Additive manufacturing of low-shrinkage alumina cores for single-crystal nickel-based superalloy turbine blade casting

We prepare bimodal particle size photo-curable ceramic pastes with high solid loadings (up to 65 vol %) and fabricate porous alumina ceramic cores with complex shapes via ceramic stereolithography (Cer-SLA) 3D printing technique. The sintering temperature is carefully selected, ranging from 1500 °C to 1650 °C, and a high holding time (>4 h) is applied to guarantee that the materials can withstand the subsequent high temperature (>1500 °C) casting process for single-crystal nickel-based superalloy hollow turbine blades. Herein, the originally spherical fine particles are found to become platelet-like after sintering, and the forming mechanism is discussed in detail. In addition, we explore the influence of platelet-like particles, coarse particles and sintering process on the microstructural evolution of alumina particles, and reveal the relationship between microstructure and properties of ceramic cores. These results illustrate that the proposed materials for SLA 3D printing exhibit a great potential in the fabrication of complex-shaped alumina ceramic cores for high-precision investment casting, e.g., manufacturing single-crystal nickel-based superalloy hollow turbine blades for an advanced aircraft engine.     

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

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

Anisotropy management on microstructure and mechanical property in 3D printing of silica-based ceramic cores

Ceramic core is an essential component in the precise casting of hollow turbine blades, and the investigation on 3D printing of silica-based ceramic cores is crucial to the development of aviation industry; however, they are suffered from difficulty in high-temperature strength and structural anisotropy. In present work, silica-based ceramic cores were prepared via DLP stereolithography 3D printing, and the anisotropy management on microstructures and properties were explored based on the particle size of fused silica powders. In 3D printed ceramic cores with coarse powders, significant anisotropy was displayed exhibiting multilayer structure with large gaps in horizontal printing and uniform porous microstructure in the vertical direction, which was further explained by the particle deposition in printing. With finer silica powders, the uniformity in the microstructures was highly improved, attributed to the enhanced particle dispersion in ceramic slurries and promoted interlayer particle rearrangement during sintering. To evaluate the anisotropy in mechanical property, the ratio of vertical strength to horizontal strength (σ_V/σ_H) was proposed, which rose from 0.48 to 0.86 as the particle size decreased from 35 µm to 5 µm, suggesting enhanced mechanical uniformity. While the average particle size of silica powders was 5 µm, the flexure strengths of ceramic cores in different directions were up to 18.5 MPa and 16.3 MPa at 1540 °C with σ_V/σ_H ratio of 0.88, which well satisfied the demands for the casting of turbine blades. This work inspires new guidance on the anisotropy management in ceramic cores prepared by 3D printing, and provides new technology for fabrication of silica-based ceramic cores with superior high temperature mechanical properties.     

Reinforcement of silica-based ceramic cores based on amorphous and polycrystalline mullite fibers

In the investment casting of turbine blades, ceramic cores are key components to form complex hollow structures. Superior mechanical property and leaching rate are demanded for ceramic cores. Herein, ceramic cores were fabricated using fused silica powders as the matrix, and amorphous and polycrystalline mullite fibers as the reinforcement phases, respectively. The microstructure and property evolution of ceramic cores rely on the crystallization degree of mullite fibers are explored. Both of the mullite fibers lead to improved crystallization of cristobalite, reduced sintering shrinkage, increased apparent porosity, and benefited bending strength, creep resistance, and leaching rate of the cores. Compared to the polycrystalline mullite fibers, the amorphous fibers are metastable with large quantities of structural defects, promoting the diffusion mass transfer and forming strong interface between fibers and matrix. Therefore, the amorphous fibers have larger promotion on the bending strength and resistance to creep deformation of ceramic cores. Moreover, the structural defects of amorphous fibers ensures the high chemical activity in alkaline solutions and exhibits excellent leaching rate. The ceramic core with 4.5 wt% of amorphous mullite fibers exhibits excellent comprehensive performance with bending strengths of 28.9 MPa and 23.8 MPa at room temperature and 1550 °C, creep deformation of 0.3 mm, and leaching rate of 1.4 g/min, well meeting the casting requirements of hollow blades.     

