【公開日：2024.07.25】【最終更新日：2024.06.17】
課題データ / Project Data
課題番号 / Project Issue Number
23TU0105
利用課題名 / Title
低温照射における不純物によるSiC物性変化の研究
利用した実施機関 / Support Institute
東北大学 / Tohoku Univ.
機関外・機関内の利用 / External or Internal Use
内部利用（ARIM事業参画者以外）/Internal Use (by non ARIM members)
技術領域 / Technology Area
【横断技術領域 / Cross-Technology Area】（主 / Main）計測・分析/Advanced Characterization（副 / Sub）-
【重要技術領域 / Important Technology Area】（主 / Main）マテリアルの高度循環のための技術/Advanced materials recycling technologies（副 / Sub）高度なデバイス機能の発現を可能とするマテリアル/Materials allowing high-level device functions to be performed
キーワード / Keywords
SiC繊維, 低温照射, 不純物,電子顕微鏡/ Electronic microscope,セラミックスデバイス/ Ceramic device,資源代替技術/ Resource alternative technology
利用者と利用形態 / User and Support Type
利用者名（課題申請者）/ User Name (Project Applicant)
袁 欣偉
所属名 / Affiliation
東北大学 金属材料研究所
共同利用者氏名 / Names of Collaborators in Other Institutes Than Hub and Spoke Institutes
ARIM実施機関支援担当者 / Names of Collaborators in The Hub and Spoke Institutes
長迫実
利用形態 / Support Type
（主 / Main）技術代行/Technology Substitution（副 / Sub）-
利用した主な設備 / Equipment Used in This Project
報告書データ / Report
概要（目的・用途・実施内容）/ Abstract (Aim, Use Applications and Contents)
This study delved into the mechanism of SiC irradiated at 300 ℃, focusing on the balance between swelling and shrinkage. Both pure CVIed-SiC and fibers with excess C impurities showed irradiation-induced swelling, with fibers exhibiting smaller swelling amounts than the matrix, suggesting a potential mitigating effect of excess C on SiC swelling. Mechanical tests revealed a decline in strength for HNLS and TSA3 fibers post-irradiation. HNLS fiber core and rim experienced reductions of approximately 27.5% and 65.8% after 10 dpa irradiation, escalating to 62.5% and 27.6% after 100 dpa irradiation. TSA3 exhibited similar trends, with 65.8% and 68.2% strength degradation for the core and rim after 10 dpa irradiation, 60.5% for the core, and a 50% increase for the rim after 100 dpa irradiation. Notably, parts of the load-displacement slopes of both fiber rims did not show significant degradation after the irradiation. Additionally, irradiation-induced ion-mixing at TSA3 grain boundaries was observed, potentially contributing to CP volume reduction in HNLS. EELS analysis revealed a π* peak in the SiC grains and the ion-mixing area, indicating the formation of π* bonds due to carbon clusters. In summary, this study provides insights into the behavior of irradiated SiC, emphasizing the roles of excess C, ion mixing, and C diffusion in influencing swelling, mechanical properties, and the formation of π* bonds. These findings contribute to a comprehensive understanding of the mechanism of differences in irradiation-induced swelling in SiC with excess C impurities, offering valuable insights for further investigations in nuclear fusion materials research.
