Stereolithography-based Additive Manufacturing Research Articles

Effect of sintering temperature on the microstructures and mechanical properties of ZrO2 ceramics fabricated by additive manufacturing

The optimization of the sintering process for ceramic stereolithography-based additive manufacturing is attracting high interest important due to its correlation with the final properties of the fabricated parts. In this work, a photosensitive zirconia suspension with low viscosity and high solid loading (48 vol%) was prepared using surface-modified zirconia ceramic powders, resulting in an improvement in long-term stability. The correlations between the sintering temperature (1400–1520 °C) and mechanical properties were investigated. The results showed that and the as-sintered zirconia parts exhibited a relatively high density of 99.5 ± 0.1 % and three-point flexural strength of 821 ± 65 MPa as well as excellent fracture toughness (4.37 ± 0.22 MPa m1/2) sintering at 1480 °C, which was attributed to the highly homogeneous microstructure without obvious pores or crack. The obtained insights regarding the correlation between sintering temperature, relative density, and flexural strength can provide practical guidance for the future applications of zirconia ceramics.

The effect of phase contents on the properties of yttria stabilized zirconia dental materials fabricated by stereolithography-based additive manufacturing

The aim is to investigate the impact of phase contents on mechanical properties, translucency, and aging stability of additively manufactured yttria partially stabilized zirconia ceramics. For that purpose, we evaluated two PSZ materials. The first type was prepared utilizing commercially available 5 mol% yttria-stabilized zirconia(5Y-PSZ), while the second type, denoted as 3Y+8Y-PSZ ceramics, was fabricated by blending 3 mol% and 8 mol% yttria-stabilized zirconia powders. Compared to 5Y-PSZ (39.90 wt% tetragonal phases and c/a2 = 1.0141), 3Y+8Y-PSZ is characterized by a greater abundance of tetragonal phases (47.68 wt%), which display higher tetragonality (c/a2 = 1.0165) and lower yttrium oxide content (2.25mol%). As a result, the 3Y+8Y-PSZ demonstrates elevated strength (816.52 MPa) and toughness (4.32 MPa m1/2), accompanied by reduced translucency(CR:0.47) and it exhibits greater susceptibility to aging. The phase contents, yttrium oxide content, and lattice parameters in the tetragonal phase play a crucial role in determining the mechanical properties, translucency, and aging stability of PSZ ceramics.

Development and optimization of PZT suspensions with high solid loading and low viscosity for stereolithography-based additive manufacturing

Achieving synergy between high solid loading and low viscosity for ceramic suspensions a critical issue in the field of stereolithography. In this work, we successfully obtained a well-dispersed PZT suspension with high solid loading (55 vol%) and low viscosity (3047.5 mPa s at 60 rpm) by adding appropriate amounts of dispersant (1 wt% KOS110) and thickening agent (2 wt% PEG300), providing a foundation for crack-free photosensitive lead zirconate titanate (PZT) samples. This work presented a simple approach for achieving synergy between the high solid loading and low viscosity of ceramic suspensions for stereolithography-based additive manufacturing.

Effect of sintering temperature and low-temperature aging on microstructure and flexural strength of Fe2O3-doped 3Y-TZP ceramics fabricated by stereolithography-based additive manufacturing

In this study, the effects of sintering temperature and low-temperature degradation (LTD) on the microstructure and flexural strength of 0.06 wt% Fe2O3-doped 3Y-TZP ceramics fabricated via stereolithography-based additive manufacturing were evaluated to assess their suitability for dental applications. The ceramics' comprehensive properties, including density, microstructure, phase composition, and three-point flexural strength, were analyzed over a range of sintering temperature from 1400 °C to 1600 °C. The findings revealed that specimens sintered at 1500 °C exhibited the highest density (6.03 g/cm3), a uniform microstructure, and superior mechanical properties (911.54 MPa). However, sintering temperatures above 1500 °C led to abnormal grain growth and martensitic transformation of tetragonal zirconia to the monoclinic phase, resulting in reduced density and material degradation. To investigate the effects of LTD on the phase structure, microstructure, and flexural strength, the specimens sintered at 1500 °C were subjected to LTD tests at 134 °C and 2 bar for 5, 10, and 20 h, respectively. The results demonstrated an increase in the m-phase content from 2.58 wt% to 21.89 wt% on the ceramics' surface. Atomic force microscopy observations revealed a gradual increase in the m-phase grain with longer aging time. Meanwhile, the flexural strength decreased but remained within the required range for dental restorations. In conclusion, the specimens fabricated via stereolithography-based additive manufacturing and sintered at 1500 °C for 4 h demonstrated high mechanical properties and good LTD resistance. These findings, in conjunction with the positive aesthetic properties obtained in previous studies, highlight their potential as a promising material for dental applications.

