3D printing of SiC ceramic: Direct ink writing with a solution of preceramic polymers

3D structured SiC ceramics with varying feature sizes (100–400?μm) were achieved by direct ink writing of polycarbosilane (PCS)/n-hexane solution. The rheological properties of the PCS solution and printing parameters were tailored for optimum writing behaviour. The integrity and clear surface of the filaments indicated the printing ability of forming the self-supporting features along with the rapid evaporation of solvent. As-printed 3D structured PCS was processed by oxidative crosslinking and pyrolysis and converted to SiC ceramic. Although strong shrinkage occurred during the pyrolysis, SiC ceramic maintained the original 3D structure. Both proper viscoelasticity of printable solutions and the homogeneous shrinkage in the pyrolysis determine the integrity and feature characteristic of 3D structured SiC using direct ink writing preceramic polymer.     

3D printing of honeycomb Si3N4 ceramic

In this paper, a honeycomb Si₃N₄ ceramic was fabricated by 3D printing with a well-preserved structure. The effects of Si₃N₄ content on the rheological properties of Si₃N₄/sol–silica ink and the printing resolution of products were investigated. The microstructure, phase composition, liner shrinkage rate, and fracture behavior of printed samples before and after sintering were systematically characterized in detail. The results showed that the modified inks had the optimized rheological properties, and the stress–shear rate curves corresponding to each slurry could be well described by Bingham and Herschel–Bulkley fluid models. The corresponding slump rates of the printed samples with different Si₃N₄ to sol–silica mass ratios were all lower than 4%, and the linear shrinkage rate of all of the samples after sintering was below 20%. The fracture behavior under compressive loading of the honeycomb Si₃N₄ ceramics tended to be non-catastrophic fractures both before and after sintering. The compressive strengths of all of the printed samples decreased with the increase of the Si₃N₄ content, and the highest compressive strength of the honeycomb ceramics could reach 131.2 MPa after sintering at 1600°C, which was about 366.9% higher than that of the samples in green state prior to the sintering.     

3D printing of porous low-temperature in-situ mullite ceramic using waste rice husk ash-derived silica

The in-situ mullite (3Al₂O₃·2SiO₂) foams are fabricated by 3D printing (direct ink writing (DIW)) technique and utilize waste rice husk ash (RHA). The Al₂O₃-SiO₂ inks are prepared using an aqueous binder with α-alumina and two different silica sources, i.e., RHA extracted biogenic nano-silica (NS) and commercial silica (CS). The ink rheological features are first designed in terms of solid-to-liquid ratio and dispersant, and found that a higher amount of dispersant is needed for functionalization of NS-containing ink than CS (micro-sized) consisting of ink. Secondly, the DIW log-pile structures are fired at different temperatures (1200?1500 °C), and NS containing samples exhibited remarkable enhanced properties at a lower firing temperature than CS. At 1400 °C, alumina and RHA nano-silica entirely transformed into mullite and retained ～75 % porosity, ～8 MPa cold compressive strength, and thermal conductivity ～0.173 W/m·k that designate a simple and effective way to fabricate of mullite foamy structure.     

Preparation of Si3N4 ceramic based on digital light processing 3D printing and precursor infiltration and pyrolysis

The emergence of digital light processing (DLP) 3D printing technology creates favorable conditions for the preparation of complex structure silicon nitride (Si₃N₄) ceramics. However, the introduction of photosensitive resin also makes the Si₃N₄ ceramics prepared by 3D printing have low density and poor mechanical properties. In this study, high-density Si₃N₄ ceramics were prepared at low temperatures by combining DLP 3D printing with precursor infiltration and pyrolysis (PIP). The Si₃N₄ photocurable slurry with high solid content and high stability was prepared based on the optimal design of slurry components. Si₃N₄ green parts were successfully printed and formed by setting appropriate printing parameters. The debinding process of printed green parts was further studied, and the results showed that samples without defects and obvious deformation can be obtained by setting the heating rate at .1°C/min. The effect of the PIP cycle on the microstructure and mechanical properties of the Si₃N₄ ceramics was studied. The experimental results showed that the mass change and open porosity of the samples tended to be stable after eight PIP cycles, and the open porosity, density, and bending strength of the Si₃N₄ ceramics were 1.30% (reduced by 97%), 2.64 g/cm³ (increased by 43.5%), and 162.35 MPa.     

