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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.

The irradiation hardening and microstructures of pure W and W – 3%Re for up to 5.0 dpa by self-ion irradiation were investigated in this work. The ion irradiation was conducted using 18 MeV W6+ at 500 and 800 °C. A focused ion beam followed by electro-polishing was used to make thin foil specimens for transmission electron microscope observations. Dislocation loops were observed in all the irradiated samples. Voids were observed in all of the specimens except the W–3%Re irradiated to 0.2 dpa. The hardness was measured by using nanoindentation. The irradiation hardening was saturated at 1.0 dpa for pure W. In the case of W – 3%Re, the irradiation hardening showed a peak at 1.0 dpa. The correlation between the microstructure and hardening was investigated.

Irradiation creep beyond the transient regime was investigated for various silicon carbide (SiC) materials. The materials examined included polycrystalline or monocrystalline high-purity SiC, nanopowder sintered SiC, highly crystalline and near-stoichiometric SiC fibers (including Hi-Nicalon Type S, Tyranno SA3, isotopically-controlled Sylramic and Sylramic-iBN fibers), and a Tyranno SA3 fiber–reinforced SiC matrix composite fabricated through a nano-infiltration transient eutectic phase process. Neutron irradiation experiments for bend stress relaxation tests were conducted at irradiation temperatures ranging from 430 to 1180 °C up to 30 dpa with initial bend stresses of up to ∼1 GPa for the fibers and ∼300 MPa for the other materials. Initial bend stress in the specimens continued to decrease from 1 to 30 dpa. Analysis revealed that (1) the stress exponent of irradiation creep above 1 dpa is approximately unity, (2) the stress normalized creep rate is ∼1 × 10 −7 [dpa −1 MPa −1 ] at 430–750 °C for the range of 1–30 dpa for most polycrystalline SiC materials, and (3) the effects on irradiation creep of initial microstructures—such as grain boundary, crystal orientation, and secondary phases—increase with increasing irradiation temperature.

In order to examine the impacts of friction stir processing (FSP) on irradiation effects in vacuum-plasma-spray (VPS) coated tungsten (W), nano indentation hardness was evaluated of three kinds of W materials after self-ion-irradiation to 5.0–5.4 dpa at 500 and 800 °C. The VPS-FSP clearly got grains refined and isotropic compared to bulk-W and the as-VPS-W. Nano indentation hardness remains unchanged for the as-VPS-W and VPS-FSP × 2-W irradiated to 5.4 dpa at 500 °C and it decreased from 1 dpa at 800 °C, while typical irradiation induced hardening was observed for the bulk-W irradiated at 500 °C.

Tungsten (W) is the primary candidate material as a plasma facing material in fusion devices, as for its high melting temperature, good thermal conductivity and low sputtering rate, and vacuum plasma spray (VPS) technique is preferred as it is applicable for large area without brittle interlayer, but the thermal conductivity of W layer is very poor, and easy to detach, mainly caused by its porous structure. W Friction stir processing (FSP) was applied on VPS-W to improve these poor properties, and it was suggested that FSP can contribute to significant improvement in both mechanical and thermal properties of the VPS-W coating.

Nuclear-grade silicon carbide (SiC) composite material was examined for mechanical and thermophysical properties following high-dose neutron irradiation in the High Flux Isotope Reactor at a temperature range of 573–1073 K. The material was chemical vapor-infiltrated SiC-matrix composite with a two-dimensional satin weave Hi-Nicalon Type S SiC fiber reinforcement and a multilayered pyrocarbon/SiC interphase. Moderate (1073 K) to very severe (573 K) degradation in mechanical properties was found after irradiation to >70 dpa, whereas no evidence was found for progressive evolution in swelling and thermal conductivity. The swelling was found to recover upon annealing beyond the irradiation temperature, indicating the irradiation temperature, but only to a limited extent. The observed strength degradation is attributed primarily to fiber damage for all irradiation temperatures, particularly a combination of severe fiber degradation and likely interphase damage at relatively low irradiation temperatures.