Investigating the effect of solid loading on microstructure, mechanical properties, and translucency of highly translucent zirconia ceramics prepared via stereolithography-based additive manufacturing

A study was conducted to explore the potential of 5 mol% yttria-partially stabilized zirconia (5Y-PSZ) ceramics for dental restorations, using stereolithography (SLA) printing technique. Four different solid loadings were established in the ceramic paste systems to study their effects on microstructure, mechanical properties, and translucency. The study examined the rheological behavior and photopolymerization performance of the ceramic pastes with varying solid loadings. Results showed that, an increase in powder concentration resulted in a decrease in cure depth (Cd) and penetration depth (Dp). A narrower pore size distribution was observed in the green bodies with a high solid loading, facilitating the achievement of final densification. The green and sintered densities were highest at 52 vol%, with values of 3.46 ± 0.01 g/cm3 and 6.01 ± 0.02 g/cm3, respectively. Additionally, all of the green strengths exceeded 30 MPa, with a maximum of 35.09 ± 2.02 MPa obtained at 44 vol%. The maximum flexural strength and minimum contrast ratio (CR) value of 746 ± 75 MPa and 0.40 ± 0.01 were achieved at 52 vol% after sintering. No significant differences were observed in the phase composition and hardness of the as-sintered ceramics. Though significant differences were observed in photopolymerization performance, four materials showed similar structural reliability considering Weibull modulus and characteristic strength.

Influence of debinding parameter and nano-ZrO2 particles on the silica-based ceramic cores fabricated by stereolithography-based additive manufacturing

The silica-based ceramic core is an essential part of the investment casting of hollow turbine blades due to their excellent thermal stability and easy demoulding. In this study, the green bodies of silica-based ceramic cores with nano-ZrO2 were fabricated by stereolithography (SLA). Firstly, the effects of the burying process and debinding heating rates on the performance and microstructure of silica-based cores were investigated. The results revealed that the burying powders provide support and a stable thermal field for the SLA ceramic cores during debinding and sintering. Ceramic cores with smaller shrinkage and higher apparent porosity were produced during the burying process at a heating rate of 0.5 °C/min. In addition, the influence of nano-ZrO2 content on the mechanical properties of silica-based ceramics was investigated. Nano-ZrO2 particles can improve bulk density and mechanical properties by promoting sintering. Additionally, it can reduce the cracks on the surface of ceramic samples. The optimal content of nano-ZrO2 should be between 1.5 and 2 wt%, producing silica-based cores with low shrinkage rate (2.91–3.19%), high apparent porosity (27.11–27.97%) and high flexural strength at room temperature (24.51–24.65 MPa) and high temperature (27.81–29.69 MPa). This work provides promising ways to fabricate high-quality ceramic cores for turbine blade application.

Fabrication of highly translucent yttria-stabilized zirconia ceramics using stereolithography-based additive manufacturing

The current study describes the mechanical properties and translucency of 5 mol% yttria-partially stabilized zirconia (5Y-PSZ) prepared via stereolithography (SLA). A stable 5Y-PSZ ceramic paste with a maximum solid loading of 52 vol% is prepared for the SLA process, and the corresponding rheological model between viscosity and shear rate is analyzed. After sintering, all samples exhibited the same hardness and fracture toughness, approaching 12.65 GPa and 3.20 MPa m1/2, respectively. Also, the density and flexural strength reached their maximum values at 1550 °C, which were 5.95 g/cm3 and 685.6 MPa, respectively, while the contrast ratio (CR) reached its minimum value of 0.43 at 1500 °C. Moreover, failure origin and Weibull analysis are performed to evaluate the structural reliability of the ceramic components. It is observed that the yttrium content in large grains was higher than the small grains, indicating large grains consisted of the cubic phase. Herein, the stronger grain boundaries are caused by the higher segregation of yttrium at grain boundaries, altering fracture mode from the intergranular fracture to the mixed mode of trans- and intergranular fracture at 1550 °C.

