Direct ink writing additive manufacturing of porous alumina-based ceramic cores modified with nanosized MgO

Alumina-based ceramic cores, widely applied to cast alloy, have been restricted by the increased complexity of castings, the resultant complex equipment and cost. In this research, to address the aforesaid disadvantages, direct ink writing, a green additive manufacturing method, is utilized to directly fabricate a new kind of nanosized MgO strengthened alumina-based ceramic cores. Slurries with various compositions exhibits ideal shear-thinning behaviors, owing to the hydrogen bond formed between polyvinylpyrrolidone and kaolin molecules. We notice that introducing nanosized MgO reduces drying shrinkage of green specimens and greatly promotes liquid-phase sintering, leading to rather more densified samples. Overall, it is anticipated that the current approach is effective in rapidly manufacturing alumina-based ceramics and some other ceramics with high strength, low shrinkage and high quality.     

Continuous carbon fiber reinforced ZrB2-SiC composites fabricated by direct ink writing combined with low-temperature hot-pressing

As one of additive manufacturing techniques, direct ink writing has significant advantages in the manufacture of ceramic matrix composites, nevertheless, the poor impregnability of ceramic slurry makes it difficult to fill the interior of fiber bundles, causing poor mechanical properties. Here, ultrasound-assisted fiber separation technique was introduced to impregnate ceramic slurry with a continuous carbon fiber bundle during direct ink writing of continuous carbon fiber/ceramic green body and subsequent low temperature hot-pressing was combined to improve its robustness. Suitable thickness of carbon coating could bring to high fracture resistance, whereas excessively thick carbon coating will adversely affect the mechanical properties. A carbon interface with thickness around 110 nm was incorporated, the flexural strength, fracture toughness and work of fracture of C_f/ZrB₂-SiC composite reached 388.3 MPa, 10.04 MPa·m^1/2 and 2380 J/m², respectively. Therefore, direct ink writing combined with low temperature hot-pressing, was effective to fabricate high-performance ceramic matrix composites.     

Direct ink writing of cordierite ceramics with low thermal expansion coefficient

Since the application of cordierite ceramics is limited by the disadvantages of traditional preparation techniques, 3D printing technology provides the only choice for the rapid preparation of cordierite ceramics with highly complex structures. In this work, the fabrication of cordierite ceramics with complex structures was achieved by direct ink writing. The near-net-shape of cordierite ceramics was realized by the volume expansion caused by the phase transformation. A cordierite ceramic with an average shrinkage rate of 1.58 % was obtained at 1400 °C. The low shrinkage avoids design and manufacturing procedures carried out for dimensional and alignment errors. In addition, the coefficient of thermal expansion was as low as 1.69 × 10^?6 °C^?1. The effect of configuration on the thermal behavior of cordierite ceramics is understood by analyzing the phase composition and microstructure. The cordierites ink reported in this work offers additional possibilities for the production of novel complex structures.     

基于浆料形态的陶瓷3D打印技术的浆料体系研究进展

3D打印技术因其操作简单便捷、成型快速灵活、可制备复杂结构的器件等优点,在精密陶瓷零件制造方面具有广泛应用。本文根据3D打印陶瓷的材料形态综述不同3D打印技术在陶瓷制备方面的特点,重点介绍了陶瓷3D打印成型技术中直写式3D打印、光固化3D打印、喷墨3D打印等技术所涉及的粘结剂、分散剂等组分的应用及作用机理,并对水基和非水基两种类型的添加剂组分进行总结和探讨,以期为3D打印技术制备高性能陶瓷样件提供参考。     

Binder-free additive manufacturing of ceramics using hydrothermal-assisted jet fusion

Ceramic additive manufacturing (AM) typically uses a high fraction of organic binders to form pre-sintered green parts that require a post de-binding process to remove. The de-binding process inevitably results in severe gas expansion and residual chars, leading to structural defects, accumulated stress, and compromised material properties in the final parts. Here we report a binder-free additive manufacturing process named hydrothermal-assisted jet fusion (HJF) that utilizes a hydrothermal method to create geometrically and compositionally complex ceramics under mild temperatures. The HJF process employs a selectively deposited volatile dissolving ink, high pressure, and mild heat to strategically fuse a ceramic powder bed into complex geometries. Compared to traditional AM methods for ceramics, the HJF process eliminates the need for organic binders in green part fabrication and offers the potential to directly co-print ceramics with other dissimilar materials, such as polymers and metals, enabling the development of novel multi-functional ceramic composites.     

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%.     

