07 Fakultät Konstruktions-, Produktions- und Fahrzeugtechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/8
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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 PA-12-zirconia-alumina-cenospheres 3D printed composites : accelerated ageing and role of the sterilisation process for physicochemical properties(2022) Nakonieczny, Damian S.; Antonowicz, Magdalena; SimhaMartynkova, Gražyna; Kern, Frank; Pazourková, Lenka; Erfurt, Karol; Hüpsch, MichałThe aim of this study was to conduct artificial ageing tests on polymer-ceramic composites prepared from polyamide PA-12 polymer matrix for medical applications and three different variants of ceramic fillers: zirconia, alumina and cenospheres. Before ageing, the samples were subjected to ethyl oxide sterilization. The composite variants were prepared for 3D printing using the fused deposition modeling method. The control group consisted of unsterilized samples. Samples were subjected to artificial ageing in a high-pressure autoclave. Ageing conditions were calculated from the modified Hammerlich Arrhenius kinetic equation. Ageing was carried out in artificial saliva. After ageing the composites were subjected to mechanical (tensile strength, hardness, surface roughness) testing, chemical and structural (MS, FTIR) analysis, electron microscopy observations (SEM/EDS) and absorbability measurements.Item Open Access Immobilization of TiO2 photocatalysts for water treatment in geopolymer based coatings(2023) Dufner, Lukas; Ott, Felix; Otto, Nikolai; Lembcke, Tom; Kern, FrankThis study presents a simple and sustainable coating technology for the deposition of photocatalytic coatings based on titanium dioxide and geopolymers, which requires no thermal post-treatment. Titania powder P25, potassium silicate and a calcium aluminate-based hardener were dispersed in water and applied to aluminum substrates using a paintbrush, a roller and a spray gun. The coatings were air-dried for 12 h. The photocatalytic activities were tested via degradation of an aqueous methylene blue solution in a batch reactor under artificial UV-A light. The roller and the spray gun-based coatings yielded well-adhering coatings with high photocatalytic activity. Brushed coatings were inhomogeneous and unstable. The presented method of producing photocatalytic coatings is very simple to apply and does not require complex technologies or energy-intensive thermal treatments.Item 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 Effect of simulated mastication on structural stability of prosthetic zirconia material after thermocycling aging(2023) Ziębowicz, Anna; Oßwald, Bettina; Kern, Frank; Schwan, WilliRecent trends to improve the aesthetic properties-tooth-like color and translucency-of ceramic dental crowns have led to the development of yttria-stabilized zirconia (Y-TZP) materials with higher stabilizer content. These 5Y-TZP materials contain more cubic or t’ phase, which boosts translucency. The tradeoff as a consequence of a less transformable tetragonal phase is a significant reduction of strength and toughness compared to the standard 3Y-TZP composition. This study aims at determining the durability of such 5Y-TZP crowns under lab conditions simulating the conditions in the oral cavity during mastication and consumption of different nutrients. The test included up to 10,000 thermal cycles from 5 °C to 55 °C “from ice cream to coffee” and a chewing simulation representing 5 years of use applying typical loads. The investigation of the stress-affected zone at the surface indicates only a very moderate phase transformation from tetragonal to monoclinic after different varieties of testing cycles. The surface showed no indication of crack formation after testing. It can, therefore, be assumed that over the simulated period, dental crowns of 5Y-TZP are not prone to fatigue failure.Item Open Access Deposition of 3YSZ-TiC PVD coatings with high-power impulse magnetron sputtering (HiPIMS)(2021) Gaedike, Bastian; Guth, Svenja; Kern, Frank; Killinger, Andreas; Gadow, RainerOptimized coating adhesion and strength are the advantages of high-power impulse magnetron sputtering (HiPIMS) as an innovative physical vapor deposition (PVD) process. When depositing electrically non-conductive oxide ceramics as coatings with HiPIMS without dual magnetron sputtering (DMS) or mid-frequency (MF) sputtering, the growing coating leads to increasing electrical insulation of the anode. As a consequence, short circuits occur, and the process breaks down. This phenomenon is also known as the disappearing anode effect. In this study, a new approach involving adding electrically conductive carbide ceramics was tried to prevent the electrical insulation of the anode and thereby guarantee process stability. Yttria-stabilized zirconia (3YSZ) with 30 vol.