Additive manufacturing of high-performance polycyanurates via photo-induced catalytic poly-trimerization

Investigation of a cyanate ester based formulation and stereolithography-based additive manufacturing via Hot Lithography to produce polycyanurates with a glass transition temperature of 336 °C without any additives.

Stereolithography-based additive manufacturing of RB-SiC ceramics by a two-step sintering method

Digital light processing technology (DLP) is an effective method to manufacture ceramics with high precision. It is a big challenge to prepare SiC green body with high solid content by DLP method due to the limitation of high light-absorbance of SiC powder in stereolithograhy. Here, we present one novel route for DLP additive manufacturing of high-performance SiC ceramics by introducing low light-absorbance SiO 2 powders and a two-step sintering process including carbothermal reduction and reactive melt infiltration. As-prepared SiC ceramic exhibited higher flexural strength of 268.66 ± 10.19 MPa, compared with reported stereolithograhy-based SiC ceramics. This method demonstrates the potential of preparing SiC ceramic composites with high mechanical properties by stereolithography additive manufacturing.

Preparation of silicon carbide ceramic slurry for stereolithography based additive manufacturing

Stereolithography-based additive manufacturing of ceramics has received tremendous attention in academic and industrial communities. In order to fabricate silicon carbide (SiC) components with complex shapes by stereolithography, a high SiC loaded ceramic slurry with low viscosity and excellent curing ability is required. However, it is challenging to meet these slurry requirements. In this work, the effects of resin formulation, dispersant, particle size, solid content and ball milling time on the properties of SiC ceramic slurry were systematically studied. The SiC slurries were prepared by using four precursor SiC powders having different particle sizes and modified by high temperature oxidation to reduce its UV absorbance. Additionally, the suitable SiC slurries for stereolithography were prepared by ball milling under appropriate processing parameters, and the geometrically complex SiC green bodies were subsequently fabricated.

A comprehensive study on zirconia slurry for stereolithography-based additive manufacturing

A comprehensive study on zirconia slurry for stereolithography-based additive manufacturing

Effect of Fe2O3 doping on color and mechanical properties of dental 3Y-TZP ceramics fabricated by stereolithography-based additive manufacturing

In this study, iron(III) oxide (Fe2O3)-doped zirconia (3Y-TZP) ceramics with desirable mechanical and color properties for dental restorations were fabricated by stereolithography-based additive manufacturing. Six zirconia ceramic paste specimens with high solid loading (58 vol%) and reasonably low viscosity were prepared according to doped content of Fe2O3 (0–0.14 wt%). Zirconia ceramics were fabricated using commercial stereolithography three-dimensional printer and sintered at 1500 °C for 4 h to obtain final dense parts with a relative density of above 99%. Effects of Fe2O3 doping on microstructure, mechanical properties, and color of 3Y-TZP ceramics were investigated. Results indicate that Fe2O3 exhibited little effect on the shrinkage and density of colored ceramics compared to uncolored ceramics. Average grain size of 3Y-TZP ceramics sintered at 1500 °C increased with increasing content of Fe2O3. X-ray diffraction analysis showed that tetragonal phase was dominant phase structure of white and colored 3Y-TZP ceramics, and monoclinic phase increased with increasing Fe2O3 content. Compared to uncolored specimens, Fe2O3 exhibited negative effects on three-point flexural strength (mean > 879.70 MPa), Vickers hardness (mean > 12.14 GPa), and indentation fracture toughness (mean > 4.23 MPa m1/2) of the colored specimens. With the increase in the content of Fe2O3 from 0 to 0.14 wt%, L* (black–white index) value decreased from 83.39 to 79.54, a* (green–red index) value increased from −2.28 to −0.74, and b* (blue–yellow index) value increased from 1.15 to 17.94. Chromaticity (L*, a*, b*) fell within the range of natural tooth color, indicating that it is suitable for dental application because of its color compatibility with natural teeth. In addition, the transmittance slightly decreased with increasing Fe2O3 content. Thus, Fe2O3-doped 3Y-TZP ceramics can be used as potential candidates for aesthetic dental restoration materials.

