Powder bed fusion of polyamide powders combined with different preceramic polymers infiltration and pyrolysis to produce complex-shaped ceramics

The fabrication of a wide range of polymer-derived ceramic parts with high geometric complexity through a novel hybrid additive manufacturing technique is presented in this article. The process that we introduced in a previous work uses the powder bed fusion technology to manufacture high porous polymeric preforms to be then converted into ceramics through preceramic polymer infiltration and pyrolysis. The cellular architectures of a rotated cube (strut-based) and a gyroid (sheet-based) with 25 mm diameter, 44 mm height and 67 % of geometric macroporosity were generated and used for the fabrication. The complex structures were 3D printed and polycarbosilane, polycarbosiloxane, polysilazane and furan liquid polymers were used to produce SiC, SiOC, SiCN and glassy carbon, respectively. Despite a linear shrinkage of about 24 %, the parts maintained their designed complex shape without deformations. The significant advantages of the proposed method are the maturity of powder bed fusion for polymers with respect to ceramic additive manufacturing techniques and the possibility to fabricate net-shape complex ceramic parts directly from preceramic precursors.     

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.     

Fabrication of dense SiSiC ceramics by a hybrid additive manufacturing process

In this work, we report the fabrication of Silicon infiltrated Silicon Carbide (SiSiC) components by a hybrid additive manufacturing process. Selective laser sintering of polyamide powders was used to 3D print a polymeric preform with controlled relative density, which allows manufacturing geometrically complex parts with small features. Preceramic polymer infiltration with a silicon carbide precursor followed by pyrolysis (PIP) was used to convert the preform into an amorphous SiC ceramic, and five PIP cycles were performed to increase the relative density of the part. The final densification was achieved via liquid silicon infiltration (LSI) at 1500°C, obtaining a SiSiC ceramic component without change of size and shape distortion. The crystallization of the previously generated SiC phase, with associated volume change, allowed to fully infiltrate the part leading to an almost fully dense material consisting of β-SiC and Si in the volume fraction of 45% and 55% respectively. The advantage of this approach is the possibility of manufacturing SiSiC ceramics directly from the preceramic precursor, without the need of adding ceramic powder to the infiltrating solution. This can be seen as an alternative AM approach to Binder jetting and direct ink writing for the production of templates to be further processed by silicon infiltration.     

Additive manufacturing of silicon carbide by selective laser sintering of PA12 powders and polymer infiltration and pyrolysis

In this work, we propose a novel hybrid additive manufacturing technique, which combines selective laser sintering (SLS) of polyamide powders and subsequent preceramic polymer infiltration and pyrolysis to manufacture Silicon Carbide components for complex architectures. By controlling the porosity of the sintered polymeric preform we are able to control the shrinkage upon the first infiltration and pyrolysis. This enabled the manufacturing of smaller features than those achievable with other manufacturing techniques. The mechanical strength of the resulting ceramic increased with the number of reinfiltration cycles up to 24 MPa, inversely the residual porosity decreased to 10 vol%. The microstructure showed two distinct phases of SiOC and SiC. The first was attributed to the interaction between the porous polyamide and the ceramic precursor during the first infiltration. SiC derived from the pyrolysis of the preceramic precursor alone.     

Complex mullite structures fabricated via digital light processing of a preceramic polysiloxane with active alumina fillers

By taking advantage of the multi-functional properties of preceramic polymers, their transformation into ceramic material at low sintering temperatures and the processing capabilities of polymer manufacturing processes, mullite components were fabricated by additive manufacturing. A photocurable silicone preceramic polymer resin containing alumina particles was shaped into complex structures via Digital Light Processing. Dense and crack-free, highly complex porous mullite ceramics were produced by firing a mixture of a commercially available photosensitive polysiloxane as the silica source, containing alumina powder as active filler, in air at a low sintering temperature (1300 °C). In particular, the developed formulations, coupled with the additive manufacturing approach, allow for precise control of the architecture of the porous ceramic components, providing better properties compared to parts with stochastic porosity.     

