Additive Manufacturing Of Ceramics Research Articles

Direct Ink Writing and Rapid Microwave Sintering of Alumina

The additive manufacturing of ceramics is gaining attention due to difficulties in fabricating complex ceramic parts because of its hard and brittle nature. Direct ink writing (DIW) is a unique process in which solid-loaded slurry is extruded to print complex-shaped ceramic parts directly. In the present work, a new composition of high-solid loaded (76 wt.%) alumina ink is prepared for printing ceramic parts with complex structures. The rheology of ink is optimized to ensure the shear thinning behavior of the ink, while thermogravimetric analysis (TGA) of the printed part was carried out to optimize the debinding temperature. The printed alumina part is sintered using the conventional furnace and rapid microwave sintering process, and a comparison has been made. Microwave, a rapid sintering method with a high heating rate, produced >97% dense specimen, while the hardness and flexural strength values of 15.18 ± 0.6 GPa and 148.87 ± 2.14 MPa were achieved, respectively. Rapid microwave sintering of additively manufactured ceramic parts can reduce the energy consumption and overall production time needed to manufacture ceramic parts.

Evaluation of zirconia ceramics fabricated through DLP 3d printing process for dental applications

Zirconia ceramics are versatile materials with remarkable properties such as a high thermal resistance, high fracture strength, and low thermal conductivity. They are chemically inert and highly wear- and corrosion-resistant, making them ideal for a wide range of applications in the aerospace, automotive, and biomedical fields. In dentistry, zirconia ceramics are used for veneers, crowns, bridges, and implants because of their biocompatibility. Despite the various benefits of zirconia ceramics, they are difficult to process because of their high hardness and brittleness. Additive manufacturing (AM) has proven to be a viable alternative to conventional fabrication processes, particularly for the processing of difficult-to-cut materials. AM of ceramics has gained significant attention in recent years because of its flexibility and ability to produce customized geometries rapidly and economically. In this study, the digital light processing (DLP) technique was employed to 3D print yttria-stabilized zirconia. The fabricated zirconia was evaluated and characterized for use in dental applications. Thermogravimetric analysis (TGA) and differential thermogravimetry (DTG) were performed on the green body to assess the decomposition of the additives in the slurry and determine the debinding temperatures. The as-built parts were subjected to debinding and sintering to obtain fully dense zirconia parts. The parts tended to shrink after sintering; therefore, the shrinkage ratios were evaluated and found to be 1.2817, 1.2900, and 1.3388 in the x-, y-, and z-directions, respectively. The average density after sintering was 6.031 g/cc. The flexural strength determined using four-point bending tests was 451.876 MPa, and the tensile and compressive strengths were 143 MPa and 298.4 MPa, respectively.

Mechanical properties of additively manufactured lattice structures composed of zirconia and hydroxyapatite ceramics

Ceramic lattices hold great potential for bone scaffolds to facilitate bone regeneration and integration of native tissue with medical implants. While there have been several studies on additive manufacturing of ceramics and their osseointegrative and osteoconductive properties, there is a lack of a comprehensive examination of their mechanical behavior. Therefore, the aim of this study was to assess the mechanical properties of different additively manufactured ceramic lattice structures under different loading conditions and their overall ability to mimic bone tissue properties.Eleven different lattice structures were designed and manufactured with a porosity of 80% using two materials, hydroxyapatite (HAp) and zirconium dioxide (ZrO2). Six cell-based lattices with cubic and hexagonal base, as well as five Voronoi-based lattices were considered in this study. The samples were manufactured using lithography-based ceramic additive manufacturing and post-processed thermally prior to mechanical testing. Cell-based lattices with cubic and hexagonal base, as well as Voronoi-based lattices were considered in this study. The lattices were tested under four loading conditions: compression, four-point bending, shear and tension.The manufacturing process of the different ceramics leads to different deviations of the lattice geometry, hence, the elastic properties of one structure cannot be directly inferred from one material to another. ZrO2 lattices prove to be stiffer than HAp lattices of the same designed structure. The Young’s modulus for compression of ZrO2 lattices ranges from 2 to 30GPa depending on the used lattice design and for HAp 200MPa to 3.8GPa. The expected stability, the load where 63.2% of the samples are expected to be destroyed, of the lattices ranges from 81 to 553MPa and for HAp 6 to 42MPa.For the first time, a comprehensive overview of the mechanical properties of various additively manufactured ceramic lattice structures is provided. This is intended to serve as a reference for designers who would like to expand the design capabilities of ceramic implants that will lead to an advancement in their performance and ability to mimic human bone tissue.

