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Leistungsstarke Verfahren zur additiven Fertigung wie der 3D Druck und das Selektive Lasersintern basieren auf dem Schichtauftrag eines fließfähigen Pulvers. Bei keramischen Pulvern ist eine gute Fließfähigkeit ab einer Partikelgröße von ca. 40 µm gegeben. Bei Pulvern mit zu feinen Partikeln sind die adhäsiven Kräfte zwischen den Partikeln vergleichbar groß wie die Kräfte, die durch die Gravitation auf die Partikel wirken, was einem gleichmäßigen Fließen des Pulvers und somit einem gleichmäßigen Schichtaufbau entgegensteht. Die Verwendung von feineren Pulvern hat jedoch Vorteile, wie z.B. eine bessere Sinteraktivität.
Neben der nötigen minimalen Partikelgröße besteht für keramische Werkstoffe ein wesentliches Problem der pulverbasierten Verfahren in der Tatsache, dass das Pulverbett, also das durch Schichtauftrag gestapelte Pulver, eine zu geringe Dichte besitzt. Dies bringt grundsätzlich zwei Nachteile mit sich: zum einen verhindert eine zu geringe Packungsdichte des Pulvers den Aufbau kompakter Grünkörper und letztlich deren Sinterung zu einer dichten Keramik, zum anderen wird im Aufbauprozess das Bauteil durch das Pulverbett nicht ausreichend gestützt. Beim Auftragen einer neuen Pulverschicht kann die bereits verfestigte Struktur im Pulverbett verschoben werden, was zu Defekten in der Struktur bis hin zum vollständigen Verlust der Struktur führt. Aus diesem Grunde ist neben dem Aufbau des zu fertigenden Bauteils u.U. der Aufbau von zusätzlich sogenannten Supportstrukturen gefordert. Diese Supportstrukturen verankern das Bauteil mit der Bauplattform und fixieren es somit im Koordinatensystem des Bauraums der Anlage. Das Entfernen der Supportstrukturen erfordert nach dem eigentlichen additiven Fertigungsprozess einen zusätzlichen Prozessschritt, der zeitaufwendig und kaum zu automatisieren ist, und daher einer autonomen Fertigung, wie sie durch die Additive Fertigung realisiert werden kann, entgegensteht.
Es werden unterschiedliche Strategien für die Stabilisierung des Pulverbetts und zur Erzielung einer hohen Packungsdichte der Partikel im Pulverbett aufgezeigt. Neben der Lagenweise SchlickerDeposition (LSD) werden Ergebnisse zur Gas Flow Assisted Powder Deposition vorgestellt.
Manipulating ceramic powder compacts and ceramic suspensions (slurries) within their volume with light requires a minimum transparency of the materials. Compared to polymers and metals, ceramic materials are unique as they offer a wide electronic band gap and thus a wide optical window of transparency. The optical window typically ranges from below 0.3 µm up to 5µm wavelength. Hence, to penetrate with laser light into the volume of a ceramic powder compound its light scattering properties need to be investigated and tailored. In the present study we introduce the physical background and material development strategies to apply two-photon-polymerization (2PP) for the additive manufacture of filigree structures within the volume of ceramic slurries.
Manipulating ceramic powder compacts and ceramic suspensions (slurries) within their volume with light requires a minimum transparency of the materials. Compared to polymers and metals, ceramic materials are unique as they offer a wide electronic band gap and thus a wide optical window of transparency. The optical window typically ranges from below 0.3 µm up to 5µm wavelength. Hence, to penetrate with laser light into the volume of a ceramic powder compound its light scattering properties need to be investigated and tailored. In the present study we introduce the physical background and material development strategies to apply two-photon-polymerization (2PP) for the additive manufacture of filigree structures within the volume of ceramic slurries.
Photon-based additive manufacturing technologies such as SLA, DLP, LCM, moreover volumetric two-photon-polymerization, Xolography and holographic technologies promise the highest accuracy and dimensional freedom. But to transfer the light through the feedstock it needs sufficient transparency at the used light wavelength. Ceramic particles used for powder processing routes act as scattering sites and therefore hinder the light transmission, unless…
The particle size and particle size distribution are chosen small and narrow enough. Particles which are smaller than roughly 1/10th of the light wavelength, mostly nanoparticles around 5nm size, decrease scattering vastly. This turns resins even with homogeneously distributed ceramic weight fraction of up to 80% transparent again. Feedstocks could be prepared for the highly accurate two-photon-polymerization gaining the smallest yttria stabilized zirconia structures with a resolution of 500nm and unique mechanical properties. The same feedstocks could be applied to DLP and LCM as layer-by-layer AM-technologies for bigger parts. Hybridizing both technologies lead to ceramic parts with microscopic accuracy at macroscopic dimensions. The feedstock was even applied to the volumetric Xolography with the highest transparency requirement so far and to versatile and flexible holographic AM.
