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published : vol. 129, no. 4, April 2021
Son Thanh NGUYEN, Tsuyoshi TAKAHASHI, Ayahisa OKAWA, Hisayuki SUEMATSU, Koichi NIIHARA and Tadachika NAKAYAMA
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In the emerging era of aircraft industry, silicon carbide (SiC) is regarded as an appropriate material for gas turbine engine blades. In order to protect this ceramic component against the oxidation and volatilization in hot steam environments, environmental barrier coating should be utilized. The composite of SiC/Yb2Si2O7–Yb2SiO5 with self-healing ability is a candidate for the top layer of this coating. In this study, the crack-healing behavior of SiC/Yb2Si2O7–Yb2SiO5 nanocomposites is investigated by pre-cracking followed by annealing in oxidizing environments. Comparing to previous studies, the healing time and healing temperature can be reduced to 15 min and 800 °C by increasing the volume fraction of SiC to 20 %. In addition, nanocomposites with both self-healing ability and superior strength were created in this research by combining two types of SiC filler (whiskers and nanoparticulates). The self-healing mechanism in these composites is the SiC oxidation and silicate transformation associated with their volume expansion, which is evidenced by X-ray diffraction and scanning electron microscope. According to the results, the best volume ratio between whisker and nanoparticulate is determined as 1/3.
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published : vol. 129, no. 4, April 2021
Yoshihiro KAWAKAMI
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In this paper, the results of evaluating vibration power generation by increasing the area of the BaTiO3 (BT) film formed on a stainless-steel substrate by aerosol deposition (AD) is presented. Fe–Cr–Al-based heat-resistant stainless steel with a thickness of 0.1 mm was used as the substrate. BT films with a thickness of about 10 µm were formed on the substrate of six different shapes with different widths and lengths and BT films were annealed at 1000 °C. Electrodes were formed on the surface of these samples, and the poling process with a voltage of 60 V was applied to prepare samples for evaluation. A weight was attached to the tip of these samples and set up in a cantilever state. A damped vibration under the same stress condition was applied to the BT film by pushing and snapping the tip of samples one time. The generated voltage on the load resistance connected in parallel to the BT film was measured and the generation energy was evaluated. As a result, it was confirmed that the generation energies of the samples with areas of 15 × 3 and 30 × 40 mm2 were 0.17 and 39 µJ, respectively. About 230 times as much energy was obtained by increasing the film area about 20 times. This result indicates that increasing the film area using AD method effectively increases the generation energy.
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published : vol. 129, no. 4, April 2021
Susumu NAKAYAMA
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In this study, phosphors based on Srx(La9.2−xTb0.8)(SiO4)6Oα (x = 2, 3, 4, 5, and 6) ceramic powders were prepared and their photoluminescence (PL) spectra were investigated. The phosphors show green emission at approximately 545 nm when excited by 378 nm UV light. X-ray photoelectron spectroscopy suggests that Tb in the Tb3+ and Tb4+ valence states coexist in phosphors at a Tb3+/Tb4+ atomic ratio of unity. [Sr2−x(La,Tb)x]SiOα was confirmed to exist in addition to Srx(La9.2−xTb0.8)(SiO4)6Oα at x = 4, 5, and 6. The PL intensity increased with increasing Sr(x) content, which is considered to be due increasing Srx(La9.2−xTb0.8)(SiO4)6Oα particle size. The strongest PL intensity was observed at x = 6, where the absorptivity, internal quantum efficiency, and external quantum efficiency were 20, 50, and 10 %, respectively.
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published : vol. 128, no.11, November 2020
Hiroya OKAZAKI, Ryota KOBAYASHI, Rei HASHIMOTO, Emiko FUKUSHI and Junichi TATAMI
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We successfully fabricated dense aluminum nitride (AlN) ceramics containing AlN whiskers by low-temperature pressureless sintering and evaluated their microstructures, thermal conductivities, and mechanical strengths. Furthermore, the anisotropy of thermal conductivities caused by the orientation of AlN whiskers was also evaluated. The thermal conductivities of the samples measured in parallel and perpendicular to the longer direction of AlN whiskers were 98 and 67 W m−1 K−1, respectively. The bending strengths of the samples without and with AlN whiskers were 147 and 235 MPa, respectively. From the observation of the fracture surface of the samples, AlN whiskers in the samples probably withstand the fracture originating from weak grain boundaries.