Preparation of photosensitive SiO2/SiC ceramic slurry with high solid content for stereolithography

Stereolithography is a popular three-dimensional (3D) printing technology, which is widely used for manufacturing ceramic components owing to its high efficiency and precision. However, it is a big challenge to prepare SiC ceramic slurry with high solid content for stereolithography due to the strong light absorption and high refractive index of dark SiC powders. Here, we propose a novel strategy to develop photosensitive SiO₂/SiC ceramic slurry with high solid content of 50–65 vol% by adding spherical silica with low light absorbance and applying a stacking flow model to improve the solid content of the slurry. The as-prepared slurry exhibits excellent stereolithography properties with a dynamic viscosity lower than 20 Pa s and curing thickness more than 120 μm. Therefore, it can be successfully applied for stereolithography-based additive manufacturing of SiC green bodies with large size (100 mm), sub-millimeter accuracy (0.2 mm), and complex structure. The stacking flow model also shows immense potential for the stereolithography of other dark-color ceramics with high solid content.     

Three-dimensional inkjet printing and low temperature sintering of silica-based ceramics

The conventional LTCC fabrication route requires a series of costly molding equipment and a complicated manufacturing process. If it is achievable to fabricate ceramics using three-dimensional inkjet printing (IJP) technology, it is anticipated that LTCC components could be designed as a more efficient and flexible additive manufacturing route using IJP technology to co-print ceramic and conductive layers and co-fire them. This research represents the first attempt to utilize IJP technology in the field of LTCC, where we developed a stable SiO₂-H₃BO₃ nanoceramic ink that can be continuously printed through a piezoelectric nozzle with an array of spray holes. The ink was supplemented with selected photosensitive resins to facilitate the curing of the printed layer under ultraviolet light irradiation. Green bodies are sintered at 950° for two hours to obtain ceramic sheets with good surface flatness and microscopic sintering degrees. The tested samples have an ultra-low dielectric constant (ε_r) of about 2.485 and a low dielectric loss (tan δ) of about 0.0038 (at 1 MHz), while being stable at high temperatures (< 400°) and high frequencies (< 10 GHz), indicating its ability to match the required dielectric properties required for microwave dielectric substrates.     

Effect of organic fibers addition on digital light processing for Al2O3 porous ceramics

Porous ceramics based on additive manufacturing have great application potential in many industries, including filtration, catalysis, and heat insulation. In this research, we propose a method for manufacturing porous ceramics with connected channels structure through ceramic digital light processing (DLP) and organic fiber decomposition. The crossed fibers in the green body, working as a pore-forming agent, were decomposed and removed to form connected channels in ceramic. It was confirmed that ball milling changed the fiber morphology during slurry preparation, which was beneficial to promote fibers crossing. Besides, we focused on the influence of the “Sponge Compression effect” during the DLP process, which affected the fibers distribution. The existence of fibers in the green body resulted in uneven pressure distribution during the debinding process, providing a potential source of cracks. Results show that this method can produce channels with a diameter of 100 μm and high connectivity, providing great potential in fabricating high connectivity porous ceramics with complex shapes and structures.     

Fine-grained relaxor ferroelectric PMN-PT ceramics prepared using hot-press sintering method

Relaxor ferroelectric PbMg_1/3Nb_2/3O₃-PbTiO₃ (PMN-PT) ceramics are high-performance piezoelectric materials that are widely used in many electronic devices. However, it is extremely difficult to manufacture thin piezoelectric components dozens of micrometers in size using commercial coarse-grained PMN-PT ceramics. This limits the application of PMN-PT ceramics to high-frequency ultrasonic devices. In this work, we prepared a dense, fine-grained PMN-PT ceramic at low temperature using a hot-press sintering (HPS) method. The HPS ceramic had small grains with an average size of 1 μm and maintained high performance with a large permittivity (ε_r = 4500), piezoelectricity (d₃₃ = 650 pC/N), and electrostrain (S_E = 0.14% at 20 kV/cm). The large volume fraction of grain boundaries led to stronger relaxor behavior of the fine-grained PMN-PT ceramic than of the normal coarse-grained one. Owing to its small grains and high piezoelectric performance, this fine-grained PMN-PT ceramic meets the strict requirements of manufacturing thin piezoelectric components. Our results demonstrate that PMN-PT ceramics have great potential for developing low-cost, high-frequency ultrasonic devices by replacing expensive piezoelectric single crystals.     