Volumetric Additive Manufacturing of SiOC by Xolography.

Additive manufacturing (AM) of ceramics has significantly contributed to advancements in ceramic fabrication, solving some of the difficulties of conventional ceramic processing and providing additional possibilities for the structure and function of components. However, defects induced by the layer-by-layer approach on which traditional AM techniques are based still constitute a challenge to address. This study presents the volumetric AM of a SiOC ceramic from a preceramic polymer using xolography, a linear volumetric AM process that allows to avoid the staircase effect typical of other vat photopolymerization techniques. Besides optimizing the trade-off between preceramic polymer content and transmittance, a pore generator is introduced to create transient channels for gas release before decomposition of the organic constituents and moieties, resulting in crack-free solid ceramic structures even at low ceramic yield. Formulation optimization alleviated sinking of printed parts during printing and prevented shape distortion. Complexsolid and porous ceramic structures with a smooth surface and sharp features are fabricated under the optimized parameters. This work provides a new method for the AM of ceramics at µm/mm scale with high surface quality and large geometry variety in an efficient way, opening the possibility for applications in fields such as micromechanical systems and microelectronic components.

Additive manufacturing of sensor prototype based on 3D-extrusion-printed zirconia ceramics

Additive manufacturing of ceramics has attracted large interest due to its unique ability to rapidly prototype, low cost, and increased geometric complexity. Material extrusion technique is often considered for processing and shaping fine and dense ceramic structures because of the high solid loading in ink. In this work, 8 mol.% yttria-stabilized zirconia ink with 70 wt% ceramic loadings was prepared to print zirconia samples in horizontal and vertical directions, following two different filament orientations: 0/90° and ±45°. The study's main objective was to evaluate printing design influences on mechanical properties. This was assessed through flexural testing and digital image correlation analysis. Experimental findings showed that samples printed horizontally with ±45° filament orientation displayed the highest strength. A detailed inspection of fracture surfaces revealed that printing defects were the critical failure location sites formed after sintering and intimately related to printing design issues. After that, a conductive sensor was integrated into the surfaces of 3D-printed specimens by screen-printing silver-based conductive ink to analyze the structural health of zirconia samples. The sensing capabilities of printed conductive patterns were investigated using the four-point bending tests. The results demonstrated that the electrical resistance of the printed silver patterns increased as the applied load on zirconia substrates rose. It indicates that hybrid material extrusion and screen printing techniques are favored ways to manufacture sensors for structural detection of advanced 3D-printed ceramics.

Additive manufacturing of ceramics: Advances, challenges, and outlook

Additive manufacturing of ceramics: Advances, challenges, and outlook

3D Printing of Ceramics with Controllable Green‐Body Configuration Assisted by the Polyvinyl Alcohol‐Based Physical Gels

Additive manufacturing of ceramics has received intense attention. In particular, 3D‐printed ceramics with customized shapes are highly desirable in the chemical industry, aerospace, and biomedical engineering. Nevertheless, developing a simple and cost‐effective process that shapes dense ceramics to complex geometries remains challenging because of the high hardness and low ductility of ceramic materials. Extrusion‐based printing, such as direct ink writing (DIW), often requires supporting materials that pose additional difficulties during printing. Herein, a simple approach is developed to produce stretchable ceramic green bodies of zirconia and alumina for DIW. The ink is composed of polyvinyl alcohol (PVA) and an aqueous suspension of ceramic powders. Besides the colloidal network formed by the ceramic particles, PVA plays an important role in tuning the printability of the aqueous ink. Through a freeze‐thaw process, PVA crystallizes to form physical networks. This strategy provides highly stretchable hydrogel green bodies that can be reprogrammed to complex geometries difficult for common DIW printing. The subsequent drying, debinding, and sintering processes produce ceramics with dense structures and fine mechanical properties. In short, this work demonstrates an efficient method for the DIW of ceramic parts that can be reprogrammed to complex geometries.