The effect of particle size of highland and mare lunar regolith simulants on their printability in vat polymerisation additive manufacturing

Lunar regolith is the most abundant natural resource on Moon's surface. It is the intensively studied prime candidate for in-situ fabrication and repair (ISFR) technologies for future crewed exploration and resource harvesting missions on the Moon. Additive manufacturing with lunar regolith is a promising ISFR method that can be used for sustainable local production of engineering tools and components. This method requires little quantities of extra materials delivered from Earth, but, like many other prospective ISFR technologies, is sensible to the quality of the pre-processed regolith powders that are used as the primary source materials. The evolution of properties of highland and mare lunar regolith simulants concerning grinding-based pre-processing was studied in this work. The effect of regolith grinding was studied for the processes, relevant to stereolithography-based additive manufacturing. Particle size distribution, mean particle size, UV–Vis, XRD and XRF spectra were acquainted from the samples, ground in a ball mill at various grinding times (to different fraction sizes). The photopolymerization efficiency was assessed for lunar simulant-infilled resins prepared from lunar regolith simulants ground with different parameters. It was found that the grinding time of lunar regolith simulants strongly influences their optical properties – the light absorption in the far UV increased by 5.5 times. Based on the measured photo-polymerization depth, the optimal grinding procedure for mare and highland lunar regolith simulants was determined.

Efficient cleaning of ceramic green bodies with complex architectures fabricated by stereolithography-based additive manufacturing via high viscoelastic paste

Complete removal of uncured ceramic paste from the surface of a green body with complex profiles fabricated by stereolithography-based additive manufacturing is critical to the ultimate achievement of the designed 3D part with high definition and ideal surface roughness. The present work provided a novel cleaning strategy for the design of cleaning agents on the basis of competitive absorption of viscosity-reducing dispersants on the surface of ceramic particles within viscoelastic pastes. In combination with cleaning agent design and auxiliary cleaning equipment, distinct dispersants were selected to enhance the flowability of the uncured paste during the ultrasonic cleaning and spraying processes. The morphology and reconstruction characteristics of specific structures illustrated the advantages and disadvantages of the two cleaning methods. The cleaning effect for small holes by ultrasonic cleaning was superior, but the structural damage of the green body was more serious. After spray cleaning, the surface roughness was lower with less damage to the green body, and there was less residual paste after cleaning. The results demonstrated that the selection of a cleaning strategy was beneficial to posttreatment of stereolithography-fabricated ceramic green bodies, achieving subsequent superior surface quality and accuracy of the internal feature size.

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

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

Stereolithography-based additive manufacturing of polymer-derived SiOC/SiC ceramic composites

In order to overcome challenges typically encountered during additive manufacturing of ceramics via the polymer precursor route, a novel polymer-derived SiOC/SiC composite system suitable for advanced geometric designs achievable by lithography-based ceramic manufacturing was established. The photoreactive resin system filled with 20 wt% SiC exhibits suitable viscosity characteristics, adequate stability against sedimentation, and a fast photocuring behavior. After printing and pyrolytic conversion, SiC particulates were well-dispersed within the polymer-derived SiOC matrix. A direct comparison with the unfilled polysiloxane-based resin system showed that the addition of particulate SiC increases handleability, reduces shrinkage, and significantly increases critical wall thicknesses up to 5 mm. The biaxial Ball-on-Three-Balls testing methodology yielded a characteristic strength of 325 MPa for SiOC/SiC composites. The results highlight the high potential of particle-filled preceramic polymer systems toward the fabrication of high-performance SiC-based materials by lithography-based additive manufacturing.

Masked stereolithography of hydroxyapatite bioceramic scaffolds: From powder tailoring to evaluation of 3D printed parts properties

This paper focuses on the tailoring of hydroxyapatite powders properties for the preparation of highly hydroxyapatite-loaded photocurable organic slurries. The suspensions were evaluated as feedstock for the production of hydroxyapatite scaffolds by stereolithography-based additive manufacturing technique. Then, a debinding-sintering process was designed to avoid the formation of cracks during the pyrolysis of the resin and sintering of the printed parts. A total porosity of 35 vol % and compression strength of 4.9 ± 0.3 MPa were obtained for the specimens printed at 45° to the building platform. A slow degradation rate was observed due to the high degree of crystallinity and intrinsic stability of the hydroxyapatite phase. The tailoring of hydroxyapatite powders was required to lower the viscosity and increase the particle stability of the suspensions. The printed hydroxyapatite scaffolds showed promising results for surgery, in the case of minor or non-load bearing implants requiring slow resorption properties.

