Eisenbasierte, Freitragende Filme Hergestellt durch Magnetron Sputtern für Biodegradierbare Anwendungen

In the work structured pure iron, iron-gold and binary FeMn alloys with different Mn contents are successfully fabricated by magnetron sputtering and characterized. For the characterization of the microstructure X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) was applied. In addition, the mechanical properties were determined by uniaxial tensile tests. Electrochemical polarization and immersion test were performed in Hanks solution in order to determine the corrosion rates. Furthermore, vibrating sample magnetometry was used in order to characterize the material in terms of its magnetic properties. It was found that in general the sputtered material exhibits a high mechanical strength compared to literature values for comparable materials. This is mainly attributed to the fine grained microstructure of sputtered material. A significant acceleration of the corrosion rates were reached by the addition of gold, due to the formation of micro galvanic elements. Against expectations the corrosion rates of FeMn alloys were found to be slower than pure iron. However, the low corrosion rate is compensated by the superior strength up to 1242 MPa. Additionally it was shown that the Mn concentrations > 15 % are sufficient in order to stabilize the non- ferromagnetic epsilon and gamma phase and in turn distinctly enhance the magnetic resonance imaging compatibility of the material. The work proofed the concept of using magnetron sputtering in combination with UV-lithography as promising alternative fabrication method of filigree structured, biodegradable iron based implants. Due to the advantages, the method offers a great potential to tailor the material properties.In der Arbeit wird gezeigt, dass Magnetron-Kathodenzerstäubung (Sputtern) in Kombination mit UV-Lithografie, eine geeignete Methode zur Herstellung von Eisen basierten biodegradierbaren Implantaten darstellt. Die Nutzung dieser Art der Herstellung bietet viele Vorteile. Zunächst einmal besitzt gesputtertes Material eine einzigartige Mikrostruktur und somit auch Materialeigenschaften. Darüber hinaus können neben der Abscheidung aller Arten von Legierungen auch Systeme aus nicht mischbaren Komponenten hergestellt werden. In dieser Arbeit wurden strukturierte Filme aus Reineisen, Eisen-Gold sowie verschiedene binäre Eisen-Mangan Legierungen erfolgreich hergestellt und charakterisiert. Es wurde gezeigt, dass im Vergleich zu Literaturwerten vergleichbarer Materialien, das gesputterte Material eine allgemein hohe Festigkeit besitzt. Dies ist hauptsächlich auf die charakteristische feinkörnige Mikrostruktur zurückzuführen. Weiterhin wurde eine signifikante Steigerung der Korrosionsrate durch das Einbringen von Goldausscheidungen erreicht, da diese als mikrogalvanische Elemente fungieren. Entgegen den Erwartungen, führte das Hinzulegieren von Mn führte zu einer geringfügigen Abnahme der Korrosionsrate. Dies wird jedoch durch die sehr hohe Festigkeit von bis zu 1147 MPa kompensiert. Zusätzlich konnte gezeigt werden, dass Mn Konzentrationen >15 %ausreichen, um die nicht-ferromagnetischen Epsilon und Gamma Phasen zu stabilisieren, was die Materialkompatibilität mit Magnet Resonanz Tomographie Untersuchungen deutlich verbessert. Die Arbeit zeigt, dass es möglich ist Magnetronsputtern in Kombination mit UV-Lithografie als alternatives Herstellungsverfahren für feinstrukturierte Implantate zu nutzen. Durch die Vorteile dieser Herstellungstechnik erscheint diese als vielversprechend um die Materialeigenschaften gemäß den Anforderungen zu optimieren

Magnetron-Sputtered, Biodegradable FeMn Foils: The Influence of Manganese Content on Microstructure, Mechanical, Corrosion, and Magnetic Properties

FeMn alloys show a great potential for the use as a biodegradable material for medical vascular implants. To optimize the material properties, with respect to the intended application, new fabrication methods also have to be investigated. In this work different Fe-FeMn32 multilayer films were deposited by magnetron sputtering. The deposition was done on a substrate structured by UV lithography. This technique allows the fabrication of in-situ structured foils. In order to investigate the influence of the Mn content on the material properties foils with an overall Mn content of 5, 10, 15, and 17 wt % were fabricated. The freestanding foils were annealed post-deposition, in order to homogenize them and adjust the material properties. The material was characterized in terms of microstructure, corrosion, mechanical, and magnetic properties using X-ray diffraction, electron microscopy, electrochemical polarization, immersion tests, uniaxial tensile tests, and vibrating sample magnetometry. Due to the unique microstructure that can be achieved by the fabrication via magnetron sputtering, the annealed foils showed a high mechanical yield strength (686-926 MPa) and tensile strength (712-1147 MPa). Owing the stabilization of the non-ferromagnetic ε- and γ-phase, it was shown that even Mn concentrations of 15-17 wt % are sufficient to distinctly enhance the magnetic resonance imaging (MRI) compatibility of FeMn alloys

