Abstract
Today, additive manufacturing technology has brought revolutionary changes to the materials and manufacturing industries. While polymer printing and metal 3D printing have been extensively researched, ceramic printing has emerged as a new trend in research. Ceramic additive manufacturing not only shares the characteristics of additive manufacturing but also faces greater challenges due to the higher melting temperatures and inherent brittleness of ceramics compared to polymers and metals. Ceramic materials possess some excellent performance characteristics. Additive manufacturing technology makes it possible to produce complex ceramic parts with shorter production cycles, lower costs, and retaining the characteristics of traditionally manufactured products. This article introduces the specific working modes of ceramic additive manufacturing technology, including SL, DLP, TPP, DIW, FDM, UP, SLS/SLM, LOM, and BJ3DP printing technologies. The current research status of ceramic additive manufacturing is discussed, as well as the preparation of slurries and the basic requirements for successful ceramic printing.
Introduction
Additive manufacturing (AM) technology, also known as three-dimensional printing (3DP) technology, is considered a revolution in the manufacturing industry. With continuous exploration, additive manufacturing has been widely adopted across numerous fields. As shown in Figure 1, 1 it respectively displays the proportion of additive manufacturing technology used in metal molds, jigs, polymer molds, education and research, cosmetic models, functional models, and end-use parts, along with the annual production volume changes of additive manufacturing from 2010 to 2020. AM technology is an advanced manufacturing process that allows for the simple creation of high-precision and complex components using 3D CAD models, which is better achievable compared to traditional part manufacturing processes. 2 The component models are digitally sliced into 2D cross-sections and converted into machine-readable G-codes. These codes then guide the manufacturing process, which involves the layer-by-layer deposition of powder, liquid, or solid sheets to create solid models with intricate geometric structures.3,4 This process is referred to as digital manufacturing, layered manufacturing, rapid prototyping, solid freeform fabrication, additive fabrication, and 3D printing.5–7 The timeline of significant developments in AM technology from the 1980s to the present is depicted in Figure 2. 8
(a) Proportion of additive manufacturing applications; and (b) the annual production volume of additive manufacturing parts worldwide (in million US dollars). 1
The development of additive manufacturing technology. 8
Initially introduced in the 1980s, AM was initially used for producing small parts or prototypes. 9 The ability to print multiple parts in a single printing operation significantly increased operational efficiency and rapidly garnered attention from the scientific and engineering communities. The AM technology demonstrates significant advantages, including high printing efficiency, the ability to fabricate complex structures with high precision, and low production costs. Despite limitations in material availability, its applications have expanded from initial medical and dental domains10,11 to diverse sectors such as automotive, aerospace, healthcare, and design-related industries.12,13 For instance, AM technology is currently utilized in the production of rocket engine components such as hollow blades, artificial heart pumps, implants, corneas, bridges, dental implants, waveguides, custom jewelry, food, cementitious materials, automotive parts, armaments (ceramic armor), heat exchangers, housing, energy, electronics, and investment casting ceramic tools.14–17
One of the primary challenges in additive manufacturing technology is the limited variety and quantity of materials required during the processing. Although the currently available additive manufacturing materials encompass multiple types, including metals, ceramics, polymers, biomaterials, and smart materials,18,19 systematic studies on their specific utilization and research remain insufficient. For instance, ceramic materials exhibit numerous exceptional properties, but ceramic additive manufacturing still lacks extensive research. Therefore, starting from the application prospects of ceramic materials, this review revolves around the discussion linking ceramic material properties and applications to fabrication methodologies. Compared to previous reviews, this work specifically emphasizes the advantages and application prospects of ceramic materials, provides a detailed comparison of the merits and limitations between traditional ceramic manufacturing processes and advanced manufacturing processes (additive manufacturing), and discusses the principle of different 3D printing techniques, printing advantages/disadvantages, and corresponding optimization strategies for each additive manufacturing technology based on the classification of ceramic additive manufacturing materials.
Ceramic applications
With the continuous development of additive manufacturing, the available materials for its AM systems are shown in Table 1.18–20 Table 1 clearly indicates that, although various efforts have been made in polymers and metal materials, more attention should be paid to ceramics. Due to the excellent properties of ceramics, such as outstanding thermal insulation and high mechanical performance over a wide temperature range, including high corrosion resistance, high temperature strength, high wear resistance, high hardness, and good tribological properties, they have attracted widespread attention.21,22 Ceramic works are shown in Figure 3.22–26
Currently, metal matrix composites (MMCs) have evolved into multifunctional and robust engineering materials with significant commercial viability in various markets. MMCs are typically composed of ceramic reinforcement phases (SiC, Al2O3, B4C, TiC, graphite, NbC, TaC, TiB2, and WC) and metal alloys (Al, Mg, Ni, Cu, Fe, and Ti).23–26
Furthermore, due to the excellent electrical insulation properties of ceramics, their application in electronic manufacturing is increasing. On the other hand, ceramics have a low coefficient of thermal expansion, so their expansion can be neglected by changing the temperature, presenting good shape consistency and finding extensive applications, including in chemical industry, mechanical, electronic, aerospace, and biomedical engineering. When functional ceramics are composed of ferroelectric materials, they exhibit excellent piezoelectric and dielectric properties. 27 As multifunctional materials, ceramics have high mechanical strength and hardness, good thermal stability and chemical stability, as well as feasible thermal, optical, electrical, and magnetic properties. When ceramics become bioceramic materials, they have good biocompatibility, poor degradability, high melting temperature, noncorrosiveness, good mechanical properties, poor plasticity, brittleness, low fracture toughness, and low elastic modulus28–31; in MMCs, they have higher strength-to-stiffness ratio, reasonable electrical conductivity, corrosion resistance, erosion resistance, and good fracture performance, such as toughness, fatigue, and impact resistance. 32 However, the shaping process of ceramic materials cannot be achieved simply using traditional forging methods and mechanical shaping methods. Therefore, this process requires many steps to achieve shaping, including powder mixtures (binder and stabilizer) and forming, such as extrusion, slip casting, pressing, tape casting, gel casting, and inkjet molding. Subsequently, the formed green body should undergo a sintering process for final consolidation.
Ceramic manufacturing method
Traditional ceramic ware covers a variety of daily necessities, such as tableware, tea sets, wine utensils, and stationery. These items include pots, jars, bowls, plates, dishes, cups, boxes, vases, inkstones, and washbasins, among dozens of other types. They feature stable and rounded shapes, smooth surfaces, and are able to meet various social needs in daily life. They are both practical and aesthetically pleasing. Traditional ceramic ware exhibits the following prominent characteristics 33 : 1. Central symmetry and stable center of gravity: Most traditional ceramic ware is centrally symmetric, which enhances stability during use. Key components such as handles, spouts, and supports often feature axially symmetric designs, adding to the convenience of use. 2. Distinctive contours and smooth curved surfaces: Traditional ceramic ware is typically based on simple yet distinctive contours, achieved through rotation or scanning to generate the shape of the ware. Meanwhile, the surfaces are usually smooth, increasing their aesthetic value and tactile comfort. 3. Regular geometric shapes and absence of sharp corners: Traditional ceramic ware commonly adopts regular geometric shapes, reducing the occurrence of sharp corners, cross-sections, or large overhanging structures. This design not only ensures the structural strength of the ware but also enhances safety during use. The production of traditional ceramic ware typically involves multiple processes including clay refining, body shaping, decoration, and high-temperature firing. The shaping of simple ceramic products mainly utilizes methods such as slip casting, pulling, coil building, and hand sculpting. These production techniques ensure the accuracy of the ceramic ware's shape while making the manufacturing process more flexible and malleable. In summary, traditional ceramic ware features stable central symmetry, distinctive contours, and smooth curved surfaces, while avoiding sharp corners and large overhanging structures in their design. Through a series of production processes, ceramic ware achieves balance and completeness in its shape and structure.