Fabrication of electrical semi-conductive SiCN ceramics by vat photopolymerization

The emergence of additive manufacturing (AM) enables ceramics to be fabricated with customized geometry, and polymer-derived ceramics (PDCs) has attracted growing attention owing to their irreplaceable advantages. The combination of 3D printing and PDCs endows the resultant ceramics with both precision and performance. However, AM of ceramics from preceramic polymers is still challenging, and insufficient investigation of functionality also limits the versatility of precursor and its derived ceramics. Herein, we propose a novel paradigm for 3D printing dense silicon carbonitride ceramic and study its electrical semi-conducting properties. The formulated photosensitive precursor inks could achieve self-polymerization and cross-linking under the radiation of UV light (405 nm). The green body with intricate structures is fabricated by digital light processing (DLP). Lightweight (1.79–2.08 g cm–3) and low porosity (< 5%) amorphous ceramics were obtained after thermal treatments. Processes of cross-linking, decomposition, and ceramization are monitored and analyzed. Furthermore, the semi-conducting behaviors of resultant ceramics are identified where the conductivity (10–5–10–1 S m–1) has a monotonic correspondence with the testing temperatures (25–1000 °C). The numerical relationship is fitted by exponential functions, and its conducting mechanism could be interpreted by the band tail hopping (BTH) model. This work could provide alternative solutions for the fabrication of PDCs and potentials for sensing applications.

UV‐curable inorganic precursors enable direct 3D printing of SiOC ceramics

Abstract3D ceramic parts are of great interest for various applications including aerospace, defense, electronics, photonics, and biomedical. Yet, additive manufacturing of ceramics is challenging due to their poor machinability. Herein, two approaches based on the chemical modification of silicon resins to obtain UV‐curable preceramic precursors of SiOC are described. The dual functionality of the synthesized resins acting both as preceramic precursor and as photopolymerizable entity under UV light is exploited. A set of characterization techniques has allowed the investigation of the mechanisms involved in the synthesis of the inorganic SiOC precursors according to the following approaches: (1) blend of the silicon resin with photoactive monomers and (2) synthesis of a single source UV‐curable preceramic silicon resin. A correlation between the nature of the precursor and the properties of the derived SiOC is analyzed. From a technological point of view, the materials can be fabricated as dense or crack‐free porous customized objects with low mass loss and optimal surface quality.

The influence of particle size distribution on rheological properties of fused silica pastes for direct ink writing

Additive manufacturing of ceramics through the direct ink writing method becomes possible when the effective parameters on rheology are optimized accurately. Successful manufacturing first requires the easy flowing of the ink through the nozzle and then a suitable viscoelastic response for the shape retention of the 3D printed structure. In the present study, fused silica pastes with different particle size distributions varying from D90 of 5–50 µm were prepared for direct ink writing of porous structures. The rheological properties of the pastes, including flow behavior and the viscoelastic moduli variations, were investigated to study the influence of particle size and its distribution on fabricating complex structures. Through investigations, it was found that the narrower size distributions were more appropriate for direct ink writing of fused silica pastes. As the distribution became narrow, the shear thinning behavior was intensified, and the pastes showed high elasticity. The sintering procedure was performed using microwave radiation to suggest a fast process for manufacturing fused silica complex parts containing partially crystallized cristobalite phase and providing porosity of about 10% and a relative density of 90%.

Stereolithography-based additive manufacturing of polymer-derived SiOC/SiC ceramic composites

In order to overcome challenges typically encountered during additive manufacturing of ceramics via the polymer precursor route, a novel polymer-derived SiOC/SiC composite system suitable for advanced geometric designs achievable by lithography-based ceramic manufacturing was established. The photoreactive resin system filled with 20 wt% SiC exhibits suitable viscosity characteristics, adequate stability against sedimentation, and a fast photocuring behavior. After printing and pyrolytic conversion, SiC particulates were well-dispersed within the polymer-derived SiOC matrix. A direct comparison with the unfilled polysiloxane-based resin system showed that the addition of particulate SiC increases handleability, reduces shrinkage, and significantly increases critical wall thicknesses up to 5 mm. The biaxial Ball-on-Three-Balls testing methodology yielded a characteristic strength of 325 MPa for SiOC/SiC composites. The results highlight the high potential of particle-filled preceramic polymer systems toward the fabrication of high-performance SiC-based materials by lithography-based additive manufacturing.

