Direct ink writing of hierarchical porous ultra-high temperature ceramics (ZrB2)

An approach to producing hierarchical multi-scale porous ultra-high temperature ceramics (zirconium diboride, ZrB₂) using 3D printing has been developed. Porous ceramic filaments can be 3D printed via Direct Ink Writing (DIW) (paste extrusion). Millimeter scale porosity is created by the 3D printed scaffold filaments. We introduce 20-micron-scale porosity into the scaffold filaments with the addition of oil to produce capillary suspension paste inks. Micron-scale porosity is also developed by partial sintering of the ceramic. The rheological (flow) properties of the capillary suspension paste inks suitable for printing by extrusion through the needle of the 3D printer have been characterized. The samples are strengthened by partial sintering at high temperatures. Complex-shaped components can be printed and sintered into crack-free components, but distortion during drying and sintering lead to poor shape and tolerance control. X-ray tomography is used to characterize the internal structure of the printed components. Printed test bars measured in 4-point bend testing exhibit high strength to density ratio. Such materials potentially have applications as insulation near very high-temperature surfaces in aerospace applications.     

First printing of continuous fibers into ceramics

This article reports a novel method for three-dimensional (3D) printing of continuous fibers into ceramics to improve the mechanical properties of printed ceramics, which is difficult in other 3D printing technologies. The ceramics were derived by pyrolysis of thermoplastic ceramic precursor feedstocks, which were prepared by two methods. One is homogeneously mixing thermoplastic resins and ceramic precursors. The feedstocks prepared by this method exhibit good thermoplastic properties and can be extruded into filaments. Ceramics were obtained by heating the feedstocks to 1100°C in argon atmosphere. The ceramics were amorphous and remained stable during 1100-1300°C; at 1400°C they decomposed into β–SiC with simultaneous volatile gas generation. Above 1400°C, their quality decreased significantly due to cracking of ceramic skeletons. The other method is directly heating, extruding and printing the ceramic precursor. The precursors showed good printability and complex ceramic structures were printed with continuous carbon fibers inside. The continuous carbon fibers improved the flexural strength of pyrolytic ceramics, which is about 7.6 times better than that of the ceramics without fibers. The novel method unravels the potential of 3D printing of continuous fibers into ceramics with complex lightweight structures to improve the strength.     

Enhanced mechanical properties of 3D printed alumina ceramics by using sintering aids

Stereolithography based 3D printing provides an efficient pathway to fabricate alumina ceramics, and the exploration on the mechanical properties of 3D printed alumina ceramics is crucial to the development of 3D printing ceramic technology. However, alumina ceramics are difficult to sinter due to their high melting point. In this work, alumina ceramics were prepared via stereolithography based 3D printing technology, and the improvement in the mechanical properties was investigated based on the content, the type and the particle size of sintering aids (TiO₂, CaCO₃, and MgO). The flexural strength of the sintered ceramics increased greatly (from 139.2 MPa to 216.7 MPa) with the increase in TiO₂ content (from 0.5 wt% to 1.5 wt%), while significant anisotropy in mechanical properties (216.7 MPa in X-Z plane and 121.0 MPa in X–Y plane) was observed for the ceramics with the addition of 1.5 wt TiO₂. The shrinkage and flexural strength of the ceramics decreased with the increase in CaCO₃ content due to the formation of elongated grains, which led to the formation of large-sized residual pores in the ceramics. The addition of MgO help decrease the anisotropic differences in shrinkage and flexural strength of the sintered ceramics due to the formation of regularly shaped grains. This work provides guidance on the adjustment in flexural strength, shrinkage, and anisotropic behavior of 3D printed alumina ceramics, and provides new methods for the fabrication of 3D printed alumina ceramics with superior mechanical properties.     

3D printing of ceramics: A review

Along with extensive research on the three-dimensional (3D) printing of polymers and metals, 3D printing of ceramics is now the latest trend to come under the spotlight. The ability to fabricate ceramic components of arbitrarily complex shapes has been extremely challenging without 3D printing. This review focuses on the latest advances in the 3D printing of ceramics and presents the historical origins and evolution of each related technique. The main technical aspects, including feedstock properties, process control, post-treatments and energy source–material interactions, are also discussed. The technical challenges and advice about how to address these are presented. Comparisons are made between the techniques to facilitate the selection of the best ones in practical use. In addition, representative applications of the 3D printing of various types of ceramics are surveyed. Future directions are pointed out on the advancement on materials and forming mechanism for the fabrication of high-performance ceramic components.     

