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.     

Fabrication and characterization of carbon fiber reinforced SiC ceramic matrix composites based on 3D printing technology

A novel method has been developed to fabricate carbon fiber reinforced SiC (C_f/SiC) composites by combining 3D printing and liquid silicon infiltration process. Green parts are firstly fabricated through 3D printing from a starting phenolic resin coated carbon fiber composite powder; then the green parts are subjected to vacuum resin infiltration and pyrolysis successively to generate carbon fiber/carbon (C_f/C) preforms; finally, the C_f/C preforms are infiltrated with liquid silicon to obtain C_f/SiC composites. The 3D printing processing parameters show significant effects on the physical properties of the green parts and also the resultant C_f/C preforms, consequently greatly affecting the microstructures and mechanical performances of the final C_f/SiC composites. The overall linear shrinkage of the C_f/SiC composites is less than 3%, and the maximum density, flexural strength and fracture toughness are 2.83?±?0.03?g/cm³, 249?±?17.0?MPa and 3.48?±?0.24?MPa m^1/2, respectively. It demonstrates the capability of making near net-shape C_f/SiC composite parts with complex structures.     

In-plane thermal expansion behavior of dense ceramic matrix composites containing SiBC matrix

In order to reveal the effect of matrix cracks resulted from thermal residual stresses (TRS) on the thermal expansion behavior of ceramic matrix composites, SiBC matrix was introduced into C_f/SiC and SiC_f/SiC by liquid silicon infiltration. The TRS in both two composites were enlarged with incorporating SiBC matrix which has higher coefficients of thermal expansion (CTEs) than SiC matrix. Due to the relatively high TRS, matrix cracks and fiber/matrix (f/m) debonding exist in C_f/SiC-SiBC, which would provide the space for the expansion of matrix with higher CTEs. For SiC_f/SiC, no matrix cracking and f/m debonding took place due to the close CTEs between fiber and matrix. Accordingly, with the incorporation of SiBC matrix, the in-plane CTE of C_f/SiC between room temperature to 1100 °C decreases from 3.65 × 10⁻⁶ to 3.19 × 10⁻⁶ K^-1, while the in-plane CTE of SiC_f/SiC between room temperature to 1100 °C increases slightly from 4.97 × 10⁻⁶ to 5.03 × 10⁻⁶ K^-1.     

Interphase degradation of three‐dimensional Cf/SiC–ZrC–ZrB2 composites fabricated via reactive melt infiltration

Layer‐structured interphase, existing between carbon fiber and ultrahigh‐temperature ceramics (UHTCs) matrix, is an indispensable component for carbon fiber reinforced UHTCs matrix composites (C_f/UHTCs). For C_f/UHTCs fabricated by reactive melt infiltration (RMI), the interphase inevitably suffers degradation due to the interaction with the reactive melt. Here, C_f/SiC–ZrC–ZrB₂ composite was fabricated by reactive infiltration of ZrSi₂ melt into sol‐gel prepared C_f/B₄C–C preform. (PyC–SiC)₂ interphase was deposited on the fiber to investigate the degradation mechanism under ZrSi₂ melt. It was revealed that the degraded interphase exhibited typical features of Zr aggregation and SiC residuals. Moreover, the Zr species diffused across the interphase and formed nanosized ZrC phase inside the fiber. A hybrid mechanisms of chemical reaction and physical melting were proposed to reveal the degradation mechanism according to characterization results and heat conduction calculations. Based on the degradation mechanism, a potential solution to mitigate interphase degradation is also put forward.     