Additive manufacturing of Al2O3 ceramic core with applicable microstructure and mechanical properties via digital light processing of high solid loading slurry

Ceramic cores are essential intermediate mediums in casting superalloy hollow turbine blades. The developing of additive manufacturing (AM) technology provides a new approach for the preparation of ceramic cores with complex structure. In this study, alumina oxide (Al₂O₃) ceramic cores with fine complex geometric shapes were fabricated by digital light processing (DLP) in high resolution. The maximum solid content of 70 vol% of ceramic slurry was adopted in the printing process, which is important for the regulation of deformations and mechanical properties. The effects of the printing parameters, including exposure intensity, printing layer thickness and sintering temperature on the microstructures and mechanical properties of printed samples were investigated. The decrease of residual stress and similar shrinkage in X, Y, and Z directions could be obtained by adjusting the printing parameters, which are crucial to prepare complex ceramic cores with high quality. Besides, the flexure strength and open porosity of ceramic cores reached 34.84 MPa and 26.94%, respectively, which were supposed to meet the requirement of ceramic cores for the fabrication of superalloy blades.     

Controlled anisotropy in 3D printing of silica-based ceramic cores through oxidization reaction of aluminum powders

Ceramic cores are key components to form inner hollow structures in aero-engine blades, and 3D printing is an ideal molding technology for ceramic cores. In this work, silica-based ceramic cores are fabricate via 3D printing of digital light processing (DLP) stereolithography, and the anisotropy in microstructure and property are controlled by aluminum powders. The ceramic cores without aluminum powders exhibit anisotropic microstructure with interlayer gaps, which get narrower and disappear with doping of 7.5–10 wt% of aluminum powders, due to the volume expansion during oxidization reaction of aluminum powders filling the interlayer gaps. The anisotropy in mechanical property is rely on the printing direction, and the ratio of strength in different directions (σ_V/σ_H) is put forward to value the mechanical anisotropy; the ratios rise from 0.40 to 0.92 at room temperature and 0.51 to 0.97 at 1540 °C, as 7.5 wt% of aluminum is doped, and the optimized ceramic cores show high-temperature strengths of 16.6 MPa and 16.1 MPa in different printing directions. Even though ceramic cores with 10 wt% of aluminum show uniform microstructure and higher σ_V/σ_H ratio, the weak particle bonding within printing layers limits their mechanical property, and the strengths decrease to 13.8 MPa and 13.4 MPa at 1540 °C. This work inspires a new technique to excellent high-temperature mechanical properties with anisotropy control in 3D printing of ceramic cores.     

Silica strengthened alumina ceramic cores prepared by 3D printing

Ceramic cores based on alumina and silica are important in the manufacturing of hollow blades. However, obtaining good properties and precision is still challenging. In this research, alumina-based ceramics cores were obtained by 3D printing technology, and the effects of silica contents on the mechanical properties of the as-obtained alumina ceramic cores were evaluated. The results showed significant improvements in flexural strengths of the ceramics from 13.3 MPa to 46.3 MPa at silica contents from 0 wt% to 30 wt% due to formation of mullite phase (Al₆Si₂O₁₃). By contrast, the flexural strengths declined as silica content further increased due to the generation of massive liquid phase. Also, porous structures and cracks were observed by scanning electron microscopy due to the removal of cured photosensitive resin and the mullitization reaction between alumina and silica, respectively. The manufacturing process of hollow blades required ceramic cores with flexural strengths greater than 20 MPa to resist the strike of metal liquid, as well as open porosity above 20 % to provide space for alkali liquor to dissolve the ceramic cores. As a result, 10 wt% silica was determined as the optimal value to yield ceramics with improved properties in terms of flexural strength (35.6 MPa) and open porosity (47.5 %), thereby satisfy the application requirement for the fabrication of ceramic cores.     

