Symposium FA
3D Printing and Beyond: State-of-the-art and New Paradigms for Additive Manufacturing Technologies


FA-1:IL02  3D Printing of Hierarchical Porous Ceramics
A.R. STUDART, A. DUTTO, ETH Zurich, Switzerland

Hierarchical porous ceramics are attractive structures for a variety of applications due to their high surface area combined with enhanced permeability. However, synthetic porous ceramics have not yet reached the elaborate architectural design and high mechanical efficiency found in natural porous materials like bamboo, bone and wood. To fill this gap, processing routes that enable deliberate control over the material’s porous structure at multiple length scales are highly demanded. In this talk, I will show how 3D printing technologies can be explored to fabricate hierarchical porous ceramics with unprecedented mechanical efficiency and architectural control. The key feature of our approach is to design emulsion or foam-based inks whose droplet/bubble sizes are sufficiently stable to withstand the shear forces developed in the printing process, while later serving as a template for the macropores generated after drying and sintering of the printed object. This methodology enables tuning of porosity and pore sizes at multiple length scales, resulting in enhanced mechanical efficiency. To demonstrate the potential of the process, we 3D printed inks into parts with complex geometries and bioinspired multiporosity features that cannot be achieved through conventional processing.

FA-1:IL03  Multimaterial 3D Printing of Functional Ceramics for Energy Applications
M. Torrell1, A. Pesce1, M. Nuñez1, N. Kostretsova1, A. Morata1, A. Tarancón1, 2, 1Catalonia Institute for Energy Research, Sant Adrià de Besòs, Barcelona, Spain; 2ICREA, Barcelona, Spain

High temperature energy devices, such as Solid Oxide Cells (SOC), are based on ceramics or cermet materials where active area and microstructure play an important role in the device performance. Therefore, the capabilities of the additive manufacturing technologies in their fabrication can bring clear advantages in terms of performance and functional complexity but also offers benefits on the production cost and fabrication processes. SOFC stack fabrication involves expensive and time-consuming processes which includes tape casting, screen printing, and high-temperature treatments. The presented work proposes a breakthrough based on ceramic hybrid 3D printing technology for a single step SOFC stack manufacturing. This research line was the core of the Cell3Ditor project which deals with the design of the 3D printing process for production of monolithic joint-less SOFC stacks. The developed multi material 3D-printer combines stereolithography (SLA) for the electrolyte printing, and robocasting (EFF) for the deposit of the electrodes and interconnects, all of them ceramic materials deposited on a single printing process followed by a co-sintering step. The results achieved during the project are discussed, from the generation of the slurries to the electrochemical characterization.

FA-1:IL05  Quality Aspects with Regard to 3D Printing of Ceramics
H. FRIEDRICH, F. RAETHER, J. VOGT, Fraunhofer Zentrum für Hochtemperatur-Leichtbau HTL, Bayreuth, Germany

The implementation of additive manufacturing in ceramic production requires a paradigm shift for the complete development and printing process. New opportunities arise for lightweight or individual component design, component integration and logistics. On the other hand, several challenges have to be met to fulfill existing quality standards for the respective applications. Due to the rapidly growing variety of printing methods, the development of standards beyond specific AM techniques is most promising. In the presentation, some general methods will be introduced which allow quantitative evaluation of quality-relevant aspects like green compact homogeneity, shape distortions and surface quality. Moreover, a systematic approach for the optimization of debinding and sintering processes is presented, which is relevant for most ceramic AM processes. It is based on in situ measurements of material changes during the heating process, a careful parametrization of measuring data and their use in special coupled finite element simulations of the processes. Specific actions for the quality control of the printing process will be discussed, and an outlook on promising new methods will be provided.