実験 / Experimental
The investigated specimens were SiC fiber-reinforced SiC matrix composites (SiCf/SiC). This is because pure SiC and C-rich SiC could be irradiated and studied simultaneously. The SiCf/SiC were unidirectionally reinforced by HNLS (NGS Advanced Fibers Co., Ltd., Toyama, Japan) and TSA3 (Ube Industries, Ltd., Ube, Japan) fibers. Fibers were primarily coated with a layer of PyC. The HNLS has a smaller free carbon packet (CP) size than the TSA3. It also caused lower C concentration in the HNLS. Furthermore, their CP concentration gradient is different. The concentration at the TSA3 core is essentially higher than its rim, while that in the HNLS does not show a gradient. For the grain size, the size of HNLS, TSA3 fibers, and the chemical vapor infiltrated SiC (CVIed-SiC) matrix is approximately ∼50 nm, 50–500 nm, and 550–650 nm, respectively, which caused a higher grain boundary volume fraction in HNLS than TSA3 and CVIed-SiC. Subsequently, a PyC/SiC multilayered interface (ML) was prepared between the fiber and matrix. The ML interface consisted of five permutations of approximately 20-nm-thick PyC layer and 100-nm-thick SiC layer five times using the CVI method. The SiC matrix was created on the thin PyC layer of ML furthest from the fiber center using the CVI method. Note that the SiC in both fibers and matrix is cubic-SiC. To investigate the behavior changes of SiC fiber after the irradiation, the SiCf/SiC composites were sliced perpendicular to the fiber axis. Then, the sliced surface was polished to a mirror-like finish using diamond abrasive paper. The superior flatness and finish of the polished fiber surface were ensured using an optical microscope.The polished specimens were settled to a heating stage to keep the temperature of specimens under irradiation close to 300 ℃. The specimen temperature was monitored during the entire irradiation test. Additionally, copper meshes with a diameter of 1.5mm mono-hole were covered on the specimen surfaces to protect a part of the specimen surface from irradiation. Hence, the surface morphology change induced by irradiation could be detected from a single specimen. After that, specimens were exposed to a 5.1-MeV Si2+ ion beam to an average damage level of over 10 dpa and 100 dpa at the Dual-beam Irradiation Facility (DuET) at Kyoto University, respectively. The incidence direction of the ion beam was perpendicular to the polished surface. The specimen surface morphology was studied using a confocal laser scanning microscope (CLSM; VK-X1000/1100 KEYENCE, Co., Osaka, Japan). Height changes of over 30 fibers of both types with different conditions were measured. That of the CVIed matrix was measured at the irradiation boundary. Six data groups at different positions were measured from two types of SiCf/SiC. Each group contained 30 pieces of data, which were then averaged. Here, the height of the polished CVIed matrix was settled as the benchmark. Then, the height difference between fiber and matrix after the irradiation was measured to estimate the swelling amount of fibers.To clarify the irradiation-induced microstructural characteristic changes of specimens, thin foils were prepared from the specimens with a damage level of over 100 dpa using the dual-beam FEI Helios NanoLab (FEI, Hillsboro, United States). These foils are approximately 10 μm in width and 6 μm in depth. The foils were observed and analyzed by an ultimate atomic resolution STEM with both TEM and STEM spherical aberration corrector (JEM-ARM200F, JEOL Ltd., Tokyo, Japan) at 200kV. To minimize the carbon contamination effects in observation, the thin foil was cleaned by plasma at 300V for 10 minutes before inserting it into the STEM. Then, it was set aside in the STEM for over 15 hours. Since the ion implantation depth of the Si2+-ion beam used in this work is approximately 2.3-2.5 μm, irradiated and as-received regions can be observed from a single foil. The dpa gradient in the direction of the incident ion beam significantly influences the irradiated specimens. Hence, locations at 630, 900, 1100, 1500, and 3500 nm depth from the irradiated surface, corresponding to 60,80, 100, and over 150 dpa and as-received on the SiC specimens, were typically selected for analysis. The mechanical properties change study investigated fiber strength using the micro-pillar compression test. The micro-pillars were prepared using FB-2100 focused ion beam system (FIB, Hitachi High-Technologies Co., Tokyo, Japan). These pillars were fabricated at the geometrical center of each fiber cross-sectional surface or the position middle of the fiber center and practical rim and named ‘core’ or ‘rim,’ respectively. After the fabrication, the compression test was finished using a nano-indenter G200 (Agilent Technologies, Inc., Santa Clara, the USA) equipped with a Φ10 μm flat diamond punch at room temperature (23 °C). The displacement rate of the micropillar compression test was 3 nm/s. No pores or cracks existed at the pillar surface. Hence, stress concentrations due to surface effects can be minimized during the tests. Over 30 pillars were tested at positions of both core and rim on two fiber types before and after irradiation to the damage levels of both 10 and 100 dpa. The nominal height of the micropillars was 2.4 ± 0.1 µm, 0.9–1.2 µm in diameter, and predominantly Φ1.2 × h2.4 µm. Note that the shape of the pillars is a circular truncated cone in the practical case; the diameter of the fiber bottom was approximately 1.6 µm. Hence, the predominant half-height cross-sectional diameter (1.4 µm) was used to calculate the fiber strength. Owing to the irradiation depth being approximately 2.3-2.5 μm, the fabricated micropillars contained most of the irradiation damage in the SiC.
