Continuous SiC fiber-reinforced SiC matrix composites (/SiC) have been considered to be a key material as structural components for aerospace and energy fields. This paper reviews novel fabrication process of continuous /SiC composites with high performance based on interfacial and microstructure control and our approach to improvement of mechanical and thermal properties of /SiC composite based on modeling and analysis. The simple fabrication process of two-dimensional /SiC composite using sheet stacking and hot-pressing based on interfacial and microstructure control was developed, and dense /SiC composite with excellent mechanical and thermal properties was successfully obtained. Furthermore, novel fabrication process of /SiC composite using EPD process was proposed and it was demonstrated that EPD process is expected to be an effective way to control the fiber/matrix interface and the microstructure of /SiC composite with high performance. Interfacial properties of /SiC composite were quantitatively evaluated by push-in test using nanoindenter, and these quantitative results well agreed with the results on their mechanical properties, and these results lead to the material design of the /SiC composite with high mechanical properties and the optimization of its fabrication process. Simple model of thermal conductivity of /SiC composite based on series model of multilayered structure was suggested by our experimental data, and higher thermal conductivity of /SiC composite was successfully achieved by microstructure control.

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A novel lanthanum monazite (LaPO₄) coating was applied to silicon carbide fiber using a simple hydrothermal method to afford a /LaPO₄/SiBCN composite that could be fabricated using resin transfer molding & polymer impregnation and pyrolysis processing technologies. Microstructural analysis showed that silicon carbide fibers were coated uniformly with a ∼700 nm layer of LaPO₄, with X-ray diffraction results confirming that the coating formed in the deposition process were compatible with the fiber and matrix materials produced during the pyrolysis process. The mechanical properties of the resultant /SiBCN, /BN/SiBCN, /LaPO₄/SiBCN composites were compared using bending, tensile strength, fracture toughness and oxidation tests. These tests indicate that the /LaPO₄/SiBCN composite exhibits excellent mechanical properties, with tests at evaluated temperatures (1350°C for 50 h) revealing that the LaPO₄ coating does not undergo oxidation. These results indicate that the /LaPO₄/SiBCN composite has good thermal properties for high temperature applications.

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The three-point bending strength of two-dimensional SiC fiber-reinforced SiC composites (SiC/) fabricated by chemical vapor infiltration (CVI) method and polymer infiltration and pyrolysis (PIP) method was measured at room and high temperatures up to 1600°C and the fracture behavior was investigated. The maximum strength of the CVI-SiC/ composite with carbon-coated Hi-Nicalon cloth was maintained at around 200MPa up to 1600°C. The fracture behavior of the CVI-SiC/ composite showed non-brittle characteristics with fiber pull-out up to 1500°C, whereas it showed brittle fracture at 1600°C. On the other hand, the maximum strength of the PIP-SiC/ composite increased gradually from 40 to 70MPa with increasing test temperature, due to the crystallization of the matrix. The PIP-SiC/ composite with carbon-coated Hi-Nicalon had higher strength and fracture energy than that with non-coated Hi-Nicalon. The PIP-SiC/ composite with carbon-coated Hi-Nicalon showed non-brittle fracture up to 1400°C, whereas that with non-coated Hi-Nicalon showed almost brittle fracture at room and high temperatures, except at 1400°C. The PIP-SiC/ composite significantly differed from the CVI-SiC/ composite in maximum strength. This could be mainly explained by bulk density.

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Ruppert's reagent, (trifluoromethyl)trimethylsilane () is now firmly established as a powerful tool for direct construction of C-CF₃ bond formation and it has been extensively studied for the synthesis of trifluoromethyl-containing compounds, particularly in the fields of medicinal chemistry and material. A large number of nucleophilic trifluoromethylation of carbonyls and imines using have been investigated, however, the addition of to electron-deficient alkenes as represented by the Michael addition reaction remains a challenge. Herein, we report the organocatalyzed allylic trifluoromethylation of Morita-Baylis-Hillman adducts using Ruppert's reagent and it was achieved in high to excellent yields via a successive S_N2'/S_N2' mode for the first time. The reaction was extended to the asymmetric allylic trifluoromethylation by the use of chiral catalysts.