FA-1:IL06  Additive Manufacturing of Ceramics and Ceramic Composites for Aerospace Applications
J.J. Bowen1, 2, L.M. Rueschhoff1, K.L. Martin1, 2, D.P. Street1, 3, M.J.S. Parvelescu1, 2, M.B. Dickerson1, 1Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, OH, USA; 2UES Inc., Dayton, OH, USA; 3NRC Research Associateship Programs, Washington, DC, USA

Additive manufacturing technologies have game changing potential for the production of ceramics and ceramic composites. One of the principal benefits of additive manufacturing is in the creation of relatively complex shaped components composed of refractory ceramics and composites. However, such materials are relatively difficult to shape or layup in complicated geometries by traditional methodologies, high-temperature ceramics components can be printed with relative ease. In this presentation, we will discuss research aimed at creating new feedstocks for the printing of ceramics. Specifically, we will highlight advances in the synthesis of new preceramic polymer systems. Such preceramic polymer systems include hybrid materials, as well as polymers that feature new cross-linking strategies and bioinspired designs. In the case of the latter, by pairing biological concepts with direct ink write, we are able to control the structuring of ceramics from the nanoscale to the macroscale. Links between the chemistry, structure, processing, and properties of these 3D printed systems will be described, including rheological effects, final ceramic composition, and mechanical properties. The potential application for ceramic additive technologies in aerospace will be discussed.

FA-1:IL08  Innovative Zirconia-based Material Shaped by SLA 3D Printing
C. CHAPUT, C. Schick, 3DCERAM-SINTO, Bonnac La Cote, France

Today a strong need for high-performance ceramic materials combined with new shaping techniques appears on the market. 3D printing technology of ceramic objects is in strong development as it opens new perspectives.
While ceramic materials are brittle and subject to catastrophic failure that is difficult to predict, ceria-stabilized zirconia-based composites can provide new ceramic materials with a plastic deformation domain before rupture, excellent resistance to processing flaws and a Weibull modulus approaching that of a steel. In this study, we explored the influence of SLA stereolithography shaping on this new ceria-stabilized zirconia-based material with unique mechanical behavior. Firstly, a slurry compatible with the CERAMAKER process was developed. Then, the specific object of the study was to evolve the influence of the shaping parameters (layer thickness, lasing power, etc.) on the green part quality. Finally, the effect of the sintering temperature on the microstructure and mechanical properties of optimized SLA-printed material was also studied. Through this study, 3DCERAM has been able to prove that this new material could be shaped by 3D SLA. Different sintering parameters have been studied to optimize densification and material properties. SEM observations show original layer structures and microstructure development attributable to the shaping process.

FA-1:IL12  A Segregation Model Study of Suspension-based Additive Manufacturing
CHANG-JUN BAE1,  J.W. Halloran2, 13D Printing Materials Center, Korea Institute of Materials Science (KIMS), Changwon, South Korea; 2Dept. of Materials Science and Engineering, University of Michigan, Ann Arbor, USA

Ceramic stereolithography (CerSLA) is being used to directly build model investment casting molds for airfoils, where the shell is integrated with the core. CerSLA builds ceramic green objects from CAD files from many thin liquid layers of powder in monomer, which are solidified by polymerization with a UV laser, thereby “writing” the design for each slice. Previous CerSLA work used submicron sized powders, the particles remain in suspension without settling for periods longer than the time required to build. But refractory-grade powders have coarse particles to impart stability at high temperatures, and these quickly sediment during building. In this paper we use modeling and experimentation to investigate the use of CerSLA for the coarse particles. In the model, we establish a model to satisfy the prerequisite that the time required to write a layer must be shorter than the time required for the suspended particle to settle a short distance. The settling time is calculated by Stokes settling rate and time and is based on the particle size, density, monomer viscosity, and volume fraction for the case of hindered settling appropriate for concentrated suspensions. The writing time model considers the layer geometry, laser power, and resin photosensitivity. Finally, with coarse silica powder (~40 μm) through a writing model derived from the settling time and writing time to solve the delamination problem, delamination free sintered ICCM is successfully fabricated.