Composites consisting of a SiC matrix prepared by chemical vapor infiltration that was reinforced by Tyranno™ SA 3rd (TSA3) or Hi-Nicalon™ Type S (HNLS) SiC fibers were irradiated with 5.1 MeV Si ions to 100 dpa at 300 °C. It was confirmed that the irradiated microstructure of TSA3 was stable up to 100 dpa. In contrast, the results of surface profilometry and cross-sectional transmission electron microscopy (TEM) showed that HNLS fibers underwent 0.8% shrinkage along the axis and 0.7% radial shrinkage. High-resolution TEM images of the highly damaged regions in the HNLS material revealed the complete loss of carbon ribbons initially distributed at the SiC grain boundaries. Ion-beam-induced diffusion of carbon into the SiC grains was indicated from the observations of the interdiffusion layer formed at the fiber/pyrocarbon interface. The π ∗ peak of the carbon K-edge spectrum was found in the electron-energy-loss spectrum of the HNLS SiC grains that were irradiated above 60 dpa; this peak was not observed in unirradiated SiC fibers, further demonstrating that carbon sp 2 bonding was only detected in HNLS SiC fibers. According to the changes in the bonding and the volume relaxation related to the carbon defects in SiC, an increase in the population of antisite C Si was likely the key underlying mechanism of the irradiation-induced shrinkage of the HNLS fibers.

The irradiation creep behavior of nano-powder sintered silicon carbide was investigated using the bend stress relaxation method under neutron irradiation up to 1.9 dpa. The creep deformation was observed at all temperatures ranging from 380 to 1180 °C mainly from the irradiation creep but with the increasing contributions from the thermal creep at higher temperatures. The apparent stress exponent of the irradiation creep slightly exceeded unity, and instantaneous creep coefficient at 380–790 °C was estimated to be ∼1 × 10 −5 [MPa −1 dpa −1 ] at ∼0.1 dpa and 1 × 10 −7 to 1 × 10 −6 [MPa −1 dpa −1 ] at ∼1 dpa. The irradiation creep strain appeared greater than that for the high purity SiC. Microstructural observation and data analysis indicated that the grain-boundary sliding associated with the secondary phases contributes to the irradiation creep at 380–790 °C to 0.01–0.11 dpa.

Understanding the cracking process of the composites is essential to establish the design basis for practical applications. This study aims to investigate the damage accumulation process and its anisotropy for nano-infiltration transient eutectic sintered (NITE) SiC/SiC composites by various characterization techniques such as the acoustic emission (AE), digital image correlation (DIC) and electrical resistivity (ER) measurements. Cracking behavior below the proportional limit stress (PLS) was specifically addressed. Similar to the other generic SiC/SiC composites, the 1st AE event was identified below the PLS for NITE SiC/SiC composites with a dependency of fabric orientation. The DIC results support that the primary failure mode depending on fiber orientation affected more than the other minor modes did. Detailed AE waveform analysis by wavelet shows a potential to classify the failure behavior depending on architecture. Cracking below the PLS is a potential concern in component deign but the preliminary ER measurements imply that the impact of cracking below the PLS on composite function was limited.

To identify a comprehensive stress envelope, i.e., strength anisotropy map, of silicon carbide fiber-reinforced silicon carbide matrix composite (SiC/SiC composite) for practical component design, tensile and compressive tests were conducted using the small specimen test technique specifically tailored for high-temperature use. In-plane shear properties were, however, estimated using the off-axial tensile method and assuming that the mixed mode failure criterion, i.e., Tsai–Wu criterion, is valid for the composites. The preliminary test results indicate no significant degradation to either proportional limit stress (PLS) or fracture strength by tensile loading at temperatures below 1000 °C. A similarly good tolerance of compressive properties was identified at elevated temperatures, except for a slight degradation in PLS. With the high-temperature test data of tensile, compressive and in-plane shear properties, the stress envelopes at elevated temperatures were finally obtained. A slight reduction in the design limit was obvious at elevated temperatures when the compressive mode is dominant, whereas a negligibly small impact on the design is expected by considering the tensile loading case.