The traditional manual ceramic preparation process is shown in Figure 4(a). 34 For the production of complex ceramic structures, it is not only necessary for the manufacturer to possess exquisite skills, but also requires a process of repairing the body after the body is dried. In the casting of parts with hollow centers, such as automobile engine blocks and turbochargers, ceramic cores are used in the manufacturing process. The production process of ceramic cores typically includes the following steps: 1. Material Preparation: Mix the base powder and mineralizer according to certain proportions, with particle size meeting the grading requirements. Meanwhile, prepare plasticizers such as paraffin, beeswax, and polyethylene. 2) Preparation of Ceramic Slurry: Mix the premixed base powder, mineralizer, and a certain proportion of plasticizer at a certain temperature to uniformly disperse them, thereby obtaining ceramic slurry. (3) Injection Molding: Use a hot-press injection machine to inject the ceramic slurry into the ceramic core mold, ensuring that it fills the entire mold cavity, forming the core blank. (4) Sintering Treatment: Slowly embed the ceramic core blank into a container filled with industrial alumina powder to prevent deformation during the sintering process. Then place the container in a calcining furnace for high-temperature debinding and sintering treatment, providing the ceramic core with a certain strength and stability. (5) Trimming and Polishing: Due to mold wear during the hot-pressing process, the sintered ceramic core usually needs to be polished and trimmed to reduce dimensional errors and other issues. (6) Strengthening Treatment: To enhance the strength of the ceramic core at room temperature and high temperatures, the trimmed core may be immersed in strengthening solutions such as ethyl silicate, epoxy resin, etc., to achieve the required dimensional accuracy and performance. In the molding of metal or glass molds, ceramic molds are used to produce complex and high-precision parts. This application is commonly seen in large-scale industrial production, such as in aviation, automotive, and marine industries. The process of ceramic mold casting can be simplified into the following steps: 1. Fabrication of the Ceramic Core: The process initiates with the fabrication of a precision ceramic core, which defines the internal geometry of the final part. This is typically achieved through hot-press injection molding, where a ceramic-filled slurry is injected into a core die under controlled conditions (e.g., temperatures of 80–120°C and pressures of 4–8 MPa). 2. Preparation of the Wax Injection Mold: A metal wax injection mold is manufactured, the cavity of which embodies the negative form of the desired metal part's external geometry and is designed to accommodate the ceramic core. 3. Assembly and Wax Pattern Formation: The ceramic core is precisely located within the wax injection mold. The annular cavity between the core and the mold wall, typically 2–10 mm thick, is then injected with molten casting wax under moderate pressure (0.5–2.0 MPa), resulting in a composite wax pattern that encapsulates the core. 4. Ceramic Shell Building: The assembled wax pattern undergoes repeated dipping into ceramic colloidal slurries and subsequent stuccoing with refractory sands (e.g., zircon or fused silica). This build-up cycle is repeated for 6–9 layers to form a robust, multilayered ceramic shell with a total thickness of 5–10 mm. (5) Dewaxing and High-Temperature Sintering: The shell is subjected to autoclave dewaxing at 150–200°C to remove the majority of the wax. Subsequently, the green ceramic mold is fired at an elevated temperature ranging from 1000°C to 1200°C. This critical step eliminates residual organics, sinters the ceramic particles to develop sufficient mechanical strength, and confers the necessary thermal stability for metal casting. (6) Alloy Pouring and Solidification: The sintered ceramic mold is preheated and then filled with molten high-temperature alloy (e.g., a nickel-based superalloy) at a pouring temperature often between 1500°C and 1600°C. The alloy is allowed to solidify under controlled conditions to form a sound metallurgical structure within the mold cavity.35,36 (7) Demolding and Core Removal: After the casting has cooled, the external ceramic shell is mechanically removed. The internal ceramic core is then selectively dissolved and removed via chemical leaching (often using a hot aqueous NaOH solution at 20–30% concentration) or other methods, yielding the final, liberated metal component. These steps give the ceramic mold casting process high precision and complexity while ensuring the quality and performance of the final metal part. When using traditional manufacturing methods, different molds need to be designed according to the different shapes of the parts. Each part corresponds to a set of molds, leading to long design and manufacturing cycles, low product quantities during mold opening, and expensive repair costs when problems occur with the molds. Therefore, it is difficult to meet the requirements for rapid development of parts. There are technical challenges in making ceramic molds or cores for complex-shaped parts.
However, the emergence of additive manufacturing technology can effectively overcome the shortcomings of traditional manufacturing. It not only has a short manufacturing cycle, but also is capable of easily manufacturing complex ceramic structures.38–40 Among them, ceramic additive manufacturing technology generally includes the following steps: 1. Use CAD for product structural design. 2. Prepare ceramic slurry according to product requirements. 3. Slice the CAD model, import the data into the printer, and adjust printer parameters. 4. Print parts using a ceramic printer based on the CAD model. As shown in Figure 4(b), it demonstrates the ceramic additive manufacturing technology in the process of printing parts. 37 5. The printed parts are sintered to remove residual organic additives, bonding the material particles together to form dense ceramic components. 6. To improve the surface quality of the product, postprocessing such as polishing, grinding, and coating can be performed. 41 Compared with traditional manufacturing, the advantages of ceramic additive manufacturing are as follows: 1. High degree of freedom, capable of manufacturing complex structures and internal cavities. 2. Material saving, additive manufacturing is a way of layer-by-layer stacking materials, which allows for on-demand use of materials and printing of multiple products. 3. It can achieve a variety of material combinations, manufacturing different ceramics according to the requirements of different products, achieving functional ceramics with multiple material combinations. 4. Improved product performance, by optimizing internal structure and pore distribution, it can enhance the performance of ceramic products, such as strength, density, and thermal conductivity. 5. Achieving integrated manufacturing, reducing manufacturing steps and shortening the production cycle. 6. Structural optimization of products is simpler, with higher manufacturing precision. 7. Postmaintenance of equipment is more convenient and cost-effective. In addition, additive manufacturing is not limited by the hardness and brittleness of molds and raw materials, and can produce ceramic structures with complex structures, high strength, thermal stability, and chemical corrosion resistance.34,42 In their paper, Bose et al. 43 elaborated on the advantages of additive manufacturing. From an economic perspective, additive manufacturing avoids the expensive tooling required in traditional processing, as it does not require part-specific tooling. Also, complex structures can be easily fabricated in additive manufacturing technique using the CAD file thereby avoiding expensive mold costs. In terms of time cost, it eliminates the need for complex structural design, while also reducing or eliminating postmanufacturing steps such as cutting, grinding, and assembly, thereby comprehensively reducing part cost and production lead time. When preparing core materials for turbines and airfoil components, 44 additive manufacturing technology can easily fabricate complex internal cooling channels the overall design cycle and development costs in the aerospace field.45,46 When discussing the application market of ceramic additive manufacturing in their paper, Abdelkader et al. 47 pointed out that additive manufacturing technology, in the aerospace and automotive industries, demonstrated the ability to produce lighter, stronger, and more efficient components, and noted that traditional manufacturing methods are often unable to create the complex shapes required for aerospace and automotive engineering, or the manufacturing costs are too high; however, the emergence of additive manufacturing technology has fulfilled this need. Meanwhile, for complex parts, especially those with small batch sizes, traditional manufacturing entails high design costs, but additive manufacturing technology reduces these costs by simplifying the production process and minimizing material waste. When designers conduct structural optimization, they can also quickly modify the design model without requiring extensive rework or the need for redesigning molds, thereby saving significant time and money.
Ceramic additive manufacturing (CAM), compared to traditional ceramic manufacturing, has many advantages. However, different additive manufacturing processes still have their own characteristics. Generally, there are two common ceramic additive manufacturing techniques. One involves using ceramic powders, selective laser sintering and binder jetting 3D printing.48–50 The other method utilizes ceramic slurries containing binders/viscosity modifiers in the case of direct ink writing and UV-curable photopolymers, such as in the case of stereolithography and digital light processing.51–53 According to the standards of the American Society for Testing and Materials (ASTM), complex-shaped ceramic parts produced using AM technology can be classified into two groups: direct or single-step, and indirect processes, also known as multistep. 32 In the multistep AM process, the manufactured green body requires postprocessing steps, such as debinding and sintering, to consolidate the green body. Sheet lamination, 54 material extrusion-based technologies (MEX), 55 binder jetting (BJT), 56 voxel-based polymerization (VPP), 57 direct inkjet printing (DIP), 58 and indirect selective laser sintering (SLS) are the most available indirect AM technologies. However, currently only two AM processes can produce complex-shaped advanced ceramic parts through one-step direct shaping and solidifying materials: laser powder bed fusion (L-PBF) and directed energy deposition (DED). Additionally, there is a method called negative ceramic AM for processing ceramics using AM technology. In this method, sacrificial polymer molds were prepared using one of the AM technologies such as fused deposition modelling (FDM), 57 material jetting (MJT), 58 SLS, 59 and stereolithography (SLA). 60 Subsequently, the polymer mold is impregnated with ceramic slurry, followed by dissolution or thermal burnout. 61 The overall steps of ceramic additive manufacturing are shown in Figure 5. 62
The steps of ceramic additive manufacturing.62
Despite the diversity of CAM techniques, each technology is invariably accompanied by inherent advantages and drawbacks. This work provides a meticulous elaboration on the fabrication mechanisms corresponding to individual additive manufacturing processes. The CAM technologies under investigation encompass: stereolithography (SL), digital light processing (DLP), two-photon polymerization (TPP), inkjet printing (IJP), direct ink writing (DIW), fused deposition modeling (FDM), laminated object manufacturing (LOM), selective laser sintering (SLS), and binder jetting 3D printing (BJ3DP). Concurrently, we systematically address three critical aspects: material preparation processes, existing technical limitations in ceramic additive manufacturing, and their corresponding solutions. The conclusions and perspectives presented establish pivotal areas for future research and development in ceramic additive manufacturing technology.
Ceramic additive manufacturing materials and technical
Although CAM technologies possess numerous advantages, material development endeavors for each CAM technology continue to present persistent challenges. Furthermore, substantial variations exist in printing material formulation across different CAM techniques. Specifically, in slurry-based additive manufacturing processes, further addition of various formulations (such as binders) and process optimization are required to provide high solid loading for the production of dense ceramic structures. However, this in turn leads to an increase in viscosity, non-uniformity, and instability (such as precipitation), thereby limiting the applicability of raw materials for manufacturing high-resolution structures. Additionally, when shaping and curing the slurry with ultraviolet light, the mismatch in refractive index between the ceramic powder and the photocurable resin significantly reduces the curing depth, and the scattering of incident light by these ceramic particles results in a coarsening of the printing resolution.32,61,63,64 Therefore, additive manufacturing of ceramic materials is a challenging task due to their demanding processing requirements.