FA-1:L13  A Guide for Selecting Dispersants for Ceramic Filled Resins for Stereolithography
W. YareD, University of Stuttgart, GSaME, Graduate School of Excellence advanced Manufacturing Engineering, Stuttgart, Germany

Polymeric dispersants are frequently used to provide steric and electrostatic stabilization of ceramic particles in photo-curable resins intended for digital light processing (DLP). However, the dispersant’s type, functionality and concentration directly influence its effectiveness. This contribution is a guide for the selection of optimum dispersants for ceramic-filled photo-curable acrylate resins. Two different ceramic powders, viz. Al2O3 and β-Ca3(PO4)2, were characterized as a case study. Micrographs revealed that anionic dispersants offer a promising dispersibility in acrylate formulations, while different types of anionic ammonium polyacrylate dispersants showed varying levels of effectiveness. Monitoring the operational pH of the suspensions revealed the dissociation mechanism of the different dispersants. Moreover, flow curves, amplitude and frequency sweeps generated on a modular rheometer were used to analyse the influence of the dispersant type and concentration on the flow and viscoelastic behaviour of the resins.The highest levels of adsorbed dispersant induced the lowest viscosity, storage and loss moduli. High levels of adsorbed dispersant, coupled with the right electro-chemical interaction, offered superior colloidal stability.

FA-1:L14  Eutectic Ceramic Microstructures using Laser Powder Bed Fusion (L-PBF)
J.E. Martinez Dosal, C. Colin, M.H. Berger, MINES Paris, PSL, Centre de Matériaux, UMR CNRS 7633, Evry, France

Oxide ceramics of eutectic composition are potential constituents for future aeronautical parts prone to thermomechanical stresses above 1200°C in oxidizing atmosphere. These ceramics are intrinsically resistant to oxidation and have a lower density than metal superalloys currently used. Their specific microstructure allows excellent creep resistance at high temperatures. However, their use is still limited in particular by the difficulty of machining complex shapes and by their low tolerance to crack propagation. A recent study at Centre de Matériaux MINES Paris demonstrated the feasibility of manufacturing parts of complex shapes from the Al2O3/ZrO2 eutectic composition by additive manufacturing via the laser powder bed fusion (L-PBF) process leading to sub-micron lamellae widths. In this work the fusion / solidification of a ternary eutectic system Al2O3/ZrO2/ Y3Al5O12 (YAG) known to be more resistant to crack propagation is presented. The relationships between process parameters, powder composition versus laser absorbance and microstructure (solidified phases, morphology, sizes,…) are investigated. Aging of eutectic microstructures at high temperatures will also be presented in order to predict the mechanical properties of the material once operating.

FA-2:IL02  Multimaterial Components by Additive Manufacturing Technologies
T. MORITZ, S. Weingarten, J. Abel, E. Schwarzer, U. Scheithauer, A. Günther, J. Schilm, K. Wätzig, Fraunhofer Institute for Ceramic Technologies and Systems, Dresden, Germany

Additive Manufacturing (AM) methods offer groundbreaking new opportunities for geometrical complexity such as for personalization and individualization of ceramic components. So far, AM technologies are mainly used for single material applications, but more and more multimaterial approaches are getting into the focus of industrial interest allowing for multifunctionalization of components. The combination of different kinds of advanced ceramics and glasses or the combination of ceramics with metals open the door to promising property couplings like electrical conductivity / electrical insulation, hardness / ductility, metallic gloss / white color and much else. The presentation will give an overview of AM methods for ceramics suited for multimaterial approaches. It will tell about the technological and material specific challenges the user is faced with, and it will show examples of successful and promising examples of multifunctional ceramic and glass components made by Additive Manufacturing.

FA-2:IL03  The Role of Rheology in Laser Sintering of Polymer Particles
r. cardinaels, P. Anderson, Polymer Technology Group, Eindhoven University of Technology, Eindhoven, Noord-Brabant, The Netherlands

Merging of particle pairs during selective laser sintering (SLS) of polymers is vital in defining final part properties. Depending on the sintering conditions, polymers can undergo full or partial sintering whereby incomplete sintering results in poor mechanical properties. In the present work, a novel in-house developed experimental setup is used to perform laser sintering experiments on polymer particle doublets while performing in-situ visualisation of the sintering dynamics. Sintering conditions such as heating chamber temperature, laser pulse energy and duration, laser spot size and particle size are precisely controlled and systematically varied. A non-isothermal viscous sintering model, extending the Frenkel model, is developed to qualitatively predict the observed effects of the various parameters. It is shown that the sintering kinetics is determined by a complex interplay between the transient rheology caused by the finite relaxation times of the polymer and the time-dependent temperature profile which also affects the polymer viscosity. The combination of a full material characterisation with sintering experiments under well-defined conditions has resulted in a general understanding of the effects of material and process parameters on laser sintering.

