Universität Stuttgart
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Item Open Access Alumina and zirconia-reinforced polyamide PA-12 composites for biomedical additive manufacturing(2021) Nakonieczny, Damian S.; Kern, Frank; Dufner, Lukas; Antonowicz, Magdalena; Matus, KrzysztofThis work aimed to prepare a composite with a polyamide (PA) matrix and surface-modified ZrO2 or Al2O3 to be used as ceramic fillers (CFs). Those composites contained 30 wt.% ceramic powder to 70 wt.% polymer. Possible applications for this type of composite include bioengineering applications especially in the fields of dental prosthetics and orthopaedics. The ceramic fillers were subjected to chemical surface modification with Piranha Solution and suspension in 10 M sodium hydroxide and Si3N4 to achieve the highest possible surface development and to introduce additional functional groups. This was to improve the bonding between the CFs and the polymer matrix. Both CFs were examined for particle size distribution (PSD), functional groups (FTIR), chemical composition (XPS), phase composition (XRD), and morphology and chemical composition (SEM/EDS). Filaments were created from the powders prepared in this way and were then used for 3D FDM printing. Samples were subjected to mechanical tests (tensility, hardness) and soaking tests in a high-pressure autoclave in artificial saliva for 14, 21, and 29 days.Item Open Access Mechanical properties and electrical discharge machinability of alumina-10 vol% zirconia-28 vol% titanium nitride composites(2020) Gommeringer, Andrea; Kern, FrankElectrical discharge machinable ceramics provide an alternative machining route independent on the material hardness which enables manufacturing of customized ceramic components. In this study a composite material based on an alumina/zirconia matrix and an electrically conductive titanium nitride dispersion was manufactured by hot pressing and characterized with respect to microstructure, mechanical properties and ED-machinability by die sinking. The composites show a combination of high strength of 700 MPa, hardness of 17-18 GPa and moderate fracture resistance of 4.5-5 MPa√m. With 40 kS/m the electrical conductivity is sufficiently high to ensure ED-machinability.Item Open Access Modelling and experimental validation of the flame temperature profile in atmospheric plasma coating processes on the substrate(2024) Martínez-García, Jose; Martínez-García, Venancio; Killinger, AndreasThis work presents a characterisation model for the temperature distribution at different substrate depths during the atmospheric plasma spray (APS) coating process. The torch heat flow in this model is simulated as forced convection defined by a surface, a temperature profile, and a convection coefficient. The simulation model considers three plasma temperature profiles of the Al2O3 coating on a 5 mm thickness flat aluminium substrate. The simple and low-cost experimental procedure, based on a thermocouple, measures the plasma plume temperature distribution of the APS coating system, and their results are used to obtain the parameter values of each of the three proposed plasma temperature profiles. The experimental method for in situ non-contact temperature measurements inside the substrate is based on an infrared pyrometry technique and validates the simulation results. The Gaussian temperature profile shows excellent accuracy with the measured temperatures. The Gaussian approach could be a powerful tool for predicting residual stress through a coupled one-way thermal-mechanical analysis of the APS process.Item Open Access Adjustment of micro- and macroporosity of ß-TCP scaffolds using solid-stabilized foams as bone replacement(2023) Dufner, Lukas; Oßwald, Bettina; Eberspaecher, Jan; Riedel, Bianca; Kling, Chiara; Kern, Frank; Seidenstuecker, MichaelTo enable rapid osteointegration in bioceramic implants and to give them osteoinductive properties, scaffolds with defined micro- and macroporosity are required. Pores or pore networks promote the integration of cells into the implant, facilitating the supply of nutrients and the removal of metabolic products. In this paper, scaffolds are created from ß-tricalciumphosphate (ß-TCP) and in a novel way, where both the micro- and macroporosity are adjusted simultaneously by the addition of pore-forming polymer particles. The particles used are 10-40 wt%, spherical polymer particles of polymethylmethacrylate (PMMA) (Ø = 5 m) and alternatively polymethylsilsesquioxane (PMSQ) (Ø = 2 m), added in the course of ß-TCP slurry preparation. The arrangement of hydrophobic polymer particles at the interface of air bubbles was incorporated during slurry preparation and foaming of the slurry. The foam structures remain after sintering and lead to the formation of macro-porosity in the scaffolds. Furthermore, decomposition of the polymer particles during thermal debindering results in the formation of an additional network of interconnecting micropores in the stabilizing structures. It is possible to adjust the porosity easily and quickly in a range of 1.2-140 m with a relatively low organic fraction. The structures thus prepared showed no cytotoxicity nor negative effects on the biocompatibility.Item Open Access Cenospheres-reinforced PA-12 composite : preparation, physicochemical properties, and soaking