Improved mechanical properties of SiB6 reinforced silica-based ceramic cores fabricated by 3D stereolithography printing

Silica-based ceramic core is an extremely critical component in the manufacture of hollow blades during investment casting. However, the traditional preparation methods rely more on the molds, and the manufacturing costs are relatively high. In this study, silica-based ceramics with silicon hexaboride (SiB₆) addition were prepared via 3D stereolithography printing. And the effects of the SiB₆ content on mechanical properties of the obtained ceramic samples were explored. As the SiB₆ content increased to 2.0 wt%, the linear shrinkage gradually decreased, while the room temperature and high temperature flexural strength were enhanced at the SiB₆ content from 0 to 1.0 wt% and reduced as the SiB₆ content further rose. As the SiB₆ content increased to 1.0 wt%, the linear shrinkage was reduced to 1.86% resulting from the oxidation reaction of SiB₆. Furthermore, with 1.0 wt% SiB₆ addition, the flexural strength of the samples at room temperature was enhanced from 6.75 MPa to 14.63 MPa due to the sintering promotion of oxidation product B₂O₃, and the flexural strength at 1550 °C was improved from 7.68 MPa to 13.08 MPa because of the enhanced β-cristobalite content, which is suitable for high temperature casting of ceramic cores. Therefore, it demonstrates the capability of fabricating SiB₆ reinforced silica-based ceramic cores with high performance via stereolithography.     

Effects of ZrSiO4 content on properties of SiO2-based ceramics prepared by digital light processing

SiO₂-based ceramic cores are widely used in the preparation of gas turbine engine hollow blades due to their excellent chemical stability and easy removal after casting. In this paper, ZrSiO₄ reinforced SiO₂-based ceramics were fabricated using digital light processing (DLP) technology. The results showed that the addition of ZrSiO₄ reduced the cure depth due to its high UV light absorptivity and refractive index. When the content of ZrSiO₄ increased to 15 wt%, the cristobalite content reached the maximum, and radial shrinkage reached the minimum of 1.4%. ZrSiO₄ grains could hinder the propagation of cracks, enhancing the room-temperature flexural strength. At 1550 °C, fracturing across SiO₂ grains in SiO₂-based ceramics led to the great improvement of high-temperature flexural strength. When the content of ZrSiO₄ reached 15 wt%, the flexural strength at room temperature and high temperature was 11.5 MPa and 36.7 MPa, respectively. Therefore, the SiO₂-based ceramics prepared using DLP technology have good room temperature and high temperature properties, and are expected to be used for hollow blade casting.     

Influence of debinding holding time on mechanical properties of 3D-printed alumina ceramic cores

Herein, alumina green bodies are fabricated by three dimensional (3D) printing technology, then, the influence of debinding holding time under vacuum and argon on mechanical properties is systematically investigated by comparing the changes in microstructure, bulk density, open porosity, grain connection situation and flexural strength of ceramics. The flexural strength of alumina ceramics acquired the maximum values of 26.4 ± 0.7 MPa and 25.1 ± 0.5 MPa after debinding under vacuum and argon for 120 min and 180 min, respectively. However, the alumina ceramics rendered the flexural strength of 19.4 ± 0.6 MPa and 9.5 ± 0.4 MPa under vacuum and argon without extended holding time, respectively. The relatively low mechanical properties can be mainly attributed to the weak interlayer binding force, which is caused by layer-by-layer forming mode during 3D printing process and anisotropic shrinkage during the sintering process. Moreover, the alumina ceramics exhibited moderate bulk density and open porosity of 2.4 g/cm³ and 42% after the sintering process, respectively, which are mainly influenced by the microstructural evolution of alumina ceramics during thermal treatment. Also, the diffusion of gases is achieved by curing of photosensitive resin and influenced by different holding times during debinding, affecting the mechanical properties of sintered ceramics. The mechanical properties of as-sintered ceramics are suitable for the utilization of ceramic cores in the manufacturing of hollow blades.     

Effect of synergism of solid loading and sintering temperature on microstructural evolution and mechanical properties of 60 vol% high solid loading ceramic core obtained through stereolithography 3D printing

Solid loading has a significant effect on the curing behavior of slurry and the microstructure and properties of the ceramic core. A high-solid loading slurry can effectively improve the sintering densification of ceramic particles and improve the interlayer bonding strength and mechanical properties at both 25 °C room and higher temperatures. Herein, based on the photopolymerization theory of ceramic slurry, the solid loading was increased from 45 to 60 vol% by adjusting the composition ratio of the resin ceramic powder. Additionally, the optimal sintering temperature of the 60 vol% solid loading ceramic core was 1200 °C. The synergistic effect of the solid loading and sintering temperature controls the sintering shrinkage of the sample within 3.2%; the porosity, high temperature, and room temperature flexural strength were approximately 30%, 24 MPa, and 10 MPa, respectively. The printing preparation of high-solid loading ceramic cores can be used to guide optimizing process parameters on an industrial scale.     

