Properties of SiC-Si made via binder jet 3D printing of SiC powder,carbon addition,and silicon melt infiltration

We report the physical and mechanical properties of ceramic composite materials fabricated by binder jet 3D printing (BJ3DP) with silicon carbide (SiC) powders, followed by phenolic resin infiltration and pyrolysis (IP) to generate carbon, and a final reactive silicon melt infiltration step. After two phenolic resin infiltration and pyrolysis cycles; porosity was less than 2%, Young's modulus was close to 300 GPa, and the flexural strength was 517.6 ± 24.8 MPa. However, diminishing returns were obtained after more than two phenolic resin infiltration and pyrolysis cycles as surface pores in carbon were closed upon the formation of SiC, resulting in reaction choking and residual-free carbon and porosity. The instantaneous coefficient of thermal expansion of the composite was found to be independent of the number of phenolic IP cycles and had values of between 4.2 and 5.0 ppm/°C between 300 and 1000℃, whereas the thermal conductivity was found to have a weak dependence on the number of phenolic IP cycles. While the manufacturing procedures described here yielded highly dense, gas impermeable, siliconized SiC composites with properties comparable to those of bulk siliconized silicon carbide processed according to conventional techniques, BJ3DP enables the manufacture of objects with complex shape, unlike conventional techniques.     

Vat photopolymerization-based additive manufacturing of high-strength RB-SiC ceramics by introducing quasi-spherical diamond

Silicon carbide is one of the most important high-performance engineering ceramics. However, SiC ceramics with complex structure and high mechanical performance are difficult to shape, sinter, and process. Additive manufacturing is expected to solve the above problems, but the photosensitive slurry with low solid content leads to high residual Si content and low strength of final components. Here, we presented one novel strategy to prepare high-strength SiC components with complex structure by introducing quasi-spherical diamond powder as the high-density carbon source through vat photopolymerization 3D printing technology and reactive melt infiltration process. The final RB–SiC ceramics exhibited a specific flexural strength of 312.45 ± 18.75 MPa and elastic modulus of 359.16 ± 4.57 GPa, demonstrating one of the highest flexural strength and elastic modules among those reported for 3D-printed SiC composites. Owing to the high mechanical performance and simple fabrication process, this strategy has significant advantages in the manufacturing of structural SiC ceramics.     

Additive manufacturing of Csf/SiC composites with high fiber content by direct ink writing and liquid silicon infiltration

Direct ink writing (DIW) provides a new route to produce SiC-based composites with complex structure. In this study, we additive manufactured short carbon fiber reinforced SiC ceramic matrix composites (Csf/SiC composites) with different short carbon fiber content through direct ink writing combined with liquid silicon infiltration (LSI). The effects of short carbon fiber content on the microstructure and mechanical properties of the DIW green parts and the final Csf/SiC composites were investigated. The results showed that the Csf content played an important role in maintaining the structure of the green parts. As the Csf content increases, the dimension deviation ratio of the sample decreased at all stages. With the Csf content of 40 vol%, the final Csf/SiC composite had low free Si content and high β-SiC content. The maximum density, tensile strength and bending strength of the Csf/SiC composites were 2.88 ± 0.06 g/cm³, 53.68 MPa and 253.63 MPa respectively. It is believed that this study can give some understanding for the additive manufacturing of fiber reinforced ceramic matrix composites.     

Silicon infiltrated silicon carbide from extruded thermoplastic wood polymer composites

Silicon-infiltrated silicon carbide (SiSiC) is an important technical ceramic material for several demanding applications such as heat exchangers, nozzles or mechanical seals. However, shaping and machining tools are quickly worn down, due to the application of hard abrasive silicon carbide (SiC) particles as part of the conventional starting compounds for monolithic SiSiC ceramics. Within this work, an alternative route fabricating SiSiC without primary SiC particles and with low residual carbon contents derived from thermoplastic wood polymer composites (WPC) is described. By varying the proportions of the raw materials, the phase compositions of the SiC ceramic could be modified. A reduction in the average wood particle size from 120 to 60 µm led to a homogenous SiSiC with high SiC content. SiSiC with flexural strengths up to 230 MPa and a Weibull modulus of 16 were developed. The residual carbon content could be reduced below 1 wt%.     