Processing of Cf/SiC composites by hot pressing using polymer binders followed by polymer impregnation and pyrolysis

Continuous carbon fiber (C_f) reinforced silicon carbide (SiC) matrix composite (C_f/SiC) was processed through hot pressing (HP) using polycarbosilane (PCS) in matrix and polysilazane in interphase regions as polymer binders. HP experiments were conducted at 4 MPa, 1200 °C and 1 h; followed by PCS polymer impregnation and pyrolysis (PIP) at 1200 °C under vacuum. The BN/SiC-Si₃N₄ interphase formed on the C_f cloth during BN dispersed polysilazane polymer coating and pyrolysis. The influence of PCS quantity during HP experiments on C_f/SiC composites was studied. Results suggest that sintering of SiC matrix in C_f/SiC composite improves by increasing PCS content during HP; however, high PCS content increases the liquidity of SiC-PCS mixture to flow out of the composite structure. The C_f/SiC composites with relative density ranging from 79 to 83% and flexural strength from 67 to 138 MPa was achieved.     

Achieving high permeability of in-situ formed lightweight Cf/SiC(rGO)px/SiC porous ceramics with improved interfacial compatibility for transpiration cooling

Making lightweight porous ceramics with excellent permeability applied for transpiration cooling is still challenging. Herein, an ingenious fabrication method is proposed to successfully prepare C_f/SiC(rGO)_px/SiC porous ceramics possessing low density, high permeability and satisfactory mechanical properties. The introduction of carbon fibers for constructing channels and SiC(rGO)_p with three-dimensional (3D) honeycomb cellular net-like structure, could effectively decrease density and improve porosity. Meanwhile, self-supporting porous skeleton, high open porosity and uniform pores distribution contribute to brilliant permeability of the products. Good interfacial compatibility among SiC(rGO)_p, carbon fibers and β-SiC/SiOxCy/C_free matrix, as well as toughening effects of carbon fibers are beneficial for enhancing fracture toughness and compressive strength. Particularly, C_f/SiC(rGO)_p0.6/SiC porous ceramics exhibit low density (1.12 g·cm^?3), low linear shrinkage (3.22%), especially high permeability (1.36 ×10^?7 mm²), satisfactory fracture toughness (1.77 MPa·m^1/2), excellent hardness (3.88 GPa) and compressive strength (6.41 MPa), focusing on potential applications as coolant medium in transpiration cooling.     

Tensile creep properties and damage mechanisms of 2D-SiCf/SiC composites reinforced with low-oxygen high-carbon type SiC fiber

Tensile creep properties of 2D-SiC_f/SiC composites reinforced with low-oxygen high-carbon type SiC fibers were studied in vacuum at 1300°C∼1430°C. The fracture morphology was observed by scanning electron microscopy and the damage of fiber in 2D-SiC_f/SiC composites was characterized by nanoindentation. Moreover, the microstructure of the composite was investigated by high-resolution transmission electron microscopy. The results show that rupture time is much shortened and steady-state creep rate increase three orders of magnitude when creep temperature is higher than 1400°C. There are two different creep damage mechanisms due to the decrease of interfacial bonding strength at high temperature. The amorphous SiO_xC_y phase in the fibers can crystallize into SiC and C and the SiC grain grows in the fiber. The microstructural changes lead to the decrease of fiber strength and degrade the creep properties of the composite above 1400°C.     

Architectural engineering inspired method of preparing Cf/ZrC–SiC with graceful mechanical responses

Inspired by grouting technique in architectural engineering, an innovative method of slurry injection and vacuum impregnation was put forward to introduce nanosized ZrC–SiC ceramics into PyC modified 3-D needle-punched carbon fiber preform homogeneously and continuously, followed by spark plasma sintering to prepare C_f/ZrC–SiC with graceful mechanical responses. The composite possessed improved fracture toughness and work of fracture at 5.37 ± 0.25 MPa∙m^1/2 and 951 ± 12 J/m², 50% and nearly one order of magnitude higher than those of ZrC–SiC composite, respectively, with rivaling flexural strength at 177 ± 8 MPa synchronously. A graceful fracture mode was embodied in an obviously extended yield plateau with increased failure displacement by 300%. This enhancement was attributed to the uniform and continuous combination of ZrC–SiC with carbon fiber preform as well as protection and interface tailoring from PyC coating. The study offered an easy and effective method of preparing 3-D fiber reinforced ceramic matrix composites.     