The Influence of Microstructure on the Flexural Properties of 3D Printed Zirconia Part via Digital Light Processing Technology.

In recent years, additive manufacturing of ceramics is becoming of increasing interest due to the possibility of the fabrication of complex shaped parts. However, the fabrication of a fully dense bulk ceramic part without cracks and defects is still challenging. In the presented work, the digital light processing method was introduced for fabricating zirconia parts. The flexural properties of the printed zirconia were systematically investigated via a three-point bending test with the digital image correlation method, scanning electron microscopy observation and fractography analysis. Due to the anisotropy of the sample, the bending deformation behaviors of the zirconia samples in the parallel and vertical printing directions were significantly different. The flexural strength and the related elastic modulus of the samples under vertical loading were higher than that of the parallel loading, as the in-plane strength is higher than that of the interlayer strength. The maximum horizontal strain always appeared at the bottom center before the failure for the parallel loading case; while the maximum horizontal strain for the vertical loading moved upward from the bottom center to the top center. There was a clear dividing line between the minimum perpendicular strain and the maximum perpendicular strain of the samples under parallel loading; however, under vertical loading, the perpendicular strain declined from the bottom to the top along the crack path. The surrounding dense part of the sintered sample (a few hundred microns) was mainly composed of large and straight cracks between printing layers, whereas the interior contained numerous small winding cracks. The intense cracks inside the sample led to a low flexural property compared to other well-prepared zirconia samples, which the inadequate additive formulations would be the main reason for the generation of cracks. A better understanding of the additive formulation (particularly the dispersant) and the debinding-sintering process are necessary for future improvement.

Formation mechanism and controlling strategy of lamellar structure in 3D printed alumina ceramics by digital light processing

Digital light processing has brought great improvements to ceramic material shaping, along with new challenges to the control of material structures and properties. Its layer-by-layer manufacturing pattern always results in a lamellar structure or sintering shrinkage anisotropy. This study introduces a simple strategy for revealing the spatial distribution of the ceramic powders and resin in a printed precursor, by which the formation mechanisms of the lamellar structure during the printing process can be studied. The results show that the sedimentation of the ceramic powders leads to resin enrichment between the layers. After the debinding process, the layers are indirectly connected by discrete ceramic particles, resulting in the lamellar structure. In addition, the evolution of the lamellar structure throughout the entire sintering process and its effects on the sintering shrinkage and strength of the printed ceramics are investigated. The disappearance of the large pores distributed at the layer interfaces during the sintering contributes to the extra shrinkage in the height direction. By combining the experimental data and finite element method, it is revealed that the lamellar structure shows different deformation behaviors under loadings with varying directions, leading to an apparent strength anisotropy. In addition, a design strategy is discussed for the lamellar structure, i.e., for controlling the strength anisotropy and its corresponding application. This study can be of great assistance for the design of structures and strengths in the additive manufacturing of ceramics.

Role of Mixing Method and Solid Content on Printability of Alumina Inks for Stereolithography 3D Printing Process

Additive manufacturing of ceramics via stereolithography method is a promising way to fabricate high-resolution ceramic parts with complex geometry, which is hard to obtain with traditional ceramic shaping methods. In order to shape the ceramics with the Digital Light Processing (DLP), a mixture of photocurable resin and ceramic powders, called ink, must be prepared. In this paper, the printability of the Alumina-glass inks, with different solid contents were prepared by two mixing methods, having long and short mixing durations. In order to evaluate the printability of inks, the rheological behavior of suspensions was investigated, and printing parameters such as curing time and layer thickness were changed. The ceramic-resin suspensions were prepared via 24-hour ball-milling and 10,000 rpm mechanical homogenizing. The suspension containing 60 wt% solid content and prepared by mechanical homogenizing showed the best stability with 8% sedimentation within 4 days and the lowest viscosity of 1.37 Pa·s at shear rates of 30 s-1, exhibiting a suitable viscosity for DLP printing. Therefore, a mechanical homogenizer can be a promising and quick method for mixing by providing simultaneously appropriate rheology and printability.