FA-2:IL04  Nanoparticle Additivation of Polymer Powders for Powder Bed Fusion of Parts with Novel Optical and Magnetic Properties
C. DONATE-BUENDIA, B. Gökce, Materials Science and Additive Manufacturing, University of Wuppertal, Wuppertal, Germany

Additive manufacturing techniques such as laser powder bed fusion (LPBF) permit the fabrication of objects and parts with custom design. Since polymer powders have material-related limitations regarding their processability, they have become a decisive factor for LPBF. Additivation with nanoparticles represent an approach to overcome these limitations and expanding the feedstock material variety. As an alternative to mechanical nanoparticle supporting procedures that suffer from agglomeration, clean and surfactant-free nanoparticles can be generated by laser ablation and laser irradiation in liquids. Based on this approach, different polymer micropowders are decorated with a variety of nanoparticles (e.g. Ag, Fe3O4 C) and processed by LPBF [1]. The controlled modification of the optical and/or magnetic properties of the nanoparticle-decorated powders and transfer of those properties to the generated parts by LPBF is achieved [2].
References: [1]T. Hupfeld, S. Salamon, J. Landers, A. Sommereyns, C. Doñate-Buendía, J. Schmidt, H. Wende, M. Schmidt, S. Barcikowski, B. Gökce, J. Mater. Chem. C. (8),12204–12217(2020). [2]T. Hupfeld, A. Wegner, M. Blanke, C. Doñate‐Buendía, V. Sharov, S. Nieskens, M. Piechotta, M. Giese, S. Barcikowski, B. Gökce, Adv. Opt. Mater. (8), 2000473(2020)

FA-2:L05  Two-photon Polymerisation of 3D PEDOT:PSS Composite Microstructures
J.M. DELENTE, S. Kolagatla, L. Florea, School of Chemistry & AMBER, The SFI Research Centre for Advanced Materials and BioEngineering Research, Trinity College Dublin, Dublin 2, Ireland; N. López-Larrea, M. Criado-Gonzalez, D. Mecerreyes, POLYMAT University of the Basque Country UPV/EHU, Donostia-San Sebastián, Spain

Two-photon polymerisation (TPP) is a fabrication method that allows for the realisation of complex 3D polymer microstructures, with sub-100 nm feature size. To date, several strategies for the fabrication of 3D conductive microstructures by TPP have been explored, such as the simultaneous photopolymerisation and photoreduction of metallic salts [1], and post-TPP inclusion of conductive materials in the prefabricated microstructures. This second approach was recently used for the inclusion of poly(3 ,4-ethylenedioxithiophene):poly(styrenesulfonate) (PEDOT:PSS), by soaking a 3D microstructure in a PEDOT:PSS dispersion, leading to the uptake of the conductive polymer into the structures, rendering the structures conductive [2]. Herein, we propose a novel strategy for the inclusion of PEDOT:PSS directly in the photoresist used for TPP. This allows for the realisation of complex 3D microstructures with controllable PEDOT:PSS content. The microstructures morphology was characterised using optical microscopy, scanning electron microscopy and atomic force microscopy (AFM), while their conductivity was measured using conductive AFM. Such 3D conductive structures find applications in microelectronics and MEMS/NEMS technologies.
[1] Adv. Mater. 2016, 28, 3592. [2] Nanoscale 2019, 11, 9176.