Combustion synthesis of SiC-based ceramics reinforced by discrete carbon fibers with in situ grown SiC nanowires

This study proposes a combustion-based ceramic matrix composite processing technique intended on single-step in situ deposition of single-crystal SiC nanowires (SiC_nw) on the surface of carbon fibers (C_f) and formation of SiC_nw–reinforced SiC matrix. This was accomplished by Ta-catalyzed combustion of poly-(C₂F₄)-containing reactive mixtures with pre-mixed chopped C_f. Depending on the combustion conditions, carbon fiber surface is subjected either to formation of diffusion layers, ceramic particle incrustation or growth of continuous arrays of carbon-coated single-crystal SiC_nw with a nearly defect-free lattice, 10–50 nm diameter and 15–20 μm length. Thermodynamics, phase and structure formation mechanisms are explored, and the optimal conditions are outlined for reproducible C_f/in situ SiC_nw dual reinforcement of SiC-based ceramics. Hot pressing at 1500 °C produced C_f/in situ SiC_nw-reinforced ceramic SiC–TaSi₂ specimens with a relative density of 97%, 19 GPa Vickers hardness, 3-point flexural strength σ = 420 ± 70 MPa and fracture toughness K_1C = 12.5 MPa m^1/2.     

Anisotropic tribological behavior of LSI based 2.5D needle-punched carbon fiber reinforced Cf/C–SiC composites

C_f/C–SiC composites were fabricated via liquid silicon infiltration with 2.5D needle-punched carbon fiber reinforced C_f/C composites. The effect of surface topography and carbon content of the C_f/C–SiC composites on the tribological properties was researched by the ball-on-disk reciprocating tribometer. The results indicate that different fiber layers and cross-section of the composites have various surface topography and show significant differences in the friction and wear properties. By the wear morphology and model analyses, the reason for the tribological anisotropy of the composites is that the distribution of carbon and SiC phases in the composites are inhomogeneous caused by the difference of the carbon fiber orientation and the relative content in each layer. Moreover, the wear rate of the short-cut fiber web layer was the lowest and there is an obvious linear decrease in coefficient of friction with increase of carbon content. The present work explains why the tribological properties of the composites are inconsistent and provides a way to adjust the friction properties of composite materials by optimizing the friction surface.     

Morphology and anti-ablation properties of composites nozzles under the Ф100mm H2O2- polyethylene hybrid rocket motor test

Environmentally friendly commercial applications spurred us to screen a suitable ablative throat material for the hybrid rocket, while preserving its cost-effective advantages as a special chemical motor. In this research, two types of carbon fiber reinforced composites, i.e. carbon/carbon (C/C) composite and C_f/C–SiC–ZrC composite utilized in high temperature environment, were employed to make the hybrid rocket nozzle. By comparison with the high-density graphite, the anti-ablation properties under the firing environment of Ф100mm H₂O₂-polyethylene hybrid rocket motor were characterized. We used whole felt preform to make C/C composite, whose matrix carbon was coming from chemical vapor infiltration of propylene; and the C_f/C–SiC–ZrC composite, which employs the same whole felt preform to make the low-density C/C billet, by infiltrated with Si and Zr organic precursors and pyrolysis at elevated temperatures repeatedly to make the advanced ceramic matrix composite. The firing test lasted 40s for all the candidate materials and the result indicated that the C_f/C–SiC–ZrC composite, whose average linear ablation rate was only 0.003 mm/s, was the most stable one in the firing environment. The SEM images gave detailed morphologies of those nozzle throat materials and proved that the fiber architecture, together with the glassy ceramic oxide, helped the nozzle to withstand the hybrid motor firing environment.     

