SiC‐fiber–reinforced binary Si eutectic alloy composites have been developed for aerospace applications using the melt infiltration method. In this study, the oxidation mechanisms of various binary ...Si eutectic alloys were evaluated at elevated temperatures. We suggest that the oxidation resistance of eutectic alloys could be predicted using the Gibbs energy change for the oxidation reaction. Based on these calculations, eutectic alloys of Si‐16at%Ti, Si‐17at%Cr, Si‐22at%Co, Si‐38at%Co, and Si‐27at%Fe were prepared. These alloys produced uniform SiO2 layers and showed the same oxidation resistance as Si at 1000°C under humid conditions. Therefore, SiC composites using Si alloys with excellent oxidation resistance can be predicted using thermodynamic calculations.
Amorphous SiC-fiber-reinforced Si-CoSi2 and CoSi2–CoSi eutectic alloys composites have been developed by a melt infiltration method, and their mechanical properties were evaluated at elevated ...temperatures up to 1220 °C. As compared to polycrystalline Si, Si–Co ingots showed a ductile transition at a lower temperature (200–400 °C) due to the ductile transition of CoSi2 and the presence of a debonding interface. Moreover, the composites using Si–Co alloys showed superior bending behavior at elevated temperatures around 1000 °C as compared to composites using Si because of the ductile behavior of the Si–Co alloys and the prevention of the degradation of the SiC fibers.
The fabrication of Tyranno ZMI fiber/SiC-based matrix composites by a melt infiltration (MI) process using Si−8.5at%Hf alloy was investigated. The Si−Hf alloy was utilized instead of pure Si for MI ...processing in order to lower the MI temperature to below 1400°C as well as to inhibit the thermal degradation of amorphous SiC fibers. Microstructural characterization revealed that the composite fabricated by Si−8.5at%Hf alloy MI at 1375°C had a highly dense matrix comprising reaction-formed SiC and unreacted Si−HfSi2 phases. The Si−Hf alloy melt-infiltrated composite exhibited approximately 35% higher bending strength than a conventional Si melt-infiltrated composite fabricated at 1450°C. Further, it was confirmed that Si−Hf alloy melt-infiltrated composite maintained its strength up to 1200°C in an Ar atmosphere. These results clearly demonstrated that the Si−8.5at%Hf alloy offers sufficient infiltration ability and reactivity to form a dense SiC-based matrix at 1375°C.
Microstructures of monolithic high purity SiC and SiC with sintering additives after neutron irradiation to a fluence of 2.0–2.5 × 1024 n/m2 (E > 0.1 MeV) at 333–363 K and after post-irradiation ...annealing up to 1673 K were observed using a transmission electron microscopy. Results showed that no black spot defects or dislocation loops in SiC grains were found after the neutron irradiation for all of the specimens owing to the moderate fluence at low irradiation temperature. Thus, it is confirmed that these specimens were swelled mostly by the formation of point defects. Black spots and small dislocation loops were discovered only after the annealing process in PureBeta-SiC and CVD-SiC, where the swelling almost diminished. Anomalous-shaped YAG grains were found in SiC ceramics containing sintering additives. These grains contained dense black spots defects and might lose crystallinity after the neutron irradiation, while these defects may annihilate by recrystallization during annealing up to 1673 K. Amorphous grain boundary phase was also presented in this ceramic, and a large part of it was crystallized through post-irradiation annealing and could affect their recovery behavior.
Neutron-irradiation-induced defects in 3C–SiC irradiated to 2.8–4.2×1026n/m2 at 480–735°C were investigated by XRD measurement, isochronal annealing and DFT calculation. The XRD peak shift revealed ...different features between the specimens irradiated at 480°C and higher temperature than 585°C. The peak shifts were larger at the higher angle in the specimen irradiated at 480°C, while the specimens irradiated at higher temperature than 585°C, amounts of their peak shifts were not simply related to the diffraction angles. Crystal lattice of the specimen irradiated at 480°C was considered to expand isotropically due to the irradiation. On the other hand, that of the specimens irradiated at higher temperature than 585°C would expand anisotropically. Modification of XRD profile by the formation of various kinds of point defects and their clusters in 3C–SiC was simulated using Rietveld method based on the DFT calculation results. Formation of the CC100 dumbbell complex defect expressed well the XRD peak shifts of 3C–SiC irradiated above 585°C.