FA-2:L06  Residual Stress and Microstructure Gradients in Additively-manufactured Metallic Components Characterized by High-energy Synchrotron X-ray Diffraction
J. Keckes, S.C. Bodner, J. Todt, Montanuniversität Leoben and Austrian Academy of Sciences, Leoben, Austria; N. Schell, Helmholtz Zentrum Geesthacht, Geesthacht, Germany

Additive manufacturing is a highly non-equilibrium process resulting in the formation of complex multiaxial residual stress fields and unique microstructures, which decisively influence functional properties of fabricated metallic components. In this contribution, examples from high-energy synchrotron cross-sectional X-ray diffraction characterization of metallic parts produced using metal powder bed fusion technology will be introduced. The experiments were conducted at the high energy materials science (HEMS) beamline P07B of PETRA III at DESY in Hamburg. Results from stainless steel 316L, Inconel 718, TiAl and hybrid structures will be presented to show monotonous and oscillatory distributions of stresses as well as complex microstructure and phase evolutions across the structures. The obtained distributions elucidated from the synchrotron data will be further correlated with mechanical properties and chemical distributions obtained by complementary scanning (and transmission) electron microscopy, hardness profiling and energy dispersive X-ray spectroscopy as well as with the applied process conditions. Finally, it will be shown that synchrotron diffraction represents a powerful tool to assess process-microstructure-stress-property relationships.

FA-2:L07  Inconel-steel Multilayers by Liquid Dispersed Metal Powder Bed Fusion: Microstructure, Residual Stress and Property Gradients
J. Keckes, S.C. Bodner, J. Zalesak, J. Todt, J.F. Keckes, V. Maier-Kiener, Montanuniversität Leoben and Austrian Academy of Sciences, Leoben, Austria; B. Sartory, Materials Center Leoben, Leoben, Austria; N. Schell, Helmholtz Zentrum Geesthacht, Geesthacht, Germany; L.T.G. van de Vorst, The Netherlands Organisation for Applied Scientific Research, Eindhoven, The Netherlands; J.W. Hooijmans, J.J. Saurwalt, Admatec Europe BV, Moergestel, The Netherlands; S. Mirzaei, Central European Institute of Technology CEITEC, Brno, Czech Republic

Synthesis of multi-metal hybrid structures represents a serious scientific and technological challenge. In this contribution, liquid dispersed metal powder bed fusion was used to fabricate a multilayered structure based on alternating Inconel 625 alloy (IN625) and 316L stainless steel (316L) layers on a 316L base plate. Analytical techniques revealed sharp compositional and microstructural boundaries between alternating ~60 µm thick alloys’ sub-regions as well as unique microstructures at different length scales. The periodic occurrence of IN625 and 316L sub-regions is correlated with a cross-sectional hardness increase and decrease and a compressive stress decrease and increase, respectively. The laser scanning strategy induced a growth of elongated grains separated by zig-zag grain boundaries. Chemical analysis indicates an intermixing of the alloy’s elements in the growth direction upwards at a morphologically sharp IN625-316L interface. A formation of reinforcing spherical chromium-metal-oxide nano-dispersoids demonstrates a possibility for reactive additive manufacturing at the nanoscale. The study shows that liquid dispersed metal powder bed fusion is an effective tool to combine dissimilar metallic alloys into unique hierarchical microstructures with synergetic properties.

FA-2:IL08  Two-color Irradiation for Volumetric Photopolymerization Confinement
T.F. Scott1,2, H.L. van der Laan3, Mark A. Burns4,5, 1Department of Chemical Engineering, Monash University, Clayton, VIC, Australia; 2Department of Materials Science and Engineering, Monash University, Clayton, VIC, Australia; 3Macromolecular Science and Engineering Program, University of Michigan, Ann Arbor, MI, USA; 4Department of Chemical Engineering, University of Michigan, Ann Arbor, MI, USA; 5Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA

