Silica-based ceramics are widely used in radome applications due to their excellent dielectric properties and thermal stability. However, traditional ceramic forming techniques face significant challenges in fabricating components with complex geometries. To improve the forming quality and mechanical properties of silica ceramics, this study employs Digital Light Processing (DLP)-based additive manufacturing to investigate the effects of different reinforcement phases. Using photosensitive resin as the matrix, composite ceramic samples are prepared by incorporating mullite particles, aluminum nitride particles, and alumina-coated particles as reinforcements. The phase composition, microstructure, bulk density, and flexural strength of the samples are systematically characterized. The results indicate that the type of reinforcement significantly affects the crystallization behavior of cristobalite and the densification process of the ceramics. Among all reinforcements, mullite particles yield the best overall performance, with vertical and horizontal shrinkage rates of 8.73% and 8.66%, open porosity of 17.44%, a bulk density of 1.80 g/cm3, and a maximum flexural strength of 17.94 MPa.
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Selective laser sintering (SLS) for fabricating silica (SiO2) ceramic cores can overcome the bottleneck of mold constraints faced by traditional methods in aerospace casting. However, it still suffers from issues such as a low packing density of SiO2 ceramic green bodies and poor mechanical properties after sintering. To address this, this work combines SLS with the vacuum infiltration (VI) process, with a focus on investigating the influence mechanism of VI time on the structure and properties of SiO2 ceramics. The results show that nanosilica sol infiltrates rapidly under the action of the Al2O3 infiltration aid, and with increasing VI time, the growth rate of the dense layer thickness on the outer surface of the green body first increases but then decreases. SEM and XRD results indicate that the interlayer delamination and pores of the green body are gradually improved, and the diffraction peaks of cristobalite in the ceramics are significantly enhanced. When the VI time is 40 min, the infiltration thickness reaches 607 μm, and the comprehensive properties of the ceramics are optimized. At this point, the infiltration weight gain rate and axial shrinkage are 30.21 wt% and 3.17%, respectively. Furthermore, the porosity decreases from 62.3% to 45.28%, whereas the flexural strength increases from 1.91 to 7.52 MPa. This study provides a process reference for the efficient preparation of SiO2 ceramics for complex hollow turbine blade cores.
It is necessary for an ideal bioceramic scaffold to have a suitable structure. The structure can affect the mechanical properties of the scaffold (i.e., elastic modulus and compressive strength) and the biological properties of the scaffold (i.e., degradability and cell growth rate). Lattice structure is a kind of periodic porous structure, which has some advantages of light weight and high strength, and is widely used in the preparation of bioceramic scaffolders. For the structure of the scaffold, high porosity and large pore size are important for bone growth, bone integration and promoting good mechanical interlocking between neighboring bones and the scaffold. However, scaffolds with a high porosity often lack mechanical strength. In addition, different parts of the bone have different structural requirements. In this paper, scaffolds with a non-uniform structure or a hierarchical structure were designed, with loose and porous exterior to facilitate cell adhesion, osteogenic differentiation and vascularization as well as relatively dense interior to provide sufficient mechanical support for bone repair.
In this work, composite ceramics scaffolds with 10% akermanite content were prepared by DLP technology. The scaffold had a high porosity outside to promote the growth of bone tissue, and a low porosity inside to withstand external forces. The compressive strength, fracture form, in-vitro degradation performance and bioactivity of graded bioceramic scaffolds were investigated. The models of scaffolds were imported into the DLP printer with a 405 nm light. The samples were printed with the intensity of 8 mJ/cm2 and a layer thickness of 50 μm. Finally, the ceramic samples were sintered at 1100 ℃. The degradability of the hierarchical gyroid bioceramic scaffolds was evaluated through immersion in Tris-HCl solution and SBF solution at a ratio of 200 mL/g. The bioactivity of bioceramic was obtained via immersing them in SBF solution for two weeks. The concentrations of calcium, phosphate, silicon, and magnesium ions in the soaking solution were determined by an inductively coupled plasma optical emission spectrometer.