Poly(methylsilane)—A High Ceramic Yield Precursor to Silicon Carbide

Preceramic polymers offer exceptional potential for low-temperature processing of both oxide and non-oxide ceramics. In addition, shapes such as fibers, films, and membranes that are not commonly available using standard processing techniques are readity available using preceramic polymers. In non-oxide ceramics, the ceramic products generally available from preceramics do not exhibit all of the typical properties associated with the same materials produced by standard, high-temperature processing approaches. In part, this appears to be because there are very few preceramic polymers that lead to high-purity, single-phase materials. Poly(methylsilane), (–[MeHSi] _x –), produced from MeSiH₃, can be used to produce relatively pure, bulk SiC at temperatures below 1000°C. The transformation process from polymer to ceramic is followed by ²⁹Si NMR and diffuse reflectance IR. The polymer first undergoes a major rearrangement from poly(silane) to poly(carbosilane) at 400°C. Above 400°C, the resulting poly(carbosilane) decomposes to a hydrogenated form of SiC as shown by spectroscopic analysis of the 600°C material. Further heating, to 1000°C for 1 h, provides very narrow ²⁹Si peaks indicative of β-SiC mixed with small amounts of α-SiC polytypes. Chemical analysis, when coupled with the ²⁹Si and XRD results, suggests that poly(methylsilane) produces resonably pure, nanocrystalline SiC at temperatures much lower than previously observed for other SiC preceramic polymers.     

Novel application of ceramic precursors for the fabrication of composites

Preceramic polymers are enabling the development of a variety of advanced shaping methods which, in turn, make possible new and cost-effective approaches for the fabrication of composite materials. This opens new perspectives for the mass production of composites which might, for example, be used in cost-sensitive areas of application in the machine and automobile industries. In two examples it will be shown how preceramic polymers can be used to obtain both metal matrix composites (MMC) and ceramic matrix composites (CMC). Their properties will be discussed in particular with respect to the usage of a preceramic polymer.The first example shows an approach to manufacturing short-fibre-reinforced CMCs by means of a plastic forming technique which involves mixing of either carbon or SiC fibres, ceramic fillers and a viscous ceramic precursor. The precursor permits a fibre-reinforced ceramic with a low porosity to be obtained. The role of the precursor in the whole process and the resulting material properties will be discussed.The second example shows a method for fabricating porous SiC ceramic preforms which are subsequently infiltrated with aluminium to form a MMC. By using the precursor route, a machinable preform with tailored porosity can be produced. Correlations between precursor, preform and MMC properties will be drawn.     

聚合物制备工程陶瓷的研究概况

随着聚碳硅烷、聚硅氮烷、聚硅氧烷以及聚硅硼烷等先进前驱体材料的开发,由含硅陶瓷预制体聚合物制备的工程陶瓷在Si-O-C-N-B体系中占有重要的地位。耐高温的SiC和SiN陶瓷纤维增强陶瓷基复合材料(CMC)已在航空、航天结构中获得应用,而耐中、低温的新型涂层、单向带,泡沫和复杂形状的构件在未来将在能源、环境、运输和通讯领域占有重要的地位。综述了陶瓷预制体聚合物的合成、聚合物制备陶瓷的性能、聚合物制备陶瓷的方法以及影响聚合物热解的主要因素。     

Preceramic organoboron–silicon polymers

Several boron-containing organosilicon polymers were synthesized from a sodium-coupling reaction of silicon and boron halides with and without alkyl halide in hydrocarbon solvents. The B–Si preceramic polymers were characterized using techniques such as IR, UV, and NMR spectrometry, gel permeation chromatography, elemental analysis, molecular weight measurement, and thermal analyses (TGA, DSC, DTA, and TMA). The chemical structures of the preceramic polymers were postulated based on the analytical results. Black ceramic materials were obtained from the precursor polymers upon thermal degradation at temperatures above 1000°C in an inert atmosphere. The precursor polymers had a ceramic yield of up to 70%. Thermogravimetric analysis of the ceramic material in air at a flow rate of 100 mL/min showed it was stable up to 1000°C with little weight gain or loss. Several methods were used to characterize the ceramic materials: XRD, solid NMR, high-temperature DTA, elemental analysis, and acid digestion. The analyses indicated that the ceramic materials comprised a mixture of silicon carbide (SiC), silicon borides (SiB₄, SiB₆), and amorphous Si–B–C ceramics, with small amounts of silica and free silicon.     