Preparation of complex SiOC ceramics by a novel photocurable precursor with liquid crystal display ( LCD) 3D printing technology

The polymer derived ceramics with complex shapes were prepared using the low-cost liquid crystal display (LCD) 3D printing technology. In this paper, we not only synthesized a liquid low-viscosity precursor with the photocurable group, but also provided a method to improve the forming precision and ceramic yield. The results showed that the introduction of KH570 could improve the curing accuracy, the ceramic yield. When the content of KH570 increased to 41 wt%, the curing shrinkage of the system decreased from 6.92% to 2.84%, the ceramic yield increased by 29.2%. Moreover, the mechanical properties of SiOC ceramics were studied and discussed. The bending strength of SiOC ceramic reached 44.2 MPa. And the ceramics after polishing were no cracks or other defects. This research demonstrates the huge potential for 3D - printed ceramics to become ubiquitous.     

Effect of internal lattice structure on the flexural strength of 3D printed hierarchical porous ultra-high temperature ceramic (ZrB2)

3D printing of technical ceramics using direct ink writing (DIW) of multiphase colloidal inks has the unique ability to create structures with hierarchical features. To facilitate the application of 3D printed hierarchical porous ultra-high temperature ceramics (UHTCs), additional limiting factors such as strength and the effect of 3D printed internal lattice structure need to be better understood. This study reports on the strength dependence of common DIW print parameters including internal lattice structure shape, nozzle diameter and spacings between adjacent filaments. The present study applies Weibull statistics to the experimental array that considers macro features introduced through print parameters as flaw types, which shows strength of 3D printed hierarchical ZrB₂ is highly dependent on the introduced 3D printed structure, size and the stressed volume. This work provides essential information that can be used in the initial stages of design when considering implementation of additively manufactured hierarchical porous UHTCs.     

Fused deposition fabrication of high-quality zirconia ceramics using granular feedstock

Benefiting from the mature technology of ceramic injection molding, Fused deposition modeling based on highly-filled ceramic-polymer granular feedstocks has been showing great potential and advantage for fabricating 3D ceramics. Herein, 3D zirconia ceramics using granular feedstock were fabricated, and typical morphology, surface quality, and effect of the thermal accumulation on 3D structure were clarified. Typical morphology of printing steps on the surface were quantitatively characterized, and determined by the surface curvature and layer height of the printed structure. Aligned triangular pores were confirmed at the junction of the deposited filaments with elliptical cross-section morphology. Simple square plates with different size were used to illustrate the influence of thermal accumulation on the morphology of 3D structure. Small printing size increased the thermal accumulation during deposition, resulting in decreased printing quality caused by the secondary over-melting of former deposited layers. Except for the pores at the junctions, dense zirconia ceramics with uniform structure and smooth surface could be achieved. A low-cost and high-quality route for the preparation of 3D ceramics was demonstrated via FDM of highly-filled granular feedstocks.     

Fabrication and properties of Si3N4 bioscaffolds with orderly–interconnected big pore channels and well–distributed small pores

This paper focuses on investigating the technical potential for fabricating porous ceramic bioscaffolds for the repair of osseous defects from trauma or disease by inverse replication of three–dimensional (3–D) printed polymer template. Si₃N₄ ceramics with pore structure comprising orderly–interconnected big pore channels and well–distributed small pores are successfully fabricated by a technique combining 3–D printing, vacuum suction filtration and oxidation sintering. The Si₃N₄ ceramics fabricated from the Si₃N₄ powder with addition of 10?wt% talcum by sintering at 1250?°C for 2?h have little deformation, uniform microstructure, low linear shrinkage of 4.1%, high open porosity of 58.2%, relatively high compression strength of 6.4?MPa, orderly–interconnected big pore channels and well–distributed small pores, which are promising bioscaffold in the field of bone tissue engineering.     