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Continuous silicon carbide fiber-reinforced silicon carbide (

/SiC) composites have been expected as next-generation highly reliable heat resistant materials. It is well-known that the interface between fiber and matrix acts as an important role for toughening and strengthening /SiC composites, and it should be optimally controlled to achieve high performance /SiC composites with excellent fracture tolerance. In this study, polypyrrole (Ppy) as an electric conductive polymer was coated on amorphous SiC fibers to increase their surface electric conductivity so that electrophoretic deposition (EPD) method can be applied to form the interphase on the SiC fibers, and carbon interphase was formed on the SiC fibers by EPD method. In addition, unidirectional /SiC composites were fabricated by polymer impregnation and pyrolysis (PIP) process, and their mechanical properties were evaluated. Thin Ppy coating with the thickness of around 200 nm drastically increased the surface electric conductivity of the amorphous SiC fibers, and the surface of Ppy-coated SiC fibers was wholly and uniformly coated with flaky graphite particles by EPD. The average thickness of the carbon interphase formed on the Ppy-coated SiC fibers by EPD became thicker with an increase in EPD voltage, and it was revealed that the /SiC composites with carbon interphase formed by EPD showed pseudo-ductile fracture behavior and excellent mechanical properties, and the formation of the thick carbon interphase (average thickness; 0.7 ± 0.4 µm, EPD voltage; 5 V) provided the higher bending strength and fracture energy under the experimental condition in present study. These results demonstrated that Ppy coating on the low-conductive SiC fibers was very effective to improve their surface electric conductivity, and uniform and sufficient carbon coating was successfully formed on the SiC fibers by EPD for achieving high performance /SiC composites.

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This paper presents an efficient method for designing 2D structural

/SiC composites based on thermal conductivity. Firstly, the effects of braiding angle, fiber volume fraction and interface layer on the effective thermal conductivity were investigated based on typical 3rd SiC fibers (Hi-Nicalon S and Tyranno SA). Then, a software package based on the simple model approach to assist in the design of 2D structural /SiC composite by chemical vapor infiltration (CVI) has been developed. Meanwhile, the validity of the software was verified by experimental data from open literature.

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Process parameters to control the microstructure of fiber reinforced metal matrix composite (FRMMC) fabricated by the low pressure infiltration process (LPI process) have been investigated. The mixed particles consisted of SiC and pure aluminum particles in various volume fraction were employed to control volume fraction and distribution of fibers in FRMMC. The Al-12 mass%Cu alloy melt was forced to infiltrate into the preform by applying a certain pressure on the melt surface. The optimum ratio of SiC particles in the mixed particles was 50 mass% to fabricate the FRMMC without any casting defects and a segregation of fibers due to preferential flow. The experimentally determined critical pressures required for the infiltration of the alloy melt into the preform were in good agreement with the theoretical ones, where an effective fiber volume fraction was considered. The volume fraction and distribution of reinforcement fibers was able to be controlled accurately by using the mixed particles having the same size with the fiber spacing calculated from the model where the reinforcement fibers distribute homogeneously in the composite. The coefficient of thermal expansion of both the 20 vol% and 30 vol%/Al-Cu composites was hardly changed during thermal cycling, suggesting that the strong bonding at the reinforcements/matrix interface was achieved in FRMMC specimens fabricated by LPI process.

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The low-temperature melt-infiltration method using eutectic Si alloys is a novel process of fabricating SiC fiber-reinforced SiC-based matrix composites (/SiCs) for high-temperature structural applications. /SiCs were fabricated by the melt-infiltration method using a eutectic Si–8.5 at%Hf alloy to evaluate their dry oxidation behavior at 800–1200°C for times ranging from 10–100 h. The oxidation behavior of monolithic HfSi₂ (Monolith) fabricated by spark plasma sintering was also evaluated in dry air. The oxidation behavior of the composite matrix and Monolith obeyed the parabolic law in dry conditions. The steps to form the oxidation layer were expected to produce HfO₂ and Si, followed by SiO₂, and, finally, HfSiO₄. The oxidation rate of the matrix was similar to that of Monolith and 10²–10⁴ times larger than that of Si. The oxidation activation energy employed in oxidation of HfSi₂ was calculated as 258 kJ/mol in dry air.