3D printing of open-porous cellular ceramics with high specific strength

We present a novel processing route for manufacturing highly open porous, hierarchically structured ceramics via direct ink writing. We manufactured cellular samples with overall porosities up to 88% that exhibit fully open-porous struts with porosities between 45 and 60% and pore sizes x_50,3 < 6 μm using capillary suspension based inks. An innovative processing strategy enabled manufacturing crack-free, undeformed cellular ceramic samples.We printed hexagonal honeycomb structures that showed exceptionally high specific strength under compression load and significantly enlarged the strength-density range that was covered by sintered capillary suspensions, so far. Without loss of mechanical strength the density of ceramic parts was decreased by about a factor of 2–3. Strength of in-plane and out-of-plane loaded hexagonal honeycomb structures varies according to common scaling laws for cellular structures. The honeycombs are mechanically more efficient than bulk specimens from capillary suspensions, since they show a distinctly lower sensitivity of strength on density.     

Preparation of high solid loading and low viscosity ceramic slurries for photopolymerization-based 3D printing

In this study, high solid loading and low viscosity cordierite slurries are successfully developed for the first time for photopolymerization-based additive manufacturing. The processability of the slurries is mainly determined by their rheological properties and photocuring parameters. The slurry preparation involves the orthogonal optimization of compositions in order to achieve suitable viscosity, stability and homogeneity. The photocuring parameters of the as-prepared slurries, including penetration depth D_p and critical exposure E_c, are also determined experimentally. Results show that viscosity increases with reduction in particle size. A higher solid-volume fraction also results in an exponential growth in viscosity. As for the dispersant amount, a concentration of 5?wt% leads to the lowest viscosity. Particle size also play an important role in the solid loading capacity of the slurries, as results suggest that smaller particles improve performance. In terms of the photocuring behaviors, the addition of 2?wt% photoinitiator generates an optimal curing process. 40?vol% solid loading leads to the thickest curing depth for all slurries with different types of particle sizes. Finally, a cordierite part with a complex hollow structure and a fine resolution is successfully fabricated. The present study offers a material basis for the polymerization-based 3D printing of porous cordierite structures.     

Mechanical and dielectric properties of direct ink writing Si2N2O composites

Si₂N₂O composites were achieved via direct ink writing technique and pressureless sintering. The design and optimization of inks and the effect of mass ratio of Si₃N₄ and SiO₂ on the phase composition, microstructure, mechanical properties and dielectric properties of composites were systematically investigated. The inks exhibit superior stability and printability. Increasing SiO₂ content facilitated densification and enhancement of mechanical property. The generation of β-Si₃N₄ and Si₂N₂O and the nucleation of cristobalite were restrained by high content SiO₂. The ceramic composites with the flexural strengths from 74.1MPa to 104.9MPa and low dielectric constant (≤4.68) were fabricated. This strategy provides a systematic reference for synthesis of high-performance porous Si₂N₂O composites based on the DIW.     

UV-assisted direct ink writing of Si3N4/SiC preceramic polymer suspensions

Direct ink writing (DIW) offers a flexible and readily available processing route for achieving ceramic components with complex shapes and geometries. The successful printing of ceramic green bodies using DIW typically requires the formulation of particle-loaded inks having a narrow window of rheological properties that enable both flow through the nozzle and support the weight of additional layers. Herein, we present a method for DIW that employs UV-curing to enable printing of otherwise unprintable inks. The inks used in this study are suspensions consisting of a commercially available polycarbosilane precursor and silicon nitride, Si₃N₄, powders. A diacrylate cross-linker and photointiator were employed to enable UV-curing. The effect of cross-linker content on UV-rheology and cure depth as they pertain to printing, and slump in self-supported lattice structures, are discussed. UV-assisted DIW produced components of a high degree of complexity, capable of supporting over-hanging structures, low shrinkage, and relatively high degree of ceramic conversion     

3D microstructure model and thermal shock failure mechanism of a Si3N4-bonded SiC ceramic refractory with SiC high volume ratio particles