Influence of bimodal particle distribution on material properties of BaTiO3 fabricated by paste extrusion 3D printing

Barium titanate (BaTiO₃) is a lead-free piezoelectric ceramic widely used in sensors and actuators applications. However, there are many manufacturing challenges to process BaTiO₃ due to the brittle nature of ceramics. Most current sensors based on piezoelectricity are limited to mold shapes or flat 2D structures, which narrow their applications. Paste extrusion (PE) 3D printing technique allows the fabrication of complex geometry ceramics with less design limitations. However, the piezoelectric property of 3D printed ceramics is typically lower than those fabricated using traditional means due to lower density. Herein, a study to evaluate the influence of bimodal particle distribution on improving density and piezoelectricity of BaTiO₃ ceramics fabricated using PE 3D printing is presented. 3D printed and compression pressed samples under the same mixing ratios were compared. The highest packing density was obtained using 50-50% vol. fraction of bimodal particles for both types of samples. A predictive model for packing density was validated by experimental results. The highest piezoelectric coefficient of 350 pC/N was obtained using 50-50% vol. bimodal particle distribution. This piezoelectric coefficient is 40% higher than the monodispersed sample using 100 nm particles with a piezoelectric coefficient of 250 pC/N.     

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.     

Digital light processing-stereolithography three-dimensional printing of yttria-stabilized zirconia

Digital light processing (DLP)-stereolithography three-dimensional (3D) printing is a well known technique for fabricating components with complex geometries. However, the application of DLP 3D printing to functional ceramics such as 8 mol% yttria-stabilized zirconia (8YSZ), which is one of the most extensively used electrolyte materials for solid oxide fuel cells, is still a great challenge. Therefore, the fabrication of fully 8YSZ monoliths via DLP 3D printing was attempted herein, including the preparation of UV-curable ceramic suspensions, shaping of green bodies, and debinding and sintering. The results show that intact green bodies printed using a 30 vol% 8YSZ-photosensitive resin suspension with 0.1 wt% oleic acid as the dispersant under the optimized printing conditions was sufficiently dense without connected pores after vacuum debinding and sintering in air. The successful fabrication of 8YSZ monoliths with design flexibility via 3D printing provides a simple method for preparing functional ceramic components and may expand the application of 3D printing technology to the energy field.     

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.     

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。     

Influence of number average molecular weight on the properties of 3D printed precursor ceramics

A deliberately selected end-capping agent was introduced into the precursor to form a low number average molecular weight precursor and meet the need for liquid crystal display (LCD) 3D printing. The influence of number average molecular weight on the photocuring properties of precursor and the physical properties of pyrolysis samples were studied in detail for the first time. The results proved that a relatively low number average molecular weight precursors had low ceramic yields after pyrolysis. As the number average molecular weight of the precursor decreased, the photocuring ability of the precursor photosensitive resin increased. With the decrease in the number average molecular weight of the precursor in the precursor photosensitive resin, the ceramic yield of 3D printed PDCs decreased from 58.4% to 30.2%, and the linear shrinkage increased from 27.2% to 40.3%. The bending strength of the LCD 3D printed specimen reached 61.5 ± 3.7 MPa. The low cost of precursor synthesis and equipment in this study points the way for the preparation of precursor non-oxide ceramic composites and can be conducive to the development and application of LCD 3D printing precursor ceramics.     

Preparation of porous SiC ceramics skeleton with low-cost and controllable gradient based on liquid crystal display 3D printing

In recent years, the demand for gradient porous ceramics is increasing in engineering field. By traditional process, the disadvantage of prepared gradient porous ceramics is its low porosity and uncontrollable pore gradient, which limits the wide application of gradient porous ceramics. In this study, the gradient porous ceramic skeleton (GPCS) was prepared by combining liquid crystal display (LCD) 3D printer with liquid silicon infiltration (LSI). Experimental results showed that the mass of ceramic powder in the ceramic slurry with optimal printing performance accounts for 45% of the mass of photosensitive resin, and the thermal decomposition rate of photosensitive resin is faster in the range of 300–450 °C. Furthermore, the effect of LSI temperature on the composition, microstructure and mechanical properties of GPCS was investigated. The GPCS is expected to be applied in the fields of energy storage, heat transfer and biofouling, among others.     

LAS glass–ceramic scaffolds by three-dimensional printing

Highly porous (>60% open porosity) glass–ceramic scaffolds with remarkable mechanical properties (compression strength of ～15 MPa) were produced by indirect 3D printing. Precursor glass powders were printed into 3D ordered structures and then heat treated to sinter and develop crystalline phases. The final glass–ceramic contained a β-spodumene solid solution together with a secondary phase of lithium disilicate.The precision of the printed geometry and the density of the struts in the scaffold depended on several processing parameters (e.g. powder size and flowability, layer thickness) and were improved by increasing the binder saturation and drying time. Two types of powders with different particle size distribution (PSD) and flowability were used. Powders with a larger PSD, could be processed within a wider range of printing parameters due to their good flowability; however, the printing precision and the struts density were lower compared to the scaffolds printed using the powder in a smaller average PSD.     