Introduction of ceramic materials
Commonly used ceramic materials in additive manufacturing include zirconia (ZrO−), alumina (Al−O−), silicon carbide (SiC), silicon nitride (Si−N−), biocompatible ceramics (e.g., bioactive glass, hydroxyapatite), and polymer-derived ceramics. Zirconia oxide ceramic slurries have the following characteristics: 1. They exhibit extremely high hardness, close to that of steel, and even surpass traditional metal materials, providing excellent wear resistance and scratch resistance in applications. 2. They possess outstanding strength and toughness, able to withstand large mechanical loads without easy fracture, making them excel in high-load and high-strength engineering applications. 3. They demonstrate excellent corrosion resistance and stability in various acidic and alkaline media, finding widespread applications in chemical, medical, and biological fields. 4. They exhibit good stability and thermal shock resistance in high-temperature environments, allowing them to work for extended periods at high temperatures without deformation or damage, suitable for high-temperature processes and applications. 5. They have excellent insulating properties, capable of blocking current conduction, hence finding broad application in electronic devices and insulating components. Zirconia is often used in ME-based additive manufacturing, SLA, BJT, and inkjet 3D printing methods for processing. Alumina oxide ceramic slurries possess high hardness, corrosion resistance, high-temperature stability, excellent insulation, and lightweight characteristics, leading to their wide applications in aerospace, chemical industry, electronic devices, high-temperature structural components, wear-resistant parts, and biomedical implants.65,66 However, pure Al2O3 ceramic materials have relatively low strength and high brittleness, limiting their mechanical applications. It is widely recognized that ZrO2 can significantly improve the strength and fracture toughness of alumina materials through stress-induced phase transformation toughening and phase transformation-induced microcrack toughening mechanisms.67–69 In recent years, significant progress has been made in the SL preparation of ZrO2-reinforced Al2O3 (ZTA) ceramic components.70–72 Silicon carbide ceramic slurries exhibit high hardness, corrosion resistance, high-temperature stability, good thermal conductivity, low thermal expansion coefficient, high electrical insulation, and oxidation resistance, making them widely used in high-temperature furnaces, semiconductor manufacturing, chemical industry, and other fields. Silicon nitride ceramic slurries have high hardness, corrosion resistance, high-temperature stability, good thermal conductivity, low thermal expansion coefficient, high electrical insulation, excellent optical performance, and oxidation resistance, leading to their wide applications in optoelectronic devices, high-temperature furnaces, and the chemical industry. Bio-compatible materials, as ceramic slurries, exhibit excellent biocompatibility, low immune response, good biointeraction with biological materials, chemical stability, and good mechanical properties, leading to their widespread use in orthopedics, dentistry, tissue engineering, and other biomedical fields, such as artificial joints, dental implants, and bone repair materials. Polymer-derived ceramics, as ceramic slurries, possess plasticity, processability, high strength and toughness, lightweight, corrosion resistance, and high-temperature resistance, indicating broad application prospects in many fields. Currently, PDC technology can be combined with 3D printing techniques.
In the development of the times, people need new structural materials to replace metals and metal alloys. People have begun to study the use of inorganic and organic metal polymers for nonoxide ceramics through the polymer pyrolysis method. Preceramic polymers (PCP) are inorganic polymer compounds that are chemically or thermally cured (or photocured) and converted into high-strength and chemically stable ceramics through pyrolysis in an inert or reactive atmosphere (this conversion is also called “ceramization”).73–75 However, the chemical compositions achievable in ceramics derived from PCP precursors are often unattainable through traditional powder-based ceramic techniques. Therefore, PCP can be used as low-loss binders mixed with various active or passive fillers to produce many advanced ceramic phases or composite materials. Also, ceramic yield (Formula 2.1) is one of the most critical indicators for evaluating the performance of a preceramic polymer.57,73,76 A high ceramic yield (typically desired to be above 70–80%) implies low mass loss during the transformation of the polymer from an organic to an inorganic state, with relatively controllable volumetric shrinkage, which is beneficial for manufacturing dense, defect-free ceramic components. A low ceramic yield is usually accompanied by high porosity and low mechanical strength, as significant mass loss leads to the formation of more voids and defects. The use of PCP in various additive manufacturing technologies to produce complex-shaped ceramic components is expected to overcome problems related to molding difficulties, heterogeneous material processing, and limited production speed and repeatability. The chemical preparation of suitable PCP is crucial in determining the final ceramic product composition and performance. In the preparation of borosilicate ceramics, organic silicon polymers containing boron are usually used, such as polyborosilane, polyborosiloxane, polyborosilazane, and their derivatives.77–79 For the preparation of boron nitride (BN) ceramics, there are mainly four types of boron-containing PCP precursors, namely: boron nitride (H3B3N3H3) (polyboron nitride), B-chloro-boron nitride (Cl3-XRX)B3N3R3 (poly[B-amino-boron nitride]), tri(alkylamino)borane B(NHR)3 (poly [B-amino-boron nitride]), and decaborane (B10H14). Boron-nitrogen heterocycles are potential candidates for single-source boron nitride precursors, offering ceramic yields of up to 83–90%.
80
However, the highly cross-linked structure of borazine hinders processing by liquid or melt shaping. Through different strategies, such as modifying the structure of borazine and resynthesizing borazine from different compounds, the thermal decomposition process of borazine has been modified to synthesize more processable polyborazines.
81
However, in these cases, the ceramic yield is limited to only 5%. Colombo et al. have discussed different methods for synthesizing boron-based PCP.82–84 Boron-based PCP have also been used to prepare boron carbide (B4C) and boron carbonitride (B/C/N) materials. However, most boron-based preceramic precursors are either unstable at room temperature, require complex processing, or exhibit a tendency to evaporate during further ceramic conversion processes. Therefore, research is underway on new molecules and polymer precursors that are insensitive to air or moisture, stable at high temperatures, have controllable polymerization and molecular weight, and have appropriate rheological properties. Table 2 lists the structural and functional ceramic materials that have been processed using AM technology.20,85
A summary of structural and functional ceramics fabricated by AM-based techniques.20,85
PZT: lead zirconium titanate; LSMO: lanthanum strontium manganite; YBCO: yttrium barium copper oxide; RO: alkaline oxide (R: Alkali); PMN: lead magnesium niobate; YSZ: yttria-stabilized Zirconia; HA-TCP: hydroxyapatite–tricalcium phosphate; HA-PC: hydroxyapatite polycarbonate; LOM: laminated object manufacturing; LENS: laser engineered net shaping; FFF: fused filament fabrication; DLP: digital light processing; IJP: inkjet printing.
AM and AM materials
With the continued advancements in science and technology, various 3D printing methodologies have been developed for ceramics. Depending on the form of the feedstock, printing methods, these technologies can generally be divided into slurry-based, powder-based, and bulk solid-based methods, as shown in Table 3. 42 Among them, as shown in Table 4, the advantages and disadvantages of each additive manufacturing method are presented. It is important to note that slurry-based technologies use ceramic or polymer mixtures, with viscosities ranging from low viscosity (∼mPa·s) inks with low ceramic loads (up to 30 vol.%) to high viscosity (∼Pa·s) pastes with higher ceramic loads (up to 60 vol.%). Slurry-based ceramic 3D printing technologies typically involve a liquid or semiliquid system in which fine ceramic particles are dispersed as raw materials, and depending on the solid load and viscosity of the system, they can exist in the form of ink or paste. The slurry content can be 3D-printed through photopolymerization, inkjet printing, or extrusion. 42 According to the ISO/ASTM52900:2021 standard, additive manufacturing technologies for the production of ceramics and polymer-derived ceramics include SL, DLP, TPP, DIW, FDM, IJP, SLS/SLM, LOM, and BJ3DP. The schematic diagrams of the printers can be seen in Figure 6. 63
Different additive manufacturing technologies and basic differences. 63
Ceramic 3D printing technologies. 42
The characteristics of each additive manufacturing method.
Polymer-derived ceramics (PDC) technology
With the continuous advancement of materials science, it has become possible for preceramic polymers (PCP) to be converted into polymer-derived ceramics (PDC) through heat treatment. The PDC technology, derived from PCP precursors, is becoming a powerful alternative to traditional ceramic synthesis and manufacturing technologies within certain ceramic systems, and it holds tremendous potential. The PDC method utilizes synthesized PCP precursors to produce ceramics, which are cross-linked after or during shaping, followed by pyrolysis. This method can create a range of high-performance nonoxide ceramics that are unattainable through traditional ceramic manufacturing methods. Materials include binary, ternary, and quaternary ceramics such as SiC, Si3N4, BN, AlN, SiCN, SiCO, BCN, SiBCN, SiBCO, and SiAlCN, in forms such as powders, fibers, wires, microtubes, coatings, thin films, bulk materials, foams, and ceramic matrix composites.73,86–92 PDC technology has been combined with 3D printing technologies such as DSL, DLP, TPP, DIW, etc.
Slurry 3D printing technology
Currently, slurry-based 3D printing technology is the most widely used. It involves mixing ceramic powders, additives, and liquids to form a slurry, which is then shaped using techniques such as stereolithography (SL), inkjet printing (IJP), or extrusion (DIW). Light-curing technologies include stereolithography (SL), digital light processing (DLP), and two-photon polymerization (TPP).
