Fig. 1. Key challenges associated with the stereolithographic three-dimensional printing of ceramic cores [[247], [248], [249]].

Fig. 2. Stereolithographic three-dimensional printing technologies: schemes, structures, and properties. (a) Two-photon polymerization: a highly focused laser beam polymerizes photopolymers via a two-photon effect in regions with submicrometer volumetric dimensions (left). Scanning electron micrographs of an alumina octet-truss nanolattice (middle). Strength as a reflection of density for different materials (right) [85]. (b) Large-area-projection microstereolithography: a portion of a two-dimensional (2D) image is formed via projection through a spatial light modulator, followed by dynamic direction via an optical scanning system onto a matching location of the resin to solidify the whole 2D layer of the liquid resin (left). Optical micrographs and scanning electron micrographs of a 3D metamaterial formed with hierarchy via large-area projection microstereolithography, with a cross-sectional emphasis on its structural hierarchy (right) [86]. (c) Continuous liquid-interface production (CLIP): an oxygen-permeable window generates a narrow, oxygen-inhibited area to regionally avoid photopolymerization, thereby permitting simultaneous UV exposure, resin renewal, and the elevation of the build support plate (left). CLIP printing speed as an effect of the characteristic optical absorption height and the combined parameter: Φ0σPI/Dc0 (middle) incident photon flux (Φ0), photoinitiator absorption coefficient (σPI), and curing dosage (Dc0). Eiffel Tower model printed by CLIP (right) [142]. Reproduced with permission [82]. Copyright 2017, Nature Reviews Materials.

Fig. 3. (a) Flowchart for the preparation of a UV-curable ceramic suspension for stereolithographic three-dimensional printing (SLA-3DP). (b) Schematic of the fabrication of Al2O3 microcomponents via SLA-3DP. (c) Fourier-transform infrared spectroscopy spectra of raw Al2O3, Al2O3 modified by 2 wt. % KH560, Al2O3 modified by 2 wt. % KH550, and Al2O3 modified by 2 wt. % SA. (d) Viscosity of various suspensions containing 60 wt. % Al2O3 solid particles at a shear rate of 30 s-1, and their corresponding contact angles. Reproduced with permission [120]. Copyright 2018, Powder Technology.

Fig. 4. (a) Overview of ceramic stereolithographic three-dimensional printing via vat photopolymerization. (b) Varying polygonal shapes with identical volumes. The orientation is specified by the unique rotation angle, θmax (denoted by the arrow). (c) Normalized intensity field I/I0 in an 8 × 8 µm2 domain for n = 3, 4, 5, 6, 8, 10, and ∞ at θ7 = π/2n. (d) Intensity fields for (from left to right) n = 3, 4, 5, 6, 8, 10, and ∞ for three different, random realizations. Reproduced with permission [121]. Copyright 2018, Computers and Mathematics with Applications.

Fig. 5. Challenges associated with the preparation of high-solid-content and low-viscosity suspensions. (a) High-solid-content and low-viscosity ceramic core slurry that is not mature. (b) Rheological behavior of a high-solid-content slurry during printing. (c) Photopolymerization behavior of the slurry. (d) Interlayer reaction mechanism of stereolithographic three-dimensional printing [[35], [36], [37], [38], [39], [40], [41], [42], [43], [44], [45], [46], [47], [48], 69, 93, [116], [117], [118], [119], [120], [121], [122], [123], [124], [125], [126], [127], [128], [129], [130], [131], [132], [133], [134], 194, 247,159].

Fig. 6. Schematic of the stereolithographic three-dimensional printing of polymer-derived ceramics. (b) Printed microlattice and honeycomb structure. (c) Scanning electron micrograph image of the microlattice structure. (d) Transmission electron micrograph diffraction pattern indicating an amorphous structure. (e) Oxidation resistance of the printed SiOC ceramic. (f) Compressive strength of the printed SiOC ceramic structure. Reproduced with permission [136]. Copyright 2016, American Association for the Advancement of Science.