Experimental investigations on enhanced alternating-magnetic field-assisted finishing of stereolithographic 3D printing zirconia ceramics

Zirconia ceramic components have great applications in the fields of medical, aerospace, and energy. Stereolithographic (SLA) 3D printing technology is widely employed for zirconia ceramic fabrication. However, the surface quality of manufactured components by direct SLA 3D printing is hard to meet stringent requirements of industrial application. In this work, an enhanced alternating-magnetic field-assisted finishing (A-MFAF) method was proposed for SLA printed zirconia ceramics. The A-MFAF was achieved using a flexible alternating-magnetic-field generator, integrating a rectangular magnetic pole and radial magnetic column. The novel finishing tool was fabricated to regulate finishing media behaviors for ensuring desirable finishing force. The unique construction of the magnetic field generator provided a controllable alternating magnetic field in the finishing zone. The magnetic control characteristics were investigated with finite element analysis (FEA). A serial of finishing experiments were carried out to verify the feasibility of the proposed A-MFAF method for SLA printed zirconia ceramics. The finishing efficiency with the developed magnetorheological shear thickening finishing (MSTF) media was improved by over 24% compared to that with the conventional magnetorheological finishing (MRF) fluids. The variation of surface roughness was qualitatively evaluated under different finishing conditions. The surface roughness of 89 nm was obtained from the initial 1.79 μm at 0.6 mm working gap and 700 r/min spindle rotational speed. Digital microscope, optical profiler and surface hydrophobicity measuring instrument were employed to investigate the surface characteristics of the finished SLA printed zirconia ceramics. Ultra-smooth surface with slight defects and deformations was obtained. The feasibility of A-MFAF method for the ultra-precision finishing of SLA printed zirconia ceramics was verified.     

The fabrication of SiBCN ceramic components from preceramic polymers by digital light processing (DLP) 3D printing technology

We present a novel method to fabricate SiBCN ceramic components with complex shapes from preceramic polymers by using digital light processing (DLP) 3D printing technology in this research work. The photocurable precursor for 3D printing was prepared by blending high ceramic yield polyborosilazane with photosensitive acrylate monomers. The material formulation and printing parameters were optimized to fabricate complicated SiBCN ceramic components with high precision. The printed SiBCN ceramic materials were pyrolyzed at different temperatures, and retained their fine features after pyrolysis. Their microstructures were characterized by FTIR, XRD and TEM respectively. Furthermore, the thermal stability and mechanical properties of the SiBCN ceramic samples were investigated and discussed in detail. The 3D printed SiBCN ceramic material exhibited excellent thermal stability and resistance to high temperature oxidation up to 1500?°C.     

Fabrication of bulk piezoelectric and dielectric BaTiO3 ceramics using paste extrusion 3D printing technique

A simple and facile method was developed to fabricate functional bulk barium titanate (BaTiO₃, BT) ceramics using the paste extrusion 3D printing technique. The BT ceramic is a lead-free ferroelectric material widely used for various applications in sensors, energy storage, and harvesting. There are several traditional methods (eg, tape casting) to process bulk BT ceramics but they have disadvantages such as difficult handing without shape deformation, demolding, complex geometric shapes, expansive molds, etc. In this research, we utilized the paste extrusion 3D printing technique to overcome the traditional issues and developed printable ceramic suspensions containing BT ceramic powder, polyvinylidene fluoride (PVDF), N,N-dimethylformamide (DMF) through simple mixing method and chemical formulation. This PVDF solution erformed multiple roles of binder, plasticizer, and dispersant for excellent manufacturability while providing high volume percent and density of the final bulk ceramic. Based on empirical data, it was found that the maximum binder ratio with good viscosity and retention for desired geometry is 1:8.8, while the maximum BT content is 35.45 vol% (77.01 wt%) in order to achieve maximum density of 3.93 g/cm³ (65.3%) for 3D printed BT ceramic. Among different sintering temperatures, it was observed that the sintered BT ceramic at 1400°C had highest grain growth and tetragonality which affected high performing piezoelectric and dielectric properties, 200 pC/N and 4730 at 10³ Hz respectively. This paste extrusion 3D printing technique and simple synthesis method for ceramic suspensions are expected to enable rapid massive production, customization, design flexibility of the bulk piezoelectric and dielectric devices for next generation technology.