MCMB–SiC composites; new class high-temperature structural materials for aerospace applications

Graphite–silicon carbide (G–SiC), carbon/carbon–silicon carbide (C/C–SiC) and mesocarbon microbeads–silicon carbide (MCMB–SiC) composites were produced using liquid silicon infiltration (LSI) method and their physical and mechanical properties, including density, porosity, flexural strength and ablation resistance were investigated. In comparison with G–SiC and C/C–SiC composites, MCMB–SiC composites have the highest bending strength (210 MPa) and ablation resistance (9.1%). Moreover, scanning electron microscopy (SEM) and optical microscopy (OM) are used to analyze the reacted microstructure, pore morphology and pore distribution of carbon-based matrices. As a result, SiC network reinforcement was formed in situ via a reaction between liquid silicon and carbon. The unreacted carbon and solidified silicon are two phases present in the final microstructure and are characterized by X-ray diffraction (XRD). Based on the results obtained and the low-cost processing of pitch-based materials, the MCMB–SiC composite is a promising candidate for aerospace applications.     

Improvement of toughness of reaction bonded silicon carbide composites reinforced by surface-modified SiC whiskers

To improve the reliability, especially the toughness, of the reaction bonded silicon carbide (RBSC) ceramics, silicon carbide whiskers coated with pyrolytic carbon layer (PyC-SiC_w) by chemical vapor deposition (CVD) were introduced into the RBSC ceramics to fabricate the SiC_w/RBSC composites in this study. The microstructures and properties of the PyC-SiC_w/RBSC composites under different mass fraction of nano carbon black and PyC-SiC_w were investigated methodically. As a result, a bending strength of 550 MPa was achieved for the composites with 25 wt% nano carbon black, and the residual silicon decreased to 11.01 vol% from 26.58 vol% compared with the composite of 15 vol% nano carbon black. The fracture toughness of the composites reinforced with 10 wt% PyC-SiC_w, reached a high value of 5.28 MPa m^1/2, which increased by 39% compared to the RBSC composites with 10 wt% SiC_w. The residual Si in the composites deceased below to 7 vol%, resulting from the combined actively reaction of nano carbon black and PyC with more Si. SEM and TEM results illustrated that the SiC_w were protected by PyC coating. A thin SiC layer formed of outer surface of whiskers can provide a suitable whisker-matrix interface, which is in favor of crack deflection, SiC_w bridging and pullout to improve the bending strength and toughness of the SiC_w/RBSC composites.     

Influence of silicon carbide particle size on the microstructure and mechanical properties of zirconium diboride–silicon carbide ceramics

The influence of silicon carbide (SiC) particle size on the microstructure and mechanical properties of zirconium diboride–silicon carbide (ZrB₂–SiC) ceramics was investigated. ZrB₂-based ceramics containing 30 vol.% SiC particles were prepared from four different α-SiC precursor powders with average particle sizes ranging from 0.45 to 10 μm. Examination of the dense ceramics showed that smaller starting SiC particle sizes led to improved densification, finer grain sizes, and higher strength. For example, ceramics prepared from SiC with the particle size of 10 μm had a strength of 389 MPa, but the strength increased to 909 MPa for ceramics prepared from SiC with a starting particle size of 0.45 μm. Analysis indicates that SiC particle size controls the strength of ZrB₂–SiC.     

Fabrication and properties of dense silicon carbide ceramic via gel-casting and gas silicon infiltration

The dense Silicon Carbide (SiC) ceramics are fabricated by means of gel-casting and gas silicon infiltration (GSI) using carbon black and α-SiC as raw materials. We have successfully introduced a new initiator AIBA which is very suitable to aqueous gel-casting system containing carbon black, overcoming the problems posed by the conventionally used initiator. We have investigated the influences of the monomer acrylamide (AM) content, the ratio of the monomer to crosslinking agent AM/MBAM content, the particle size distribution and the solid content on the mechanical and structural properties of samples. The result show that, the linear shrinkage of the green body can be reduced to 1.0% and its bending strength can reach 59.2 MPa at the optimized gel-casting process that has an AM content of 25 wt%, an AM to MBAM ratio of 12, a SiC particle distribution of 3/2 and a solid content of 60 vol%. After the GSI process, the bending strength and elastic modulus of the final products from such green bodies can reach 245 MPa and 220 GPa respectively. The study highlights that the combined application of the gel-casting and the GSI processes can produce high-quality silicon carbide ceramics that are suitable in the space optical applications.     