The properties of ceramics can be improved by controlling the microstructure through texturing ceramics in a strong magnetic field. Fabricating dense boron carbide (B4C) requires high temperature ...sintering, therefore sintering additives are often used in order to densify B4C ceramics at lower temperatures. However, combined effect of texturing and sintering additives on densification of B4C has not been made clear yet. Here we report the effect of alumina (Al2O3) sintering additive on texturing in a strong magnetic field and densification of B4C. Texturing was performed by rotating superconducting magnet at 12 T during slip casting process. Electron backscatter diffraction (EBSD) was used to observed the texturing projection. {0001} plane is clearly oriented in the plane parallel to rotating magnetic field. In addition, Lotgering factor was also calculated as quantitatively evaluation of texturing degree. Results on densification showed that addition of Al2O3 successfully increased density of B4C sintered by spark plasma sintering (SPS) at 1800oC to 97.8%. Formation of aluminum borate (Al5BO9) as secondary phase was detected by X-Ray diffraction (XRD). It is considered that the generation of Al5BO9 assisted finer densification of B4C ceramic. Textured B4C sintered at 1700oC by SPS without alumina addition exhibited the highest orientation of c-axis. Addition of alumina caused decrease in degree of orientation of c-axis.
To develop the
48
Ca enrichment process, a feasibility study on a band chromatography was made using 9 M HCl solution and crown ether resin synthesized in porous silica beads. Prior to the ...chromatographic experiments, distribution coefficients, Kd, of Ca
2+
and Sr
2+
were measured at different concentrations of these ionic species. The frontal boundary of the chromatography was made by a usual manner of the breakthrough mode of calcium feeding, and the rear boundary was made by introducing strontium as a following ion on the basis of the observed Kd values. It was confirmed that the heavy isotope
48
Ca was depleted in the rear boundary region, while
48
Ca was enriched in the front boundary region. The values of separation coefficient ε (= α - 1) in three chromatographic operations at different temperatures were observed as 2 × 10
−3
~ 3 × 10
−3
. The separation coefficients observed in the front boundary regions, where
48
Ca was enriched, agreed with those observed in the rear boundary regions, where
40
Ca was enriched.
We focused on microstructure design and control of SiCf/SiC composite based on our fabrication process and the simple model of thermal conductivity of the SiCf/SiC composite, and the improvement of ...their thermal conductivity was investigated. Submicron-sized α-SiC with coarse α-SiC particles addition was used as the starting materials for SiC matrix layers between SiC fiber cloths because it showed higher thermal conductivity. The thermal conductivity of PCS-composite, EPD-composite and Untreated-composite was 18, 45 and 56W/mK, respectively, and these values were much higher than that of the composites reported in our previous papers. Untreated composite is simply considered as a multilayered composite consisting of the SiC fiber layers with high thermal conductivity and the SiC matrix layers with high thermal conductivity. The experimental thermal conductivity of the Untreated composite well agreed with the theoretical thermal conductivity calculated by series model. Thermal conductivity of EPD-composite was lower than that of Untreated composite. In EPD-composite, the thermal conductivity of SiC fiber layers with the SiC matrix should be lower than that of SiC fibers themselves due to the SiC matrix with slightly lower thermal conductivity in SiC fiber cloths. The SiC matrix formed in SiC fiber cloths in PCS-composite was derived from PCS, and this matrix would show much lower thermal conductivity due to its low crystallinity. PCS-composite is considered as a multilayered composite consisting of the SiC fiber layers with very low thermal conductivity and the SiC matrix layers with high thermal conductivity, and thus the PCS-composite has low thermal conductivity. In this study, higher thermal conductivity of SiCf/SiC composite was successfully achieved by EPD process and using microstructure-controlled SiC matrix and polycrystalline SiC fibers.
The R&D on SiC/SiC composites under the broader approach (BA) activities between Japan and the EU for fusion DEMO developed a fundamental database of mechanical (Task-1) and physical/chemical ...(Task-2) properties, with a primary target of the application of SiC/SiC composites as functional structure to be used in the dual coolant breeding blanket concept. This paper aims to summarize previous 10-years activities of the R&D of Japan and to provide the key deliverables toward the DEMO design. In Task-1, good creep and fatigue durability were first demonstrated. Besides, in-plane and inter-laminar strength anisotropy maps at elevated temperatures were comprehensively identified. In parallel, the irradiation effects of SiC materials were specifically determined as input parameters of the analytical model to provide for the irradiation-induced residual stresses. In Task-2, the apparent dose-dependence of the radiation-induced electrical conductivity and the indicative radiation-induced electrical degradation was identified by various irradiation sources. In addition, good gas confinement was identified. Furthermore, no accelerated corrosion for duration of 3000 h at below 1173 K was first demonstrated. With these achievements, it is suggested that the in-vessel component technology, e.g., material corrosion database development, activated corrosion product evaluation code development, compact module tests for validation of the key functions of the components, technology integration assessment for fusion nuclear tests, etc., should be further developed toward DEMO in near-term.
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