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2673 |
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Optimization of high velocity suspension flame sprayed (HVSFS) bioactive coatings on Ti substrates by DoE approach |
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Giovanni Bolelli* / Department of Engineering "Enzo Ferrari", University of Modena and Reggio Emilia, Italy Devis Bellucci / University of Modena and Reggio Emilia, Department of Materials and Environmental Engineering, Italy Valeria Cannillo/ University of Modena and Reggio Emilia, Department of Materials and Environmental Engineering, Italy Rainer Gadow/ Universität Stuttgart, Institute for Manufacturing Technologies of Ceramic Components and Composites, Germany Andreas Killinger/ Universität Stuttgart, Institute for Manufacturing Technologies of Ceramic Components and Composites, Germany Luca Lusvarghi/ University of Modena and Reggio Emilia, Department of Materials and Environmental Engineering, Italy Antonella Sola/ University of Modena and Reggio Emilia, Department of Materials and Environmental Engineering, Italy Nico Stiegler/ Universität Stuttgart, Institute for Manufacturing Technologies of Ceramic Components and Composites, Germany |
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The high velocity suspension flame spraying (HVSFS) process enables the direct feeding of fine particles, dispersed in a liquid medium, into a modified gas-fuelled HVOF torch. It has already shown good potential for the deposition of bioactive coatings intended to favour osseointegration of metallic prosthetic implants (e.g. for orthopaedic and dental applications); however, proper control over the deposition parameters is required to avoid the formation of uncontrolled defects. In this study, tricalcium phosphate (TCP) coatings and bioactive glass coatings (46.0mol% SiO2, 2.6mol% P2O5, 27.0mol% CaO, 24.4mol% K2O, designated as Bio-K ) were produced by the HVSFS process. Both coating materials, reduced to micron-sized powder form by attrition milling in isopropanol, were dispersed (20wt.%) in a mixture of 60wt.% water + 40wt.% isopropanol and sprayed onto grit-blasted Ti plates, pre-heated to ~200230°C. Half of these plates had preliminarily been coated with an APS TiO2 layer. Five different process parameter sets were tested, varying the oxygen and fuel (propane) flow rate and the stand-off distance according to a 2-level fractional factorial design-of-experiment (DoE) plan. All of the coatings were deposited by performing one torch cycle only, as this is sufficient in order to deposit 20 40 ¼m thick layers, suitable for osseointegration applications. The deposition efficiency was measured during the spraying process. The coatings were characterised by scanning electron microscopy (SEM), X-ray diffractometry (XRD), micro-Raman spectroscopy, stylus profilometry and tensile adhesion testing (TAT); samples subjected to TAT were further inspected by SEM to observe the fracture morphology. Their reactivity in a simulated body fluid (SBF) solution was evaluated by immersion tests for different times (up to 2 weeks): soaked samples were inspected by XRD, SEM and micro-Raman spectroscopy; moreover, the pH and chemical composition of the SBF solution was monitored in order to characterise the ionic release by the coatings. |