The selection of binders in ceramic additive manufacturing plays a high role in determining the feasibility and quality of printed components. This study investigates the performance of sodium carboxymethylcellulose (CMC) and hydroxypropylmethylcellulose (HPMC) as bio-based binders in aqueous alumina suspensions for direct ink writing (DIW). CMC, characterized by its polyelectrolyte nature, demonstrated rapid dissolution, exceptional dispersion stability, and consistent rheological properties, facilitating smooth extrusion and the formation of high-quality surfaces. These characteristics are critical for DIW, where ink homogeneity and stability directly impact printing resolution and part integrity. HPMC, by contrast, exhibited slow dissolution, thermally induced gelation, and printing inconsistencies, likely due to its lack of electrostatic stabilization. Microstructural and mechanical evaluations of sintered parts confirmed that CMC-based systems achieved higher density, homogeneity, and microhardness. This study highlights the significance of CMC as a binder, providing a pathway to overcome common challenges in DIW, such as agglomeration, foaming, and poor sintered properties, while enabling the production of high-performance ceramic components.

Pressureless of boron carbide (B4C) is very promising to produce high performance B4C parts useful in many applications. However, processing dense, complex-shaped components from coarse B4C powders remains particularly challenging due to coarsening-driven sintering and the very high temperatures required. In this work, direct ink writing (DIW) printable B4C suspensions were formulated using a tailored anionic carboxymethylcellulose binder, specifically designed to enable rapid, high height printing of coarse B4C powders. The recyclability of defective printed parts was also investigated. Conventional dilatometric sintering confirmed that coarse B4C powders undergo extensive grain coarsening and incomplete densification at 2200 degrees C, and sintering aids did not yield significant improvements. To overcome these limitations, ultra-high temperature pressureless spark plasma sintering (UHTP-SPS) was applied at similar to 2350 degrees C with rapid heating (200 degrees C/min), achieving near-full densification without additives. The resulting bimodal microstructure delivered high hardness values up to 33.6 GPa while maintaining flexural strength despite grain growth. Notably, recycled-route parts showed comparable properties to conventional ones, confirming the feasibility of reusing defective components. This study establishes a promising pathway for the cost-effective and sustainable fabrication of dense B4C components from coarse powders through rapid and high-temperature sintering.

Hard carbon derived from bio-based sources such as tannins is gaining attention for applications in energy storage, catalysis, and lightweight structures, due to its sustainability and high mechanical properties. However, the fabrication of 3D hard carbon objects via vat photopolymerization (VP) remains challenging because of rheological instability, polymerization inhibition by tannins, and shrinkage during pyrolysis. In this study, we demonstrate that tannin can be processed using professional VP with an optimized photocurable formulation composed of highly reactive, viscous dipentaerythritol hexaacrylate (DPHA), 1,6-hexanediol diacrylate (HDDA) as a fluidifying agent, and a photoinitiator, without added dispersants. By systematically increasing the tannin content (30-50 wt%) and adjusting the DPHA/HDDA ratio, we optimized viscosity, suspension stability, curing behavior, and dimensional fidelity during pyrolysis. Unlike previous approaches that mainly focus on porous carbon architectures, our method maximizes tannin loading (up to 45 wt%) to achieve nearly fully dense and high mechanical performance hard carbon with controlled shrinkage deformations. The optimized formulation, featuring a DPHA/HDDA ratio of 80/20, delivers the best compromise between rheology, curing performance, and structural integrity. Significantly improved directional mechanical properties were obtained, with 39 MPa of compressive strength, which is between porous hard carbon (<5 MPa) and dense graphite (similar to 150 MPa). This work establishes a robust pathway for VP-based fabrication of complex, defect-free 3D hard carbon objects from bio-derived precursors, offering high mechanical performance and pyrolysis-based tunable electro-thermal properties ranging from an insulating to a conductive state. This represents potential applications in high-strength, high-temperature materials or 3D electronic architectures with tunable properties.