In this study, an efficient method was proposed to establish 3D microstructure model of a Si₃N₄-bonded SiC ceramic refractory with SiC high volume ratio particles and its failure mechanism under thermal shock was studied based on the established microstructure model. The proposed modeling method based on modified 3D Voronoi tessellation method and “precise shrinkage ratio method” was able to establish 3D geometric model of a SiC ceramic refractory with SiC high volume fraction particles more quickly than usual methods. The modified 3D Voronoi tessellation method generated Voronoi polyhedrons (VPs) limited in finite space perfectly. The proposed “precise shrinkage ratio method” achieved a precise volume fraction of SiC particles in the established microstructure model. The crack initiation and propagation under thermal shock were calculated by employing the extended finite element method (XFEM) on the established microstructure model. The results showed the failure mode on micro-scale clearly and efforts of interface strength on the failure mode were also explored. The proposed modeling method was especially suitable for establishing 3D microstructure models of ceramic composites or isotropic metal-ceramic particle composites with high volume fraction particles and extended the use of VPs.     

Fabrication and characterization of carbon fiber reinforced SiC ceramic matrix composites based on 3D printing technology

A novel method has been developed to fabricate carbon fiber reinforced SiC (C_f/SiC) composites by combining 3D printing and liquid silicon infiltration process. Green parts are firstly fabricated through 3D printing from a starting phenolic resin coated carbon fiber composite powder; then the green parts are subjected to vacuum resin infiltration and pyrolysis successively to generate carbon fiber/carbon (C_f/C) preforms; finally, the C_f/C preforms are infiltrated with liquid silicon to obtain C_f/SiC composites. The 3D printing processing parameters show significant effects on the physical properties of the green parts and also the resultant C_f/C preforms, consequently greatly affecting the microstructures and mechanical performances of the final C_f/SiC composites. The overall linear shrinkage of the C_f/SiC composites is less than 3%, and the maximum density, flexural strength and fracture toughness are 2.83?±?0.03?g/cm³, 249?±?17.0?MPa and 3.48?±?0.24?MPa m^1/2, respectively. It demonstrates the capability of making near net-shape C_f/SiC composite parts with complex structures.     

3D printing of piezoelectric barium titanate with high density from milled powders

Piezoelectric ceramics are essential for electronic industries due to the capabilities of converting mechanical stresses to an electric field, or vice versa. Three-dimensional printing provides the shaping flexibility, however, piezoelectric properties should be further improved. In this work, barium titanate is manufactured by extrusion freeforming derived from milled precursors. The pure tetragonal phase is formed at 950 °C, which is lower than conventionally required temperature for un-milled counterparts. Upon extrusion, a self-supporting green part could be obtained. Moreover, post processing is necessary for the solid-state reaction and particle sintering to achieve dense structures. It is observed that sintered ceramics reach the maximum density of 5.66 g/cm³ which exhibits excellent piezoelectric and dielectric properties of 420 pC/N and 4380 at 1 kHz, respectively. This printing technique from milled powders is a promising approach to enable the mass production and customization of piezoelectric devices, a cost reduction is therefore foreseen.     

Preparation of broadband transparent Si3N4-SiO2 ceramics by digital light processing (DLP) 3D printing technology

Wave-transmitting materials are a kind of multi-functional materials that protect the normal operation of communication and guidance systems of spacecraft in harsh environments. In this paper, we fabricate a broadband microwave transparent Si₃N₄-SiO₂ composite ceramic with excellent performance through digital light processing (DLP) 3D printing technology. The influences of sintering temperature on the weight increase rate, density, dimensional shrinkage, phase composition, microstructure, bending strength and dielectric properties of Si₃N₄-SiO₂ ceramic were all systematically studied. The strength of Si₃N₄-SiO₂ ceramic sintered at 1350 ℃ was 77 ± 5 MPa. The relative permittivity of the ceramic is within the range of less than 4, and the loss tangent can be below 0.003. The 3D printed Si₃N₄-SiO₂ ceramic material exhibited excellent wave-transparent performance.     

Comparative study on the electrochemical performance of LiFePO4 cathodes fabricated by low temperature 3D printing,direct ink writing and conventional roller coating process