Additive manufacturing of Csf/SiC composites with high fiber content by direct ink writing and liquid silicon infiltration

Direct ink writing (DIW) provides a new route to produce SiC-based composites with complex structure. In this study, we additive manufactured short carbon fiber reinforced SiC ceramic matrix composites (Csf/SiC composites) with different short carbon fiber content through direct ink writing combined with liquid silicon infiltration (LSI). The effects of short carbon fiber content on the microstructure and mechanical properties of the DIW green parts and the final Csf/SiC composites were investigated. The results showed that the Csf content played an important role in maintaining the structure of the green parts. As the Csf content increases, the dimension deviation ratio of the sample decreased at all stages. With the Csf content of 40 vol%, the final Csf/SiC composite had low free Si content and high β-SiC content. The maximum density, tensile strength and bending strength of the Csf/SiC composites were 2.88 ± 0.06 g/cm³, 53.68 MPa and 253.63 MPa respectively. It is believed that this study can give some understanding for the additive manufacturing of fiber reinforced ceramic matrix composites.     

Damage tolerance in additively manufactured ceramic architected materials

Technical ceramics exhibit exceptional high-temperature properties, but unfortunately their extreme crack sensitivity and high melting point make it challenging to manufacture geometrically complex structures with sufficient strength and toughness. Emerging additive manufacturing technologies enable the fabrication of large-scale complex-shape artifacts with architected internal topology; when such topology can be arranged at the microscale, the defect population can be controlled, thus improving the strength of the material. Here, ceramic micro-architected materials are fabricated using direct ink writing (DIW) of an alumina nanoparticle-loaded ink, followed by sintering. After characterizing the rheology of the ink and extracting optimal processing parameters, the microstructure of the sintered structures is investigated to assess composition, density, grain size and defect population. Mechanical experiments reveal that woodpile architected materials with relative densities of 0.38–0.73 exhibit higher strength and damage tolerance than fully dense ceramics printed under identical conditions, an intriguing feature that can be attributed to topological toughening.     

陶瓷增材制造

陶瓷的脆性和高硬度使得传统陶瓷成型工艺不易制备具有复杂形状和结构的陶瓷制件。本文总结了目前发展较快的激光选区熔融、激光选区烧结、三维打印、立体光固化、自由挤出成型等增材制造工艺在陶瓷领域的研究进展。面向复杂结构和高性能陶瓷制品的定制化快速制造需求,陶瓷增材制造技术展现出极大优势,在传统陶瓷行业、生物医疗等领域得到了应用。但是,陶瓷增材制造仍面临着打印材料及大尺寸、高致密度复杂结构陶瓷零件制造等难题,这些也将是增材制造技术未来发展的重要研究方向。     

Direct ink writing of macroporous lead-free piezoelectric Ba0.85Ca0.15Zr0.1Ti0.9O3

Direct ink writing (DIW) has become a widespread additive manufacturing technique for material engineering, but its application in lead-free Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃ piezoelectric ceramics from aqueous systems has not been reported so far to our knowledge. The main obstacle is the high extent of hydrolysis reactions undergone by the starting powders when dispersed in water, hindering the attainment of stable water-based colloidal suspensions. This paper reports on the preparation of stable aqueous inks from a deagglomerated and surface-treated powder synthesized by solid-state reaction and on DIW of macroporous lead-free piezoelectrics. Based on zeta potential and rheological measurements, the optimal amounts of processing additives (dispersant, binder, and coagulating agent) were selected to transform the initial fluid suspension to a viscoelastic paste with sufficient stiffness and stability for the printing process. Dielectric and piezoelectric properties of samples sintered under different temperatures were also investigated.     

Simultaneous realization of high transparency and piezoelectricity in low symmetry KNN-based ceramics

Transparent piezoelectric ceramic, as a lead-free multifunctional ceramic, is in dire need of development for future high-tech industries. However, excellent piezoelectricity and high transmittance are usually hard to achieve simultaneously, mainly due to the two mutual restricting factors (phase structure and grain size). In this work, we report that high piezoelectricity and transmittance can be obtained simultaneously in K_0.5Na_0.5NbO₃ ceramics via Sr(Sc_0.5Nb_0.5)O₃ (SSN) modification. The superior piezoelectric performance comes from the retain of orthorhombic phase structure at room temperature (RT); while the high transparency (>70% at 780 nm) can be attributed to the improved relative density and reduced grain size via SSN modification. Remarkably, in the sample with 0.05SSN modification, we realized a comprehensively high transmittance (73% at 780 nm) accompanied by a superior piezoelectric constant (d₃₃ = 101 pC/N), which outperform other reported KNN-based transparent ceramics to our best knowledge. Our results may provide insight for further developing the transparent piezoelectric ceramics by controlling the grain size and phase structure.     