Influences of mullite fibers on mechanical and thermal properties of silica-based ceramic cores

Mullite fibers composite silica-based ceramic cores were successfully prepared by injection molding. The effects of mullite fibers on the mechanical and thermal properties of ceramic cores were investigated. The results indicated that the linear shrinkage was significantly decreased and the porosity was gradually increased with the increase of mullite fibers. In addition, the flexural strength for the room temperature and the simulated casting temperature of 1500°C was increased to a maximum value when the content of mullite fibers was about 1 wt.%, and then decreased with the increase of mullite fibers. The mullite fibers of 1 wt.% presented excellent mechanical properties with a linear shrinkage of .65%, a porosity of 6.96%, and a flexural strength of 17 MPa at room temperature and 34.83 MPa at the simulated casting temperature of 1500°C. Besides, the change in microstructure and properties in various contents of mullite fibers were analyzed.     

Properties of alumina coatings prepared on silica-based ceramic substrate by plasma spraying and sol-gel dipping methods

Silica-based ceramic cores are widely used in the manufacturing of hollow, nickel-based, superalloy turbine blades. However, elemental Hf, Ti, Al, and other active metals in the superalloy can react with silica-based ceramic cores during casting, resulting in a reduction in the quality of the turbine blades. In this study, both plasma spraying and sol-gel dipping methods were used to prepare alumina coatings on silica-based ceramic substrates to prevent the interfacial reaction. The performance of the alumina coatings prepared by both methods was evaluated by comparative analysis of the surface roughness, bonding interface morphologies, and the adhesive characteristics of the coating. The plasma-sprayed alumina coating has a roughness greater than 5 μm and peeled away from the substrate due to the difference in thermal expansion between SiO₂ and Al₂O₃ at temperatures above 1500 °C, rendering the silica-based substrate with the plasma-sprayed alumina coating unfit for the application requirements of the casting process. The alumina coating prepared by the sol-gel dipping method improved the roughness of the substrate from Ra 2.39 μm to Ra 1.83 μm, and no peeling was observed when heated to 1550 °C for 30 min due to the pinning characteristics of the coating on the substrate. Furthermore, the interfacial reaction between the DZ125 superalloy melt and the silica-based substrate coated with alumina by sol-gel dipping method were investigated. The alumina coating effectively inhibited the interfacial reaction and no reaction products were detected during the directional solidification with pouring temperature of 1550 °C and withdraw rate of 5 mm/min. While a uniform, 4–5 μm thick HfO₂ reaction layer formed between the uncoated substrate and the DZ125 alloy melt. Two dipping-drying cycles were required to ensure the alumina sol completely covered the surface of the substrate.     

Binder stabilization and rheology optimization for vat-photopolymerization 3D printing of silica-based ceramic mixtures