Synergistic reinforcement effects of ZrB2 on the ultra-high temperature stability of Cf/SiC composite fabricated by liquid silicon infiltration

A carbon fiber-reinforced silicon carbide (C_f/SiC) composite was fabricated with ZrB₂ via the liquid silicon infiltration (LSI) method. A prepreg was prepared by impregnating the phenolic resin with the ZrB₂ powder. The as-LSIed composites were tested for 5 min with an oxyacetylene torch to evaluate their ablation and oxidation properties under an ultra-high temperature environment. The ZrB₂ powders and SiC matrix between carbon fiber bundles generated a dense ZrO₂-SiO₂ layer, which inhibited further oxygen diffusion into the composite and minimized the ablation and oxidation of the carbon fibers. Weight loss and linear ablation rate were further reduced with the addition of ZrB₂ to the C_f/SiC composite; moreover, the synergistic effect of ZrB₂ and SiC reinforced the ablation properties with increased ZrB₂ content. ZrB₂ also reduced the amount of residual silicon, which was detrimental to the mechanical properties of C_f/SiC composite.     

Characterization of partially densified 3D Cf/SiC composites by using mercury intrusion porosimetry and nitrogen sorption

The microstructure of partially densified three-dimensional carbon fiber fabrics reinforced silicon carbide (C_f/SiC) composites are characterized by both mercury intrusion porosimetry (MIP) and isothermal nitrogen sorption (INS). By comparison, MIP is preferable to the characterization for its wide effective probing ranges. Based upon multiple measurements, in the C_f/SiC composite, exists a complicated three-dimensional porous network formed by the interconnecting pores and necks with various sizes, diverse shapes and rough surfaces.     

Dynamic fracture of C/SiC composites under high strain-rate loading: microstructures and mechanisms

We investigate dynamic fracture of C/SiC composites under high strain-rate compression or tension with split Hopkinson pressure bar (SHPB) and gas gun loading. Components of the as-fabricated composites are mapped and quantified with X-ray computed tomography, including C fibers and fiber bundles, SiC matrix, and inter- and intrabundle voids. Compression loading is applied along the out-of- and in-plane directions by SHPB at strain rates of 10²–10³ s⁻¹ along with in situ X-ray phase contrast imaging. Out-of-plane direction compression and tension are examined with gas gun impact at strain rates 10⁴–10⁵ s⁻¹. For the out-of-plane loading, compression induces fracture via void collapse and shear damage banding, while delamination dominates fracture for the in-plane direction compression. With increasing strain rates, the compression failure modes transit from interbundle to intrabundle fracture of SiC, and then to fiber and bundle breaking. Tensile failure involves delamination, fiber pullout and fiber breaking. In contrary to normal solids, dynamic tensile or spall strength decreases with increasing impact velocities, owing to compression-induced predamage before subsequent tensile loading.     

Fabrication of carbon fiber reinforced ceramic matrix composites with improved oxidation resistance using boron as active filler

Boron was introduced into C_f/SiC composites as active filler to shorten the processing time of PIP process and improve the oxidation resistance of composites. When heat-treated at 1800 °C in N₂ for 1 h, the density of composites with boron (C_f/SiC-BN) increased from 1.71 to 1.78 g/cm³, while that of composites without boron (C_f/SiC) decreased from 1.92 to 1.77 g/cm³. So when boron was used, two cycles of polymer impregnation and pyrolysis (PIP) could be reduced. Meanwhile, the oxidation resistance of composites was greatly improved with the incorporation of boron-bearing species. Most carbon fiber reinforcements in C_f/SiC composite were burnt off when they were oxidized at 800 °C for 10 h. By contrast, only a small amount of carbon fibers in C_f/SiC-BN composite were burnt off. Weight losses for C_f/SiC composite and C_f/SiC-BN composite were about 36 and 16 wt%, respectively.     

Morphology and anti-ablation properties of PIP Cf/C–SiC composites with different CVI carbon content under 4.2 MW/m2 heat flux oxy-acetylene test

In this work, the needled carbon fiber preforms were used to make seven groups of carbon/carbon composite billets with different matrix carbon contents by controlling the processing time of chemical vapor infiltration (CVI). C_f/C–SiC composites were prepared by infiltration of SiC into these C/C composites billets using polycarbosilane (PCS) through precursor infiltration and pyrolysis (PIP). After oxy-acetylene torch testing (heat flux of 4.2 MW/m²) for 200s, 300s and 400s, respectively, it revealed that the anti-ablation properties of the C_f/C–SiC composite samples were enhanced by a higher content of SiC matrix. Additionally, specimens bearing longer duration tests showed a trend of lower average ablation rates. The lowest linear ablation rate is 0.008 mm/s and the mass ablation rate is 0.0019 g/s for those high SiC content samples tested for 400s. The SEM images of the tested samples showed the mechanism and the non-linear process of ablation resistance progression.     