Additive manufacturing of ceramics and cermets: present status and future perspectives

The present decade has witnessed a huge volume of research revolving around a number of Additive Manufacturing (AM) techniques, especially for the fabrication of different metallic materials. However, fabrication of ceramics and cermets using AM-based techniques mainly suffers from two primary limitations which are: (i) low density and (ii) poor mechanical properties of the final components. Although there has been a considerable volume of work on AM based techniques for manufacturing ceramic and cermet parts with enhanced densities and improved mechanical properties, however, there is limited understanding on the correlation of microstructure of AM-based ceramic and cermet components with the mechanical properties. The present article is aimed to review some of the most commonly used AM techniques for the fabrication of ceramics and cermets. This has been followed by a brief discussion on the microstructural developments during different AM-based techniques. In addition, an overview of the challenges and future perspectives, mainly associated with the necessity towards developing a systematic structure-property correlation in these materials has been provided based on three factors viz. the efficiency of different AM-based fabrication techniques (involved in ceramic and cermet research), an interdisciplinary research combining ceramic research with microstructural engineering and commercialisation of different AM techniques based on the authors’ viewpoints.

Additive manufacturing of ceramics and cermets: present status and future perspectives

Additive manufacturing of ceramics and cermets: present status and future perspectives

Unit cell estimation of volumetrically-varying permittivity in additively-manufactured ceramic lattices with X-ray computed tomography

Additive manufacturing of ceramics is transforming electromagnetics by providing density-varying lattices and stochastic foams within arbitrary envelopes. Periodic structures can now be fabricated with zirconia which offers the highest permittivity of any 3D printable material possible to be printed with nearly-full-density. By arranging a lattice with variation in the strut and node sizings as well as unit cell dimensions, the effective density of a structure can be spatially-modulated gracefully and with unprecedented freedom. These variations in density directly translate into variations in the effective permittivity of the bulk lattice (estimated locally and globally with a combination of mixing formulas, curve fits, and capacitance models). A lattice had previously been fabricated with a rectangular envelope for evaluation of effective global permittivity of the overall structure using a network analyzer. For this work, the structure was scanned with X-ray computed tomography (CT) to capture the three dimensional density of the structure including both the solid ceramic elements as well as the interstitial space. Software was developed that reads CT scan data and provides a 3D data structure with a pointwise unit cell estimation of the effective permittivity throughout the volume - a model well suited for electromagnetic simulations to optimize advanced microwave devices. The proposed technique serves as a foundation for the non-destructive estimation of space-varying permittivity within 3D printed lattices and foams.

Additive manufacturing of ceramics from thermoplastic feedstocks

Ceramics are a class of materials delicate to shape due to their inherent inability to plastically deform. Conventional shaping processes utilizing thermoplastic feedstock that mimic plastic deformation were successful in providing ceramic parts with high quality, but with limited shape complexity. Additive manufacturing (AM) has revolutionized the shaping of ceramics, allowing for realization of components with increased complexity and precision. This paper reviews the current state of AM technologies with emphasis on the techniques based on modelling of thermoplastic feedstocks. Namely, fused filament fabrication (FFF) is widespread and cost-effective AM technology, however, limited by relatively low resolution and poor surface finish. On the other hand, thermoplastic 3D printing (T3DP), emerged recently as a high-precision, high surface finish AM technology. With further development in these processes as well as materials that can be shaped, it is expected that thermoplastic feedstock based processes will be more prominent in AM of ceramics.

3D printing of fine alumina powders by binder jetting

Additive manufacturing of ceramics is still at an early-development stage; however, the huge interest in custom production of these materials has led to the development of different techniques that could provide highly performing devices. In this work, alumina (α-Al2O3) components were produced by binder jetting 3D printing (BJ), a powder-based technique that enables the ex-situ thermal treatment of the printed parts. The employment of fine particles has led to high green relative density values (>60 %), as predicted by Lubachevsky-Stillinger algorithm and DEM modelling. Then, extended sintering has been observed on samples treated at 1750 °C that have reached a final density of 75.4 %. Finally, the mechanical properties of the sintered material have been assessed through bending test for flexural resistance and micro-indentation for Vickers hardness evaluation.

Additive Manufacturing of Ceramics Using a Fused Deposition Modeling (FDM)-Type 3D Printer and Their Microwave Sintering and HIP Treatment

Additive Manufacturing of Ceramics Using a Fused Deposition Modeling (FDM)-Type 3D Printer and Their Microwave Sintering and HIP Treatment