Browsing by Author "Latella, BA"

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    Adhesion of sol-gel derived hydroxyapatite nanocoatings on anodised pure titanium and titanium (Ti6Al4V) alloy substrates
    (Elsevier, 2011-02-25) Roest, R; Latella, BA; Heness, G; Ben-Nissan, B
    The mechanical properties and adhesion behaviour of sol–gel derived hydroxyapatite (HA) nanocoatings on commercially pure (cp) titanium (Ti) and Ti6Al4V alloy have been determined and related to anodising treatment. The surface roughness, wetting and coating characteristics were examined using profilometry, contact angle, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Nano-indentation was used to determine the Young's modulus and hardness of the coatings, while microtensile tests were used to introduce controlled strains in the coatings through the cp Ti and TiAl6V4 alloy substrates, from which the strength, fracture toughness and adhesion behaviour could be ascertained based on multiple cracking and delamination events. The toughness of the HA coatings is found to be slightly lower to that of equivalent bulk pure HA ceramics. The substrate and the anodized layer thickness have the most influence on the interfacial adhesion of HA, with nanocoatings on Ti6Al4V exhibiting superior interfacial bonding in comparison to cp Ti. © 2011, Elsevier Ltd.
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    Characterisation and properties of low temperature ALD TiO2 films
    (Pielaszek Research, 2007-09-18) Triani, G; Evans, PJ; Campbell, JA; Latella, BA; Atanacio, AJ; Attard, DJ; Burford, RP
    The atomic layer deposition of films under conditions outside the ALD window involves additional processes that have to be accounted for in order to achieve good quality films. [1] In the present study, the growth of ALD TiO2 films on silicon and polycarbonate in the temperature range 80 - 120°C has been investigated in detail for two combinations of pulsing times. Furthermore, both substrate materials were exposed to a low-pressure water plasma to investigate the effect of pre-treatment on the deposited films. A suite of characterisation techniques including XRD, SIMS, RBS, AFM, XTEM and spectroscopic ellipsometry was used to probe the physical and chemical properties of the films. In addition, microtensile testing of the films enable the interface energy and toughness to be determined. These measurements showed water plasma treatment prior to deposition increased the interface energy and interface toughness from 11 to 26 Jm-2 and 1.24 to 1.96 MPa.m1/2 respectively. The contact angle of the TiO2 films was measured to assess their wettability. These tests involved subjecting the films to single and cumulative exposures of UV radiation followed by measurement of the contact angle. For an 85 nm film on polycarbonate, the contact angle decreased from 60° for the as-deposited surface to 10° following a 15 minute exposure. A 25 nm film yielded a similar decrease though this was only achieved after a 50 minute exposure. 1.M. Ritala and M. Leskelä, in Handbook of Thin Film Materials, Volume 1: Deposition and Processing of Thin Films, H.S. Halwa (ed.), Chap. 2, Academic, NY, 2002. © 2007 Pielaszek Research
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    Delamination of brittle films on polymeric substrates
    (Engineers Australia, 2005-02-16) Latella, BA; Ignat, M; Triani, G
    Miniaturisation in microelectromechanical systems (MEMS) and continuing advances in fabrication of functional and complex thin film structures approaching the nanoscale has seen adhesion and mechanical stability as key issues. The reliability of thin film-substrate systems when subjected to externally applied stresses is strongly influenced by the intrinsic film properties and the associated interfacial adhesion characteristics. Accordingly, understanding the fracture damage and adhesion performance of thin films to applied stresses is crucial. Using micro-mechanical in-situ tensile experiments it is possible to detect and analyse the critical conditions for cracking and decohesion of the thin film. In this work it will be shown that these types of experiments offer new insights into evaluating mechanical response and interfacial adhesion using a titanium oxide thin film on polycarbonate as the model system. © 2005 Engineers Australia
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    Effect of grain size on Hertzian contact damage in 9 mol% Ce-TZP ceramics
    (Elsevier, 2002-05-15) Latella, BA; Liu, T; Atanacio, AJ
