Browsing by Author "Franks, GV"

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    Colloidal processing of zirconium diboride ultra-high temperature ceramics
    (John Wiley and Sons, 2013-05-21) Tallon, C; Chavara, DT; Gillen, AL; Riley, D; Edwards, L; Moricca, SA; Franks, GV
    Colloidal processing of the Ultra-High Temperature Ceramic (UHTC) zirconium diboride (ZrB2) to develop near−net-shaping techniques has been investigated. The use of the colloidal processing technique produces higher particle packing that ultimately enables achieving greater densification at lower temperatures and pressures, even pressureless sintering. ZrB2 suspension formulations have been optimized in terms of rheological behavior. Suspensions were shaped into green bodies (63% relative density) using slip casting. The densification was carried out at 1900°C, 2000°C, and 2100°C, using both hot pressing at 40 MPa and pressureless sintering. The colloidally processed materials were compared with materials prepared by a conventional dry processing route (cold pressed at 50 MPa) and subjected to the same densification procedures. Sintered densities for samples produced by the colloidal route are higher than produced by the dry route (up to 99.5% relative density by hot pressing), even when pressureless sintering is performed (more than 90% relative density). The promising results are considered as a starting point for the fabrication of complex-shaped components that can be densified at lower sintering temperatures without pressure. © 2013, The American Ceramic Society.
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    Mechanical properties of tungsten copper composites: direct measurement by neutron diffraction
    (Australian Institute of Physics, 2014-02-04) Mignone, PJ; Finlayson, TR; Kabra, S; Zhang, SY; Franks, GV; Riley, DP
    The composite W-10 wt%Cu (19.35% by volume, assuming negligible porosity) has been studied using the ENGIN-X beamline at the ISIS pulsed neutron source at the Rutherford Appleton Laboratory. An as-machined, compression sample was initially measured in order to check for the presence of residual stresses in the composite, using a mixed powder sample of the same elemental weight fractions as the “zero stress” comparison. Then a series of mechanical tests were carried out on the composite for applied compressive loads up to 250 MPa at both room temperature and 100ºC and compared with similar tests carried out on pure tungsten and copper samples. Residual stress values of -280 MPa (for the tungsten matrix) and 480 MPa (for the copper particulate phase) were measured for the as-machined sample. This is a surprising result, given that the yield stress for copper is typically less than 100 MPa but is not inconsistent with residual stresses reported in the literature for W-Cu composites. The mechanical properties for the composite have also been determined from the results of these in-situ, mechanical tests and compared with finite element calculations based on microstructural models for the composite material.
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    A novel multi-scale modelling approach for determining the bulk properties of difficult-to-characterise composites
    (Australian Institute of Physics, 2013-02-05) Mignone, PJ; Wang, M; Finlayson, TR; Echlin, MP; Mottura, A; Pollock, TM; Riley, DP; Franks, GV
    A multi-scale modelling approach is presented for determining the bulk properties of copper-infiltrated Tungsten (W-Cu). A three-dimensional (3D) data-set of the W-Cu microstructure was generated using a novel serial-sectioning instrument. The image data were then reconstructed into a 3D Finite Element (FE) mesh. This made it possible to determine the bulk properties of W-Cu by simulating a representative volume of the microstructure.
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    Three-dimensional characterization of the permeability of W–Cu composites using a new “triBeam” technique
    (Elsevier, 2014-02) Echlin, MP; Mottura, A; Wang, M; Mignone, PJ; Riley, DP; Franks, GV; Pollock, TM
    Large three-dimensional microstructural datasets have been gathered for two W–Cu composites of 10 and 15 wt.% Cu using the TriBeam system via in situ femtosecond laser sectioning in a scanning electron microscope. Laser ablation was performed on W–Cu samples along a 90 ° edge, milling parallel with the imaging surface. Secondary electron images for 1000 two-dimensional slices were segmented into binary images representing Cu and W components using EM/MPM (expectation–maximization/maximization of the posterior marginals) image-processing algorithms. A statistically random volume sampling approach has been employed to evaluate the microstructural and property volume element sizes necessary for the assessment of volume fraction, surface-area to volume ratio and permeability, respectively. This approach also characterizes the mean values and variability in microstructure and properties for volume elements ranging from 10 μm to 160 μm on edge. The converged values of the volume fractions of Cu closely match experimental values measured by the Archimedes technique.© 2013 Acta Materialia Inc.
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    A tribute to Eric Raymond (Lou) Vance: Ceramic materials physicist and nuclear wasteform expert – 15th November, 1942‐7th March, 2019
    (John Wiley & Sons, Inc, 2020-05-09) Finlayson, TR; Franks, GV; Gregg, DJ
    This special issue of the Journal of the American Ceramic Society is a tribute to the life and work of Eric Raymond Vance. He was known to most of his friends and colleagues from his youth not as “Eric” or “Raymond” but “Lou” (taken from the name of his father “Albert Louis Vance”). © 1999-2020 John Wiley & Sons, Inc.