Additive manufacturing of high mechanical strength continuous Cf/SiC composites using a 3D extrusion technique and polycarbosilane-coated carbon fibers

A novel additive manufacturing approach is herein reported for manufacturing high mechanical strength continuous carbon fiber-reinforced silicon carbide (C_f/SiC) composite materials. Continuous carbon fibers were coated with polycarbosilane (PCS) using a colloidal evaporative deposition process and then coextruded with high solid content SiC ink. The zeta potential of the SiC ink was adjusted to optimize the printing ability of the suspension. During sintering, small SiC grains and whiskers were generated in the gaps in and around the PCS-coated carbon fibers, which led to the improved flexural strength and density of the composites. Meanwhile, the PCS coating on the surface of the carbon fibers prevented the carbon fibers from reacting with SiO gas generated by reactions between the SiC matrix and SiO₂ and sintering additives (Al₂O₃ and Y₂O₃), effectively preserving the structural integrity of the carbon fibers. Compared to the SiC specimens containing uncoated carbon fibers, the density of the specimens fabricated with coated carbon fibers was increased from 2.51 to 2.85 g/cm³, and the strength was increased from 190 to 232 MPa.     

Additive manufacturing of continuous carbon fiber–reinforced silicon carbide ceramic composites

A material extrusion (MEX) technology has been developed for the additive manufacturing of continuous carbon fiber–reinforced silicon carbide ceramic (C_f/SiC) composites. By comparing and analyzing the rheological properties of the slurries with different compositions, a slurry with a high solid loading of 48.1 vol% and high viscosity was proposed. Furthermore, several complex structures of C_f/SiC ceramic composites were printed by this MEX additive manufacturing technique. Phenolic resin impregnation–carbonization process reduces the apparent porosity of the green body and protects the C_f. Finally, the reactive melting infiltration (RMI) process was used to prepare samples with different C_f contents from 0 to 2 K (a bundle of carbon fibers consisting of 1000 fibers). Samples with C_f content of 1 K show the highest bending strength (161.6 ± 10.5 MPa) and fracture toughness (3.72 ± 0.11 MPa·m^1/2) while the thermal conductivity of the samples with the C_f content of 1 K reached 11.0 W/(m·K). This study provides a strategy to prepare C_f/SiC composites via MEX additive manufacturing and RMI.     

Microstructure and mechanical properties of quasi-isotropic chopped fiber-reinforced PyC–SiC matrix composite prepared by novel nondamaging method

In this work, quasi-isotropic chopped carbon fiber-reinforced pyrolytic carbon and silicon carbide matrix (C_f/C–SiC) composites and chopped silicon carbide fiber-reinforced silicon carbide matrix (SiC_f/SiC) composites were prepared via novel nondamaging method, namely airlaid process combined with chemical vapor infiltration. Both composites exhibit random fiber distribution and homogeneous pore size. Young's modulus of highly textured pyrolytic carbon (PyC) matrix is 23.01 ± 1.43 GPa, and that of SiC matrix composed of columnar crystals is 305.8 ± 9.49 GPa in C_f/C–SiC composites. Tensile strength and interlaminar shear strength of C_f/C–SiC composites are 52.56 ± 4.81 and 98.16 ± 24.62 MPa, respectively, which are both higher than those of SiC_f/SiC composites because of appropriate interfacial shear strength and introduction of low-modulus and highly textured PyC matrix. Excellent mechanical properties of C_f/C–SiC composites, particularly regarding interlaminar shear strength, are due to their quasi-isotropic structure, interfacial debonding, interfacial sliding, and crack deflection. In addition to the occurrence of crack deflection at the fiber/matrix interface, crack deflection in C_f/C–SiC composites takes also place at the interface between PyC–SiC composite matrix and the interlamination of multilayered PyC matrix. Outstanding mechanical properties of as-prepared C_f/C–SiC composites render them potential candidates for application as thermal structure materials under complex stress conditions.     