結果と考察 / Results and Discussion
To investigate the mechanism behind the irradiation-induced modification of SiC in detail, the cross-sectional microstructure of the irradiated SiCf/SiC composites was observed. A band was identified at a depth of about 2.3 μm. This is the interface between the irradiated (top) and unirradiated (bottom) regions. The PyC interface was firmly attached to the rim surface of the fiber before or after irradiation. However, it swelled in the fiber radial direction. This is because a large difference in the PyC width was measured between the unirradiated (about 244 nm for HNLS and about 78 nm for TSA3 specimens) and irradiated (about 357 nm for HNLS and 105 nm for TSA3 specimens) regions. Also, a clear step difference can be observed between PyC and CVIed-SiC on the irradiated surface. The irradiated surface of PyC is about 290 nm lower than that of CVIed-SiC. This strongly suggests that the PyC layer may shrink along the axis perpendicular to the incidence direction. The CP size in HNLS is significantly larger than that in TSA3 fiber, with the CPs in HNLS fiber being on the scale of several nanometers, whereas the CPs in TSA3 fiber are on the scale of tens of nanometers. The CPs were indicated by black arrows. After irradiation with HNLS, the amount and area of CPs appeared to decrease. The amount of CPs after 100 dpa irradiation was smaller and rarer than in the as-received specimen. However, no significant changes were found in TSA3 fiber, even in the 100 dpa irradiated specimen. This result is consistent with reports from literature works. Namely, the area and number of CPs located at grain boundaries in HNLS fiber decreased with increasing irradiation dose. Spectra of CPs, PyC layers, and ion-mixed regions in TSA3 fiber were also displayed. EELS spectra were acquired from single SiC grains or CPs to prevent inelastic scattering of electrons. For SiC, the spectrum of the particles before irradiation showed only a clear σ* peak at 296 eV. When the irradiation dose exceeded 80 dpa, a discernible shoulder or peak at 288 eV appeared in the spectrum of the TSA3 fiber, corresponding to SP2 .-π* peak. According to the literature, the appearance of this π* peak also appeared in irradiated HNLS fibers. In addition, a π* shoulder appeared in the spectrum of CVIed-SiC after irradiation beyond 150 dpa. Importantly, CVIed-SiC exhibited a very high purity level, nearly stoichiometric; therefore, its spectrum appeared only as an initial σ* peak. Furthermore, the spectra of the CP and PyC layers yielded both a σ* peak and a clear π* shoulder or peak in the ion-mixed region.
図・表・数式 / Figures, Tables and Equations
その他・特記事項（参考文献・謝辞等） / Remarks(References and Acknowledgements)
成果発表・成果利用 / Publication and Patents
論文・プロシーディング（DOIのあるもの） / DOI (Publication and Proceedings)
-
Xinwei Yuan, Effects of grain boundary volume fraction on the threshold dose of irradiation-induced SiC amorphization at 30 °C, Journal of the European Ceramic Society, 43, 5125-5135(2023).
DOI: https://doi.org/10.1016/j.jeurceramsoc.2023.04.042
口頭発表、ポスター発表および、その他の論文 / Oral Presentations etc.
特許 / Patents
特許出願件数 / Number of Patent Applications：0件
特許登録件数 / Number of Registered Patents：0件