    The Hertzian contact damage in 9 mol% Ce-TZP ceramics with different grain sizes has been investigated. Single-cycle tests were conducted on materials of four grain sizes, 1.1, 1.6, 2.2 and 3 μm. The indentation stress–strain curves for all materials show striking nonlinearity and deviation from the Hertzian elastic response, illustrating a significant quasi-plastic component in the contact damage response. Subsurface damage patterns for these four materials are compared and contrasted using a bonded-interface sectioning technique. The transformation and deformation behaviour, characterised using optical and scanning electron microscopy, of the surface and subsurface regions revealed extensive deformation and compression-driven subsurface damage in the materials. Acoustic emission was used as a complementary technique in order to identify the damage processes during a load–unload cycle. Contact deformation and radial bands extending from the indent impressions due to autocatalytic tetragonal–monoclinic transformation are evident in all except the finest grained (1.1 μm) material. Irrespective of grain size there is no evidence of ring or cone cracking with all material showing hemispherical subsurface damage or yield zones resulting from the stress-induced tetragonal–monoclinic (t–m) transformation with extensive distributed microcracking within these areas for the 1.6, 2.2 and 3 μm grain-size materials. © 2002 Elsevier Science Ltd
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    Enhanced adhesion of atomic layer deposited titania on polycarbonate substrates
    (Elsevier, 2007-01-22) Latella, BA; Triani, G; Zhang, Z; Short, KT; Bartlett, JR; Ignat, M
    Interfacial adhesion of atomic layer deposited titania films on polycarbonate substrates with and without a water-plasma treatment has been studied using in situ observation during microtensile testing. Specific attention is paid to multiple tension-generated transverse cracks in the titania films when subjected to externally applied uniaxial tensile stresses. The strength, fracture toughness and interfacial adhesion of the titania film on polycarbonate were deduced from theoretical models based on experimentally determined parameters. The tensile tests were conducted in a micromechanical tester positioned under an optical microscope allowing in situ viewing of cracking damage. The strain to initiate first cracking and the crack density as a function of strain were obtained. The in situ observations indicated different interfacial behaviour between water-plasma-treated and non-treated samples. It is shown that the water plasma treatment drastically improves the adhesion of the titania film to polycarbonate. Calculations show that the fracture energy required for film debonding in the plasma-treated polycarbonate is 5.9 J/m2 compared to 2.5 J/m2 for the untreated sample. A simple chemical structure model was used to explain the observed differences. © 2007, Elsevier Ltd.
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    Fabrication and properties of recycled cellulose fibre-reinforced epoxy composites
    (Taylor & Francis, 2012-04-02) Low, IM; Somers, J; Kho, HS; Davies, IJ; Latella, BA
    Epoxy matrix composites reinforced with recycled cellulose fibre (RCF) were fabricated and characterized with respect to their flexural and impact properties. Reinforcement of the epoxy by RCF resulted in a significant increase in the strain at failure, fracture toughness and impact toughness but only a moderate increase in flexural strength and flexural modulus. The effect of accelerated exposure to seawater on the flexural and impact properties was also investigated. The salient toughening mechanisms and crack-tip failure processes were identified and discussed in light of observed microstructures, in particular the orientation of RCF sheets to the applied load. © 2020 Informa UK Limited
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    Fatigue damage mechanisms in CeO2 stabilized tetragonal ZrO2
    (Springer Nature, 2002-06-01) Latella, BA; Atanacio, AJ; Liu, T
    Hertzian indentation studies, where an indenting sphere is subjected to single-cycle or repeated loading on a flat ceramic specimen surface, have provided useful insights into contact damage accumulation and fatigue processes at the scale of the microstructure (short-crack region) in numerous ceramic-based systems [1–3]. The nature of the degradation has been shown to be strongly dependent on the material microstructure. In homogeneous, fine-grained ceramic microstructures conical cracks form in the region of limited tension around the contact circle whereas in heterogeneous, coarse-grained microstructures, distributed shear faults develop within a subsurface zone of compression-shear beneath the contact [4]. Cyclic loading of toughened heterogeneous ceramics readily exhibit cumulative damage events at the microscale, leading to strength degradation and material removal [2, 5, 6]. Consequently, the Hertzian test is relevant to assessing fatigue damage mechanisms and evolution on a localized level in ceramics. © 2002 Springer Nature Switzerland AG.