Stereolithography (SL) refers to the uniform mixing of micro and nano ceramic powders and photosensitive resins (including monomers, photoinitiators, etc.) to prepare ceramic paste, which is then cured by irradiation of a specific wavelength light source (generally ultraviolet light source). The principle of stereolithography technology is shown in Figure 7. 93 The photocuring process of stereolithography is generally point-to-line and line-to-surface printing layer by layer. When a layer of curing is completed, the height of the platform supporting the parts will rise or fall depending on what we set (the rise or fall depends on whether the printing process is top-down or bottom-up), and finally the ceramics will be obtained through post-treatment processes such as drying, degreasing and sintering.94,95 SLA is a liquid resin-based 3D printing technology that builds objects by curing the resin layer by layer. It contains a liquid resin tank, a model building platform, and an ultraviolet (UV) laser. In the SLA process, the entire tank is filled with liquid resin, which can be a mixture of organic molecules, monomers, oligomers, or prepolymers, to which photoinitiators and other functional additives may also be added. And the ultraviolet laser is focused on a specific location on the surface of the resin, and through the light emitted by the ultraviolet laser, the photoinitiator in the resin is activated, triggering a polymerization reaction in the resin, forming a highly cross-linked polymer network. This process takes place on each cross-section, building the object layer by layer. When the first layer is fully polymerized, the model building platform is lowered slightly, and a scraper or blade sweeps across the cross-section of the object to reapply a fresh layer of resin to the cured layer. The model building platform then moves down again so that the next layer is at the focal point of the UV laser. The UV laser solidifies the resin again to form the next layer. This process is repeated until the entire sample is built. SLA methods typically use as little resin as possible, and excess resin can be reused during construction or removed from the sample.6,96 The size and number of generated objects affect build speed, with larger objects and more layers taking longer to complete. As the first light curing printing technology in the field of additive manufacturing, although it can produce parts with high precision, smooth surface finish and good adhesion between layers,97,98 the printing process from point to line and line to surface is very time-consuming, exposing its disadvantages of low work efficiency. On the other hand, the key difficulty is the preparation of ceramic paste. In the photosensitive resin, ceramic particles should be evenly distributed, and the size of particles should be moderate, and the solid content should be moderate.93,99 In this way, problems such as deformation and cracking can be avoided, both during the removal of the as-printed part from the substrate and in the substrate and debinding/sintering. In traditional stereoscopic lithography based additive manufacturing, photosensitive organic solutions are used to print objects, 100 which are composed of organic monomers or oligomers, photoinitiators sensitive to specific wavelengths of light, and other components that affect the rheology, foamability, and adhesion of the solution. There are sometimes 9–12 chemicals in the solution. Ceramic 3D printing based on stereolithography technology is to control the dispersion and settlement of solid particles by adding fine ceramic powder 101 to a photosensitive solution, and adding chemical substances such as dispersants and plasticizers. The organic part of this mixture is called the adhesive. When the ceramic-binder mixture has a high viscosity, it is called a “slurry.” Mixtures with relatively low viscosity are called “suspensions.” The slurry and suspension are formulated to maintain the long-term stability of the mixture (not allowing the ceramic particles to separate and settle over a period of days or even months) and to produce a special rheological property that allows the slurry to shear thin and the suspension to have a relatively low viscosity. The mass fraction of ceramic powder in the mixture reaches 70–80 wt% for the slurry and 60–70 wt% for the suspension. The higher the mass fraction of ceramic powder, the lower the shrinkage rate of ceramic product, and the greater the final density. Since 1994, Halloran et al. have extensively studied SLA technology, first using high concentrations of ceramic suspensions up to 65 vol.%, including silica, alumina, and silicon nitride.101–105 The fabricated multiceramic materials exhibited tunable thermal expansion coefficients and were defect-free multiceramic triangle structures. The ceramic materials manufactured by SLA are summarized in Table 5.
Principle of stereolithography. 93 P1, P2, PN: They are the first layer, the second layer and the N layer of stereolithography. d: layer thickness.
Overview of ceramic materials manufactured by SLA.
Digital Light Processing (DLP) is a method of direct photocuring of the plane of ceramic slurry based on three-dimensional lithography technology, so as to directly accumulate layer by layer. The Schematic diagram of DLP light curing 3D printing is as shown as Figure 8. 112 In DLP technology, high-resolution digital optical processor projectors are used as light sources and liquid light curing monomers are used as reaction materials. Under ultraviolet light, the reaction material polymerizes and wraps ceramic particles in it. Through layer-by-layer light curing, ceramic materials with three-dimensional structure are finally formed. 113 Due to the tradeoff between resolution and print size, DLP printing is not suitable for manufacturing large parts. 114 DLP printers can operate according to the “bottom-up” or “top-down” method. The shape of the component (batch or microporous) determines which technology is more suitable for manufacturing defect-free parts, and the “bottom-up” method is more suitable for manufacturing bulk, nonporous components. 115 DLP technology has been used in the manufacture of various ceramic materials such as zirconium oxide and alumina.116,117 The advantages of DLP compared with SL technology118,119: 1. DLP technology is relatively fast. By projecting an image of the entire layer, DLP technology can print multiple models at the same time in a single irradiation, so it is faster than SL technology. 2. DLP technology has higher resolution. DLP technology uses a projector or laser to project the entire image onto the surface of a liquid resin, allowing finer patterns to be achieved. 3. The cost of DLP equipment is relatively low and easy to manufacture. DLP printers do not require sophisticated optics and moving platforms, making them easier to manufacture and maintain. 4. the liquid resin used by DLP technology can be cured at room temperature, without heating and cooling process, so it is more energy saving and more environmentally friendly. The disadvantages include: 1. Limited printing accuracy by the projection resolution and the thickness of the lithographic layer, so it cannot print highly precise parts. 2. DLP technology uses liquid resins as printing materials, which are usually more expensive than SLA printing materials. 3. DLP technology, high energy light irradiation of liquid resin will produce high temperature and thermal stress, easy to lead to the problem of interlayer stripping. 4. The shrinkage rate of the manufactured structure after sintering is higher than 10%, and the accuracy is low. This is primarily attributed to the inherent limitation of DLP printing technology, which results in weak interlayer bonding within the ceramic structure. Consequently, this weakness leads to anisotropic shrinkage during the sintering process, 39 ultimately contributing to its relatively lower precision. In the field of precision casting of hollow turbine blades, Chen et al. 120 prepared silicon oxide based ceramic core samples, and studied the influence of microstructure and properties of ceramic core samples in different printing directions through DLP light curing 3D printing technology and high temperature sintering, laying a technical foundation for the application of DLP technology in core manufacturing. Hollow blades usually use silicon oxide base and alumina base as ceramic cores, and their two core pairs are shown in Table 6. 120 Although the alumina based ceramic core has shown excellent performance in many aspects, such as good structural stability and amorphic transformation in the production and use process, its development has been restricted due to the difficulty of core-stripping, but in contrast, the silicon oxide based ceramic core at home and abroad started earlier and the system is relatively perfect. Silica based ceramic core is usually graded quartz glass powder as the matrix material (accounting for more than 80% of the total weight), and through sintering of mullite, alumina, zirconium silicate, rare earth oxide, and other mineralizing agents incorporated into it (to control the amount of quartz precipitation). The firing temperature of the ceramic core is between 1150 and 1250°C, and the casting temperature is between 1520 and 1560°C. 121 In the process of roasting and casting, silicon oxide will undergo polycrystalline phase transformation.122–124 The phase transition occurs in both the heating and cooling stages, and when the temperature is raised to 1200°C, the amorphous quartz glass will change into α-cristobalite and the volume will also have a certain expansion, when the temperature is reduced to 180 ∼ 270°C, α-cristobalite will change into β-cristobalite, but its volume will shrink by about 3.7%. It is easy to have small cracks inside the core, especially when there is internal stress, so controlling the amount of quartz precipitation is an important problem in the production process of ceramic core. At present, promoting or inhibiting the precipitation of cristobalite by using some mineralizing agents has become the focus of ceramic core research. In general, when the content of cristobalite is 8–16 wt%, the comprehensive performance of ceramic core is the best. 125
Structure diagram of DLP light curing 3D printing equipment. 112
Advantages and disadvantages of two typical ceramic cores. 120
DLP and SLA are two common 3D printing technologies that differ in their basic materials and light projection methods. The SLA method uses a high-viscosity slurry as the base material, typically composed of photosensitive resin and other additives. Within the construction platform, UV laser is used to draw contours and shadow regions on the slurry surface, gradually solidifying the resin layer by layer to build the three-dimensional object. SLA technology offers high precision and surface quality, making it suitable for manufacturing complex shapes and detailed models. On the other hand, the DLP method uses a suspension as the base material, containing photosensitive resin particles. Within the construction platform, a physical mask is used to project UV or visible light across the entire platform, or a digital micromirror device (DMD) may be used, which includes an array of micro-mirrors. When activated, these micro-mirrors selectively reflect the light onto the construction platform, solidifying the photosensitive resin particles and constructing the three-dimensional object. DLP technology generally boasts faster printing speeds, although it may sacrifice some surface quality and details compared to SLA technology. Therefore, when the application demands superior surface finish, maximum dimensional accuracy, complex curved surfaces, and fine features, SLA printing technology is the preferred choice. For printing small-sized parts where high printing speed and cost-effectiveness for small to medium-sized components are prioritized, DLP printing technology is selected. Beyer et al. 126 in their study on surgical guides for dental implants, discussed the manufacturing accuracy, printing speed, and resin consumption of both SLA and DLP printing technologies. They concluded that SLA technology achieves higher accuracy than DLP at specific angles, while also consuming less material. However, DLP technology offers shorter printing times for parts. Furthermore, Katheng et al. 127 in their research comparing the mechanical properties of different 3D printing technologies, similarly noted that parts fabricated using SLA exhibit superior flexural strength and the smoothest surface finish, making