Conventional photolithographic rapid prototyping approaches typically achieve reaction confinement in depth through patterned irradiation of a photopolymerizable resin at a wavelength where the resin strongly absorbs such that only a very thin layer of material is solidified. Consequently, three-dimensional objects are fabricated by progressive, two-dimensional addition of material, significantly curtailing fabrication rates. To address the deficiencies of contemporary additive manufacturing approaches, we have applied volumetric photopolymerization confinement to stereolithographic 3D printing where, in conjunction with compatible resins, two parallel irradiation patterns are projected into a resin vat at wavelengths that independently either effect resin solidification or prevent it, confining in depth the region polymerized. This process enables a continuous additive manufacturing process for the production of large cross-sectional area parts by facilitating high reflow into thicker inhibition volumes. Additionally, by employing two perpendicular irradiation patterns to independently effect polymerization initiation and inhibition, we enable three-dimensional photopolymerization patterning in bulk resin, thereby complementing emergent approaches to volumetric 3D printing.

FA-2:IL10  Microstructure Control of Metals via Additive Manufacturing Processes
M. Seita, School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore

One of the main drivers for the adoption of additive manufacturing (AM) in the industry is the ability to build near-net-shape parts with topology-optimized geometry. This paradigm has enabled the production of structural components that combine lightweight and mechanical strength. One additional feature of AM that is currently underutilized is the ability to create solids with “topology-optimized microstructure”—namely materials with a controlled distribution of dissimilar microstructures. The key advantage of this paradigm is that it provides a broader—yet so far unexplored—design space for materials that combine multiple properties. In this talk, I will present two strategies to control the microstructure of stainless steel 316L via laser powder bed fusion. The first—which we refer to as LEGO (layer-wise engineering of grain orientation)—enables the production of parts with site-specific crystallographic textures. The second—which we call A-GBE (additive grain boundary engineering)—allows controlling the grain boundary character distribution in the alloy. Novel AM strategies such as LEGO and A-GBE open the path to designing materials with superior properties and more predictable behavior by engineering their microstructure to an unprecedented level of detail.

FA-2:IL12  Multi- Material / Modality / Scale / Axis: Realizing Multi-Functional Products with Next-Generation AM Processes
C.B. WILLIAMS, Virginia Tech, Blacksburg, VA, USA

Additive Manufacturing’s layer-wise fabrication approach empowers engineers to selectively place (multiple-) materials to realize products that satisfy multiple functions and design objectives. However, to fully realize this potential, AM processes are in need of further advancements in material selection and process capability. To address this need, it is necessary to tailor both materials for the unique constraints imposed by AM processes, and the processes for the unique properties of the materials. The aim of this talk is to highlight research in which materials and AM processes are concurrently designed to realize direct printing of multi-functional products. Specifically, AM of (i) fully-aromatic polyimides (via multi-scale vat photopolymerization), (ii) composite metal lattices (via multi-material binder jetting of foundry sand), (iii) fiber reinforced composites with embedded actuation and sensing (via multi-modal AM), and (iv) composite structures featuring optimized topology and toolpathing (via multi-axis robotic deposition) will be highlighted.

FA-2:IL14  Additive Manufacturing of Architected Composites with Exceptional Energy Absorption
L. VALDEVIT, J. BAUER, M. Sala CasanovaS, University of California, Irvine, Irvine, CA, USA

Traditional composite materials derive their superior mechanical properties from the microscale nature of the ceramic reinforcements, which allows fibers and particulates to achieve nearly theoretical strength. Conventional manufacturing methods, though, only allow 0D, 1D or 2D reinforcement topologies, namely particles, fibers or platelets; integration of these discontinuous reinforcements in a matrix inevitably results in weak planes and directions, limiting the potential of composite structures. The recent emergence of a wide gamut of additive manufacturing (AM) approaches is now enabling fabrication of Interpenetrating Phase Composites (IPCs) in a range of different material combinations, size scales and phase topologies. Here we demonstrate polymer/polymer and metal/ceramic IPCs developed with different AM processes. After exploring the roles of constituent materials, volume fractions and topologies of the reinforcement and matrix phases on the mechanical properties and failure mechanisms of the IPCs, we demonstrate novel materials with unprecedented ability to dissipate energy under compressive loads. The emergence of novel scalable manufacturing approaches is also discussed.