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    In situ neutron diffraction study on the effect of aluminium fluoride on phase transformation of mullite from alumina/clay
    (John Wiley & Sons Inc, 2007-09-16) Tezuka, N; Low, IM; Davies, IJ; Alecu, I; Stead, R; Avdeev, M; Mehrtens, EG; Latella, BA
    The effect of aluminium fluoride (AIF3) on the phase transformation sequence of mullite (3AI2032Si02) from two different types of kaolin (kaolinite and halloysite) (AI2Si20s(OH)4-2H20) within an alumina (A1203) matrix for a temperature range of 20 - 1500 C was investigated using in situ neutron diffraction. Samples containing a mixture of A1F3 (0 - 5 wt%), AI203 and kaolin were heated up to 1500 C and then furnace cooled. During the heating procedure, one hour neutron diffraction scans were conducted at 600, 900, 1100, 1200, 1300 and 1400 C, followed by six consecutive one hour scans at 1500 C and finally a one hour scan at room temperature upon cooling. The diffraction patterns collected between 1100 and 1500 C were analyzed by Rietveld analysis. The observed phase transformations exhibited a typical sequence found inclay/alumina ceramics. Corundum, mullite and cristobalite were observed. A common feature among the specimens containing different amounts of AIF3 and kaolin was that the content of corundum decreased as the amount of mullite increased, whilst the cristobalite content tended to peak near the temperature where the amounts of corundum and mullite were approximately equal. The mullitization temperature was reduced as the AIF3 content increased for both kaolinite and halloysite. The presence of AIF3 appeared to reduce the onset temperature for mullite nucleation, which is at a much lower temperature compared to that of grain growth. However, AIF3 also seemed to lower densification. Likewise mechanical properties of the resulting specimens were determined. © MS&T07
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    An investigation of sol gel coated zirconia thin films on anodised titanium substrate by secondary ion mass spectrometry and scanning electron microscopy
    (Institute of Materials Engineering Australasia, 2007-12-12) Roest, R; Atanacio, AJ; Latella, BA; Wuhrer, R; Ben-Nissan, B
    Zirconia sol-gel-derived ceramic coatings have a variety of uses, due to their ease of production and ability to coat complex shapes. The sol-gel's nanocrystalline grain structure results in improved mechanical properties of the zirconia coating, which further aids their use in a variety of applications from thermal barrier coating to improved tribological properties on titanium substrates. Stabilised zirconia thin films were spin coated on anodised titanium substrates. The titanium was anodised in a dilute H3PO 4ZH2SO4 solution before spin coating with the zirconia sol gel. These films were then studied using secondary ion mass spectrometry (SIMS), to depth profile the elemental species through to the titanium substrate. In conjunction, scanning electron microscopy (SEM) and X-ray microanalysis were used to examine the craters formed by SIMS to gain an understanding of the diffusion gradient existing with the anodised titanium substrate and zirconia thin film. © 2007 Institute of Materials Engineering Australasia.
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    Low temperature atomic layer deposition of titania thin films
    (Elsevier, 2010-04-02) Triani, G; Campbell, JA; Evans, PJ; Davis, J; Latella, BA; Burford, RP
    This paper presents a comprehensive study of atomic layer deposition of TiO2 films on silicon and polycarbonate substrates using TiCl4 and H2O as precursors at temperatures in the range 80–120°C. An in-situ quartz crystal microbalance was used to monitor different processing conditions and the resultant films were characterised ex-situ using a suite of surface analytical tools. In addition, the contact angle and wettability of as-deposited and UV irradiated films were assessed. The latter was found to reduce the contact angle from ≥ 80° to < 10°. Finally, the effect of surface pre-treatment on film toughness and adhesion was investigated and the results show a significant improvement for the pre-treated films. © 2010, Elsevier Ltd.