3D printing of high-purity silicon carbide

A method for advanced manufacturing of silicon carbide offering complete freedom in geometric complexity in the three-dimensional space is described. The method combines binder jet printing and chemical vapor infiltration in a process capable of yielding a high-purity, fully crystalline ceramic—attributes essential for ideal performance in very high-temperature applications or in the presence of displacement damage. Thermal conductivity and characteristic equibiaxial flexural strength of the resulting monolithic SiC at room temperature are 37 W·(m·K)⁻¹ and 297 MPa, respectively.     

Biomorphic silicon/silicon carbide ceramics from birch powder

A novel process has been developed for the fabrication of biomorphic silicon/silicon carbide (Si/SiC) ceramics from birch powder. Fine birch powder was hot-pressed to obtain pre-templates, which were subsequently carbonized to acquire carbon templates, and these were then converted into biomorphic Si/SiC ceramics by liquid silicon infiltration at 1550 °C. The prepared ceramics are characterized by homogeneous microstructure, high density, and superior mechanical properties compared to biomorphic Si/SiC ceramics from birch blocks. Their maximum density has been measured as 3.01 g/cm³. The microstructure is similar to that of conventional reaction-bonded silicon carbide. The Vicker's hardness, flexural strength, elastic modulus, and fracture toughness of the biomorphic Si/SiC were 19.6 ± 2.2 GPa, 388 ± 36 MPa, 364 ± 22 GPa, and 3.5 ± 0.3 MPa m^1/2, respectively. The outstanding mechanical properties of the biomorphic Si/SiC ceramics are assessed to derive from the improved uniform microstructure of the pre-templates made from birch powder.     

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.     

Application of SiO2-coated SiC powder in stereolithography and sintering densification of SiC ceramic composites

Stereolithography additive manufacturing of SiC ceramic composites has received much attention. However, the forming efficiency and mechanical properties of their products need to be improved. This study aimed to prepare SiC ceramic composites with complex shapes and high flexural strength using a combination of digital light processing (DLP) and reactive solution infiltration process (RMI). A low-absorbance SiO₂ cladding layer was formed on the surface of SiC powder through a non-homogeneous precipitation process. With the densification of the cladding layer at high temperatures, SiO₂-coated SiC composite powder was used to formulate a photosensitive ceramic slurry with a solid content of 44 vol%. The resulting slurry exhibited a considerable improvement in curing thickness and rate and was used to mold ceramic green body with a single-layer slicing thickness of 100 μm using DLP. The ceramic blanks were then sintered and densified using a carbon thermal reduction combined with liquid silica infiltration (LSI) process, resulting in SiC ceramic composites with a density of 2.87 g/cm³ and an average flexural strength of 267.52 ± 2.5 MPa. Therefore, the proposed approach can reduce the manufacturing cycle and cost of SiC ceramic composites.     

Lattice-structured SiC ceramics obtained via 3D printing,gel casting,and gaseous silicon infiltration sintering

In view of technical difficulties in preparing ceramics with complex shapes, gel casting combined with 3D printing was here adopted to prepare silicon carbide ceramic green body, and gaseous silicon infiltration sintering was used to prepare 3D lattice-structured ceramics. The preparation of the slurry, gel curing, and ceramic molding was investigated. Results demonstrate that the ratio of components affects the fluidity and stability of slurry. However, when volume fraction of the solid phase of the slurry reaches 56%, the viscosity of slurry is only 300 mPa s, and drying shrinkage rate of green body is 6.6%; these characteristics make slurry suitable for 3D complex model injection molding. Furthermore, both the temperature and the initiator affect gel curing speed. As the temperature and initiator content increase, the induction and gel time are rapidly shortened. When demolding at 300 °C and when gaseous silicon infiltration sintering is carried out at 1550 °C, a 3D lattice-structured ceramic with relative density of 87% and average compressive strength of 433 MPa can be obtained.     

The fabrication and mechanical properties of SiC/SiC composites prepared by SLS combined with PIP

Traditionally, SiC components with complex shapes are very difficult or even impossible to fabricate. This paper aims to develop a new manufacturing process, combining selective laser sintering (SLS), cold isostatic pressing (CIP) and polymer infiltration pyrolysis (PIP), to manufacture complex silicon carbide parts and improve the mechanical properties of silicon carbide ceramic parts. The density and porosity of SiC/SiC composites were measured. Furthermore, the mechanical properties of the specimens with cold isostatic pressing and the specimens without cold isostatic pressing were compared. The bending strength of the specimens with cold isostatic pressing was 201?MPa, and the elastic modulus was 1.27?GPa. And, the bending strength of the specimens without cold isostatic pressing was 142?MPa, and the elastic modulus was 0.88?GPa. Increasing the density of SiC/SiC can enhance the mechanical properties of SiC/SiC composites.     