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SiC繊維強化SiC基（/SiC）複合材料は，高温ガスタービン，宇宙航空分野及び核融合炉などへの適用が期待されている材料である．本講演では，著者らの行ってきた界面・微構造制御に基づく高性能/SiC複合材料の新規作製プロセスの開発及び/SiC複合材料の熱的・機械的特性の解析・モデル化に関して，これまでに得られた成果を発表する．気相あるいは液相を利用した従来法と比較して，単純なプロセスで高密度の/SiC複合材料の作製が可能であると考えられるホットプレス法，シート積層法及び電気化学的手法を組み合わせた新たな/SiC複合材料の作製プロセスを開発し，優れた熱的・機械的特性を有する/SiC複合材料の作製に成功した．さらに，複合材料の繊維/マトリックス界面特性を定量的に評価し，機械的特性との関係を明らかにすることで，複合材料設計指針を導出した．また，本研究で得られた結果に基づいて簡易な熱伝導率モデルを構築・解析し，本研究のプロセスによる2次元/SiC複合材料の高熱伝導率化の指針を導き出し，この材料設計指針に基づき，/SiC複合材料として世界トップレベルの熱伝導率を達成した．

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The present research attempts to analyze and evaluate the mechanical behavior of in /SiC composites with and without soft coatings. The effects of soft fiber coating in the alleviation of indentation or flexural stress in the layered structure are investigated. Boron nitride and/or pyrocarbon as soft coating layer on SiC fiber are selected for the structure. Modeling is performed by changing the type of fiber, the type of soft layer, and layered stacking sequence of the soft layer. Finite element method (FEM) analyses are conducted to evaluate stress distributions under indentation or flexure loadings by displacement loading. Experimentally, the fiber coatings are conducted in the SiC fiber reinforced SiC composites. It was found that BN and/or pyrocarbon coating on the fiber alleviate the stress under the contact or flexure loading, which indicates that the appropriate design by soft layer on the fiber can reduce the maximum stress.

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Three-dimensional SiC fiber-reinforced /SiC composites were fabricated by melt infiltration (MI) method using a Si-Hf alloy. The matrix of /SiC composites consisted of SiC and small amounts of Si and HfSi_2- The molar ratio of Si and HfSi_2 was 82.9% and 17.1%, respectively. Moreover, the endothermic reaction temperature of /SiC composites fabricated with Si-Hf alloy was about 26℃ as higher as that of raw Si-Hf alloy powder. Three-point bending strength and the fracture behavior at room temperature and 1200℃ were investigated. The /SiC composite fabricated with Si-Hf alloy at 1375℃ showed higher bending strength than composite fabricated with conventional Si-MI at 1450℃.

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SiC fiber-reinforced SiC matrix composite (

/SiC_m) is one of the most promising materials for application in hot section components of gas turbine engines. However, due to the insufficient chemical durability of /SiC_m under combustion environment, environmental barrier coating (EBC) is required as a protective coating on /SiC_m surfaces. To determine the suitable materials for EBC, a synthetic process of ceramic powders with excellent compositional controllability should be established, and its calcination and sintering conditions should be determined to allow the preparation of a dense sintered body. Since ytterbium silicates are promising materials as an EBC, in this study, we investigated the synthesis of a precursor polyester containing Yb and Si components through the polymerizable complex (PC) method, which could achieve compositional homogeneity of the obtained oxide powder, as well as the dependence of the densification behavior of Yb–Si–O powder prepared by the calcination of the precursor polyester on calcination temperatures and periods. We successfully obtained a single-phase Yb₂SiO₅ sintered body using the Yb–Si–O powder prepared by the calcination of the precursor polyester synthesized using the PC method. In terms of calcination conditions, calcination at 800–1100 °C for 24 h and at 1100–1400 °C for 1 h were considered appropriate to obtain dense Yb₂SiO₅ sintered body with a relative density of >95 % at the sintering condition with 1700 °C for 5 h.

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In the next-generation of turbine engines, improving the heat resistance and reducing the weight are the essential solutions to increasing the thermal efficiency and reducing fuel consumption and CO₂ emissions. Silicon-based ceramics (e.g.,

/SiC ceramics matrix composites (CMCs) and monolithic Si₃N₄) are the leading candidates for these applications because of their extreme light weight and superior heat resistance compared to the current Ni-based alloys. The main challenge of the Si-based ceramics is oxidation and volatilization of the silica in the high-temperature combustion gas environment with the water vapor and thereby its rapid recession. The most promising approach is protecting the surface of the ceramic matrix composites from the water vapor attack by an external environmental barrier coating (EBC) layer. Since the early 1990s, a lot of efforts have been made to develop suitable EBCs; however, no single material can satisfy all the EBC requirements. Thereby, the current EBC trends are directed to the development of multilayered EBCs, with different functions as a significant solution to prevent CMC recession and to maximize its performance for next engine generation. This paper discusses the history, current status, and future trends of EBC development not only in the world but also in Japan. Furthermore, it introduces future prospects of fine particle spraying in EBC developments.