Highly filled nano-particle containing transparent ceramic feedstocks open the way for technical ceramics in high precision manufacturing where the performance and durability and accessibility are increased and created by the unique ceramic properties such as mechanical strength, chemical and thermal resistance and biocompatibility
Here we demonstrate that by applying exclusively Martian resources a processing route involving suspensions of mineral particles called slurries or slips can be established for manufacturing ceramics on Mars. We developed water-based slurries without the use of additives that had a 51 wt. % solid load resembling commercial porcelain slurries in respect to the particle size distribution and rheological properties. These slurries were used to slip cast discs, rings and vases that were sintered at temperatures between 1000 and 1130 °C using different sintering schedules, the latter were set-up according the results of hot-stage microscopic characterization. The microstructure, porosity and the mechanical properties were characterized by SEM, X-ray Computer tomography and Weibull analysis. Our wet processing of minerals yields ceramics with complex shapes that show similar mechanical properties to porcelain and could serve as a technology for future Mars colonization. The best quality parts with completely vitrificated matrix supporting a few idiomorphic crystals are obtained at 1130 °C with 10 h dwell time with volume and linear shrinkage as much as ~62% and ~17% and a characteristic compressive strength of 51 MPa.
Ceramic additive manufacturing (AM) requires a complex process chain with various post-processing steps that require expensive machines and special expertise. The key to further market penetration is AM that makes it possible to integrate into an already established ceramic process chain. Most successful AM technologies for ceramics are, however, based on processes that initially have been developed for polymeric materials. For ceramics AM, polymers or precursors are loaded with ceramic particles. This strategy facilitates the entry into AM, however the introduction of organic additives into the ceramic process chain represents a considerable technological challenge to ultimately obtain a ceramic component after additive shaping. In the present communication, two technologies based on ceramic suspensions will be introduced, the “layerwise slurry deposition” (LSD) and “laser induced slip casting” (LIS) technology. Both technologies take advantage of the high packing densities reached by conventional slip casting and moreover enable the processing of fines, even nanoparticles.
Additive Manufacturing (AM) covers a wide range of processes, ranging from rapid prototyping technologies for polymers to directed energy deposition and powder bed fusion processes for metals and ceramics. In all cases, AM processes involve the layer-by-layer deposition of material from a digital file. Even though these processes may be known by a variety of commercial names, the general characteristics of the processes are similar, as are their impacts on different material systems.
The flexibility of the process provides unprecedented design freedom by allowing the direct fabrication of complex geometries with unique material combinations. However, the interactions between the high energy density sources (laser and electron beams) and the materials being deposited create complex processing conditions that have a significant impact on the material properties. With the wide ranging possibilities inherent in AM produced components, a fundamental understanding of the process/structure/property relationships across different material systems will allow for specific material properties to be obtained.
This Focus Issue of Journal of Materials Research is dedicated to the most recent advances in the characterization of processing/structure/property relationships in AM produced metallic, ceramic, and polymer systems. The breadth of different properties and behaviors across these different materials systems makes the characterization of AM materials extremely complex and a fertile subject for investigation. Many of these issues are addressed in this collection of papers. Such a wide range of unique research areas and the breadth of materials examined in this issue is evidence of the scope of materials issues in additive manufacturing and a glimpse into the future.
We are grateful to both the authors and reviewers of the many high-quality manuscripts submitted to this JMR Focus Issue on The Materials Science of Additive Manufacturing.
BACKGROUND CONTEXT: Targeted delivery of osteoinductive bone morphogenetic Proteins (eg, GDF5) in bioresorbable calcium phosphate cement (CPC), potentially suitable for vertebroplasty and kyphoplasty of osteoporotic vertebral fractures, may be required to counteract augmented local bone catabolism and to support complete bone regeneration. The biologically optimized GDF5 Mutant BB-1 may represent an attractive drug candidate for this purpose.
PURPOSE: The aim of the current study was to test an injectable, poly (l-lactide-co-glycolide) acid (PLGA) fiber-reinforced, brushite-forming CPC containing low-dose BB-1 in a sheep lumbar osteopenia model.
STUDY DESIGN/ SETTING: This is a prospective experimental animal study.
METHODS: Bone defects (diameter 5 mm) were generated in aged, osteopenic female sheep and were filled with fiber-reinforced CPC alone (L4; CPC+fibers) or with CPC containing different dosages.