Enhancing inlet gas temperature in aero/gas turbines to reduce their carbon-footprint, has led to a strive for better performing inlet cooling mechanism of the turbine blades. The internal cooling of the blades is made by ceramic cores in their casting process, but conventional ceramic molding has long reached its maximum possible geometrical complexity, hence shedding light on 3D printing of these cores. The objective of this study is to develop low-viscous, fully stabilized, commercially viable ink for vat-photopolymerization of silica-based ceramics. This paper investigates the best dispersion type and amount for different formulated monomer mixtures, and explains the best correlation between viscosity, solid loading, binders, dispersants, peeling forces and mechanical properties, and offers an optimized mixture to avoid the common ceramic printing issue, namely crack propagation of cores during sintering. Among five dispersant agents, the SOL20, SOL24 and FA4611 exhibited better performance than other dispersion agents, and the optimum concentration level for each binder and dispersant agent was ensured through sedimentation test. Their dispersion capability and long-term stability were further investigated to designate the best dispersion agent for each binder system. Further verification was made by sedimentation study of the samples at 40 °C for 40 days and reducing the superficial area of the used powder mixture. According to the result of the rheology analysis, the best dispersions were achieved using SOL20 for the loaded binder mixtures of M1 and M4, SOL24 for M3and FA4611 for M2. The instability of M1 and M2 with their respective dispersant agent was coordinated through the thixotropic agent of TX/2, and complete stabilization and near-Newtonian behavior were achieved. However, the research showed that the addition of TX/2 to fully stabilized M4 and M2 suspensions negatively impacts the mixtures’ rheological behavior from near-Newtonian to shear-thickening. In the final stage of this study, peeling forces, sintering and three-point bending tests were conducted to determine the final formulated suspension to print ceramic core components. M4 and SOL20 combination was selected for SiO₂-ZrSiO₄ loading and dispersing, respectively. The impact of solid loading between the range of 58 and 65 vol% on the rheological behavior of the final suspension and the mechanical properties of sintered bodies were investigated to assign an optimum solid rate. The adequate strength on sintered and degree of viscosity for ceramic vat-polymerization processing was achieved at 58 vol%. Lastly, a validation study is conducted by printing a complex ceramic core model by a commercial LCD hobby printer. This validation shows the significance of this study to scale up the manufacturing of complex-shaped ceramic cores and to revolutionize the sector, by printing inexpensive and readily available irregular-shaped (non-atomized) ceramic powder, using the most cost-effective LCD printers (non-specialized expensive ceramic printers).     

Effect of TiO2 addition on microstructure and mechanical properties of alumina-based cores prepared by sol-gel method

Alumina-based ceramic cores have widespread applications especially in the investment casting of turbine blades due to chemical inertness with most of the superalloys, capability of machining in the green state, and their mechanical stability at high temperatures. The present work studied the effects of TiO₂ addition to the alumina-based cores. These cores were prepared via the sol-gel method process by mixing alumina powders with NH₄Cl and silica sol. The effects of adding different amounts of titania from 5 to 30 wt% and different sintering procedures on mechanical, physical, thermal, chemical, and microstructural features of the bodies were investigated. According to the results of rheology measurements of the slurries and flexural strength of the green bodies, the suitable amount of solid loading was 45 vol. %. The results showed that there is an optimum content for TiO₂ addition. The specimen contained 15 wt. % titania and sintered at 1400°C for 2 hours had the thermal expansion coefficient as low as 4.8 × 10⁻⁶/°C (25-900°C), suitable mechanical properties as a result of tialite formation, and apparent porosity of 28 vol. %, respectively. The result of creep deformation test showed that this specimen had near zero deformation at 1650°C.     

Enhancing fracture strength of ceramic core using sodium silicate as the binder

Ceramic cores used in the casting must exhibit high heat resistance because they come in direct contact with molten metals. Therefore, in this study, ceramic cores with high heat resistance and fracture strength were fabricated using sodium silicate as the binder instead of a commonly used organic binder. In addition, the prepared ceramic core was coated with Si and Si-Na precursors as the inorganic binder to improve the firing strength of the ceramic core. The thermal stability and firing strength of the sample were investigated. The results revealed that the firing strength of the ceramic core was significantly improved up to 15.2 MPa owing to the formation of a glass phase between the ceramic particles, which was formed by the reaction of sodium silicate and the inorganic binder precursor. In addition, the core was completely decomposed in an NaOH solution at a relatively low temperature of 60°C, indicating the excellent elution properties of the sample. These results indicate that the method proposed in this study is suitable for the preparation of ceramic cores with high fracture strength and excellent elution behavior.     

Heat treatment effects on microstructure and mechanical properties of CVI SiCf/PyC/SiC composites with Cansas-Ⅲ SiC fibers

The microstructure and mechanical properties of CVI-Cansas-III/PyC/SiC composites were systematically investigated after heat treatment under high temperature argon atmosphere, ranging from 1000 °C to 1500 °C, for different time durations. The results showed that the Cansas-III fibres degraded with increasing heat treatment temperature, resulting in degradation of the fibre properties due to pyrolysis of the SiOC phase inside the fibres. The bending strength of the composites remained nearly constant upon heat treatment at 1000 °C and 1250 °C, while a decline in bending strength was observed upon increasing the heat treatment temperature and time, specifically at 1350 °C and above. Moreover, the composites maintained their pseudo-plastic fracture behaviour below 1450 °C, while displaying brittle fracture of the ceramic after 100 h of heat treatment at 1500 °C, due to the complete crystallisation of the fibres.     

