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Abstracts (International Journals and Books)

[20]   I. J. Davies and T. Ishikawa, “Comparison of fibre/matrix interface strength for a 3D woven SiC/SiC composite”, Composite Interfaces, 7(5-6) pp. 479-485 (2001).

Abstract: The fibre/matrix interface shear strength, t_P, was determined by analysis of fibre pullout length distributions for a 3-D woven SiC/SiC-based composite that had undergone tensile testing between room temperature and 1300 ^oC in vacuum and air. Data was compared with the fibre/matrix interface shear strength, t_S, obtained previously for this system by analysis of in situ fibre strength distributions. t_P was found to follow the same general trend as that of t_S and this was explained in terms of the carbon-rich fibre/matrix interface region. However, t_P was smaller than t_S by a factor of 3-4 for all cases but the reason for this remains unclear although several tentative suggestions have been put forward.

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[19]   I. J. Davies, T. Ogasawara, T. Ishikawa, and N. Suzuki, “Case study of failure in a glass-sealed SiC/SiC-based composite (NUSK-CMC) creep tested at 1100 ^oC in air”, Maters. Letts., 48(3-4) pp. 205-209 (2001).

Abstract: A scanning electron microscopy study of failure was carried out for a glass-sealed SiC/SiC-based specimen that had failed following creep testing for 2.6 x 10⁶ s at 1100 ^oC in air under a creep stress of 140 MPa. It was concluded that the specimen fracture surface exhibited two distinct regions; oxidised and unoxidised. The oxidised region was characterised by a flat fracture surface with the majority of fibres possessing negligible fibre pullout and no evidence of a fracture mirror. On the other hand, fibres in the unoxidised region showed significant pullout and generally had a fracture mirror. These characteristics were explained in terms of the relative degrees of oxidation damage and increase in the fibrer/matrix interface shear strength. The point of initial oxygen ingression into the specimen was traced to one corner of the specimen where oxygen breached the outer glass coating.

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[18]   T. Ogasawara, T. Ishikawa, N. Suzuki, I. J. Davies, M. Suzuki, J. Gotoh, and T. Hirokawa, “Tensile creep behavior of 3-D woven Si-Ti-C-O fiber/SiC-based matrix composite with glass sealant”, J. Maters. Sci., 35(4) pp. 785-793 (2000).

Abstract: The present work investigates the tensile creep behavior (deformation and rupture) at 1100-1300 ^oC in air of a 3-D woven Si-Ti-C-O (Tyranno^TM) fiber/SiC-based matrix composite with and without glass sealant. The composite contained Si-Ti-C-O fibers with an additional surface modification in order to improve interface properties. Although a significant decrease in tensile strength was observed in the unsealed composite beyond 1000 ^oC in air (and attributed to oxidation of the fiber/matrix interface), the composite with glass sealant possessed excellent mechanical properties for short-term (<1 hr.) exposure in air. In this study, tensile creep testing was conducted at 1100–1300 ^oC in air and the effect of glass sealant on medium- and long-term strength was investigated. In addition, chemical stability of the glass sealant was evaluated by X-ray diffraction analysis (XRD) and energy dispersive X-ray spectrometer (EDS). The creep rupture behavior of the composite with glass sealant under long-term exposure is suggested to depend on several factors including decomposition, evaporation, and crystallization of the glass sealant material, in addition to the applied stress.

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[17]   I. J. Davies, T. Minemura, N. Mizutani, M. Aizawa, and K. Itatani, “Sinterability of b-SiAlON powder prepared by carbothermal reduction and simultaneous nitridation of ultrafine powder in the Al₂O₃-SiO₂ system”, J. Maters. Sci., 36(1) pp. 165-172 (2001).

Abstract: Three types of b-SiAlON (Si_6-zAl_zO_zN_8-z) powder were prepared by the carbothermal reduction and simultaneous nitridation of ultrafine powders in the Al₂O₃-SiO₂ system. The ultrafine starting oxide powders, prepared using the vapour-phase reaction technique, were mixed with carbon powder and heated at 1400 ^oC for 1 h under flowing nitrogen to form b-SiAlON and followed by heating at 570 ^oC for 1 h in air to remove residual carbon. The resulting powders contained only b-SiAlON with z values of 1.63, 2.05, and 2.99. The relative density (bulk density/true density) of b-SiAlON compacts pressureless sintered at 1800 ^oC for 1 h under flowing nitrogen increased with z and reached 89.9% at z=2.99. When the b-SiAlON compact with z=2.99 was hot pressed at 1800 ^oC for 1 h under flowing nitrogen, a maximum relative density of 93.6% was achieved. Although this hot pressed compact contained a small amount of 15R-SiAlON in addition to b-SiAlON, it possessed a small average grain size (typically 0.5 mm diameter) and high Vickers hardness (19.2 GPa).

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[16]   I. J. Davies, S. Abe, G. Pezzotti, H. -J. Kleebe, and T. Nishida, “Effect of sintering conditions on mechanical and physical properties of MgO ceramic reinforced with chopped Si-C-O fibre”, Maters. Letts., 43(4) pp. 203-207 (2000).

Abstract: A ceramic matrix composite comprising of 20 mass% chopped Si-C-O fibre in a magnesium oxide (MgO) matrix was prepared using the hot isostatic pressing (HIP) sintering route. A similar composite was prepared using a standard sintering route as a comparison. Although a relative density of 99.9% could be achieved at 1623 K, mechanical properties were generally no better than for monolithic MgO. This behaviour was attributed to the large thermal mismatch between matrix and fibres at room temperature.

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