Electrodes for lithium-ion batteries can be fabricated in many ways including conventional roller coating and 3D printing. Roller coating is a standardized process in current lithium-ion battery industry, while 3D printing has been used to fabricate three-dimensional (3D) unconventional electrodes with tailored geometries. Our previous study proposed a low temperature 3D printing process to fabricate highly-porous LiFePO₄ (LFP) electrodes. However, there still lack a study on the comparison of electrochemical performance of LFP electrodes fabricated via the three different fabrication processes including low temperature direct writing-based 3D printing (LTDW), room temperature direct ink writing (DIW) and roller coating process. In this study, we fabricated LFP cathodes using these three fabrication processes from LFP inks with different solid contents. By varying the solid content, LFP electrodes with different geometries (including width and thickness), morphologies and porous microstructures were obtained via LTDW and DIW. Mercury porosimetry was performed to examine the differences of the three types of LFP electrodes in porous microstructures. Electrochemical performance including charge/discharge, rate performance, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) of the three types of electrodes were measured and compared. Results showed that electrode fabrication processes have important effects on the electrochemical performance of LFP electrodes depending on the ink solid content. LTDW-fabricated electrodes had the best performance at high solid content (≥0.467 g/mL) and conventional roller coated electrodes performed better at low solid content (≤0.356 g/mL). Relationships between ink solid content, fabrication process, resulting porous microstructures and electrochemical performance were discussed. Finally, an optimal specific capacity of ∼82 mAh.g-1 @ 10C was achieved at a solid content of 0.467 g/mL by LTDW process.     

Mechanical and dielectric properties of Si3N4-SiO2 ceramics prepared by digital light processing based 3D printing and oxidation sintering

Si₃N₄-SiO₂ ceramics are considered as the preferred high-performance wave-transmitting material in the aerospace field. However, traditional fabrication methods for Si₃N₄-SiO₂ ceramics have the disadvantages of high cost and complicated fabrication process. In this paper, Si₃N₄-SiO₂ ceramics with excellent mechanical and dielectric properties were fabricated by digital light processing-based 3D printing combined with oxidation sintering. Firstly, the curing thickness and viscosity of slurries with different solid loadings for vat photopolymerization-based 3D printing were studied. Then, the effects of the sintering temperature on the linear shrinkage, phase composition, microstructure, flexural strength, and dielectric properties of Si₃N₄-SiO₂ ceramics, and the influences of solid loading on them were explored. The curing thickness and viscosity of the slurry with a solid loading of 55 vol% were 30 μm and ∼1.5 Pa‧s, respectively. The open porosity and the flexural strength of Si₃N₄-SiO₂ ceramic with a solid loading of 55 vol% were 4.3 ± 0.61% and 76 ± 5.6 MPa, respectively. In the electromagnetic wave band of 8–18 GHz, the dielectric constant of Si₃N₄-SiO₂ ceramics was within the range of less than 4, and the dielectric loss remained below 0.09. The method of digital light processing-based 3D printing combined with oxidation sintering can be further extended in the preparation of Si₃N₄-based structure-function integrated ceramics.     

Photosensitive Si3N4 slurry with combined benefits of low viscosity and large cured depth for digital light processing 3D printing

Digital light processing 3D printing can be applied to fabricate complex silicon nitride (Si₃N₄) components. However, because of the surface hydroxyl groups and large refractive index, it is still a foremost challenge to realize a stable photosensitive Si₃N₄ slurry with combined benefits of low viscosity and large curing depth. In this study, we propose a new formulation strategy to prepare Si₃N₄ slurry. Starting from the optimization of monomer ratio, we have systematically optimized powder particle size, dispersant and photoinitiator on the rheological properties and curing properties of Si₃N₄ slurry. Specifically, we have fabricated a stable photosensitive Si₃N₄ slurry (48 vol%) with a viscosity of 2.09 Pa s (30 s^?1), a critical curing energy of 126.09 mJ/cm² and a maximum curing depth of 80 µm. Finally, based on this optimized slurry, we have successfully obtained complex Si₃N₄ green body with no defect, which demonstrates great potential to fabricate arbitrary complex ceramic components for various applications.     

Microstructure and properties evolution of silicon-based ceramic cores fabricated by 3D printing with stair-stepping effect control

A ceramic core is the key component in the manufacture of the hollow turbine blades of aeroengines. Compared with the traditional injection molding method, 3D printing is more suitable for manufacturing ceramic cores with a complex geometry at high precision. However, the stair-stepping effect is inevitable in the 3D printing process and affects the surface roughness and strength of the ceramic core. In this study, to explore the influence of nano-silica content on the microstructure and properties of the ceramic core, silicon-based ceramic cores were fabricated with the addition of nano-silica powder by digital light processing and subsequent sintering at 1200 °C. The results showed that the apparent porosity and pore size of the ceramic core gradually decreased as both the nano-silica powder content and bulk density increased. Meanwhile, the printing interlayer spacing was significantly reduced, resulting in a low surface roughness, high flexural strength, and creep-resistance. To simulate the entire casting process of a superalloy blade, the thermal deformation behavior of the ceramic core was observed by heating and cooling cycles performed in a thermal dilatometer at 1540 °C. The total linear shrinkage decreased as the nano-silica powder content increased, which was mainly due to the phase transformation of cristobalite and the densification of the ceramic core sintered at 1200 °C. The low surface roughness and linear shrinkage as well as high flexural strength of the ceramic core can contribute to the excellent quality of cast superalloy blades.     