FA-2:L16  Numerical Analysis and Characterization of a 3D Printed Metallic Load Frame
M. HAMID, Kh. McMillan, A.R. Tiano, K. Olson, J. Utter, J. Torok, IBM, Rochester, MN, USA

Recently, metal additive manufacturing is experiencing a rising attention in a variety of industry applications. Depending on geometry of a part and quantity of production, additive manufacturing can yield less expensive final product costs and shorter production times. To optimize the design process, modeling techniques can be applied to mitigate cost of metallic additive manufacturing parts. In this work, a finite element model was built with Ansys Additive Suite for a metallic load frame. The applied material for the load frame was 17-PH Stainless Steel and simulations were completed for 3D printing of the part based on PBF technique. The modeling was handled over three main steps of printing supports on the base plate and the load frame (built part) and finally detaching the support from the built part by applying required heat treatment. Next, a verification study was completed to compare the pattern and deflection values on the printed part with the simulation results. The load frame was printed by applying direct metal laser sintering method. A similar deflection pattern was observed between simulation results and testing.

FA-2:L17  Mechanical Properties of a Case-hardened Low-alloyed Steel produced by PBF-LB
K. Kutleša, S.C. Bodner, J. Keckes, Montanuniversität Leoben, Leoben, Austria

The application of additively manufactured steel products in various high demanding industries is undisputedly closely connected to a targeted development of AM powders. In order to meet the requirements of the specific application cases, further tailoring of certain physical properties can be achieved by different heat treatments. For this study, commercial gas-atomized E185 AMPO - a low alloy steel for motorsport, engineering and prototype applications - was processed by PBF-LB on a EOS 290 M to produce tensile samples (Ø12mm) and steel blocks (20×20×40 mm³). A thermo-chemical heat treatment (carburizing before standard quenching) was applied to modify the surfaces of the AM bulk samples. Tensile tests revealed ultimate tensile strength values of 1092 MPa for the as-built and 1535 MPa for the case-hardened condition, respectively. Vickers hardness profiling was used in the near-surface regions parallel and perpendicular to the build direction to evaluate the case hardening depths as well as the influence of the generated chemical gradients on local mechanical properties of the samples. The results indicate that carbon diffusion modifies the near-surface properties of the steel to a depth of ~1mm.

FA-3:IL01  Moving 4D Printed Active Polymer Structures
G. SCALET, Department of Civil Engineering and Architecture, University of Pavia - Italian Interuniversity Consortium on Materials Science and Technology (INSTM), Pavia, Italy

Active polymers are smart materials whose physical properties (e.g., shape, stiffness, color) can be controlled by external stimuli (e.g., temperature, pH, light, electric or magnetic field). When combined with 3D printing, they open powerful perspectives for designing 4D printed structures with customized architectures and autonomous, tunable property changes over time (the 4th dimension). However, the design of such structures is not trivial and requires careful attention at different levels, i.e., during printing, experimental characterization, modelling, and simulation. This work presents our recent research efforts to achieve programmable behavior in light- and thermally-responsive soft structures manufactured via stereolithography and fused deposition modeling 3D printing. Experimental and numerical results will be presented and discussed. New application examples will be provided, with a special focus on soft actuators and drug delivery systems.

FA-3:L02  4D Sugar Responsive Microstructures Fabricated via Two Photon Polymerisation
a. ennis, D. Nicado, C. Delaney, L. Florea, School of Chemistry & AMBER, the SFI Research Centre for Advanced Materials and BioEngineering Research, Trinity College Dublin, the University of Dublin, College Green, Dublin, Ireland