Additive manufacturing of yttrium-stabilized tetragonal zirconia: Progressive wall collapse, martensitic transformation, and energy dissipation in micro-honeycombs

For zirconia-based technical ceramics, the unique advantages of micro-architecture geometries combined with the potent mechanical and functional properties have been challenging to implement owing to additive manufacturing restrictions. In this work, we present a stereolithography-based additive manufacturing approach involving slurry development for yttrium-stabilized tetragonal zirconia polycrystals (Y-TZP), followed by printing using a custom-built large-area projection micro-stereolithography system. After post-processing, i.e., polymer burnout and sintering, 98% relative density is reached in the printed Y-TZP parts. Thanks to the good manufacturing quality, the bulk-scale Y-TZP micro-honeycombs are able to display typical stretch-dominated behavior in out-of-plane compression, showing elastic loading (Stage I) and protracted brittle failure of individual walls over a significant strain (Stage II). For a Y-TZP micro-honeycomb consisting of 5 × 4 hexagonal cells with a wall thickness of 300 μm and a cell diameter of 1.40 mm, the energy dissipation density is measured to be 9.45 J/g, substantially higher than other ceramic honeycombs and packings reported earlier. This energy dissipation capability is mostly attributed to the progressive wall collapse seen in Stage II deformation, in which the perimeter walls are preferentially fragmented relative to the interior walls. According to finite element analysis, this phenomenon is a result of the deviation from uniaxial compression and the presence of stress gradients in the perimeter walls. We also find evidence for stress-induced martensitic transformation in the Y-TZP micro-honeycomb after compression, which may be another contributor to the observed energy dissipation capability.

Improving cure performance of Si3N4 suspension with a high refractive index resin for stereolithography-based additive manufacturing

Silicon nitride (Si3N4) slurries with high solid loading, low viscosity and good stability is difficulty prepared, due to low intrinsic surface charge and a large refractive index (RI) difference between Si3N4 powder and resin. In this paper, the curing behavior of Si3N4 slurry with different functional group and RI of resin monomer were systematically researched, and then the kind and optimum content of dispersant were investigated. Subsequently, a high solid loading Si3N4 slurry (44 vol%) with good curing behavior, low viscosity and favorable stability was successfully prepared. Lastly, the dense Si3N4 ceramic parts were fabricated by the suitable Si3N4 slurry (44 vol%) via stereolithography. After debinding and sintering process, the relative density and flexural strength of Si3N4 ceramic were 98.28% and 800 ± 27.28 Mpa, respectively.

Evaluation of Stereolithography-Based Additive Manufacturing Technology for BaTiO3 Ceramics at 465 nm

A piezoceramic BaTiO3 material that is difficult for 3D printing was tested with a homemade laser-based stereolithography (SLA) setup. The high light absorbance of BaTiO3 in the spectral range of 350–410 nm makes this material hardly usable with most commercial SLA 3D printers. The typical polymerization depth of BaTiO3 ceramic pastes in this spectral range hardly reaches 30–50 µm for 40 vol % powder loading. A spectral change to 465 nm was realized in this work via a robot-based experimental SLA setup to improve the 3D printing efficiency. The ceramic paste was prepared from a preconditioned commercial BaTiO3 powder and used for 3D printing. The paste’s polymerization was investigated with variation of powder fraction (10–55 vol %), speed of a laser beam (1–10 mm/s, at constant laser power), and a hatching spacing (100–1000 µm). The polymerization depths of over 100 µm were routinely reached with the 465 nm SLA for pastes having 55 vol % powder loading. The spectral shift from 350–410 nm spectral region to 465 nm reduced the light absorption by BaTiO3 and remedied the photopolymerization process, emphasizing the importance of comprehensive optical analysis of prospective powders in SLA technology. Two multi-layered objects were 3D-printed to demonstrate the positive effect of the spectral shift.