tests(2022) Nakonieczny, Damian S.; Antonowicz, Magdalena; Heim, Thomas; Swinarew, Andrzej S.; Nuckowski, Paweł; Matus, Krzysztof; Lemanowicz, MarcinThe main aim of this research was the preparation of a polymer–ceramic composite with PA-12 as the polymer matrix and modified aluminosilicate cenospheres (CSs) as the ceramic filler. The CSs were subjected to an early purification and cleaning process, which was also taken as a second objective. The CSs were surface modified by a two-step process: (1) etching in Piranha solution and (2) silanization in 3-aminopropyltriethoxysilane. The composite was made for 3D printing by FDM. Raw and modified CSs and a composite with PA-12 were subjected to the following tests: surface development including pores (BET), real density (HP), chemical composition and morphology (SEM/EDS, FTIR), grain analysis (PSD), phase composition (XRD), hardness (HV), and static tensile tests. The composites were subjected to soaking under simulated body fluid (SBF) conditions in artificial saliva for 14, 21, and 29 days. Compared to pure PA-12, PA-12_CS had generally better mechanical properties and was more resistant to SBF at elevated temperatures and soaking times. These results showed this material has potential for use in biomedical applications. These results also showed the necessity of developing a kinetic aging model for aging in different liquids to verify the true value of this material.Item Open Access Additive manufacturing of β-tricalcium phosphate components via Fused Deposition of Ceramics (FDC)(2020) Eßlinger, Steffen; Grebhardt, Axel; Jäger, Jonas; Kern, Frank; Killinger, Andreas; Bonten, Christian; Gadow, RainerDas Paper beschreibt die Compoundierung bioaktiver Keramik (Beta-Tricalciumphosphat) in einer organischen Matrix, die anschließende Extrusion zu Filamenten, die für den FDM-3D-Druck geeignet sind, sowie die Formgebund zu Scaffolds mittels additiver Fertigung. Weiterhin werden fertigungsprozessbegleitende Untersuchungen zur Entbinderung und Sinterung durchgeführt.Item Open Access Inversely 3D-printed β-TCP scaffolds for bone replacement(2019) Seidenstücker, Michael; Lange, Svenja; Esslinger, Steffen; Latorre, Sergio H.; Krastev, Rumen; Gadow, Rainer; Mayr, Hermann O.; Bernstein, AnkeItem Open Access Mechanical properties of an extremely tough 1.5 mol% yttria-stabilized zirconia material(2024) Kern, Frank; Osswald, BettinaYttria-stabilized zirconia (Y-TZP) ceramics with a drastically reduced yttria content have been introduced by different manufacturers, aiming at improving the damage tolerance of ceramic components. In this study, an alumina-doped 1.5Y-TZP was axially pressed, pressureless sintered in air at 1250–1400 °C for 2 h and characterized with respect to mechanical properties, microstructure, and phase composition. The material exhibits a combination of a high strength of 1000 MPa and a high toughness of 8.5-10 MPa√m. The measured fracture toughness is, however, extremely dependent on the measurement protocol. Direct crack length measurements overestimate toughness due to trapping effects. The initially purely tetragonal material has a high transformability of >80%, the transformation behavior is predominantly dilational, and the measured R-curve-related toughness increments are in good agreement with the transformation toughness increments derived from XRD data.Item Open Access Properties of 2 mol% yttria stabilized zirconia-alumina-cerium hexaaluminate composites(2020) Kern, FrankYttria stabilized zirconia (Y-TZP) has become a standard material in a variety of biomedical and mechanical engineering applications due to its high strength and toughness. In order to obtain improved properties in terms of strength, hardness and low temperature degradation resistance second phases, typically alumina are added. In this study an alumina toughened zirconia recipe with 20 vol% alumina in a 2Y-TZP matrix was modified by progressive substitution of alumina by up to 10 vol% cerium hexaaluminate (CA6). Samples were produced by hot pressing. The cerium hexaaluminate was synthesized in situ by reduction of tetravalent ceria and reaction sintering with alumina at 1450 °C. The materials reach attractive 4-point bending strength values of greater than 1170-1390 MPa at a fracture resistance of 6.4-7 MPa√m. Vickers hardness is slightly reduced from 1405 HV10 to 1380 HV10 with increasing CA6 fraction. Results show that substitution of alumina by low amounts CA6 does not lead to drastic changes in the mechanical properties. Hardness is slightly reduced while strength reaches a flat maximum at 4 vol% CA6 substitution. The toughness slightly declines with CA6 addition which is caused by reduced transformability of the tetragonal zirconia phase despite a slight coarsening of the matrix observed upon CA6 addition.Item Open Access Funktionsschichten für industrielle Anwendungen : Energieeinsparung durch neue Glaskeramikkochsysteme, Leichtmetallwerkstoffe im Fahrzeugbau, Schichtverbundstrukturen für Implantate(2003) Killinger, AndreasDas komplexe Anforderungsprofil moderner ingenieur- und werkstofftechnischerAufgabenstellungen bedingt in zunehmendem Maße den Einsatz von Werkstoffkombinationen in Form von Verbundmaterialien und Verbundbauweisen. Ein Einzelwerkstoff kann in seiner Funktion den gestellten Anforderungen im Allgemeinen nicht mehr gerecht werden.