This study explores the influence of SiC reinforcement on the microstructure, mechanical properties and ballistic performance of Al2O3-SiC composites fabricated by Spark Plasma Sintering. Composites containing 1 to 30 vol% SiC were processed using optimized SPS cycles to ensure high densification and controlled microstructural development. The addition of SiC led to significant improvements in hardness, fracture toughness and Young's modulus with the best compromise observed at 25 vol% SiC, sintered at 1600 degrees C. At this composition, a 30 % reduction in residual depth of penetration versus 7.62 mm x 51 FMJ/PB/HC AP P80 (0.308 Win) threat was measured compared to pure alumina, confirming the effectiveness of SiC reinforcement in enhancing ballistic resistance. Although higher SiC contents (>= 25 vol%) resulted in the formation of mullite and a slight decrease in fracture toughness, the 25 vol% SiC composite offers an optimal balance between mechanical performance and cost-efficiency. These results position Al2O3-SiC composites as promising materials for lightweight and affordable ballistic protection systems.

Vat photopolymerization debinding exhibits complex behavior depending on layer-by-layer deposition, scraping, lasing conditions, anisotropy of shrinkage, polymer decomposition, and shape thickness environments, making debinding cracks difficult to predict through conventional modeling approaches. One alternative is to experimentally explore different lasing, printing, and geometrical features and map the parameter space by regions where cracks appear. Since this space is challenging to model analytically, machine learning can be effectively used to predict outcomes within this experimentally determined domain. This experimental-modeling approach offers a simple and practical method to determine the probability of cracking for a given shape type. Despite the small dataset size (45 samples), the structured (grid-like) experimental design and use of cross-validation enable robust modeling of crack formation in honeycomb geometries.

High speed and automation are key aspects of Industry 4.0. With the advent of Ultrafast High Temperature Sintering (UHS), the concept of ultrafast, energy-efficient fabrication is becoming a reality. However, this fast sintering approach is limited by the long prior stages of production, including printing, drying, and debinding. In this work, a significant breakthrough has been achieved to enable ultrafast printing under specific rheological conditions using Direct Ink Writing (DIW), while drastically reducing both drying and debinding times. A low-organic content suspension was developed, enabling the ultrafast extrusion of self-supported, thin-walled complex parts with nozzle sizes down to 0.4 mm. With this formulation, drying and debinding times were significantly reduced, from several days to just 20 and 30 min, respectively. The sintering process, based on UHS, was successfully adapted through Pressureless Spark Plasma Sintering (P-SPS), allowing the densification of large and complex parts. A comprehensive multiphysics simulation tool for large-scale UHS was developed, capable of capturing the complex thermal irradiation environment and its impact on final microstructures. Finally, the concept of a continuous ultrafast manufacturing line is introduced and demonstrated, showcasing the potential for producing complex ceramic parts within just a few hours.

Ultrafast High-Temperature Sintering (UHS) enables near-instantaneous densification of ceramics but is limited by part size, wall thickness, and cracking due to thermal inhomogeneities. This work introduces a scalable UHS approach using a modified Spark Plasma Sintering (SPS) chamber with a large working volume (similar to 113 cm(3)) and precise control, enabling the sintering of complex ceramic parts up to 30 mm. Direct Ink Writing (DIW) is employed to shape and debind components efficiently while preserving UHS advantages. A parametric study identifies optimal heating rates and critical wall thicknesses (<= 1 mm) to minimize thermal stress. Finite element simulations link thermal gradients to stress development, offering predictive capability for complex geometries. The results reveal that organic binder decomposition strongly affects grain growth and residual porosity under ultrafast heating. This work demonstrates the feasibility of industrially scalable UHS and provides key insights for microstructure control and simulation-guided process design.