Mechanical Properties and In Vitro Degradation of Sputtered Biodegradable Fe-Au Foils

Iron-based materials proved being a viable candidate material for biodegradable implants. Magnetron sputtering combined with UV-lithography offers the possibility to fabricate structured, freestanding foils of iron-based alloys and even composites with non-solvable elements. In order to accelerate the degradation speed and enhance the mechanical properties, the technique was used to fabricate Fe-Au multilayer foils. The foils were annealed after the deposition to form a homogeneous microstructure with fine Au precipitates. The characterization of the mechanical properties was done by uniaxial tensile tests. The degradation behavior was analyzed by electrochemical tests and immersion tests under in vitro conditions. Due to the noble Au precipitates it was possible to achieve high tensile strengths between 550 and 800 MPa depending on the Au content and heat treatment. Furthermore, the Fe-Au foils showed a significantly accelerated corrosion compared to pure iron samples. The high mechanical strength is close to the properties of SS316L steel. In combination with the accelerated degradation rate, sputtered Fe-Au foils showed promising properties for use as iron-based, biodegradable implants

Magnetron Sputtering as a Fabrication Method for a Biodegradable Fe32Mn Alloy

Biodegradable metals are a topic of great interest and Fe-based materials are prominent examples. The research task is to find a suitable compromise between mechanical, corrosion, and magnetic properties. For this purpose, investigations regarding alternative fabrication processes are important. In the present study, magnetron sputtering technology in combination with UV-lithography was used in order to fabricate freestanding, microstructured Fe32Mn films. To adjust the microstructure and crystalline phase composition with respect to the requirements, the foils were post-deposition annealed under a reducing atmosphere. The microstructure and crystalline phase composition were investigated by scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction. Furthermore, for mechanical characterization, uniaxial tensile tests were performed. The in vitro corrosion rates were determined by electrochemical polarization measurements in pseudo-physiological solution. Additionally, the magnetic properties were measured via vibrating sample magnetometry. The foils showed a fine-grained structure and a tensile strength of 712 MPa, which is approximately a factor of two higher compared to the sputtered pure Fe reference material. The yield strength was observed to be even higher than values reported in literature for alloys with similar composition. Against expectations, the corrosion rates were found to be lower in comparison to pure Fe. Since the annealed foils exist in the austenitic, and antiferromagnetic γ-phase, an additional advantage of the FeMn foils is the low magnetic saturation polarization of 0.003 T, compared to Fe with 1.978 T. This value is even lower compared to the SS 316L steel acting as a gold standard for implants, and thus enhances the MRI compatibility of the material. The study demonstrates that magnetron sputtering in combination with UV-lithography is a new concept for the fabrication of already in situ geometrically structured FeMn-based foils with promising mechanical and magnetic properties

Magnetron Sputtering a New Fabrication Method of Iron Based Biodegradable Implant Materials

It was shown in the previous decade that pure-iron has a large potential as a biodegradable medical implant material. It is necessary to tailor the material properties according to the intended use of the device. It is of great interest to investigate not only the influence of processing on the material properties but also alternative fabrication methods. In this work for the first time magnetron sputtering in combination with UV lithography was used to fabricate free standing, patterned pure-iron thick films. For the intended use as biodegradable implant material free standing thick films were characterized in terms of microstructure, degradation performance, and mechanical properties before and after various heat treatments. The influence of microstructural changes on the degradation behavior was determined by linear polarization measurements. The mechanical properties were characterized by tensile tests. Microstructure, surface, and composition were investigated by scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) measurements. The foils exhibited a preferential orientation in 110 direction and a fine grained structure. Furthermore they showed a higher strength compared to cast iron and corrosion rates in the range of 0.1 mm/year. Their mechanical properties were tuned by grain coarsening resulting in a slight increase of the degradation rate