Silicon carbide (SiC) continuous fiber-reinforced, SiC-matrix composites (SiC/SiC composites) are industrially available materials that are promising for applications in nuclear environments. The SiC/SiC composites consisting of near-stoichiometric SiC fibers, stoichiometric and fully crystalline SiC matrices, and the pyrocarbon (PyC) or multilayered PyC/SiC interphase between the fiber and the matrix are considered particularly resistant to very high radiation environments. This paper provides a summary compilation of the properties of these composites, specifically those with the chemically vapor-infiltrated (CVI) SiC matrices, including newly obtained results. The properties discussed are both in unirradiated condition and after neutron irradiation to intermediate fluence levels (most data are for

Unidirectional silicon carbide (SiC)-fiber-reinforced SiC matrix (SiC/SiC) composites fabricated by a nano-infiltration and transient eutectic-phase (NITE) process were irradiated with neutrons at 600 °C to 0.52 dpa, at 830 °C to 5.9 dpa, and at 1270 °C to 5.8 dpa. The in-plane and trans-thickness tensile and the inter-laminar shear properties were evaluated at ambient temperature. The mechanical characteristics, including the quasi-ductile behavior, the proportional limit stress, and the ultimate tensile strength, were retained subsequent to irradiation. Analysis of the stress–strain hysteresis loop indicated the increased fiber/matrix interface friction and the decreased residual stresses. The inter-laminar shear strength exhibited a significant decrease following irradiation.

The through thickness (interlaminar) shear strength and trans-thickness tensile strength of three different nuclear-grade SiC/SiC composites were evaluated at room temperature by the double-notched shear and diametral compression tests, respectively. With increasing densification of the interlaminar matrix region, a transition in failure locations from interlayer to intrafiber bundle was observed, along with significant increases in the value of the interlaminar shear strength. Under trans-thickness tensile loading, cracks were found to propagate easily in the unidirectional composite. The 2D woven composite had a higher trans-thickness tensile strength (38 MPa) because the failure mode involved debonding, fiber pull-out and fiber failure.

A silicon carbide fiber reinforced silicon carbide matrix (SiC/SiC) composite is a promising candidate for a fusion DEMO blanket. To develop design codes in practical use of them, strength anisotropy is an important issue to be clarified and therefore this study aimed to evaluate the failure behavior of the SiC/SiC composites to provide a strength map. For this purpose, detailed tensile, compressive and in-plane shear failure behaviors were evaluated by the acoustic emission (AE) technique for a plain–weave (P/W) chemically vapor-infiltration (CVI) SiC/SiC composite. The AE results distinguished damage accumulation processes by separately discussing localized variations of power within a time series by wavelet analysis. Of particular emphasis is that matrix cracking occurred prior to the proportional limit stress (PLS) by both tensile and compressive tests. This is because the rough-surface of SiC fibers resulted in the strong frictional stress at the fiber/matrix (F/M) interface, showing linearity in the stress–strain curve beyond the actual matrix cracking stress (i.e., possibly no sliding of the fibers at the F/M interface). In this paper, an updated failure envelope was provided by referring the true matrix cracking stresses as more realistic and reasonable failure criteria.

This paper reviews recent achievements as to "nuclear-grade" SiC composites in particular for materials-system integration. SiC composite component development are reviewed including VHTR control rod scale model and compact intermediate heat exchanger scale mode by current joining and assembly techniques. Joining methods for SiC to metal and results of characterization of joint shear strength by the torsion tests using small specimens were also reviewed. The recent results of neutron irradiation experiments were also reviewed including detailed analysis of mechanical properties, irradiation creep and preliminary results on tritium behavior in SiC.

A SiC/SiC composite is a candidate material for a demonstration fusion power reactor (DEMO). Identifying the inherent anisotropy of composites is required to predict axial/off-axial mechanical properties for various failure modes. This study evaluated crack propagation behavior by the various modes to provide strength anisotropy maps and we discussed a method to analytically predict this trend. The strength anisotropy maps identified for various fabric orientations clearly indicate that the composites failed in the mixed modes. Specifically, due to the axial anisotropy, five individual mode strengths such as tensile/compressive strengths in the axial/transverse directions, respectively, as well as the in-plane shear strength, are identified to become essential input parameters. With the analytical criterion based on the Tsai–Wu model, the strength anisotropy could satisfactorily be described.