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    Low temperature bonding of ceramics by sol-gel processing
    (Springer Nature, 2001-12) Barbé , CJ; Cassidy, DJ; Triani, G; Latella, BA; Mitchell, DRG; Finnie, KS; Bartlett, JR; Woolfrey, JL; Collins, GA
    Sol-gel bonds were produced between smooth, clean silicon or polycrystalline alumina substrates by spin-coating solutions containing partially hydrolysed silicon alkoxides onto both substrates. The two coated substrates were assembled and the resulting sandwich was fired at temperatures ranging from 300 to 600°C. The influence of the sol-gel chemistry on the film microstructure and interfacial fracture energy was investigated using a wide range of techniques, including ellipsometry, FTIR, TG-DTA, rheology, TEM and micro-indentation. For silicon wafers, an optimum water-alkoxide molar ratio of 10 and hydrolysis water pH of 2 were found. Such conditions led to relatively dense films (>90%), resulting in bonds with significantly higher fracture energy (3.5 J/m2) than those obtained using classical water bonding (typically 1.5 J/m2). Aging of the coating solution was found to decrease the bond strength. Poly-crystalline alumina substrates were similarly bonded at 600°C; the optimised silica sol-gel chemistry yielded interfaces with fracture energy of 4 J/m2. © 2000 Kluwer Academic Publishers.
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    Mechanical properties and adhesion characteristics of hybrid sol–gel thin films
    (Elsevier, 2004-07-28) Atanacio, AJ; Latella, BA; Barbé, CJ; Swain, MV
    The hardness and Young's modulus of organic–inorganic hybrid coatings, synthesised using sol–gel technology, deposited on silicon and copper were determined using indentations at low forces with a spherical tipped indenter and found to depend strongly on the size of the organic substituent. The indentation creep response of the coating systems was compared based on fast loading rates and for different times at maximum load. The adhesion characteristics of the coatings on copper were examined to ascertain the influence of the organic substituents on the film cracking behaviour and debond tendencies. For this purpose, coated tensile test specimens were strained uniaxially in a universal testing machine while the surface was examined using an optical microscope. The mechanical response was analysed from the multiple cracking patterns observed and the extent of film delamination from the underlying substrate. The results indicate that the interfacial adhesion and film toughness are dramatically affected by the nature of the organic substituent. © 2004 Elsevier B.V
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    Mechanical properties of biodegradable polyhydroxyalkanoates/single wall carbon nanotube nanocomposite films
    (Springer Nature, 2008-04-15) Yun, SI; Gadd, GE; Latella, BA; Lo, V; Russell, RA; Holden, PJ
    The nanocomposite films of poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxyoctanoate) (PHO) with single wall carbon nanotubes (SWCNTs), were prepared. The Optical microscopy showed that the crystalline size substantially decreased for PHB/SWCNTs nanocomposites with a 1 % weight fraction of SWCNTs relative to PHB (PHB/(1%)SWCNTs), indicating the effective nucleation of PHB crystallization by SWCNTs. Mechanical properties of the nanocomposite films were measured by nanoindentation. Both polymer nanocomposite films showed an increase in hardness (H) and Young’s modulus (E), with SWCNTs concentration. The PHB/SWCNTs nanocomposite films are found to be more brittle than neat PHB films. © 2008 Springer-Verlag
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    Mechanical stability of a Ti02 coating deposited on a polycarbonate substrate
    (Routledge, 2005) Ignat, M; Getin, S; Latella, BA; Barbé, CJ; Triani, G
    The demands imposed on mechanical durability of film-substrate systems in many leading technologies (particularly microelectronics, photonics and biomaterials) are becoming more stringent and, thus, associated problems have to be understood and solved. Film-substrate systems are subjected to internal stresses, caused by thermoelastic mismatch, or to external mechanical stresses applied monotonically or cyclically. When reaching critical levels, these stresses may activate damage mechanisms such as cracking and de-adhesion of the film. Identifying these failures and understanding the critical conditions which cause them is essential, prior to any technological application of the system. © 2005 CRC Press
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    Micro- and nano-indentation of a hydroxyapatite-carbon nanotube composite
    (American Scientific Publishers, 2008-08) Kealley, CS; Latella, BA; van Riessen, A; Elcombe, MM; Ben-Nissan, B