In this work, a hierarchical Gyroid structure HA-AK10 scaffold (sintered at 1100 ℃) with a radial internal porosity of 50% and an external porosity of 70% is prepared, and the influence of structural form on the compressive strength and degradation performance of the scaffold is investigated. The biological activity of the bioceramics in vitro is also verified. The mechanical simulation results show that the stress distribution corresponds to the porosity distribution of the structure, and the low porosity is larger and the overall stress concentration phenomenon does not appear. After soaking in SBF solution, Si—OH is firstly formed on the surface of bioceramics, and then silicon gel layer is produced due to the presence of calcium and silicon ions. The silicon gel layer is dissociated into negatively charged groups under alkaline environment secondary adsorption of calcium ions and phosphate ions, forming amorphous calcium phosphate, and finally amorphous calcium phosphate crystals and adsorption of carbonate ions, forming carbonate hydroxyapatite. This indicates that the composite bioceramics have a good biological activity in-vitro and can provide a good environment for the growth of bone cells. A hierarchical Gyroid ceramic scaffold with a bone geometry is prepared via applying the hierarchical structure to the bone contour scaffold. The maximum load capacity of the hierarchical Gyroid ceramic scaffold is 8 times that of the uniform structure.
The hierarchical structure scaffold designed had good overall compressive performance, good degradation performance, and still maintained a good mechanical stability during degradation. In addition, in-vitro biological experimental results showed that the surface graded composite scaffold could have a good in-vitro biological activity and provide a good environment for bone cells. Compared to the heterosexual structure, the graded scaffold had greater mechanical properties.
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Fabrication of silicon carbide (SiC) ceramics by digital light processing (DLP) technology is difficult owing to high refractive index and high ultraviolet (UV) absorptivity of SiC powders. The surface of the SiC powders can be coated with silicon oxide (SiO2) with low refractive index and low UV absorptivity via high-temperature oxidation, reducing the loss of UV energy in the DLP process and realizing the DLP preparation of the SiC ceramics. However, it is necessary to explore a high-temperature modification process to obtain a better modification effect of the SiC powders. Therefore, the high-temperature modification behavior of the SiC powders is thoroughly investigated in this paper. The results show that nano-scale oxide film is formed on the surface of the SiC powders by short-time high-temperature oxidation, effectively reducing the UV absorptivity and the surface refractive index (nʹ) of the SiC powders. When the oxidation temperature is 1300 ℃, compared with that of unoxidized SiC powders, the UV absorptivity of oxidized SiC powders decreases from 0.5065 to 0.4654, and a curing depth of SiC slurry increases from 22±4 to 59±4 μm. Finally, SiC green bodies are successfully prepared by the DLP with the the oxidized powders, and flexural strength of SiC sintered parts reaches 47.9±2.3 MPa after 3 h of atmospheric sintering at 2000 ℃ without any sintering aid.
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Bone scaffolds require both good bioactivity and mechanical properties to keep shape and promote bone repair. In this work, T-ZnOw enhanced biphasic calcium phosphate (BCP) scaffolds with triply periodic minimal surface (TPMS)-based double-layer porous structure were fabricated by digital light processing (DLP) with high precision. Property of suspension was first discussed to obtain better printing quality. After sintering, T-ZnOw reacts with β-tricalcium phosphate (β-TCP) to form Ca19Zn2(PO4)14, and inhibits the phase transition to α-TCP. With the content of T-ZnOw increasing from 0 to 2 wt%, the flexural strength increases from 40.9 to 68.5 MPa because the four-needle whiskers can disperse stress, and have the effect of pulling out as well as fracture toughening. However, excessive whiskers will reduce the cure depth, and cause more printing defects, thus reducing the mechanical strength. Besides, T-ZnOw accelerates the deposition of apatite, and the sample with 2 wt% T-ZnOw shows the fastest mineralization rate. The good biocompatibility has been proved by cell proliferation test. Results confirmed that doping T-ZnOw can improve the mechanical strength of BCP scaffolds, and keep good biological property, which provides a new strategy for better bone repair.
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Silica ceramic cores have played an important part in the manufacture of hollow blades due to their excellent chemical stability and moderate high-temperature mechanical properties. In this study, silica-based ceramics were prepared with Al2O3 addition by stereolithography, and the influence of Al2O3 content on mechanical properties of the silica-based ceramics was investigated. The Al2O3 in silica-based ceramics can improve the mechanical properties by playing a role as a seed for the crystallization of fused silica into cristobalite. As a result, with the increase of Al2O3 content, the linear shrinkage of the silica-based ceramics first decreased and then increased, while the room-temperature flexural strength and the high-temperature flexural strength first increased and then decreased. As the Al2O3 content increased to 1.0 vol%, the linear shrinkage was reduced to 1.64% because of the blocked viscous flow caused by Al2O3. Meanwhile, the room-temperature flexural strength and the high-temperature flexural strength were improved to 20.38 and 21.43 MPa with 1.0 vol% Al2O3, respectively, due to the increased α-cristobalite and β-cristobalite content. Therefore, using the optimal content of Al2O3 in silica-based ceramics can provide excellent mechanical properties, which are suitable for the application of ceramic cores in the manufacturing of hollow blades.
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