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Abstracts (International Journals and Books)

[15]   I. J. Davies, T. Shimazaki, M. Aizawa, K. Itatani, H. Suemasu, and A. Nozue, “Physical properties of hot-pressed magnesium silicon nitride compacts with yttrium oxide addition”, J. Soc. Inorg. Mater. Jpn., 6 pp. 276-284 (1999).

Abstract: Magnesium silicon nitride (MgSiN₂) powders with 0, 0.5, 1, 2 and 3 mass% of yttrium oxide (Y₂O₃) addition were hot-pressed between 1450 ^oC and 1650 ^oC for 90 min in a nitrogen atmosphere under a uniaxial load of 31 MPa. Densification of the MgSiN₂ compacts was promoted by the addition of Y₂O₃. The optimum hot-pressing temperature to fabricate dense MgSiN₂ compacts was first examined by fixing the amount of Y₂O₃ addition to be 3 mass%. The MgSiN₂ compact with 3 mass% of Y₂O₃ addition possessed a maximum relative density of 96.5% at 1550-1650 ^oC whilst a maximum hardness of 19.2 GPa was achieved at 1550 ^oC. On the basis of these results, the optimum amount of Y₂O₃ addition required to fabricate a dense MgSiN₂ compact was further investigated by fixing the hot-pressing temperature to be 1550 ^oC. A maximum relative density of 99.9% was achieved for the case of 1 mass% Y₂O₃ addition whilst the fracture toughness (»1 MPa×m^1/2) showed only a slight dependence on the amount of Y₂O₃ addition. The only phases detected by X-ray diffraction were MgSiN₂ and Y₂Si₃O₃N₄ whilst a thermal conductivity of 20-21 W×m^-1×K^-1 was achieved for 0-3 mass% Y₂O₃ addition at 1550 ^oC.

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[14]   I. J. Davies, H. Uchida, M. Aizawa, and K. Itatani, “Physical and mechanical properties of magnesium silicon nitride compacts with yttrium oxide addition”, J. Soc. Inorg. Mater. Jpn., 6 pp. 40-47 (1999).

Abstract: The effect of yttrium oxide (Y₂O₃) addition on the pressureless sintering of magnesium silicon nitride (MgSiN₂) powder has been examined. The sintering conditions examined in this paper were firing temperature (1400 and 1500 ^oC), firing time (1 to 7 h), and the amount of Y₂O₃ (1 to 7 mass%). The phases present, microstructures, flexural strength, and thermal conductivity of the resulting sintered compacts were evaluated using X-ray diffractometry, scanning electron microscopy, flexural testing, and atomic force microscopy. When the MgSiN₂ compact without Y₂O₃ addition was fired at 1500 ^oC for 1 h or more, it partly decomposed to form a- and b-silicon nitride (Si₃N₄). The formation of a- and b-Si₃N₄ upon firing at 1500 ^oC for 3 h could be restricted by the addition of Y₂O₃ as a sintering aid; no a- and b-Si₃N₄ were detected with increasing Y₂O₃ amount up to 3 mass%; further increases in the amount of Y₂O₃ up to 7 mass%, however, produced Y₂Si₃O₃N₄. Maximum relative density (~90%) was attained when a MgSiN₂ compact with 3 mass% of Y₂O₃ addition was fired at 1500 ^oC for 3 h. The flexural strength of MgSiN₂ compacts with 3 to 7 mass% of Y₂O₃ addition fired at 1500 ^oC for 3 h attained 160 to 200 MPa. Thermal conductivities of the sintered MgSiN₂ compacts with 1 to 7 mass% of Y₂O₃ addition were in the approximate range of 15 to 18 Wm^-1K^-1.

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[13]   I. J. Davies, T. Ishikawa, M. Shibuya, and T. Hirokawa, “Fibre strength parameters measured in situ for ceramic matrix composites tested at elevated temperature in vacuum and air”, Composites Sci. Technol., 59(6) pp. 801-811 (1999).

Abstract: In situ fibre fracture characteristics were investigated for Si-Ti-C-O fibres after tensile testing up to 1380 ^oC in vacuum and air. Specimens tested in air at 1100 ^oC and 1200 ^oC generally had flat fracture surfaces with less than 20% of fibres exhibiting fracture mirrors and attributed to oxygen ingress into the fibre bundles. Fibre strength characteristics normalised to a 10^-3 m gauge length indicated fibres tested in air at elevated temperature to have significantly lower strengths and average Weibull parameter, m, compared to the room temperature, 1200 ^oC/vacuum, and 1300 ^oC/vacuum cases and attributed to oxygen damage of the fibre together with oxidation of the fibre/matrix interface. The fibre/matrix interface shear strength, t, was low for the room temperature specimens and increased slightly with temperature when tested in vacuum, possibly due to a change in the thermal mismatch. Values of t for specimens tested at 1100 ^oC and 1200 ^oC in air were an order of magnitude greater compared to room temperature specimens, indicating a significant degree of oxidation damage at the fibre/matrix interface to have occurred.

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[12]   I. J. Davies, T. Ishikawa, M. Shibuya, T. Hirokawa, and J. Gotoh, “Fibre and interfacial properties measured in situ for a 3-D woven SiC/SiC-based composite with glass sealant”, Composites Part A, 30(4) pp. 587-591 (1999).

Abstract: In situ fibre parameters and fibre pullout length were investigated for a 3-D woven SiC/SiC-based composite with a glass sealant oxidation protection system after tensile testing at 1000 ^oC and 1200 ^oC in air. Results were similar to that previously for unsealed specimens tested in vacuum, but significantly different from the case of unsealed specimens tested in air. Overall, the glass sealant provided excellent oxidation protection for the composite for the test conditions employed.

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[11]   I. J. Davies, T. Ishikawa, M. Shibuya, and T. Hirokawa, “Optical microscopy of 3-D woven SiC/SiC-based composites”, Composites Sci. Technol., 59(3) pp. 429-437 (1999).

Abstract: Optical microscopy was used to determine fracture surface and damage characteristics for a SiC/SiC-based composite after tensile testing in air and vacuum up to 1380 ^oC. The composite, which utilised a surface-modified experimental Si-Ti-C-O fibre and densified using the polymer conversion technique, exhibited “tough” fracture surface characteristics when tested at room temperature and elevated temperature in vacuum. However, brittle failure was observed when tested in air at 1100 ^oC and 1200 ^oC and attributed to oxidation of the fibre/matrix interface. Fracture surface and damage characteristics were broadly reflected in previously determined mechanical properties.

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