Curtin University of Technology - Department of Mechanical Engineering including Mechatronics - Staff - Dr Ian Davies - Publications

[45] K. Itatani, T. Tanaka, and I. J. Davies, "Thermal properties of silicon carbide composites fabricated with chopped Tyranno^® Si-Al-C fibres", J. Europ. Ceram. Soc., 26 pp. 703-710 (2006).

Abstract: Thermal diffusivity, a, and thermal conductivity, k, between room temperature and 600 K were investigated for SiC composites containing 0–50 mass% of Tyranno^® Si-Al-C (SA) fibre (mean length: 394 mm) hot-pressed at 1800 ^oC for 30 min under a pressure of 31 MPa. The monolithic SiC specimen possessed k of 32.1 W·m^-1·K^-1 at room temperature; no significant changes were found for the SiC composite containing ≤20 mass% of SA fibre addition. However, further increases in the amount of SA fibre to 50 mass% improved k to a maximum of 56.3 W·m^-1·K^-1. The value of a for the SiC composite containing 40 mass% of SA fibre was 0.185 cm²·s^-1 at room temperature and decreased to 0.120 cm²·s⁻¹ at 600 K. In addition, SiC composites using 40 mass% of SA fibres with a carbon interface of approximately 100 nm were fabricated. The effect of this interface on a and k was marginal.

[44] I. J. Davies, “Effect of variable radius on the initial creep rate of ceramic fibres”, J. Maters. Sci., 40(23) pp. 6187-6193 (2005).

Abstract: The effect of variable fiber radius on the initial creep rate, e*, of monofilament ceramic fibres was investigated using a numerical integration method. The following parameters were studied: (i) radius variation geometry, (ii) creep stress exponent, n, (iii) fractional radius variation, r_v, and (iv) fraction, m, of the characteristic radius variation wavelength, l; the ranges of n (0 < n < 3) and r_v (0 < r_v < 0.5) were chosen to be similar to those for current ceramic fibers based on the silicon carbide (SiC) system. Values of e* were found to be consistently greater compared to those for a constant radius fibre with an equivalent mean radius and increased with both n and r_v. The main result of this work was a recommendation for creep testing of monofilament ceramic fibres to be limited to certain radius variation geometries and gauge lengths.

[43] K. Itatani, T. Tanaka, H. Suemasu, A. Nozue, and I. J. Davies, “Fabrication and fracture behaviour of silicon carbide composites containing chopped Tyranno^® Si-Al-C fibre”, J. Australasian Ceram. Soc., 41(1) pp. 1-7 (2005).

Abstract: Silicon carbide (SiC) composites reinforced with 0~50 mass% (0~47 vol%) of chopped Tyranno^® Si-Al-C (SA) fibres (mean length: 394 mm) and 5 mol% of aluminium carbide (Al₄C₃) sintering aid were fabricated using the uniaxial hot pressing method (1800 ^oC/30 min/31 MPa). The maximum relative density of the specimens was 96.8% for the case of 40 mass% of SA fibre addition. The mean fracture toughness, K_IC, of the composite specimens was always higher compared to that of the monolithic SiC specimen (2.6 MPa·m^1/2) with a maximum K_IC value of 4.0 MPa·m^1/2 being achieved for the composite containing 30 mass% of chopped fibre. Furthermore, the use of 30 mass% of chopped SA fibre containing a carbon interface (interface thickness: ~100 nm) increased the value of K_IC to 5.8 MPa·m^1/2.

[42] I. J. Davies, T. Ogasawara, and T. Ishikawa, “Distribution of fiber pullout length and interface shear strength within a single fiber bundle for an orthogonal 3-D woven Si-Ti-C-O fiber/Si-Ti-C-O matrix composite tested at 1100 ^oC in air”, J. Eur. Ceram. Soc., 25(5) pp. 599-604 (2005).

Abstract: The distributions of fibre strength, pullout length, and fibre/matrix interface shear strength within a single fibre bundle were investigated for a 3-D woven SiC/SiC composite tensile tested at 1100 ^oC in air. Fibre pullout lengths were largest at the fibre bundle center with an embrittled region of approximate width 15 mm at the perimeter. Whereas the fibre strength varied by less than a factor of 2 across the fibre bundle, the fibre/matrix interface shear strength varied by a factor of ~23 with a minimum (100 ± 16 MPa) at the center and a maximum (2.25 ± 0.21 GPa) close to the embrittled region. The minimum fibre/matrix interface shear strength required for the transition between pseudo-ductile and brittle behaviour was thus estimated to be 2.25 ± 0.21 GPa for this composite system.

[41] K. Itatani, M. Abe, T. Umeda, I. J. Davies, and S. Koda, “Morphological and microstructural changes during the heating of spherical calcium orthophosphate agglomerates prepared by spray pyrolysis”, China Particuology, 2(5) pp. 200-206 (2004).

Abstract: The microstructural changes taking place during heating of calcium orthophosphate (Ca₃(PO₄)₂) agglomerates were examined in this study. The starting powder was prepared using the spray-pyrolysis of calcium phosphate (Ca/P ratio=1.50) solution containing 1.8 mol∙dm^-3 Ca(NO₃)₂, 1.2 mol∙dm^-3 (NH₄) 2HPO₄, and concentrated HNO₃ at 600 ^oC, using an air-liquid nozzle. The spray-pyrolyzed powder was found to be comprised of dense spherical agglomerates with a median diameter of 1.3 mm. This powder was further heat-treated at a temperature between 800 ^oC and 1400 ^oC for 10 min. When the spray-pyrolyzed powder was heated up to 900 ^oC, only b-Ca₃(PO₄)₂ was detected and median pore size of the spherical agglomerates increased together with (i) the elimination of residual water and nitrates, (ii) rearrangement of primary particles within the agglomerates, and (iii) coalescence of small pores (below 0.1 mm). Amongst the heat-treated powders, pore sizes within spherical agglomerates were observed to be largest (0.1 to 4 mm) for the powder heat-treated at 900°C for 10 min. With an increase in heat-treatment temperature up to 1100 ^oC, the powder transformed from b- to a-Ca₃(PO₄)₂ whilst the mean agglomerate diameter increased slightly and formed shells with smaller pore diameters as a result of the sintering of primary particles together with the coalescence of agglomerates with diameters below 1 mm into the larger agglomerates. Upon further heating to 1400 ^oC, the hollow spherical agglomerates collapsed as a result of sintering, thus leading to the formation of a three-dimensional porous network.