Fig. 7. Schematic of the working principle of the employed printers: (a) “bottom-up” and (b) “top-down.” (c) 3D models, base cells, and cross-sections of three geometries generated via additive manufacturing: lattice with 3.25-mm cells and 0.5-mm-diameter struts (average surface area of slices: 12 mm2). (d) Scanning electron micrograph images of the structure of sintered printed lattices: “bottom-up” approach and fracture surface, (e) “top-down” approach and fracture surface. Reproduced with permission [138]. Copyright 2019, Journal of the European Ceramic Society.

Fig. 8. Challenges associated with controlling the printing accuracy of high-solid-content ceramic core suspension: (a) Step effect. (b) Beer-Lambert light absorption model [93]. (c) Attenuation-effect model of ultraviolet light in suspension [93]; (d) Influence of printing parameters on curing thickness; where E0 is the incident energy dose and RI is the refractive index. Reproduced with permission [35]. Copyright 2016, Annual Review of Materials Research and 2018, Mechatronics.

Fig. 9. (a) Design principle of continuous liquid-interface production technology. (b) The thickness of the dead zone as a function of photon flux in varying atmospheres. (c) Relationship between the resolution and speed of printing. (d) Open-book benchmark structures printed with different slicing thicknesses. (e) Scanning electron micrograph images showing an Eiffel Tower model (10 cm in height) and a shoe cleat (20 cm in length) printed using a continuous liquid-interface production technique. Reproduced with permission [142]. Copyright 2015, American Association for the Advancement of Science.

Fig. 10. 3D printing performed on fused silica glass. (a) Mixture of UV-curable monomer with amorphous silica nanopowder framed in a stereolithographic system. (b) and (c) Examples of printed and sintered glass structures: Karlsruhe Institute of Technology logo and a pretzel. (d) Illustration of the strong thermal resistance of printed fused silica glass. (e) Characterization of sintered glass and a high-resolution nanocomposite. (f) Left: UV-visible transmission of the index-matched nanocomposite for microstereolithography and the non-index-matched casting slurry. Right: Casting and microstereolithographic nanocomposites. (g) Microstructuring of fused silica glass. Microstereolithography of a hollow castle gate. (h) Microlithography of a sample microfluidic chip. (i) Micro-optical diffractive structure creating the optical projection pattern shown below. (j) Microlenses fabricated via grayscale lithography. Reproduced with permission [147]. Copyright 2017, Springer Nature.

Fig. 11. Challenges associated with stereolithographic three-dimensional printing of large double-walled ceramic cores with complex structures: (a) model of a double-walled ceramic core, (b) printing at different angles, and (c) precision control of different layers: 366th layer and 1639th layer.

Fig. 12. (Ⅰ) Flow profile of a mobile interface allowing continuing printing. A: Scheme of 3D-printed components from the high-area rapid printing (HARP) 3D-printer. B: Velocity profiles of components printed at varying flow speeds, showing the presence of a slip boundary. C: Slip boundary flow profile under the printing components with a representative, experimentally observed flow profile. (Ⅱ) IR thermal images of an emerging 3D-printed part fabricated under three kinds of printing conditions. A: Stationary print interface, B: mobile interface, and C: mobile interface with active cooling. (Ⅲ) Manufacture-ready components and resolution. A: Type I dog-bone structures generated from an ABS-like polyurethane acrylate resin demonstrate isotropic mechanical properties and are worthy of comparison to a component molded from the same resin or injection-molded ABS (gray line). B: HARP additionally allows high spatial resolution and print fidelity. C: A computed tomography scan of a printed part and its CAD design file revealing a volumetric correlation of 93%. D: Representative height profile scans alongside the print direction for an arrangement of 3-mm-thick dog bones with different widths. (Ⅳ) A wide palette of resins. A: A hard, machinable polyurethane acrylate part that has a hole drilled opposite to the print direction. Traditional discrete layer-by-layer printing methods generally delaminate and fracture if drilled in this location. B: A post-treated, silicon-carbide ceramic printed lattice stands up to a propane torch. C and D: A printed butadiene-rubber component in a state of ease (C) and in a state of tension (D). E: Polybutadiene rubber restores to the expanded lattice after compression. (F) A hard polyurethane acrylate lattice approximately 1.2 m in length and printed in less than 3 h. Scale bar: 1 cm. Reproduced with permission [151]. Copyright 2019, American Association for the Advancement of Science.