them more suitable for applications requiring robust and high-quality surfaces. Consequently, parts produced by SLA demonstrate high precision. In the application of piezoceramics as discussed in the paper “Progress and challenges of 3D-printing technologies in the manufacturing of piezoceramics,” the use of stereolithography-based ceramic manufacturing technology offers high precision and resolution. Typically, this technology can achieve intra-layer accuracy as low as 30 μm, with layer thickness ranging from 10 to 50 μm. Additionally, due to the shrinkage that occurs during the sintering process of 3D-printed parts, with an average shrinkage rate of 15–25%, the final resolution can be even higher. Using SLA and DLP technologies typically requires a two-step heat treatment process to achieve dense ceramic parts. The first step, called “debinding,” involves gradually heating the green part (the ceramic green object 3D-printed through layer-based photopolymerization operations) to temperatures as high as 500–600°C to completely decompose and burn off the organic binder. During this process, the green body transforms into a loosely consolidated, high porosity material consisting only of ceramic particles (with porosity ranging from 20 to 40%). The second step, known as “sintering,” involves further heating the part to high temperatures (exceeding 1000°C) and holding it for a period of time, typically several hours, to densify the material. Following sintering, the porosity can be reduced to 1–5% depending on the process parameters. In summary, ceramic manufacturing based on stereolithography technology offers high precision and resolution. Through the debinding and sintering steps, green body materials can be transformed into dense ceramic parts. This technology holds potential for manufacturing high-precision, complex-shaped ceramic components and finds applications in various fields such as medical, aerospace, and automotive industries. From the work of Woodward et al. 128 utilizing DLP technology to produce complex ultrasonic transducers, to the efforts of Song et al. 129 using DLP technology for 3D printing of piezoelectric ceramic parts based on BT, and finally, Chen et al. 130 studying the use of DLP technology for PZT ceramic 3D printing in the fabrication of 2D array transducers, the production of ultrasonic transducers using DLP technology involves a ceramic suspension composed of 40 vol.% PMNT powder, 1,6-hexanediol diacrylate (HDDA), di-pentaerythritol hexaacrylate (DPPHA) as monomer oligomers, Triton X-114 dispersant, and Irgacure 784 (BASF) photoinitiator. Meanwhile, for the BT-based piezoelectric ceramic parts, several ceramic suspensions were prepared with 30–80 wt% 1 μm-sized BT powder, commercial SI500 (EnvisionTec Inc., Ferndale, MI) photocurable resin, Phospholan PS-131, and Triton x-100 as dispersants. Preliminary experiments indicated that for suspensions with a load of 60–80% wt%, an optimal layer thickness of 20 μm was achieved with exposure times ranging from 2 to 8 s. For the 2D array transducer fabricated using DLP technology, a ceramic suspension was prepared. This suspension comprised 500 nm PZT-5H powder, 1,6-hexanediol diacrylate (HDDA), polyethylene glycol (PEG), aliphatic urethane acrylate (U600), and decanol (Sigma Aldrich) as the monomer/oligomer blend, suitable dispersants, and photoinitiators. 131
Two-photon polymerization (TPP) is a three-dimensional printing (3DP) technology based on the principle of photopolymerization, as shown in Figure 9. 132 Unlike traditional SL and DLP technologies, TPP uses the dual-photon polymerization effect in the near-infrared wavelength range (760–1000 nm) for shaping. In traditional photopolymerization techniques, ultraviolet light (250–400 nm) is used to irradiate photosensitive materials, and the energy of a single UV photon is sufficient to initiate the polymerization reaction of the photosensitive material. In TPP, however, it is necessary to use two photons of near-infrared wavelength simultaneously to trigger the polymerization reaction in the material. This is because the energy of a single photon in the near-infrared wavelength is insufficient to initiate the polymerization reaction, but when two photons act simultaneously, their energies overlap, reaching the energy threshold required for polymerization. Near-infrared wavelength photons have high penetration capability and minimal scattering, giving TPP an advantage in manufacturing nano-scale components. By precisely controlling the focal point position and intensity distribution of the laser beam, high-resolution, and high-precision nanoscale structure printing can be achieved. 133 The main advantage of two-photon polymerization printing technology lies in its ability to achieve high precision and precise positioning deep within the resin. Compared to the traditional single-photon polymerization process, two-photon polymerization can cause polymerization reactions inside the resin, achieving sub-micron-level curing, while traditional single-photon polymerization only occurs at the liquid surface. 134 The principle of two-photon polymerization involves focusing high-intensity light in a specific space within the photosensitive resin, and absorbing two photons (usually near-infrared or green laser) to activate the polymerization reaction. 135 The rate of this two-photon absorption is proportional to the square of the incident laser intensity, enabling two-photon polymerization to achieve a resolution of 200 nm or close to the diffraction limit. In 1992, Wu et al. first demonstrated the possibility of three-dimensional graphics manufacturing by producing simple shapes with high aspect ratio grooves. 136 Subsequently, Maruo et al. demonstrated the feasibility of two-photon polymerization in manufacturing complex three-dimensional microstructures by preparing a spiral structure with a diameter of 7 μm using polyurethane acrylate resin. 137 As the technology continued to develop, it has been widely explored and developed globally in the field of photon devices and micromechanical components, even manufacturing feature structures with lateral resolutions below 100 nm.138,139 TPP technology has broad prospects in the field of micro-nano manufacturing. It can be used to manufacture micro-optical components, biochips, microfluidic devices, and various micro-nano structures. Due to its high resolution and precise control capabilities, TPP can also be used to manufacture complex micro-nano devices and biomimetic structures. In conclusion, Two-photon polymerization (TPP) is a 3DP technology that uses the dual-photon polymerization effect in the near-infrared wavelength. Compared to traditional ultraviolet photopolymerization technology, TPP has higher resolution and precision, and is suitable for manufacturing nanoscale components. 140 However, it still has some shortcomings. For instance, the use of fine particles to promote sintering and the high particle loading required in photopolymerizable slurries result in very high viscosity. To facilitate curing during the layer-by-layer process, suitable methods are needed to generate uniform thin layers, which leads to a significant increase in equipment complexity and cost. Furthermore, stabilizing particles in nonaqueous media is often challenging and can lead to segregation phenomena within the slurry, which is undesirable with the required long printing times. Additionally, the difference in refractive index between the particles and the surrounding liquid can cause scattering, leading to a loss of resolution. Coupled with the high absorbance of certain materials, this can significantly reduce the penetration depth of the radiation, thereby impairing the curing capability. 43 Moreover, Two-Photon Polymerization (TPP) can only use precursors that are “transparent” to the laser; conventional ceramic slurries cannot be used due to their opacity. In addition, the forming size is small and the efficiency is low. 42
Working principle of two-photon polymerization direct writing. 132
Ink-jet printing (IJP) is a well-known 3D printing technology that involves jetting liquid-phase materials (i.e., “ink”) onto paper, plastic, or other substrates through the print head nozzles driven by piezoelectric or thermal effects to form liquid droplets, thereby realizing layer-by-layer or overall 3D printing process.
141
IJP can operate in two modes: continuous or drop-on-demand (DOD),
142
primarily using the drop-on-demand (DOD) printing mode.143,144 The working schematic of DOD operation in IJP technology is shown in Figure 10.
145
DOD mode offers high positioning accuracy, small droplet size, and can be achieved through thermal excitation or piezoelectric effect for ink ejection. Since then, IJP has further developed as a thin-layer material deposition technology on substrates. The range of ink materials has expanded, including polymers or metals for electronic patterns,146,147 solder pastes for microelectronic soldering, and cells for tissue engineering repair.
148
Components printed may appear in 2D structures and may not necessarily have proper 3D features. However, due to the very small volume of the material used (i.e., ink), IJP is limited to printing microcomponents, as commercial printers currently only eject a few nanoliters of ink per droplet. According to the printing principle, ink-jet printing technology can be divided into piezoelectric drop-on-demand and thermal drop-on-demand. In 1995, Blazdell and colleagues first described the application of IJP in ceramic component printing,149,150 using ZrO2 and TiO2 ceramic inks with volume fractions as low as 5 vol.%, but only produced simple multilayer structures with poor surface quality. Subsequently, the group successfully printed a small column array based on submicron ZrO2 particles loaded in the ink at 14 vol.%,
151
and studied the significant influence of different ink properties, especially viscosity and surface tension, on printing performance. Seerden et al.
152
later reported the use of ceramic inks prepared with up to 40 vol.% of Al2O3 loading to produce ceramic components with feature sizes smaller than 100 μm. The performance of ceramic inkjet printing (IJP) is largely dependent on critical factors of ceramic powders and ink formulation, as well as their properties, particularly rheological aspects such as dispersibility, stability, viscosity, and surface tension. Additionally, maintaining an appropriate pH level is necessary to prevent ink corrosion of the jetting system. A uniform particle size distribution with particles smaller than 1/100 of the nozzle diameter in micrometers is essential to prevent nozzle clogging as per the printer manufacturer's requirements,
153
and this significantly reduces printing efficiency and product accuracy.
154
The even dispersion of ceramic powders in the ink is a crucial prerequisite for smooth ink flow through the printhead nozzle. The jetting performance of ceramic inks is largely influenced by their viscosity. Insufficient jetting or excessive velocity may result from excessively high or low viscosity, respectively.
155
The viscosity of ceramic inks is typically low, in the range of a few mPa·s, leading to long drying times and significant shrinkage due to the low solid loading, which may adversely affect the final accuracy of printed parts. Increasing the solid loading may be beneficial, but it can alter the ink's rheological behavior. Thus, various optimizations are required to ensure the achievement of appropriate solid loading and rheological characteristics. Seerden and colleagues156,157 demonstrated that the use of alumina wax inks can minimize drying shrinkage to the greatest extent, while achieving good sintering density remains challenging. Chen et al.
158
reported a detailed investigation on the optimization of different formulations. They indicated that with the aid of zeta potential, viscosity, and surface tension tests, as well as sedimentation, drying, and sintering experiments, the suspension formulation was optimized. Using TEA as a dispersant and adjusting the pH to 5.8 (zeta potential of 41.8 mV), the prepared suspension INK-T1 achieved optimal dispersion stability. Inkjet printing tests also demonstrated ideal printability. Long-term stability with a shelf life of >90 days and uniformity were achieved. Other studies have also shown that, with the assistance of the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory between particles, long-term stable printable inks with good dispersion of ceramic powders can be obtained by adjusting the ink's zeta potential.