Complex geometry macroporous SiC ceramics obtained by 3D-printing,polymer impregnation and pyrolysis (PIP) and chemical vapor deposition (CVD)

We present here an original route for the manufacturing of SiC ceramics based on 3D printing, polymer impregnation and pyrolysis and chemical vapor deposition (CVD). The green porous elastomer structures were first prepared by fused deposition modeling (FDM) 3D-printing with a composite polyvinyl alcohol/elastomer wire and soaking in water, then impregnated with an allylhydridopolycarbosilane preceramic polymer. After crosslinking and pyrolysis, the polymer-derived ceramics were reinforced by CVD of SiC using CH₃SiCl₃/H₂ as precursor. The multiscale structure of the SiC porous specimens was examined by X-ray tomography and scanning electron microscopy analyses. Their oxidation resistance was also studied. The pure and dense CVD-SiC coating considerably improves the oxidation resistance.     

Fabrication of SiC ceramic architectures using stereolithography combined with precursor infiltration and pyrolysis

Stereolithography based additive manufacturing provides a new route to produce ceramic architectures with complex geometries. In this study, 3D structured SiC ceramic architectures were fabricated by stereolithography based additive manufacturing combined with precursor infiltration and pyrolysis (PIP). Firstly, photosensitive SiC slurry was prepared. Then, stereolithography was conducted to fabricate complex-shaped green SiC parts. Polymer burn-out was subsequently performed, and porous SiC preforms were produced. After that, precursor infiltration and pyrolysis was used to improve the density and strength. Finally, 3D-structured SiC ceramic architectures with high accuracy and quality were obtained. It is believed that this study can give some fundamental understanding for the additive manufacturing of SiC ceramic structures.     

UV-curable inorganic precursors enable direct 3D printing of SiOC ceramics

3D ceramic parts are of great interest for various applications including aerospace, defense, electronics, photonics, and biomedical. Yet, additive manufacturing of ceramics is challenging due to their poor machinability. Herein, two approaches based on the chemical modification of silicon resins to obtain UV-curable preceramic precursors of SiOC are described. The dual functionality of the synthesized resins acting both as preceramic precursor and as photopolymerizable entity under UV light is exploited. A set of characterization techniques has allowed the investigation of the mechanisms involved in the synthesis of the inorganic SiOC precursors according to the following approaches: (1) blend of the silicon resin with photoactive monomers and (2) synthesis of a single source UV-curable preceramic silicon resin. A correlation between the nature of the precursor and the properties of the derived SiOC is analyzed. From a technological point of view, the materials can be fabricated as dense or crack-free porous customized objects with low mass loss and optimal surface quality.     

Macrostructural design of highly porous SiOC ceramic foams by preceramic polymer viscosity tailoring

Highly porous SiOC ceramic foams with gradient or uniform macrostructures were obtained through polymer derived ceramic routes. Precuring of preceramic polymers and introduction of SiO₂ powders were used to tailor precursor viscosity and hence SiOC foam macrostructure. Effects of polymer viscosity on porosity, pore size, pore distribution were investigated by light microscopy and micro-computed tomography techniques. SiOC ceramic foams. Foams from one unmodified precursor, showed pore size gradient with small pores located at bottom and large pores at the top. To address this non-uniformity, the viscosity of the precursor was increased by pre-curing the preceramic polymer, which resulted in decrease of the average pore size and improvement in pore size uniformity. For a different system with a self-foaming preceramic polymer, because of the simultaneous release of foaming gases and rapid increase in viscosity during crosslinking, the foam had non-uniform macrostructure with large pores and thick struts at the bottom. By addition of SiO₂ fillers, the crosslinking reaction rate was reduced leading to homogeneous pore nucleation and uniform small pore size foams.     

3D printing of SiC ceramic: Direct ink writing with a solution of preceramic polymers

3D structured SiC ceramics with varying feature sizes (100–400?μm) were achieved by direct ink writing of polycarbosilane (PCS)/n-hexane solution. The rheological properties of the PCS solution and printing parameters were tailored for optimum writing behaviour. The integrity and clear surface of the filaments indicated the printing ability of forming the self-supporting features along with the rapid evaporation of solvent. As-printed 3D structured PCS was processed by oxidative crosslinking and pyrolysis and converted to SiC ceramic. Although strong shrinkage occurred during the pyrolysis, SiC ceramic maintained the original 3D structure. Both proper viscoelasticity of printable solutions and the homogeneous shrinkage in the pyrolysis determine the integrity and feature characteristic of 3D structured SiC using direct ink writing preceramic polymer.     