Fig. 13. Ceramic core fracture challenges due to ceramic particle segregation. (a) Tearing cracks in the shell, (b) ceramic powder particle segregation, (c) continuous cracks through the structure, and (d) rapid settling of large particles during stereolithographic three-dimensional printing. Reproduced with permission [247], [248], [249]. Copyright 2019, Journal of the European Ceramic Society.

Fig. 14. Integrally cored ceramic mold for a superalloy turbine airfoil with a complex internal hollow structure formed by ceramic stereolithography. (a) CAD file, (b) sintered body, (c) printed green body, and (d) cross-section of the green body with the core and shell mold at the 630th layer. (e and f) Scanning electron micrographs at different locations of a sample sintered at 1400 °C for 8 h. Thermal facets signifying cristobalite were located near the microcracks. (g) Arrhenius plot of incubation time versus annealing temperature yields an incubation energy (Q) of 161 ± 13 kcal g-1 mol-1). (h) Time exponent (n) of the cristobalite transformation plotted against normalized time and a transformed weight scale. The slope, n, was between 1.0 and 1.7. (i) Weight percent of transformed cristobalite versus annealing time. Fused silica powder containing no initial cristobalite (unseeded powder) was fired. Reproduced with permission [159] Copyright 2019, Journal of the European Ceramic Society.

Fig. 15. (Ⅰ) Powder processing and sintering during the production of ceramic components. (Ⅱ) Anisotropic powder packing that may be induced by tape casting. (Ⅲ) Micromechanics in sintering, interaction between two particles, multiparticle interactions, periodic equilibrium structure, and random non-equilibrium structure. (Ⅳ) Sintering of a ring of three spheres by coupled grain-boundary diffusion and surface diffusion. The upper component suggests pore channel pinch-off. The lower component indicates the distribution of regular stress at a grain boundary. (Ⅴ) Relationship between sintering force and effective contact radius. Open circles signify the generation of a closed pore, while crosses signify the disappearing pore. Effect of the range of particles (N). (Ⅵ) Effect of γgb/γs (where γs is the surface energy γgb is the ratio of the grain-boundary energy, Ψ is the equilibrium dihedral angle, and δDgb is the grain-boundary diffusion times the grain-boundary thickness). (Ⅶ) Shrinkage of a closed pore. The pore volume is plotted as a function of dimensionless time. Reproduced with permission [164]. Copyright 2019, Materials Today: Proceedings and 2019 Journal of the European Ceramic Society.

Fig. 16. Deformation and cracking during debinding and sintering of ceramic cores. (a) Shell model, (b) shrinkage of the printing layers, (c) cracking during sintering, and (d) bending deformation [67].

Fig. 17. Concept of stereolithographic three-dimensional printing of ceramic cores [[35], [36], [37], [38], [39], [40], [41], [42], [43], [44], [45], [46], [47], [48], 67, 69, 93, [116], [117], [118], [119], [120], [121], [122], [123], [124], [125], [126], [127], [128], [129], [130], [131], [132], [133], [134], 159, 194, 247].

Fig. 18. Flowchart of the research and development of stereolithographic 3D printing of ceramic cores.

Fig. 19. Core of a machine-learning-based accelerated design strategy. It is suitable for the design of ceramic materials applied in the stereolithographic three-dimensional printing of ceramic cores, which are needed to optimize multiple contradictory properties simultaneously [[217], [218], [219], [220], [221], [222], [223], [224], [225], [226], [227], [228], [229], [230], [231], [232], [233], [234], [235], [236], [237], [238], [239], [240]].