High purity chemically vapor-deposited (CVD) silicon carbide (SiC) and near-stoichiometric SiC fiber, chemically vapor-infiltrated (CVI) SiC matrix composite were evaluated following neutron irradiation to ∼28 dpa at 300 and 650 °C and to ∼41 dpa at 800 °C, respectively. The irradiated swelling, thermal conductivity, and elastic modulus indicated no additional changes in these properties at high fluences after saturation at low fluences. With a statistically meaningful sample population, no change in flexural strength of CVD SiC was observed after 300 °C irradiation. A slight decrease in strength was observed after 650 °C irradiation but was attributed to an experimental artifact; specifically, a reaction between samples and the capsule components. The Hi-Nicalon™ Type-S, CVI SiC composite retained the pre-irradiation strength and the non-linear fracture mode. The electrical resistivity measurement revealed a relatively minor effect of irradiation. Overall, irradiation-insensitivity of the high purity SiC ceramics and composite to neutron irradiation to doses 30–40 dpa at temperatures 300–800 °C was demonstrated.

The dimensional stability, elastic modulus, and flexural strength of a high quality, three-dimensional balanced weave carbon fiber composite has been evaluated over a range of neutron fluence to ∼32 dpa at ∼800 °C. Results indicate that while the composite exhibits continuous strengthening over this dose range, this occurs with measurable loss of mass, increased volume, and for the highest dose studied, a large reduction in elastic modulus. While the balanced-weave composite was orthogonally isotropic, a significant anisotropic dimensional change occurred under irradiation. Dimensional change was dominated by fiber dimensional change and the overall shrinkage or swelling in a direction was determined by the extent to which intrinsic fiber shrinkage was capable of restraining swelling of matrix and fiber bundles.

Six different composite materials of various near-stoichiometric silicon carbide (SiC) fiber reinforcements and pyrolytic carbon or SiC/pyrolytic carbon multilayer interphases were neutron-irradiated to ∼6 × 10 25 n/m 2 ( E > 0.1 MeV) at nominal temperatures of 800 °C and 1300 °C, and tested for tensile properties at room temperature. Only insignificant or very minor modifications to the tensile strength were realized. However, statistical analysis on relatively large specimen populations revealed minor but statistically significant strength degradation for some composites. From 50 to 150 nm appeared to be within the optimum PyC interphase thickness range for the SiC fibers used in terms of tensile properties. The misfit stresses present in the unirradiated samples were significantly reduced after irradiation. The change in misfit stress may be attributed to the irradiation-induced modification of coefficient of thermal expansion or potential differential swelling between the fibers and the matrix. True matrix cracking stress estimated from the proportional limit stress and misfit stress did not appear to degrade by neutron irradiation.

Irradiation effects in a SiC/SiC composite reinforced by Tyranno-SA fibers and produced by an innovative processing method, nano-powder infiltration and transient eutectic phase (NITE) processing, were investigated. Dual-beam ion irradiation methods and energy-filtered transmission electron microscopy were used in the investigation. The NITE SiC matrix had dense, isotropic grains several hundreds nm in diameter. A small amount of secondary phases from residual additives were found within the SiC fiber bundles. Dual-ion irradiations achieved a dose of 60 dpa at 1200 °C. TEM investigation showed no significant modification by irradiation in either the Tyranno-SA fibers or the NITE SiC matrix, except for a small amount of micro-cavity formation. The synergistic effects of heavy irradiation and helium atoms in NITE SiC/SiC composites at elevated temperature are discussed.

The effect of neutron irradiation on tensile properties in advanced 2D-SiC/SiC composites was evaluated. The composites used were composed of a SiC matrix obtained by the forced-flow chemical vapor infiltration (FCVI) process and either Tyranno™-SA Grade-3 or Hi-Nicalon™ Type-S fibers with single-layered PyC coating as the interphase. Neutron irradiation fluence and temperature were 3.1 × 10 25 n/m 2 ( E > 0.1 MeV) and 1.2 × 10 26 n/m 2 at 740–750 °C. Tensile properties were evaluated by cyclic tensile test, and hysteresis loop analysis was applied in order to evaluate interfacial properties. Both composites exhibited excellent irradiation resistance in ultimate and proportional limit tensile stresses. From the hysteresis loop analysis, the level of interfacial sliding stress decreased significantly after irradiation to 1.5 × 10 26 n/m 2 at 750 °C.