This study focuses on preparing and optimizing a submicron zirconia (ZrO2) suspension for vat photopolymerization (SLA) 3D printing. The suspension includes TZ-3YS-E zirconia powder, acrylate-based monomers (HDDA and TMPTA), a dispersant (Disperbyk-103), and a photoinitiator (TPO). It was prepared using a ball-milling process to ensure homogeneity and optimal dispersion. Rheological properties were assessed to determine the ideal dispersant concentration and milling time, aiming for a low-viscosity and stable suspension. Sedimentation tests were performed to evaluate suspension stability, identifying optimal parameters at 5 wt.

Direct Ink Writing (DIW), or robocasting, is a rapid extrusion-based additive manufacturing technique offering significant potential for fabricating complex ceramic technique components as alumina, due to its exceptional mechanical strength, thermal stability, and wear resistance. This study explores the preparation of aqueous alumina suspension with different alumina powder with a minimal organic content to optimize suspension preparation for robocasting. Three alumina powders, including expensive fine grain powder to cheaper and coarser powder (BMA15, P172LSB and APA-0.5), were used to develop suspensions via a one-step ball milling process, aiming at replicating the properties of a reference suspension of the finest powder while minimizing the amount of organic additives. The suspensions were designed to exhibit shear thinning behavior with defined yield stress for smooth extrusion and post deposition shape retention. The developed suspensions, containing less than 5 vol% of organic additives have demonstrated excellent stability, homogeneity, and absence of agglomerates. Successful printing of two distinct parts with these three suspensions confirmed their capability to maintain high yield stress, enabling the stacking of multiple layers and fabrication of complex geometries. The parts made from the finest alumina powder exhibit a microstructure and mechanical properties (BMA15: 1874 +/- 48 HV, 2.78 mu m of grain size) comparable to those conventionally manufactured ceramic. The two other suspensions, with coarser powders, exhibit similar mechanical properties (P172LSB: 1794 +/- 30 HV and 3.3 mu m of gran size, APA-0.5: 1718 +/- 60 HV and 2.76 mu m of grain size).

Stereolithography of UV-curable ceramic suspensions is an additive manufacturing technique with high precision and great resolution to fabricate complex ceramic parts. While it widens the possibilities of applications, one of the drawback of this method is the low wall-thickness of the parts. The polymers forming the network structure upon cross-linking undergo pyrolysis in a step called debinding. During debinding, the gaseous compounds going through evacuation channels create internal pressures, often resulting in crack formation. So far, the critical wall-thickness where crackfree parts are obtained is located around 4 millimeters for silicon nitride. This paper reports the successful debinding of silicon nitride parts obtained by stereolithography. Thanks to an optimization of the debinding relying on TGA analysis, defectless parts with a wall-thickness of up to 11mm were obtained, yielding parts of 9mm after sintering. The mechanical properties were measured, showing values equivalent to silicon nitride obtained through conventional methods.

Material extrusion, also known as Robocasting or Direct Ink Writing (DIW) is an efficient and eco-friendly additive manufacturing method for fabricating large and thick ceramic components, such as alumina. While screwbased extrusion is the prevalent approach due to its precise control over printing parameters, pneumatic-based extrusion is gaining attention for its suitability in automated processes and reduced handling requirements. However, pneumatic extrusion faces challenges, primarily the narrower range of printable rheological behavior. Achieving a balance between extrudability and the self-supporting capacity of printed structures is critical. Moreover, bubble elimination, easily addressed in screw-based extrusion, remains a significant challenge in pneumatic systems. To overcome these issues, optimal concentrations of dispersants, ceramic loading, and additives were determined to achieve the desired shear-thinning rheological properties suitable for pneumatic extrusion. Additionally, this study, by employing a rapid one-step ball milling method for suspension preparation, is somewhat unique, providing a streamlined alternative to traditional processes. A degassing study was conducted to minimize bubble formation, ensuring print quality. Using the optimized parameters, including extrusion pressure and layer height, complex structures were successfully printed. After sintering at 1450 degrees C, the samples exhibited a 99.5 % dense microstructure with an average grain size of 1.71 mu m. The alumina demonstrated excellent mechanical properties, achieving a hardness of 2094 HV at 1450 degrees C, which is well aligned with the literature.