Transparent alumina ceramics fabricated by 3D printing and vacuum sintering

Transparent alumina ceramics were fabricated using an extrusion-based 3D printer and post-processing steps including debinding, vacuum sintering, and polishing. Printable slurry recipes and 3D printing parameters were optimized to fabricate quality green bodies of varying shapes and sizes. Two-step vacuum sintering profiles were found to increase density while reducing grain size and thus improving the transparency of the sintered alumina ceramics over single-step sintering profiles. The 3D printed and two-step vacuum sintered alumina ceramics achieved greater than 99 % relative density and total transmittance values of about 70 % at 800 nm and above, which was comparable to that of conventional CIP processed alumina ceramics. This demonstrates the capability of 3D printing to compete with conventional transparent ceramic forming methods along with the additional benefit of freedom of design and production of complex shapes.     

双光子聚合3D打印

3D打印是一种快速成型的增材制造技术。光固化立体印刷(SLA)是技术较成熟和应用较广的一种3D打印技术。SLA是采用紫外激光的单光子聚合过程,其加工分辨率受经典光学衍射极限的限制,难以满足分辨率高的微纳结构的加工。不同于SLA,利用近红外波长飞秒激光的双光子聚合3D打印技术可以突破经典光学衍射的限制,制造分辨率高的纳米尺度任意形状三维结构。本文将介绍双光子吸收和双光子聚合的原理、双光子聚合的发展和双光子聚合3D打印技术的应用,最后对该技术的发展进行展望。     

Rheological behavior and curing deformation of paste containing 85 wt% Al2O3 ceramic during SLA-3D printing

The preparation of high solids loading Al₂O₃ paste is of great significance for improving the properties of ceramics formed by UV-curing. However, the solid contents of alumina slurry used by digital light processing (DLP) and traditional alumina paste for stereolithography (SLA) are both less than 80 wt%. With increase in solid content, the viscosity of paste increases sharply, and rheological property deteriorates. In this study, ceramic paste containing 85 wt% (62 vol%) Al₂O₃ was prepared for SLA-3D printing of ceramics, and more than 85 wt% solid content was achieved by dispersant and other additives. Effects of different dispersants on rheological and curing properties of Al₂O₃ ceramic paste were studied. At room temperature, the viscosity of 85 wt% Al₂O₃ ceramic paste was 51733 mPa s at shear rate of 30 s^?1. A novel method was proposed to control curing deformation of parts during printing. As-manufactured ceramic did not show any cracks by naked eye and exhibited excellent mechanical properties, with three-point bending strength of 540 MPa, fracture toughness of 4.19 MPa m^1/2, Vickers hardness of 16 GPa, surface roughness of 0.463 μm, and density of 3.86 g/cm³.     

Extrusion-based 3D printing alumina-silica inks: Adjusting rheology and sinterability incorporating waste derived nanoparticles

The nanoparticle (NP) exhibits numerous distinctive and extraordinary properties than micron level and up. The inclusion of NP effects in the rheological and densification behavior of extrusion-based (direct ink writing (DIW)) inks has been extensively investigated. The aqueous-based alumina-silica inks were first designed using waste rice husk ash (RHA) derived nano-silica (NS) (0–10 wt%) and found that the solid-to-liquid ratio reduces continuously with NS addition for printable rheology. For functionalization of NS, dispersant requirement is increased that improve the solids loading of inks. Second, the optimized inks are printed via DIW technique and sintered at a temperature of 1400–1650 °C. The NS has remarkably enhanced the shrinkage, density, and morphology of sintered DIW specimens and 7.5 wt% RHA NS reduces the sintering temperature ∼150 °C. Incorporating NP in the 3D printing ink is a clean approach to filling pores generated by binder-burnout and fabricating a dense ceramic at a low temperature.