Formation of Ti3SiC2 interphase coating on SiCf/SiC composite by electrophoretic deposition

To improve the oxidation resistance of SiC composites at high temperature, the feasibility of using Ti₃SiC₂ coated via electrophoretic deposition (EPD) as a SiC fiber reinforced SiC composite interphase material was studied. Through fiber pullout, Ti₃SiC₂, due to its lamellar structure, has the possibility of improving the fracture toughness of SiC_f/SiC composites. In this study, Ti₃SiC₂ coating was produced by EPD on SiC fiber; using Ti₃SiC₂‐coated SiC fabric, SiC_f/SiC composite was fabricated by hot pressing. Platelet Ti₃SiC₂ powder pulverized into nanoparticles through high‐energy wet ball milling was uniformly coated on the SiC fiber in a direction in which the basal plane of the particles was parallel to the fiber. In a 3‐point bending test of the SiC_f/SiC composite using Ti₃SiC₂‐coated SiC fabric, the SiC_f/SiC composite exhibited brittle fracture behavior, but an abrupt slope change in the strength‐displacement curve was observed during loading due to the Ti₃SiC₂ interphase. On the fracture surface, delamination between each layer of SiC fabric was observed.     

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.     

Mechanical and electromagnetic shielding properties of carbon fiber reinforced silicon carbide matrix composites

Carbon fiber reinforced SiC matrix composites (C_f/SiC) were fabricated through chemical vapor infiltration. Effects of SiC content on the mechanical and electromagnetic properties of the as-prepared materials were studied systematically. The high volume fraction of SiC matrix is beneficial to the transfer of load to carbon fiber. With the increase of SiC content from 21.5 to 42.2 vol.%, the total porosity decreases from 38.5 to 17.8 vol.%, the flexural strength and fracture toughness of C_f/SiC increase from 38 ± 4 to 375 ± 10 MPa and from 6.2 ± 0.7 to 21 ± 0.3 MPa m^1/2. The electromagnetic interference shielding effectiveness of as-prepared C_f/SiC decreases from 43 ± 1.4 to 31 ± 1.1 dB over the frequency range of 8.2–12.4 GHz with the increase of SiC content. The decease of electromagnetic interference shielding effectiveness is mainly attributed to the decline of absorption loss. With the increase of SiC content, the electrical conductivity of C_f/SiC diminishes, leading to the conspicuous drop of the conductive loss, which plays the key role in lowering the absorption loss of electromagnetic waves.     

A novel vibration-assisted slurry impregnation to fabricate Cf/ZrB2-SiC composite with enhanced mechanical properties

The three dimensional needle-punched carbon fiber reinforced ZrB₂-SiC composite (C_f/ZrB₂-SiC) with highly uniform distribution was fabricated successfully via a novel vibration-assisted slurry impregnation and low-temperature (1450 °C) hot pressing technique using nanosized ZrB₂ powders. The carbon fiber/ceramic matrix interfaces were clear without obvious reaction products detected by the high resolution transmission electron microscopy (HR-TEM), indicating the degradation of carbon fiber was effectively inhibited. The C_f/ZrB₂-SiC composite exhibited a typical non-brittle fracture feature with a high work of fracture of 1104 J/m², which was approximately twice that of composite fabricated only by slurry impregnation and hot pressing. The enhancement in work of fracture was attributed to multiple toughening mechanisms of continuous carbon fibers such as extensive fiber bridging and pull-out accompanied by obvious crack deflection and branching. This work provides a valuable potential of preparing continuous carbon fiber reinforced ceramic composites with uniform component distribution and enhanced mechanical properties.