Si3N4 is an advanced ceramic highly attractive for applications in aeronautics, aerospace, and other industries. Additive manufacturing (AM) is suitable for producing advanced ceramic parts with complex shapes, eliminating the need for machining to achieve the final component (near-net-shape concept), thereby reducing costs. In this context, direct ink writing (DIW), which involves the extrusion of low organic aqueous suspensions, is well-suited for the rapid printing of large shapes with varying wall thicknesses. In this work, the formulation of a Si3N4 aqueous suspension has been fully developed. The optimal adding amounts of dispersant, ceramic loading, and organic binders have been determined to achieve suitable rheological properties for DIW. The suspension rheology has been adjusted to produce tall, self-supported, thinner parts, such as radomes, which are particularly challenging due to their sensitivity to slumping. These parts were sintered at 1850 °C in N2 atmosphere and exhibit a distinctive microstructure with typical non-equiaxed Si3N4 needle-like grains. The microhardness value of 1505 HV and the flexural strength of 374 MPa were comparable to Si3N4 ceramics fabricated through conventional processing.

Honeycomb lattice structures are commonly used to optimize the weight-to-strength ratio in 3D printing, but during high-temperature sintering, these parts are prone to distortions that current tools struggle to predict. To address this, we developed a comprehensive lattice/shell sintering model. Our approach calculates the effective sintering moduli of the honeycomb using virtual shear and isostatic tests, accounting for both material and structural anisotropy. A key challenge was ensuring synchronized sintering behavior between the thick shell and lattice, preventing distortion errors. This continuum simulation method, validated through bar sintering tests, significantly reduces computational demands, making it ideal for design and optimization studies.

This study presents the development of a fully instrumented sinter-forging process using a 915MHz solid-state microwave source for the rapid and controlled sintering of dense oxide ceramics. Compared to conventional magnetron-based systems, the solid-state microwave source enables precise frequency tuning for optimal impedance matching and resonance conditions. Modeling and experimental characterization of the microwave applicator have enabled us to position the sample correctly in the cavity, ensuring efficient energy transfer and homogeneous heating. Sintering experiments carried out on alumina powder, both with and without applied pressure, revealed that the pressure-assisted process significantly improved densification, yielding near-complete density and increased hardness (21.6GPa), while maintaining fine microstructures. This method highlights the potential of microwave-assisted sinter-forging for producing advanced ceramics with improved properties.

This study investigates the influence of punch holes, designed for temperature measurements using an axial pyrometer during Spark Plasma Sintering (SPS), on pressure and temperature distribution and its potential connection to microstructural heterogeneities in dense ceramics. By combining experimental investigations using pressure measurement films and finite element simulations, the results reveal significant pressure gradients exceeding 80 MPa for a nominal applied load of 100 MPa, caused by the presence of punch holes. The study further explores strategies to optimize punch design to reduce pressure gradients while maintaining accurate temperature measurements. It is shown that optimizing the tooling design improves microstructural homogeneity and leads to a slight increase in the ceramic's relative density. However, some residual heterogeneity remains, primarily due to lateral stresses and thermal gradients, rather than the punch design. This work provides practical guidelines for improving SPS processing conditions to achieve more homogeneous sintered ceramics.