Advanced SiC/SiC composites composed of highly-crystalline and near-stoichiometric SiC fibers, SiC matrix by CVI method, and PyC interphase were irradiated up to 1:0 � 10 25 n/m 2 (E > 0:1 MeV, � 1 dpa) at 1273 K. Unload/reload cyclic tensile test and hysteresis loop analysis were carried out in order to identify neutron irradiation effects on interfacial properties of advanced SiC/SiC. The composites exhibited good irradiation resistance in ultimate tensile strength (� 10% increase), but there were slight reduction of elastic modulus and proportional limit stress (PLS) (� 10%). Wider hysteresis loops and lower gradient of the curves beyond PLS from the strain–stress curves, and longer pullouts of fiber from the SEM observation were observed, which imply weaker F/M interactions after neutron irradiation. From the hysteresis loop analysis, degradation of interfacial sliding stress and negative increment of misfit stress after neutron irradiation were obtained.

The microstructural evolution of SiC/SiC composites after Si{sup 2+} with/without He{sup +} ion irradiation was studied using transmission electron microscopy. The temperature, displacement damage level, and He/dpa ratio were 1273/1673K, 10/100dpa and 0/60appmHe/dpa, respectively. In 10dpa single-ion irradiation, no cavity was detected at 1273 and 1673K. But cavities were observed locally at 1673K, 100dpa. In dual-ion irradiation, cavities were observed at 1673K, 100dpa. Helium bubbles (d

Silicon carbide (SiC) matrix composites reinforced by SiC fibers is a candidate structural material of fusion gas-cooled blanket system. From the viewpoint of material designs, it is important to investigate the swelling by irradiation, which results from the accumulation of displacement damages. In the fusion environment, (n,) nuclear reactions are considered to produce helium gas in SiC. For the microstructural evolution, a dual-ion irradiation method is able to simulate the effects of helium. In the present research, 1.7 MeV tandem and 1 MeV single-end accelerators were used for Si self-ion irradiation and helium implantation, respectively. The average helium over displacement per atom (dpa) ratio in SiC was adjusted to 60 appm/dpa. The irradiation temperature ranged from room temperature to 1400C. The irradiation-induced swelling was measured by the step height method. Helium that was implanted simultaneously with displacement damages in dual-ion irradiated SiC increased the swelling that was larger than that by single-ion irradiated SiC below 800C. Since this increase was not observed above 1000C, the interaction of helium and displacement damages was considered to change above 800C. In this paper, the microstructural behavior and dimensional stability of SiC materials under the fusion relevant environment are discussed.

Structure of a complex superstructure self-organized by thermotropic mesogen, 1,2-bis(4'- n-alkoxybenzoyl)hydrazine [BABH(n), where n is the number of carbon atoms in an alkoxy chain] was studied while paying special attention to the structure at the molecular level. Maximum entropy (MEM) analysis revealed that the molecular cores form two kinds of aggregates: Jungle gym with 3-fold junctions roughly on P minimal surface and spherical shells.

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The authors have proposed a new divertor concept using SiC composite with directional high thermal conductivity enhanced with fiber as substrate of the divertor structure in fusion reactor. In this study, unidirectional SiC composite with pitch-based carbon fibers (UD-Cf/SiC) was fabricated as the model material. The thermal conductivity (or thermal diffusivity) in directions parallel (0°), inclined (45°), and transverse (90°) to the Cf orientation was measured by the laser flash method. The results were compared with monolithic SiC (mono-SiC) in order to evaluate the enhancement of thermal conductivity by an introduction of Cf. Although the thermal conductivity of the UD-Cf/SiC in directions of 45° and 90° was relatively lower than that of the mono-SiC, that of the UD-Cf/SiC in direction of 0° was ten times as large as that of the mono-SiC.