 

This Paper was Originally Published in Japanese in J. Jpn. Thermal Spray Soc. 57 (2020) 76–87.

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In this paper we present a multi-view single camera and a novel model of scale and illumination invariant feature detection for a service robot in indoor environment. Vision-based simultaneous localization and mapping (VSLAM) has received much attention. It is used for VSLAM that are single cameras, multiple cameras in a stereo setup or Omni-directional cameras. We propose a different approach which multiple mirrors are mounted on a vision system in a single-view-point (SVP) configuration. This vision system is easily to acquire no distortion image sequences without any preprocessing. Robust feature detection method is also described for VSLAM of a service robot in indoor environment. This method can detect scale and illumination invariant corner point in any environment.

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Melt infiltration (MI) method is a practical process to fabricate dense

/SiC composites in a short time. In our previous works, dense /SiC compositeswith excellent mechanical properties were fabricated by melt infiltration (MI) process using Si-16at%Ti alloy. In this study, wet oxidation behavior of Si-TiSi₂ eutectic matrix in the SiC fiber-reinforced composites and monolithic TiSi₂ were evaluated. Oxide layer consisting of TiO₂ and SiO₂ was formed on monolithic TiSi₂ after oxidation. On the other hand, SiO₂ was produced in the eutectic matrix after oxidation, and the matrix showed superior oxidation resistance similar to the Si. These results were explained based on Gibbs energy change of oxidation reaction.

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炭化ケイ素（SiC）やアルミナ（Al₂O₃）をベースとしたセラミックス基繊維強化複合材料は，次世代高信頼性耐熱材料として，航空宇宙分野や環境・エネルギー分野での適用が期待されている．セラミックス基繊維強化複合材料において繊維/マトリックス界面は，優れた機械的特性を発現するために，極めて重要な役割を担っており，直径10 μm程度のセラミックス繊維表面に，数十～数百nmの最適な界面層を形成し，界面制御することが重要である．本研究では，電気泳動堆積（EPD）法を用いたセラミックス繊維表面（ミクロ基材）への数十～数百nmのナノスケール被覆層（界面層）の革新的形成プロセスの構築を目的とし，EPD法による導電性SiC繊維及び低導電性SiC繊維表面へのカーボン被覆層及び六方晶窒化ホウ素被覆層の形成プロセスについて検討した．

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Silicon carbide (SiC) has been considered as one of the promising Accident Tolerant Fuel (ATF) cladding materials. The multi-layer cladding designs consisting of both monolithic SiC(mSiC) and SiC fiber/SiC matrix composites (

/SiC) have been considered as a candidate for light water reactors, meeting the engineering requirements of safety improvement. A twodimensional axisymmetric mechanical model with anisotropic material properties was developed and integrated into the fuel performance code FROBA. The developed mechanical model was solved through the finite difference method and can be employed to analyze both inter-layer interaction and pelletcladding mechanical interaction (PCMI) of anisotropic multilayer claddings. Mechanical performance and failure probability of SiC cladding fuel during normal operation was then simulated. The results suggest that during steady-state operation, SiC cladding show a higher fuel temperature, no PCMI occurs during operation, the hoop stress is in safety level, and the cladding remains integrity.

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It is well-known that dense SiC matrix composites reinforced by SiC fibers with BN coating can be fabricated by subsequent reaction sintering with molten Si. In this experiments, it was confirmed that the mechanical properties of continuous Si-C fibers (Hi-Nicalon) were not affected by the thickness of the BN coating using CVD process and the bending strength of reaction-sintered SiC increased from 500 to 1000MPa with decreasing the size of residual silicon. The effect of SiC matrix strength on the matrix cracking stress in unidirectional fiber-reinforced /SiC composites was investigated by use of these data. As a result, it made clear that the matrix cracking strength in /SiC composites increased with increasing the SiC matrix strength. There are the upper limits of the SiC matrix strength deduced from the SiC fiber strength and the fiber volume fraction to achieve the apparent ductile fracture of the /SiC composites.

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