•The oxidation rate vary by a factor of two in temperature range 720 to 870 K.•Orientation-dependent oxidation is different for a nm thick oxide layer and a μm thick oxide layer.
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