This study was performed to elucidate the status of the implementation of health promotion programs (HPPs) and future tasks in occupational settings in Japan. A survey was conducted using a multiple type questionnaire mailed to 395 companies throughout Japan in 1993. The questionnaire was mailed back, after having been answered anonymously, with a response rate of 59%. Companies with more than 300 employees accounted for 76% of the sample. Approximately 70% of the companies implemented HPPs of which health guidance and fitness programs were the two most frequently adopted programs. Nutrition education and mental health programs seemed to be emphasized as future possibilities. Smoking cessation programs were not as common as segregation policies, such as zoning of smoking areas. Currently, 45% of the companies used only in-house health personnel for HPPs, but the prospective percentage in the future was 24%. Most of the companies shared the cost of HPPs with a Health Insurance Society. Lack of health personnel and budgetary restrictions on HPPs constituted the major barriers to the implementation of HPPs. Small-scale enterprises were noted to be particularly influenced by these barriers.

The combination of focused ion beam (FIB) micro-processing and the lift-out technique using the micro pick-up system was applied to the preparation of TEM specimens of irradiated SiC/SiC composites. The deformation caused by microstructural evolution was observed in the pyrolitic carbon interphase, and several helium bubbles and cavities were detected in the CVI matrix.

Unidirectional SiC/SiC composites fabricated with highly-crystalline and stoichiometric fibers and matrix, but with three different interfacial types (single-layer pyrolytic carbon (PyC), multilayered SiC/PyC, and pseudo porous SiC interfaces) were irradiated up to 1.0 × 1025 n/m2 (E > 0.1 MeV) at 1073 and 1273 K. Tensile, inter-laminar shear, and flexural properties were evaluated to compare the role of different interfaces on neutron irradiation behavior. There was nearly no significant degradation in tensile and flexural strength after high-temperature neutron irradiation, except for porous SiC interphase composite. Moreover, no meaningful reduction of tensile modulus was identified regardless of interphase types, although 20–40% degradation in flexural moduli occurred due to a reduction in inter-laminar shear modulus. In contrast, matrix cracking stress was significantly dependent on interfacial properties. Multilayer interphase composites exhibited the best irradiation stability. Irradiation instability of thick PyC and porous SiC interphase resulted in 20% and 40% degradations of matrix cracking stress, respectively.

The effects of irradiation-induced swelling of constituents on tensile properties of advanced SiC/SiC composites were examined. After the swelling of the fiber and matrix ion-irradiated up to 1dpa at 1000°C was measured, the modified four phase model was applied in order to estimate the residual stress in each constituent. The swelling mismatch was obtained between Hi-Nicalon™ Type-S fiber (0.27%) and ICVI-matrix (0.48%), which increases the residual stresses according to the model. These increases of the residual stresses were roughly consistent with the tensile stress-strain behavior of the same SiC/SiC composites after neutron irradiation up to 1dpa at 1000°C and the behavior of the misfit stress obtained by the hysteresis loop analysis methodology, which is related with the residual stress. These results suggest that irradiation-induced residual stress caused by the differential swelling of each constituent may affect the tensile properties in this irradiation condition.

A new process for fabricating of SiC/SiC composite, the Nano-powder Infiltration and Transient (NITE) method produces dense, high strength SiC materials with potential applications in fission or fusion reactors. Irradiation effects reduce the performance of materials due to accumulation of point defects. In this research, SiC/SiC composite fabricated by the NITE process was irradiated with Si-ions. Post-irradiation investigation was performed by TEM. The ion-irradiation experiments were performed using a 1.7 MeV tandem accelerator at DuET facility in Institute of Advanced Energy, Kyoto University. Irradiation temperature and dose were up to 1200 °C and 10 dpa. The SiC matrix was well crystallized and contained a small amount of secondary phases. The EDX analysis specified that the secondary phase was aluminum-rich. The SiC grains and the secondly phase exhibited enough microstructural and dimensional stability after the Si-ion.