Development and evaluation of Al2O3–ZrO2 composite processed by digital light 3D printing

Digital Light Processing (DLP) is a promising approach to fabricate delicate ceramic components with high-fidelity structural features. In this work, the alumina and zirconia/alumina ceramic suspensions with low viscosity and high solid loading (40 vol%) were prepared specifically for DLP 3D printing. After debinding and sintering, the final parts were obtained without any defects. The surface morphologies and mechanical properties of alumina (Al₂O₃) and zirconia toughened alumina (ZTA) composites were investigated and the results showed that the final parts exhibited high relative densities and good interlayer combination at the sintering temperature of 1600 °C. Comparing with the Al₂O₃, the ZTA composites exhibited significantly enhanced density (99.4%), bending strength (516.7 MPa) and indentation fracture toughness (7.76 MPa m^1/2).     

Mechanical performances of AlN/Al metallized ceramic substrates fabricated by transient liquid phase bonding and pre-oxidation treatment

For the miniaturization of high-power electronic components, AlN/Al is a promising metallized ceramic substrate due to its superior mechanical and thermal performances. Numerous bonding processes have been proposed for fabricating the metallized ceramic substrate. Unfortunately, the influences of various bonding techniques on the mechanical performance of AlN/Al metallized ceramic substrate remain undetermined to date. The objective of this study was thus to investigate the effects of the transient liquid phase (TLP) technique and pre-oxidation treatment on the bonding, microstructure, and mechanical strength of the AlN/Al metallized ceramic substrate.The results indicated that the three-layered AlN/Al/AlN specimen could be effectively bonded by the TLP process and pre-oxidation treatment. However, the bending strengths of the specimens fabricated by the two techniques were obviously divergent. The bending strength of raw AlN substrate was 333 MPa. In contrast, the bending strengths of the three-layered specimens with AlN substrates pre-oxidized at 1050 °C, 1150 °C, and 1250 °C were 292 MPa, 250 MPa, and 224 MPa, respectively. Raising the pre-oxidation temperature of the AlN substrate from 1050 °C to 1250 °C obviously increased the thickness of the Al₂O₃ layer and deteriorated the bending strength, for the fracture propagated along the Al₂O₃ layer and the Al₂O₃/AlN interface. For the TLP bonding, the Cu film deposited on the AlN substrate contributed to the generation of Al–Cu transient liquid and to bonding. The bending strength of the three-layered specimens fabricated by TLP at 650 °C was 417 MPa, which was 25% and 43% better than those of the raw AlN substrate and the three-layered specimens prepared by the pre-oxidation treatment, respectively.     

Effect of silica sol on performance and surface precision of alumina ceramic shell prepared by binder jetting

Using 3D printing technology to prepare ceramic shell used for precision investment casting can realize short process and efficient preparation of the ceramic shell, which has a great application potential in the casting field. However, the 3D printed ceramic shells often have the problems of low strength and accuracy. In this paper, a silica sol room temperature dip coating treatment combined with high temperature sintering method was proposed to improve the strength and surface precision of the ceramic shell prepared by the binder jetting. The effects of silica sol concentration and dip coating time on performance and surface precision of the alumina ceramic shell were studied. The mechanical properties and surface precision of the alumina ceramic shell prepared by the binder jetting were improved significantly with the increases of the sol concentration and dip coating time. With the dip coating time of 90 s and sol concentration of 30%, the maximum bending strength of the alumina ceramic reached 44.8 MPa, which was 18.9 times higher than that of the untreated alumina ceramic. The top surface roughness and side roughness of the alumina ceramic decreased from 6.87 μm to 5.70 μm and 7.55 μm–6.46 μm, respectively, compared to those of the untreated alumina ceramic.