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The inks used in DOD inkjet printers should have good printability and Fromm and his colleagues
160
proposed a quantitative characterization of the physical properties of inks based on this printability, introducing a dimensionless reciprocal ratio Z that is independent of jetting speed, i.e., the Ohnesorge number Oh, given by equation (2), where Re and We are the Reynolds and Weber numbers, respectively. These numbers are expressed as Re = 
Schematic diagram of the working principle of IJP technology: (a) Continuous Inkjet Printing, (b) Drop-on-Demand Inkjet Printing.145
Direct ink writing (DIW), 185 also known as robocasting (RC), is a 3D printing technology that involves the extrusion of high-viscosity inks or pastes containing fine solid particles onto a substrate without heating. The process, illustrated in Figure 11, 186 is used to fabricate 3D objects layer by layer. Initially developed for processing concentrated materials such as low organic content ceramic pastes, DIW is an extrusion-based 3D printing technique that operates at room temperature. The nozzle used in DIW has a larger opening compared to traditional inkjet printing devices due to the high viscosity of the materials. By moving the nozzle, the designed shapes are constructed layer by layer until the part is completed. 187 Subsequently, debinding and sintering processes are conducted to remove organic components. However, the different rheological properties of the ink significantly influence the quality of the final printed part. del-Mazo-Barbara et al. 188 specifically described the rheological properties required for Direct Ink Writing (DIW) technology. They pointed out in their paper that the ink must be able to pass through a narrow nozzle and be extruded smoothly without clogging, printable a continuous filament. Simultaneously, the extruded filament must be able to retain the shape imposed by the nozzle, accurately reproduce the printed path, and support layer stacking to prevent the collapse of the printed structure. Figure 12 respectively shows the shapes printed with different rheological properties. 188 From the figure, it can be seen that the ink with good shape conformity and support capability yields the highest printing quality, whereas parts printed with ink having unsuitable rheological properties lack precision. In summary, if the viscosity is too low, the ink will spread under its own weight, leading to line widening, blurred features, and decreased dimensional accuracy. Conversely, if the viscosity is too high, it may result in uneven extrusion, poor interlayer adhesion, or even nozzle clogging. Therefore, to meet the requirements for the printed parts, the DIW ink must exhibit fluid-like behavior during extrusion and elastic behavior at rest. They indicated that this can be achieved by preparing a high-concentration paste. A high-concentration printing paste is a highly concentrated slurry of ceramic particles (typically 40–50 vol.% or 60–80 wt%) in a low-viscosity liquid (usually water) with a small amount of organic additives (<2 vol.% 189 or ≤1 wt% 190 ). In comparison to photopolymerization-based 3D printing technologies, DIW utilizes high-viscosity materials and does not require support structures during the fabrication process, resulting in a more cost-effective and faster manufacturing process with larger print envelopes. 191 The advantages of DIW include low cost, high printing speed, large print envelopes, and a simplified printing system. However, the rheological properties of ceramic inks are crucial as they need to possess sufficient yield stress and storage modulus, with precise control over viscosity and elastic properties to maintain shape, particularly for structures with overhanging features.192–194 The printing resolution is significantly influenced by the nozzle diameter, which can range from tens to hundreds of micrometers, leading to stair-stepping effects, reduced resolution of printed parts, poor surface finish, and high geometric and mechanical anisotropy. 195 Utilizing semiliquid pastes with high solid loading and viscoelasticity enables DIW to retain the shape of the printed structure, allowing for the fabrication of independent structures with high aspect ratios or spanning components without the need for support materials, such as powder beds, liquid baths, or print supports. 191 DIW technology can be used to fabricate various types of structures, including solid monolithic components, 194 complex porous scaffolds, 196 and composite materials. 197 In the field of piezoelectric devices, this technology has demonstrated potential for manufacturing small electronic components and lattice structures, such as transducers,198,199 bandgap structures200–202 (e.g., photonic crystals), catalyst supports195,203 (for energy devices), filters,204,205 and tissue engineering applications. 206 DIW is gaining popularity in ceramic printing, especially when printing resolution and surface roughness are not the primary concerns, as long as the prepared inks exhibit specific rheological properties. Various forms of structures have been fabricated using DIW, such as solid monolithic components, pylon-based piezoelectric transducers, 207 magnetic separation devices, 208 photonic crystals,200,201 electrodes, 209 porous scaffolds, 196 composite structures, bioengineering structures, 210 as well as high-temperature and corrosion-resistant components. Subsequently, Liu et al. 203 investigated the method of preparing LiFePO4 electrodes using low-temperature DIW and found that the performance of the printed electrode was improved due to the highly porous structure generated during low-temperature printing. Similarly, the manufacturing of bioceramic implants is one of the most widely applied areas of DIW technology.190,211,212 By preparing implants with a porous lattice structure, the growth of transplanted human tissue can be promoted. Furthermore, with advancements in medical imaging techniques, it is now possible to replicate the true microstructural model of the part to be repaired in an accurate 3D digital format. This aids in producing artificial parts with precise geometric shapes very similar to the original missing parts. Due to their outstanding biocompatibility and bone-like porous structure, both calcium phosphate glass and hydroxyapatite (HA) have been widely used in the manufacturing research of artificial bone scaffolds.213–215 Simon et al. 216 achieved good results in bone growth by using DIW to prepare HA scaffolds with a three-dimensional periodic pore structure, which can mimic the natural microstructure of human bones in reality and demonstrate the capability to construct multiscale pores, showing significant potential for bone repair and replacement. Additionally, Cesarano et al., 170 using CT-assisted modeling, successfully produced custom mandibular implants with a lattice structure. They used HA slurry for DIW and obtained good mechanical performance by controlling sintering to form submicron-sized pores. Implant surgery and subsequent testing results showed a good match with the patient's defect area. This custom implant can replace the cumbersome autologous transplantation process, avoiding bone harvesting surgery and effectively reducing the cost, time, and complexity of the surgery. This study demonstrates that bone-printed implants utilizing CT-assisted design have different porosities and good conformity with the patient's defect area. The application of DIW technology in the manufacturing of metal-based and ceramic-based composite materials, 217 structural engineering ceramics, etc., can achieve filament formation and maintain the initial shape by adjusting factors such as paste viscosity, yield strength, and drying kinetics. 218 Composite materials can be formed using methods such as robotic casting, molten glass, alloy, or slurry infiltration into wood piles. DIW technology can be used to produce ceramic components of different shapes and compositions, and sufficient mechanical performance and high sintering density can be obtained through processes such as pressureless spark plasma sintering. 219 Furthermore, other variants such as cryogenic extrusion manufacturing 220 have been developed to successfully manufacture functional CaCO3 components and multiple ceramic components with gradient compositions. 221 These studies provide a new manufacturing method for preparing parts with complex structures and excellent performance. The application of PCP in DIW technology and its advantages in the preparation of composite materials and ceramic components allow for changes in the phase, composition, and properties of the final product by adjusting the type and content of fillers or dopants in the PCP. 222 Some studies have utilized PCP containing organic silicon resins and oxide powders or precursors to manufacture ceramic components with sufficient performance, such as single-phase 223 or multiphase ceramic components 197 for tissue engineering applications. Additionally, the formability of PCP allows for the fabrication of complex-shaped ceramic-based composite material structures, 224 such as inks containing chopped microfibers. In the manufacturing of bioceramic scaffolds, the decomposition of fillers after firing can produce secondary pores, which is useful for cell culture. In conclusion, while DIW technology is ideal for producing customized porous ceramic structures with periodic features, it has certain limitations in processing dense engineering ceramics. In conclusion, it can be stated that DIW additive manufacturing technology employs a wide variety of materials. 225 This technology is suitable for applications requiring specific functional materials, and it is characterized as simple, highly adaptable, and low-cost. However, its accuracy is relatively lower compared to other additive manufacturing technologies, resulting in inferior surface quality. 226
Working principle diagram of DIW. 186
Illustrative image of the concept of shape fidelity. The same pattern was printed with three ceramic inks having different rheological properties. (a) Ceramic ink with good conformability and self-supporting ability. (b) Unsatisfactory ceramic ink with insufficient shape retention and self-supporting ability. (c) Ink with inappropriate rheological properties, lacking conformability, and self-supporting ability. 188
Powder-based 3D printing technology
Powder-based 3D printing technology refers to the process conducted on a powder bed rich in ceramic particles, where the ceramic particles are bound together using a binder or the thermal energy provided by a laser beam. This includes 3DP, selective laser sintering (SLS), and selective laser melting (SLM). The former technique uses a print head to selectively jet liquid binder onto the powder, while the latter two techniques use the energy of a laser beam to selectively sinter/melt the ceramic powder. It is important to note the distinction between the terms “3DP” and “3D printing.” Due to historical reasons, the abbreviation “3DP” has been retained for the specific 3DP technology, while “3D printing” is now a general and popular term representing the assembly of additive manufacturing technology.