As a powerful tool to analyse microstructural evolution under irradiation and the interaction of moving dislocations with radiation-induced defects, a focused ion beam (FIB) method was applied to ion-irradiated SiC followed by the nano-indentation test. An FIB method has excellent capability to prepare thin foils from the area of interest with a high accuracy of location and wide flexibility in the sampling direction. These advantages are demonstrated in the application to Si ion-irradiated SiC by transmission electron microscope observation.

Intra- and post-operative oxygenation of graft liver and subsequent oxidation of the intramitochondrial redox state of pyridine nucleotide were studied in liver transplantation from living related donors with the arterial ketone body ratio (AKBR), the ratio of oxidized flavoprotein to reduced pyridine nucleotide (FP/PN ratio), and oxygen saturation of hemoglobin in liver tissue (hepatic SO2). The subjects involved in this study consisted of 20 pediatric patients. Hepatic SO2 was measured by near-infrared tissue spectroscopy. FP/PN ratio was measured by two-dimensional fluorometric scanning. Tissue oxygenation was normalized at the end of the operation. By contrast, AKBR remained at a low value at the end of the operation. At 24 and 48 h after the operation, the AKBR values increased to near the control value, indicating that it took 24 h for the intramitochondrial redox state to be normalized. The FP/PN ratio also remained at a low value at the end of the operation as compared with the control value. In conclusion, the observed delay in oxidation of the intramitochondrial redox state as compared with tissue oxygenation indicated the transition of the redox state associated with the changes in the metabolic state, and suggested the important role of microcirculation in the normalization of the redox state.

Silicon carbide composites (SiC/SiC) are attractive candidate materials for structural and functional components in fusion energy systems. The effect of neutron irradiation on damage tolerance of the nuclear grade SiC/SiC composites (plain woven Hi-Nicalon™ Type-S reinforced CVI matrix composites multilayer interphase and unidirectional Tyranno™-SA3 reinforced NITE matrix with carbon mono-layer interphase) was evaluated by means of miniaturized single-edged notched beam test. No significant changes in crack extension behavior and in the load-loadpoint displacement characteristics such as the peak load and hysteresis loop width were observed after irradiation to 5.9 × 1025 n/m2 (E > 0.1 MeV) at 800°C and to 5.8 × 1025 n/m2 at 1300°C. By applying a global energy balance analysis based on non-linear fracture mechanics, the energy release rate for these composite materials was found to be unchanged by irradiation with a value of 3±2 kJ/m2. This has led to the conclusion that, for these fairly aggressive irradiation conditions, the effect of neutron irradiation on the fracture resistance of these composites appears insignificant.

Polymer impregnation and pyrolysis (PIP) is one of the most attractive fabrication processes for silicon carbide (SiC) composites due to the shape flexibility, mass production and relatively low cost. In particular, advanced PIP SiC/SiC composite with high-crystallinity and nearstoichiometric composition is expected to have superior thermo-mechanical properties including good oxidation resistance, due to the reduction of impurities and well-organized crystal structure. Additionally, by applying a thin carbon interphase by chemical vapor infiltration (CVI), control of the crack propagation and oxidation resistance are also achieved. In this study, a CVI + PIP hybrid process based on the recently developed stoichiometric PIP process was performed. Specifically, matrix crystallization was enhanced by heat treatment in Ar, and its effect on microstructures and mechanical properties were evaluated. Stoichiometric SiC/SiC composites exhibit superior flexural strength up to 1573 K in Ar and 1273 K in air. This is because the stoichiometric composition in PIP-SiC matrix reduces inner oxidation by impurities. Also, the thin pyrolytic carbon interphase tailored by CVI process effectively controls crack propagation at fiber and matrix interphase. In a similar manner, the microstructure of the stoichiometric PIP-SiC matrix, constructed by the mixture of amorphous SiC and highly crystalline SiC, was stable against the high-temperature heat exposure up to 1773 K in Ar. In particular, stoichiometric SiC/SiC composites heated at 1773 K in Ar provides superior stability of mechanical properties up to 1573 K even in air atmosphere, although extensive crystallization, in the case of heat treatment at 1973 K in Ar, caused brittle composite fracture.