    The mechanical properties of pure synthetic hydroxyapatite and hydroxyapatite-carbon nanotube composites were examined. Vickers microhardness and nanoindentation using a Berkovich tipped indenter were used to determine the hardness, fracture toughness and Young's modulus of the pure hydroxyapatite matrix and the composite materials. Microscopy showed that for the composites produced the carbon nanotubes were present as discrete clumps. These clumps induced a detrimental effect on the hardness of the materials, while the fracture toughness values were not affected. This would be undesirable in terms of using the material for biomedical implant applications. It should be noted that the carbon nanotubes used contained free graphite. As the properties of the composite materials studied were not greatly improved over the matrix, it is speculated that if the graphite phase were removed from the reagent, this could in-turn enhance the properties of the material. © 2008, American Scientific Publishers
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    Permanability and mechanical properties of porus mullite-alumina ceramics
    (Institute of Materials Engineering, Australasia Ltd, 2004-11-29) Henkel, L; Latella, BA; Mehrtens, EG
    High porosity materials are used widely in specialty filtration applications. Structural ceramic filters are common in hot gas filtration environments particularly coal combustion and gasification, catalytic recovery and petrochemical processes [1]. The leading ceramic filter candidates are cordierite, mullite, alumina and silicon carbide. The design requirements for these ceramic filters, whose main function is removal of fine particles at temperature, are high porosity, adequate strength, erosion and thermal shock resistance and decent flow (i.e. permeability) characteristics. In this presentation we report the gas permeability and mechanical properties of mullite-alumina ceramics with different levels of porosity. The materials were characterised in terms of microstructure and strength properties at ambient and elevated temperatures. The room temperature gas permeability of the porous structures was investigated over a range of flow velocities to quantify and assess the permeability changes due to processing and microstructural variables. The reliability and issues concerning the estimation of permeability constants will be discussed. The implications of microstructural tailoring for optimising gas permeability and strength are considered.
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    Spray-dried microspheres as a route to clay/polymer nanocomposites
    (Wiley-Blackwell, 2008-05-05) Yun, SI; Attard, DJ; Lo, V; Davis, J; Li, HJ; Latella, BA; Tsvetkov, F; Noorman, H; Moricca, SA; Knott, RB; Hanley, HJM; Morcom, M; Simon, GP; Gadd, GE
    A new strategy for the preparation of well-dispersed clays in a polymer matrix by a spray-drying method is presented. Scanning electron microscopy and transmission electron microscopy measurements show that the spray-drying process produces clay/polymer microspheres in which the clay is trapped in a well-dispersed state throughout the polymer matrix. The microspheres have been successfully extruded into clay/poly(methyl methacrylate) nanocomposite bulk structures without any perturbation of the well-dispersed clay nanostructure in the original microspheres. Transmission electron microscopy and small-angle X-ray scattering show that the clay particles in the extruded materials range from single platelets to simple tactoids composed of a few stacked clay platelets, indicating an excellent degree of dispersion. The results show that sprayed microspheres are very good precursors for further processing such as extrusion or melt blending with other polymers for bulk nanocomposite fabrication. © 2008, Wiley-Blackwell. The definitive version is available at www3.interscience.wiley.com
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    Synthesis and characterisation of titanium vanadium nitride thin films
    (Australian Institute of Physics, 2005-01-31) Taylor, MB; Davies, KE; Gan, BK; McKenzie, DR; Bilek, MMM; McCulloch, DG; Latella, BA; Wilksch, PA; McPherson, M; Van den Brink, RA
    Many transition metal nitrides form very hard and wear resistant thin film coatings. Alloying of transition metal nitrides creates the possibility of producing films with even higher hardness and wear resistance. In this paper we look at alloying TiN and VN utilising a dual source pulsed cathodic arc. TiN and VN both form face centred cubic structures, have similar lattice parameters and are completely miscible over the entire range in bulk form . Of interest is the correlation between intrinsic stress, indentation hardness, microstructure and optical properties of Ti(1-x)VxN films over a range of compositions from x = 0 to x = 1. Previous work by Knotek [using magnetron sputtering showed that thin films of Ti(1-x)VxN made using a metal target of 25 atomic percent V and 75 atomic percent Ti showed the best wear resistance in a pin-on-disc test and the highest Vickers microhardness. In this work we vary the ratio of pulses applied to each cathode in the dual source filtered cathodic arc system to change the composition of the resultant film in a controllable manner. In this way, the properties over a range of composition can be evaluated. In addition to hardness, this work will explore the variations in optical properties of the alloys. Nitrides frequently exhibit attractive colours; for instance, the colour of TiN thin films deposited by plasma immersion ion implantation has been found to vary widely with the conditions of deposition. However, little has been published on the optical properties of the Ti(1-x)VxN alloy.