Pressure-assisted sintering models involve numerous closely correlated parameters that depend on temperatures, porosity, and microstructure development. Consequently, the identification of the model parameters is relatively lengthy and requires experiments to extract the underlying creep behavior (pressure/temperature dependent), shear, bulk sintering moduli that are porosity-dependent, and grain growth. Knowing that certain sintering mechanisms are grain-size dependent, it is very difficult to assess the densification behavior for the case of ceramics. We have already developed a sinter-forging method to assess independently all parameters for ceramics. However, this method implies numerous interruption tests to measure the specimen diameter evolution, and the capillarity forces were neglected. In this study, an instrumented microwave sinter-forging prototype avoiding highly repetitive interruption tests has been developed to record the specimen diameter evolution of submicronic alumina powder samples. The new method includes the effect of the capillarity forces on the identification equations, making the model more realistic for submicronic ceramics. The resulting model was tested on a finite element code for validation and to explore its stability for complex shapes.

Most parts printed with additive manufacturing used a bioinspired filling strategy with a dense shell and internal lattices. Such strategy helps optimizing the part strength/weight ratio through topology optimization and significantly improve the printing time and quality. However, simulate such complex porous inner structures would imply calculation instabilities and a colossal increase of the simulation time through the high number of degrees of liberty. Consequently, there is today no robust solution to simulate the sintering of printed parts with inner lattices, despite the fact that it represents the majority of the printed objects. This study circumvents this issue by a continuum approach that can simulate real parts and the complex lattice behavior with a computation time representing a small fraction of the sintering time. The lattice geometry is first simulated by a sub-model with identifies their effective moduli for different porosity. These effective moduli are then used to simulate the sintering in the lattices zones of the printed parts. The lattices also significantly decrease the inner part thermal conductivity. An additional sub-model is used to extract the effective lattice thermal conductivity by a simulation considering the thermal conduction in the lattice skeleton and the cavities thermal radiation and convection. A robust thermomechanical simulation is then possible to quickly and efficiently predict the parts firing with the developed thermal gradients and the distortions it results as well as the inherent anisotropy that greatly influence the final part dimensioning.

The production by Spark Plasma Sintering (SPS) of parts with a high complex shapes is difficult due to the die pressing which imposes adapting the die and punches in too complex and fragile configurations. To overcome this problem, a patented approach called “DEFORMINT”, allows the production of fully dense complex shape parts by coupling 3D printing and SPS technologies. Thus, an assembly of two powder beds, one constitutive of the desired complex shape part while the second one is sacrificial, separated by a 3D printed interface sinter simultaneously. The easiest way to avoid any shape distortions of the part is to use the same powder for both the complex shape and the sacrificial parts. However, for high-added value parts, the cost of the materials and the high quantity of sacrificial material needed in this method reduces its inherent economic interest. To circumvent this issue particularly for Ti–6Al–4V, a low-cost ceramic–metal powder mixture that mimics its sintering was identified and tested in this study. SPS experiments were used to determine a densification model of this sacrificial powder and to predict the densification distortions of two shapes: a thick cone and a thin and complex turbine blade. The simulated and experimental distortions were compared and showed a good correlation with the predicted shape distortions. Microstructural analysis revealed a high hardness globular microstructure and a skin effect in the contact with the interface. This process provides valuable outcomes for prototyping, as well as for complex structural parts with thick geometries that are less sensitive to the skin effect (in contrast to SLM, which is more effective for thin shapes). It can create significant opportunities in the space, aeronautics, and engine industries.

The production of complex shapes via Spark Plasma Sintering (SPS) is challenging due to intricate die configurations. The "DEFORMINT" approach combines 3D printing with SPS and sacrificial powder to fabricate fully dense shapes. Using the same powder for both the component and sacrificial part avoids distortions, but high costs of titanium alloys like Ti-6Al-4 V are limiting. This study tested a low-cost ceramic powder that mimics Ti6Al-4 V's behavior, forming a pseudo-isostatic configuration above 1250 K. SPS experiments established a densification model and predicted distortions in a thick cone and a thin, complex turbine blade, showing good correlation with experimental results. The new sacrificial mix does not imply additional deformation and allows the fabrication of turbine blades. The only defect is a 600 mu m skin effect at the contact interface.