Direct ink writing of chopped carbon fibers reinforced polymer-derived SiC composites with low shrinkage and high strength

The chopped carbon fiber reinforced SiC (C_f/SiC) composite has been regarded as one of the excellent high-temperature structural materials for applications in aerospace and military fields. This paper presented a novel printing strategy using direct ink writing (DIW) of chopped fibers reinforced polymer-derived ceramics (PDCs) with polymer infiltration and pyrolysis (PIP) process for the fabrication of C_f/SiC composites with high strength and low shrinkage. Five types of PDCs printing inks with different C_f contents were prepared, their rheological properties and alignment of carbon fiber in the printing filament were studied. The 3D scaffold structures and bending test samples of C_f/SiC composites were fabricated with different C_f contents. The results found that the C_f/SiC composite with 30 wt% C_f content has high bending strength (～ 7.09 MPa) and negligible linear shrinkage (～ 0.48%). After the PIP process, the defects on the C_f/SiC composite structures were sufficiently filled, and the bending strength of C_f/SiC composite can reach up to about 100 MPa, which was about 30 times greater than that of the pure SiC matrix without C_f. This work demonstrated that the printed C_f/SiC composites by using this method is beneficial to the development of the precision and complex high-temperature structural members.     

Direct laser sintering of reaction bonded silicon carbide with low residual silicon content

Additive manufacturing (AM) techniques are promising manufacturing methods for the production of complex parts in small series. In this work, laser sintering (LS) was used to fabricate reaction bonded silicon carbide (RBSC) parts. First, silicon carbide (SiC) and silicon (Si) powders were mixed in order to obtain a homogeneous powder. This powder mixture was subsequently laser sintered, where the Si melts and re-solidifies to bind the primary SiC particles. Afterwards, these SiSiC preforms were impregnated with a phenolic resin. This phenolic resin was pyrolysed yielding porous carbon, which was transformed into secondary reaction formed SiC when the preforms were infiltrated with molten silicon in the final step. This resulted in fully dense RBSC parts with up to 84?vol% SiC. The optimized SiSiC combined a Vickers hardness of 2045?HV, an electrical conductivity of 5.3?×?10³?S/m, a Young's modulus of 285?GPa and a 4-point bending strength of 162?MPa.     

Chemical conversion during transient liquid-phase hot pressing of TaSi2–TaC–SiC SHS-powder

This article presents a study on the manufacturing of three-phase TaSi₂–TaC–SiC ceramics through self-propagating high-temperature synthesis (SHS) and their subsequent chemical conversion to TaC–SiC carbide composites during transient liquid-phase hot pressing (HP). The effect of carbon black doping, ranging from 0% to 7%, on the degree of chemical conversion, structure, mechanical, and thermophysical properties of the ceramics was investigated. Our results showed that the proportionate increase of carbide content and decrease of TaSi₂ content in hot-pressed samples was achieved through carbon black doping. The increase of TaSi₂ content during hot pressing led to an increase in porosity from 4.3% to 23.8%, while the density decreased from 6.3 to 4.6 g/cm³. Superior mechanical properties were obtained when SHS-powder was doped with 1.5% carbon black (HV = 15.2 GPa, K_IC = 4.8 MPa × m^1/2, and σ_bend = 331 MPa). The structure of the ceramics was characterized by a TaSi₂–SiC matrix and highly dispersed TaC grains predominantly residing inside TaSi₂, with the TaC–TaSi₂ and TaSi₂–SiC interface being incoherent, as demonstrated through TEM studies. Complete conversion of TaSi₂ to TaC and SiC was achieved through 7% carbon black doping, resulting in the hot-pressed sample consisting solely of carbide grains. Two-stage hot pressing was employed to enhance the relative density of the two-phase TaC–SiC sample, resulting in ceramics characterized by HV up to 22.3 GPa, K_IC up to 6.1 MPa × m^1/2, σ_bend up to 256 MPa, and λ up to 36 W/(m × K).