Two photon-polymerisation (2PP) enables the generation of complex 3D microstructures with feature sizes below 100 nm. Traditionally the photoresists used for 2PP result in hard, highly crosslinked polymer structures. In recent years, there has been a growing interest in developing photoresists for the realisation of soft, 4D microstructures, with application in soft robotics, micro-sensors, and microfluidics.[1] Herein we present a photoresist based on phenylboronic acid (PBA) co-monomers, that is compatible with 2PP and results in microstructures which undergo reversible sugar-induced actuation. While PBA-based hydrogels have been previously explored for their sugar sensing capabilities at the macro-scale, the long response times associated with slow diffusion of analytes to receptor sites, has hindered their adoption for sensing applications. As 2PP allowed for a dramatic reduction in size (from mm to μm), the response time was improved by several orders of magnitude (from hours to s). As such, PBA-hydrogel microstructures, reached equilibrium swelling within 30 s of the addition of 5 mM D-fructose, showing an area increase of up to 90%. Microstructures of bioinspired design showing programable 4D response to sugars, will also be demonstrated.
1 Nanotech. Rev. 2020, 9 (1),1118

FA-3:L03  Cyclic Ketene Acetals as Additives for the Formulation of Subtractive Manufacturing Resists: Properties and Applications
m. carlotti, O. Tricinci, V. Mattoli, Center for Materials Interfaces, Italian Institute of Technology, Pontedera, Italy

Direct laser writing (DLW) is an innovative technology based on two-photon polymerization processes which allow the 3D printing of architectures with arbitrary complexity at the (sub)micrometer scale. As such, this platform is becoming increasingly appealing for the fabrication of MEMS, metamaterials, and functional surfaces. While most of the research interest in this field relies on additive manufacturing, subtractive approaches can be extremely helpful in nano/microfabrication, allowing the preparation of expendable scaffolds, repleceable parts, and protection for fragile structures. In this study, we show that the simple addition of cyclic ketene acetal compounds to a series of different acrylate-based photoresists results in functional formulations that allow the 3D-printing of degradable poly(ester-co-acrylate) microsctrucutres via DLW. These latter could be degraded reliably under mild conditions compatible with other photoresists and materials of common use in the fabrication of MEMS, thus opening new opportunities to design novel fabrication procedures. In particular, we show the potential of these photoresists in the fabrication of shadowing masks on 3D objects and their selective degradation employing a photobase.

FA-4:IL01  Additive Manufacturing - Recent Developments and Future Challenges
D.L. BOURELL, The University of Texas at Austin, Austin, TX, USA

Modern Additive Manufacturing (AM) began about 35 years ago, but earlier precedents date back to the 1860s. Precedents are categorized into three groups: prehistory (no computer), precursors (computer, but few knew how to use them) and modern additive manufacturing. The current landscape of AM will be presented, along with a description of the placement of AM within the broad field of manufacturing. Current and future trends in this technology will also be provided. This will include consideration of the following topics: COVID-19 response, feedstock development, functional service parts, marine applications, environmental issues, design for additive manufacturing.

FA-4:L02  Integration of 3D Laser Lithography and Micro-contact Printing for Bioinspired Surfaces with Advanced Wettability
O. TRICINCI, F. Pignatelli, V. Mattoli, Center for Materials Interfaces, Istituto Italiano di Tecnologia, Pontedera (PI), Italy

Direct laser lithography (DLL) has recently emerged as a powerful tool for fabricating 3D micropatterned surfaces, with features at the nanoscale, for optics, photonics, microfluidics, life sciences. We investigated the possibility to use DLL in combination with micro-contact printing (MCP) to achieve new solutions in surface engineering in the field of wettability. We extended the range of applications of DLL to multifunctional plant-inspired surfaces, whose complex hierarchical microstructures are almost impossible to be fabricated at such scale and with necessary resolution by other techniques. We replicated the Salvinia effect (SE) at the microscale. This plant is a floating fern, which possesses the remarkable property of long-term air retention on the surface of the leaves, when submerged in water, thanks to peculiar 3D hairs (egg-beater like) and their related high hydrophobicity that is due to morphology and localized chemical coating. MCP allowed to chemically functionalize the micropatterned surfaces made with DLL in order to resemble the same dual wettability of the natural counterpart: super-hydrophobic hairs with hydrophilic tips. Roll-off and static contact angles and air retention experiments reproduced the SE, confirming the effectiveness of the proposed approach.


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