% titanium carbide (TiC) targets are used in a non-reactive HiPIMS process. The main focus of this study is a parameter inquisition. Different HiPIMS parameters and their impact on the measured current at the substrate table are analyzed. This study shows the successful use of electrically conductive carbide ceramics in a non-conductive oxide as the target material. In addition, we discuss the observed high table currents with a low inert gas mix, where the process was not expected to be stable.Item Open Access Mechanical properties of 2Y-TZP fabricated from detonation synthesized powder(2020) Kern, Frank; Gommeringer, AndreaYttria stabilized zirconia (Y-TZP) is frequently used in dental and engineering applications due to its high strength and fracture resistance. In this study, 2Y-TZP samples were manufactured from commercially available powder produced by detonation synthesis. Tests of the mechanical properties exhibited an unusual combination of both very high strength and toughness. The materials show a very weak correlation between toughness and grain size. The transformability, measurable by XRD, cannot explain the high toughness. Fractographic analysis revealed a broad transformation affected zone with secondary cracks and shear bands on the tensile side of bending bars which can be made responsible for the high toughness and non-linear stress-strain curves.Item Open Access Effect of calcination temperature on the phase composition, morphology, and thermal properties of ZrO2 and Al2O3 modified with APTES (3-aminopropyltriethoxysilane)(2021) Nakonieczny, Damian S.; Kern, Frank; Dufner, Lukas; Dubiel, Agnieszka; Antonowicz, Magdalena; Matus, KrzysztofThis paper describes the effect of calcination temperature on the phase composition, chemical composition, and morphology of ZrO2 and Al2O3 powders modified with 3-aminopropyltriethoxysilane (APTES). Both ceramic powders were modified by etching in piranha solution, neutralization in ammonia water, reaction with APTES, ultrasonication, and finally calcination at 250, 350, or 450 °C. The obtained modified powders were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, particle size distribution (PSD), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDS), and thermogravimetric analysis (TGA).Item Open Access Spark plasma sintering of electric discharge machinable 1.5Yb-1.5Sm-TZP-WC composites(2022) Walter, Ella; Rapp, Maximilian; Kern, FrankElectrically conductive zirconia tungsten carbide composites are attractive materials for manufacturing precision components by electrical discharge machining due to their high strength, toughness and electrical conductivity. In this study, nanocomposite ceramics with a ytterbia samaria co-stabilized zirconia 1.5Yb-1.5Sm-TZP matrix and 24–32 vol.% tungsten carbide dispersion were manufactured by spark plasma sintering (SPS) at 1400 °C for 15 min at 60 MPa pressure. The materials exhibited high strengths of 1300–1600 MPa, a moderate fracture resistance of 6 MPa√m and an ultrafine microstructure with grain sizes in the 150 nm range. Scanning electron microscopy and RAMAN spectroscopy revealed the in situ formation of carbon during the SPS process and carbon formation scales with tungsten carbide content, and this apparently impedes bending strength.Item Open Access Influence of the feedstock preparation on the properties of highly filled alumina green-body and sintered parts produced by fused deposition of ceramic(2023) Heim, Thomas; Kern, FrankThis paper investigates new approaches for the blending and plastification of ceramic powder with a binder to form fused deposition of ceramic (FDC) feedstock. The fabrication of highly filled ceramic filaments was accomplished using the granulation by agitation technique, followed by twin-screw extruder homogenization and single-screw extruder filament extrusion. The feedstocks are based on alumina (Al2O3) powders, which were prepared with an industrial binder through three different routes: wet granulation, melt granulation and melt granulation with a suspension. After printing cubic samples and tensile test specimens on a commercial fused deposition modelling (FDM) printer, the properties of the resulting green-body and sintered parts were investigated. The green-body mechanical values are compared with results from commercially available filaments. Mixing the binder with the alumina powder and surfactant in a suspension produces the lowest viscosity and the best elongation at break.