Stereolithography-based additive manufacturing of gray-colored SiC ceramic green body

The stereolithography-based additive manufacturing of white-colored Al₂O₃ and ZrO₂ ceramics has been widely reported, whereas the stereolithography-based additive manufacturing of gray-colored SiC ceramic is very difficult and challenged. In this paper, the reasons for the difficulty which SiC ceramic facing during stereolithography were discussed and compared to Al₂O₃ and ZrO₂ ceramics. The effects of particle size, solid loading, stereolithography parameters, and photoinitiator kind and concentration on the curing ability of SiC slurries were further studied in detail. Finally, complex-shaped SiC ceramic green parts with high accuracy and high quality were successfully fabricated. This study demonstrated that the stereolithography-based additive manufacturing had a great possibility for preparing gray-colored SiC ceramics.     

Excellent temperature stability of strain in PZ-PT-BNT ternary ceramics

Lead-based Pb(Zr, Ti)O₃ ceramics have been widely applied in piezoelectric actuators, and yet high temperature stability and large strain have been pursued for further application. In this work, a novel PbZrO₃–PbTiO₃-(Bi_0.5Na_0.5)TiO₃ (PZ-PT-BNT) piezoelectric ceramic is designed and prepared by solid-state route. It is found that the introduction of BNT constituent enhances the relaxation behavior of PZ-PT ceramic, inhibits the abrupt change in dielectric properties near Curie temperature, and increases the proportion of tetragonal phase with high temperature stability. Meanwhile, the patterns of electric domains are intentionally modified by adjusting composition of PZ-PT-BNT. Short and broad electric domains in PZ-PT-0.03BNT ceramic are observed by piezoresponse force microscopy, which are insensitive to temperature and have faster response under electric field, contributing to strain characteristics. As a result, through integrating phase structure and electric domain configuration, a strain of 0.21% and excellent temperature stability where the variation of strain is less than 8% in the temperature range of 25–250 °C are achieved in PZ-PT-0.03BNT ceramic. The findings provide an effective strategy for improving the strain stability of PZ-PT-based piezoelectric ceramics, and demonstrate that PZ-PT-BNT ceramics have potential application prospects in high-temperature piezoelectric actuators.     

Polymer-derived silicon nitride ceramics by digital light processing based additive manufacturing

In this work, silicon nitride ceramic components with simple cuboid and complex honeycomb and lattice structures from preceramic polymers were fabricated by using digital light processing (DLP) based additive manufacturing and pyrolysis. The photosensitive precursor for DLP based additive manufacturing was prepared by mixing high ceramic yield polysilazane with commercial acrylic resin and photoinitiator. The material formulation and the structure of the green body were characterized by using FTIR. Si₃N₄ ceramic cuboid, 2D-structured Si₃N₄ ceramic honeycomb, and 2D-structured Si₃N₄ ceramic lattice with high precision were fabricated. The DLP-prepared specimens were pyrolyzed at different temperatures, and the crystalline phases after pyrolysis were analyzed by using XRD. The optimal pyrolysis temperature was found to be 1400°C.microstructures were characterized by using SEM. The compressive behavior of the complex-shaped Si₃N₄ ceramic structures was measured and discussed in detail.     

Direct ink writing of aluminum-phosphate-bonded Al2O3 ceramic with ultra-low dimensional shrinkage

Three-dimensional (3D) printing of ceramics has attracted increasing attention in various fields. However, the pyrolysis of organic components used for binding or polymerization in 3D printing commonly causes a large shrinkage (up to 30 %–40 %), high porosity, and cracking or deformation, severely limiting practical applications. In this study, 3D printing of Al₂O₃ ceramic architectures with ultra-low shrinkage is realized by introducing inorganic binder aluminum dihydrogen phosphate (Al(H₂PO₄)₃, AP) as a ceramic precursor. Compared to organic binders, the inorganic AP binder can undergo crystallization conversion, which reduces mass loss during sintering at high temperatures, resulting in low shrinkage. Moreover, AP can be used as a rheological modifier to regulate the printability of the ceramic ink for direct ink writing of Al₂O₃ ceramic architectures, such as wood-piled scaffolds, honeycomb structures, and tubes with high fidelity. The resultant Al₂O₃ structural ceramics sintered at 1250 °C exhibit good mechanical performance and structural integrity. Most importantly, the linear shrinkage of the printed ceramics is less than 5 %, which is several times lower than that of ceramics with organic binders. This study provides a viable strategy for fabricating high-performance ceramic architectures with good dimensional fidelity for practical applications.