Three-dimensional printing is a technology that takes place on a powder bed. In the 3D printing process, an organic binder solution is jetted onto the surface area of the powder bed in the form of droplets through the printer's nozzle, and the solid layer is formed as the permeable liquid binder is surrounded by the powder and then bonded. After forming, another layer of powder is coated, and this process is repeated until the part is shaped. 3DP technology, as shown in Figure 13, 227 involves the removal of loose powder to reveal the part. Although 3D printing can be considered as an indirect ceramic inkjet printing process, its unique feature is the use of a powder bed, which is why 3D printing is classified as a powder-based technology in this article. The powder can be deposited in a dry or wet state in a liquid carrier, which helps achieve a higher green density.228,229 In the liquid carrier, the binder solution is jetted onto the selected area of the powder bed through the print head. Then, to allow the successful jetting of the binder and its proper solidification, the liquid content must evaporate before applying the bonding material. Therefore, during the printing process, certain characteristics are required, such as appropriate rheological properties, to ensure that the binder solution can be effectively jetted and solidified through the print head. After manufacturing, a sintering process is usually required to remove the organic binding agent and achieve the desired mechanical properties. Sintering involves heating ceramic materials to high temperatures to form bonds between particles, achieve material densification, and enhance strength. During this process, the organic binding agent is burned off, resulting in a solid structure. However, it should be noted that the sintering process may cause part shrinkage, depending on the percentage of binder present and the nature of the material. The mentioned raw materials include granular ceramics, 230 metals, 231 plastics, 232 and their combinations. 233 In the 1990s, 3D printing technology began to be applied to ceramic manufacturing, utilizing alumina and silicon carbide particles as the powder material and colloidal silica as the binder. 230 When exploring the biomedical field, including the manufacturing of tissue engineering components, these components typically have lower requirements for resolution and surface finish accuracy, as well as porous characteristics for culturing purposes. Commonly used biocompatible ceramics in 3D-printed bone replacement scaffolds include hydroxyapatite (HA), 234 calcium phosphate 235 (CP), and tricalcium phosphate 236 (TCP). To achieve high porosity and biocompatibility in 3D-printed ceramic components, preceramic polymers can be used as binders. In subsequent studies, silicone resin was used as a binder and reacted with fillers to form the desired ceramic phase, ultimately resulting in ceramic components with approximately 64% porosity. 237 In vitro experiments showed that this ceramic had no cytotoxic effects on cells. Another study on the performance of binders found that the molecular weight of organic binders affects their penetration behavior on ceramic powder beds. Moon et al. 238 suggested that the molecular weight of binders should be less than 15,000 to promote penetration. Furthermore, the rheological properties of binders, such as surface tension and viscosity, need to be optimized to achieve smooth jetting and high dimensional accuracy. Lauder et al.'s research 239 concluded that by optimizing process parameters such as layer thickness, line spacing, droplet spacing, and position, the microstructure and surface finish of 3D-printed parts can be improved. Additionally, using finer powders can result in smoother and thinner layers, but this can also increase the difficulty of powder diffusion on the work surface. 240 It was also found that reducing layer thickness can effectively reduce porosity, thereby improving the mechanical properties of printed parts. 241 The resolution of printed parts is also affected by the size and shape of the powder material, as well as the characteristics of the binder droplets. The interaction between the binder and the powder, as well as the diffusion rates of the powder and binder, are also important factors determining resolution. 242 High-performance ceramics are typically fully dense, making porosity undesirable in these materials. 243 However, difficulties are often encountered when 3D printing dense ceramics, necessitating additional measures in postprocessing, such as adding sintering aids, infiltrating porous parts, and isostatic pressing before sintering. Some studies have shown that using ZnO and SiO2 as sintering aids can reduce porosity from 9.2 to 6.9%, 244 and liquid silicon infiltration and reaction with TiC at high temperature can also produce high-strength Ti3SiC2-based ceramics. 245 Cold isostatic pressing can achieve extremely high density of 99% when preparing complex geometries of Ti3SiC2 structures. 246 Therefore, by adopting different postprocessing methods, it is possible to achieve 3D-printed high-performance ceramics and improve their mechanical properties. Despite advantages such as highly flexible geometric design and the absence of support structures, 3D printing technology is most suitable for manufacturing porous ceramic parts. However, it also has some drawbacks. These disadvantages mainly manifest in the following areas: Resolution: Compared to other ceramic processing methods, the resolution of 3D printing technology is relatively low. The use of larger powder particles results in higher surface roughness of the manufactured parts, making it difficult to achieve very fine details and complex geometric shapes. Surface finish: Parts manufactured using 3D printing technology typically have lower surface finish. This is because during the printing process, the binder mixes with the powder and solidifies, leaving behind some traces and textures. Therefore, if a highly smooth surface is required, additional surface treatment steps may be necessary. Mechanical performance: The mechanical performance of parts manufactured using 3D printing technology is usually lower compared to other advanced ceramic material processing methods. Due to the structural and material properties during the curing process, the printed parts may have some weaknesses or defects, affecting their strength and durability. Therefore, although 3D printing technology holds potential in some application areas, its application in advanced ceramic material processing is subject to certain limitations. 247 To overcome these limitations, continuous improvements in materials, printing parameters, and postprocessing techniques are needed to enhance resolution, surface finish, and mechanical performance, thus expanding the application range of 3D printing technology in the field of advanced ceramics.
3DP technology schematic diagram. 227
Selective laser sintering (SLS) and selective laser melting (SLM) both utilize high-energy lasers as a heat source. Figure 14 131 illustrates the working principle of SLS, and Figure 15 227 depicts the SLM process and printing direction. The printing process of SLS involves selectively irradiating the surface of the target powder bed with a high-power laser beam. The powder is then heated to sinter, forming large connected blocks. After each sintering cycle, a new layer of powder is spread on the sintered surface for the next laser irradiation, repeating these steps to print the designed part. In the SLS process, because the parts are continuously surrounded by loose powder on the bed, there is no need for additional support structures for overhanging areas. SLS has been widely researched for processing various powder materials, starting from low-melting/softening point plastics and polymer powders248–251 such as acrylonitrile butadiene styrene (ABS), polyvinyl chloride (PVC), polyether ether ketone (PEEK), polycarbonate (PC), and polyamide (PA), as well as composite materials. It has later expanded to higher-melting point metals (such as aluminum, iron, and copper) and composite powders.252–254 It should be noted that in the SLS process, ceramic powders require a low-melting binder to connect the ceramic particles. Under laser irradiation, the binder melts, causing the ceramic particles to bond together.255,256 SLM and SLS have similarities in principle but also have some differences. SLM uses a high-energy density laser source in a powder bed to directly melt metal powder into a liquid state, achieving rapid densification in the manufacturing process. Unlike SLS, SLM does not require the use of secondary low-melting-point binding agent powders. This allows SLM to produce nearly fully dense, uniform parts without the need for postprocessing. Compared to SLS, which heats the powder to partially melt at particle junctions and fuse at specific points, SLM completely melts the powder into a liquid phase, ensuring rapid densification. Initially used for solid metal parts manufacturing, such as aluminum, copper, and stainless steel, SLM has advanced to include advanced alloys, particularly for lightweight components in the aerospace industry. 257 Parts manufactured by SLM exhibit higher functionality, superior end-use properties, lower porosity, and better-controlled crystal structures. Therefore, SLM is widely used across various sectors including aerospace, automotive, and medical device manufacturing. Using submicron powders and a wavelength of approximately 1 mm solid-state laser, an improved method known as Laser Micro Sintering (LMS) has significantly enhanced the resolution and surface roughness of ceramics prepared through SLM.258,259 The successful production of fully dense components from several types of ceramic materials (such as Al2O3 and SiC-based ceramics) has been demonstrated, with resolutions as low as tens of micrometers and surface roughness in the order of micrometers, both of which are orders of magnitude higher than those manufactured using traditional SLM technology, producing parts with very fine resolution and intricate features. However, it is feasible to use LMS to manufacture very small volume parts. After the completion of the SLS process, printed parts undergo de-powdering and high-temperature treatment to remove the binding agent. SLS requires optimization of many key processing parameters such as laser power, scanning speed, scanning patterns, particle size and packing density, layer uniformity and thickness, bed and build area temperatures, atmosphere, etc.260,261 SLS faces challenges rough surface quality and high porous structure, requiring further surface treatment and densification. Although the SLS method for printing ceramic components presents certain limitations, such as low resolution, poor surface finish, and high porosity, this process is well-known for the indirect fabrication of ceramic parts 34 and has been adopted across various fields. 42 Among these applications, SLS is prevalent in the tomographic-assisted manufacturing of scaffolds for biomedical purposes.262,263 Numerous bone implants have been fabricated via the SLS process using materials such as hydroxyapatite combined with ceramic–polymer/glass mixtures, 264 polycarbonate, 263 and silica mixed with polyamide. 265 For example, someone 48 has fabricated porous ceramic components with 3D pore structures via SLS. They produced porous silicate ceramic parts with straight-pore honeycomb and gyroid honeycomb lattice structures. While significant progress has been made in ceramics using SLM, the application of ceramic parts produced by SLM is still very limited. This is mainly due to the production of porous microstructures, low surface roughness, and low dimensional accuracy, making it difficult to densify into pore-free, isotropic ceramic bodies. Therefore, further improvements in material properties, manufacturing processes, and postprocessing are necessary to achieve the true defect-free, high-precision, fully dense ceramic parts manufacturing.
Typical workflow of SLS.131
SLM technology and printing direction. 227
Based on block solid 3D printing technology
The 3D printing technology based on bulk solid materials refers to the process of using solid blocks or filaments as raw materials, processing them through laser cutting or melting, slicing according to digital models, layer-by-layer forming, and ultimately obtaining 3D-printed parts.
Laminated object manufacturing (LOM) is a process that involves placing ceramic materials on a worktable and using a computer-controlled laser cutter to cut them into ceramic sheets according to a designed pattern. These formed ceramic sheets are then stacked together using adhesives or heat pressure, layer by layer, to ultimately produce the desired parts. 266 The LOM process flow is shown in Figure 16 163 LOM can process a variety of raw materials without using toxic chemicals or complex chemical reactions. 267 Many demonstrations of LOM have been reported, including SiC, 268 Si/SiC composite materials, 269 ZrO2 and ZrO2/Al2O3 composite materials, 270 TiC/Ni composite materials, 271 LiO2-ZrO2-SiO2-Al2O3 (LZSA) glass-ceramic composite materials, 272 and functional ceramics such as PZT 273 for functional actuators and HA 274 for bone implants. Attention has also been focused on the LOM manufacturing of new lightweight ceramic components based on filled ceramic powders, such as Al2O3 and SiC.275,276 It is worth noting that later research reported the manufacture of Si3N4 components using LOM, 277 with an average volume shrinkage rate of 40% and a final average density after sintering relative to the theoretical density of 97%. The microstructure and mechanical properties of the final parts, such as Young's modulus, flexural strength, and fracture toughness, are comparable to those prepared by traditional methods such as reaction bonding, slip casting, and pressureless sintering.278,279 However, LOM is limited to laminated sheet materials, and due to the weak interface bonding between sheets, issues such as poor surface quality, delamination, anisotropy along the build direction and plane direction may exist. 280 In terms of complexity, LOM is only suitable for manufacturing structures with simple geometric shapes and relatively large sizes. Additionally, removing unprocessed materials is both time-consuming and costly, resulting in a significant amount of material waste.