Preparation of ultra-high temperature SiC–TiB2 nanocomposites from a single-source polymer precursor

SiC–TiB₂ ceramic nanocomposites are valuable ultra-high temperature materials, which are rarely prepared from preceramic polymers. In this work, we synthesized SiC–TiB₂ nanocomposites from a new preceramic polymer called titanium- and boron-modified polycarbosilane (TB–PCS). The polymer structure was characterized by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR) spectroscopy. The structure, composition, and morphology of the resulting ceramic products were investigated by FT-IR, X-ray diffraction, and transmission electron microscopy. The elements of titanium and boron were incorporated into the preceramic polymer, and nanoscale TiB₂ and β-SiC grains generated in situ were detected in the pyrolyzed ceramic products at temperatures higher than 1400 °C. The new preceramic polymer presents a novel approach to preparing SiC–TiB₂ nanocomposites.     

Stereolithography 3D printing of SiC ceramic with potential for lightweight optical mirror

Silicon carbide (SiC) ceramic is the most prospective candidate material for space-based lightweight optical mirror. Stereolithography 3D printing has been reported to fabricate many kinds of ceramics, showing great potential for fabricating lightweight SiC ceramic optical mirror. In this paper, SiC ceramic was fabricated using stereolithography 3D printing combined with polymer burn-out, pre-sintering, and precursor infiltration and pyrolysis (PIP). The relative density, flexural strength, and microstructure during each step were investigated. The as-prepared lightweight SiC ceramic optical mirror exhibited high accuracy and high quality. Finally, it was proved that stereolithography 3D printing has a great potential for lightweight SiC ceramic optical mirror fabrication.     

Stereolithography-based additive manufacturing of gray-colored SiC ceramic green body

The stereolithography-based additive manufacturing of white-colored Al₂O₃ and ZrO₂ ceramics has been widely reported, whereas the stereolithography-based additive manufacturing of gray-colored SiC ceramic is very difficult and challenged. In this paper, the reasons for the difficulty which SiC ceramic facing during stereolithography were discussed and compared to Al₂O₃ and ZrO₂ ceramics. The effects of particle size, solid loading, stereolithography parameters, and photoinitiator kind and concentration on the curing ability of SiC slurries were further studied in detail. Finally, complex-shaped SiC ceramic green parts with high accuracy and high quality were successfully fabricated. This study demonstrated that the stereolithography-based additive manufacturing had a great possibility for preparing gray-colored SiC ceramics.     

Fabrication of Porous SiC Ceramics with Special Morphologies by Sacrificing Template Method

Sacrificial template technique is widely used in producing porous materials with controlled morphologies and tailored properties. In this paper, unique templates such as filters, carbon nanotube, carbon fiber and silica were used to make porous SiC ceramic with special morphologies. Template derived porous ceramic plates, SiC nano-net, fiber-inverse and bead-inverse porous SiC ceramic were successfully prepared from the preceramic precursor, polymethylsilane (PMS). The synthesis procedures were involved with the infiltration of the templates with appropriate concentration of the preceramic polymer, their curing, pyrolysis and subsequent template removal. The synthesized porous SiC was characterized by SEM, TEM, XRD and BET methods.     

Multiple metals doped polymer-derived SiOC ceramics for 3D printing

Multiple metals doped polymer-derived SiOC ceramics with octet truss structure were prepared by employing a photosensitive methyl-silsesquioxane as preceramic polymer through sol-gel method and Digital Light Processing 3D printing. The physical and chemical properties of the preceramic polymers and printed octet truss structure SiOC ceramics were investigated. Results show that the organosilicon preceramic polymers have outstanding photocuring properties and could transform into amorphous SiOC ceramics at 800–1200?°C. It is illustrated that the excellent mechanical properties of SiOC ceramics with octet truss structure (after 3D printing and pyrolysis) are attributed to the metal elements pinning in the amorphous matrix on the atomic level. Doping other metal elements such as Fe, Ni, Co, Pt, etc, is thought to bring promising properties for the lattice structure SiOC ceramics and potentially further expand its applications in the future.     

用有机聚合物连接碳化硅陶瓷及陶瓷基复合材料

用陶瓷先驱体有机聚合物连接陶瓷及陶瓷基复合材料是一种成本低廉、工艺新颖、可满足特殊高温条件下连接件要求的新型连接技术。介绍了近年来采用先驱体有机聚合物连接SiC及其复合材料的研究现状，重点对影响连接强度的因素进行分析，并提出相应的改进措施。由于该技术具有连接温度较低、连接过程简单、接头热应力小，连接件的热稳定性高等特点，因此它是陶瓷及其复合材料最有前途的连接方法之一。