LOM process flow chart. 163
Fused deposition modeling (FDM) works by moving a nozzle and extruding molten thermoplastic composite material in the form of a long filament. The material extruded from the nozzle has a higher melting point than the polymer material, causing it to melt. This melted material is then layered and heated onto a build platform, where it cools and solidifies to create a 3D object, with the material immediately solidifying on the previously printed layers. 281 The process flow diagram for FDM is shown in Figure 17. 282 FDM offers a simple construction process, flexible unit sizing, ease of use, do-it-yourself capability, and low costs for both machines and raw materials. 283 The most commonly used materials for FDM 3D printing are in the form of long filaments of thermoplastic polymers, 284 including ABS, PC, PA, and polylactic acid (PLA), while alumina, 285 mullite, 286 and silicon nitride 287 are also used as FDM manufacturing materials. The application of ceramic FDM has shifted to the manufacturing of bio-ceramic scaffolds288–292 and photonic crystal bandgap structures.293,294 However, there are many factors affecting the ceramic materials used in FDM processes,295–297 including ceramic particle size, distribution and dispersion within the filament, the ratio and viscosity of ceramics/binders/additives, and the flexibility of the filament. The viscosity of the melt should generally be between 10–100 Pa·s, and ceramic particles should be dispersed in the melt to achieve constant and stable flow. FDM also has several drawbacks, with the main one being the staircase effect, which is easily observed when printing ceramic parts due to the limited control in the z-direction determined by the size of the extruded filament.
FDM process flow chart. 282
In future research, further exploratory studies can be conducted based on existing ceramic additive manufacturing technologies. For example, recent reports have covered multimaterial ceramic additive manufacturing, 298 large-scale ceramic additive manufacturing, 299 and machine learning methods for enhancing the additive manufacturing process. 300 Regarding multimaterial ceramic additive manufacturing, as applications become increasingly complex and the demand for material combinations grows, this has led to the development of functionally graded materials, which achieve multifunctionality through compositional gradients. Multimaterial ceramic additive manufacturing technology enables the direct creation of highly complex geometries. This geometric functionalization can be combined with the excellent properties of ceramic materials, significantly reducing the need for postprocessing. The additive manufacturing of multimaterial components can further enhance functionality. Moreover, this method has been successfully used to produce heatable ceramic tools, reactors, and mixers with integrated temperature control, which can improve the efficiency of various processes. Some researchers have also developed multi-degree-of-freedom manufacturing platforms for multimaterial additive manufacturing. Through this innovation, products with multiple material types and desired complex geometries can be manufactured on demand. Additionally, they synthesized a multimaterial (polymer/ceramic/metal) printed magnetoelectric pressure sensor. Leveraging this multimaterial filament transfer and laser manufacturing strategy, their additive manufacturing robotic arm demonstrates broad application prospects in the advanced manufacturing of embedded electronics, sensors, soft robotics, and customizable medical devices. 301 For large-scale ceramic additive manufacturing, challenges such as platform size limitations and structural collapse persist. 302 Thus, some studies have suggested segmenting a large component into multiple parts for printing individually. Subsequently, research has proposed reassembling multiple green bodies via bridge joints, 303 enabling control over ceramic parts and shapes before sintering. Consequently, further research has been conducted on fabricating large-scale parts using SLA technology. By combining uniquely shaped joint connections with silica sol infiltration technology, they successfully produced large-sized alumina ceramic components. They noted that the performance of internal interlocking joints surpasses that of external joints, and after silica sol infiltration, not only can liquid phase formation be promoted during sintering, but a mullite phase can also be generated, leading to densification at the joint–part interfaces. This provides a promising solution for applying SLA technology in the manufacturing of large-scale ceramic components. Regarding machine learning methods for enhancing the additive manufacturing process, researchers have pointed out 304 that although vat photopolymerization ceramic additive manufacturing offers high flexibility, efficiency, and precision, the influence of random defects during the recoating process poses challenges to the yield rate of finished products. Currently, the industry mainly relies on manual visual inspection for defect detection, which is an inefficient method. To address this limitation, a deep learning-based framework for defect detection in ceramic vat photopolymerization has been proposed. This framework innovatively adopts a dual-branch object detection approach: one branch utilizes a fully convolutional network to extract features from fused images, while the other branch employs a differential siamese network to extract difference information from consecutive two-layer images. Through this dual-branch design, decoupling of image feature layers and extraction of image spatial attention weights are achieved, thereby mitigating the impact of minority outliers on training results and playing a key role in stabilizing the training process, making it suitable for training on small-scale datasets. Comparative experiments have been conducted, and the results indicate that the method meets the requirements for real-time detection. By monitoring the recoating process in real time, it can effectively enhance the manufacturing smoothness of industrial equipment and help improve the yield of ceramic additive manufacturing products.
In conclusion, while numerous challenges remain in the development of ceramic additive manufacturing, further research on this technology fundamentally relies on a deep theoretical understanding of its underlying principles.
Conclusion
In recent decades, with the continuous exploration of 3D printing, ceramic 3D printing has become a new and promising field. Advanced ceramics have been widely applied in industrial and engineering domains. This review introduces the development of 3D printing, the application of ceramic materials, common forms of ceramic 3D printing, and a comparison between 3D printing technology and traditional ceramics. Specific 3D printing technologies are discussed, including slurry-based 3D printing, powder-based 3D printing, and solid-based 3D printing. The basic materials and raw material configurations in various fields such as aerospace, medical, and piezoelectric domains are also detailed, along with the advantages and disadvantages of this technology in each respective field. Overall, it is emphasized that 3D printing represents a process. While it is more convenient compared to traditional manufacturing, it involves multiple steps, and the correct execution of these steps is crucial for obtaining ceramic components. The final ceramic components must undergo binder removal and sintering processes to achieve their desired properties, which depend on the composition and microstructure. Challenges related to the production of large-sized components are highlighted. Despite the capabilities of additive manufacturing processes to produce large parts, the manufacture of large components without cracks or deformations remains challenging. Issues arise during the removal of binders and the sintering process for large ceramic components due to significant variations in cross-sectional thickness and differences in thermal properties and shrinkage rates. In the context of powder-based fusion methods, the successful manufacturing and structural control of components will rely on further understanding of the dynamic interactions between laser and ceramic particles, as well as the layer deposition mechanism and melting process. Residual stresses generated by thermal gradients within ceramic parts under rapid laser heating and cooling remain a major factor leading to defects such as cracks and distortions. Furthermore, limitations such as low surface finish quality, undesirable porosity, and significant shrinkage rates after processing restrict the application range of ceramic components. The formation of voids and gaps between layers and beads is detrimental to ceramic materials. Depending on the specific additive manufacturing processes, the quality of the printed parts varies. In extreme cases, this may result in delamination of parts during debinding or sintering steps. Ceramic objects produced using extrusion-based additive manufacturing technology are especially susceptible to these limitations. Nevertheless, these defects can be minimized through high solid loading in the raw materials, precise control of material viscosity and ambient temperature during construction, and nozzle design modifications in the extrusion process. In comparison, photopolymerization-based methods for ceramic manufacturing show greater promise, as they can achieve controlled feature resolution and surface finish with ideal mechanical properties for manufactured parts.
However, several challenges remain to be addressed in future development. First, precise coordination and control of the entire manufacturing chain from material formulation to sintering must be achieved. Although ceramic additive manufacturing enables the fabrication of complex geometries, this capability alone is far from sufficient to meet practical application requirements. The focus must shift toward predictable performance and reliability. A key scientific obstacle herein is the lack of a comprehensive, quantitative understanding of the interdependencies among slurry/powder characteristics, printing parameters, and sintering kinetics. We recommend that future work prioritize the development of multiphysics and multiscale models capable of accurately predicting stresses during printing, binder burnout kinetics, and most importantly, the evolution of microstructure and final properties during sintering. Integrating in-situ monitoring with machine learning could create a closed-loop feedback system for real-time process adjustment. Furthermore, a trade-off exists among printing resolution, surface quality, and printing speed in current ceramic additive manufacturing technologies. The ‘stair-stepping’ effect and the difficulty in reproducing fine features limit applications in high-precision fields such as microelectronics and micro-medicine. Meanwhile, the slow printing speeds of high-resolution processes remain a major bottleneck for large-scale part production. We believe the next breakthrough will stem from innovations in both hardware and materials science. This includes developing new printhead designs, advanced support material systems, and novel rapid curing or fusion mechanisms that can simultaneously enhance both vertical resolution and printing speed.
In summary, although the path forward is challenging, overcoming these barriers will unlock the full potential of ceramic additive manufacturing, paving the way for its widespread adoption in the most demanding applications across aerospace, energy, healthcare, and electronics.
Footnotes
Funding
The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article. This work was sponsored by the Natural Science Foundation of Xinjiang Uygur Autonomous Region (2023D01C192), the Xinjiang Tianchi Talent Introduction Plan (51052300585), and the Fundamental Research Funds for Autonomous Region Universities (XJEDU2022P002).
Declaration of conflicting interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.