Polymer Infiltration And Pyrolysis Research Articles

Effect of polymer infiltration and pyrolysis (PIP) on microstructure and properties of high volume fraction SiC/Al composites prepared by a novel hybrid additive manufacturing

High-volume-fraction SiC/Al (HVF-SiC/Al) composites have a wide range of applications in aerospace, optics, automotive and electronic packaging. However, because the hardness, brittleness and wear resistance increase with the increase in the volume fraction, it is difficult for traditional methods such as machining, to process HVF-SiC/Al composites to complex components. Therefore, in this paper, a novel method of the hybrid additive manufacturing is proposed to fabricate complex-structures SiC/Al composite parts. The effect of polymer infiltration and pyrolysis (PIP) on microstructure and properties of HVF-SiC/Al composites is investigated. The results show that the mechanical properties of the SiC preforms can be effctively enhanced by the PIP process, and this enhancement makes the SiC preforms meet the conditions for subsequent vacuum-pressure infiltration. The mechanical property of HVF-SiC/Al composites show a huge increase when in creasing the volume fraction of SiC. In particular, the flexural strength of HVF-SiC/Al composites increased from 202.28 MPa to 380.87 MPa, and the coefficient of thermal expansion (CTE) has also been reduced from 11.80 to 6.28 × 10−6/K, when the volume fraction of SiC increases from 42 to 80 vol%. For optimise the PIP process in the future, three theoretical models are used to predict the relationship between the CTE and the volume fraction of SiC. The results show that the experimental data are more consistent with the predicted values based on the Kerner's model, but deviate from the Rule-of-mixture (ROM) and Turner's models. Importantly, the complex-structures SiC/Al composite parts was successfully fabricated by this hybrid additive manufacturing.

Design and preparation of sandwich structured Si3N4 ceramics for broadband microwave transmission

To develop high-temperature structural materials with broadband microwave transmission ability used for high-speed aircraft radome, a sandwich-structured silicon nitride (Si3N4) ceramic consisting of porous core and dense shell is designed based on CST simulation, which helps to obtain the optimized structural and dielectric properties. After that, its near-net-shape preparation strategy is presented by a controllable combined process including gel-casting (GC), polymer infiltration and pyrolysis (PIP), and chemical vapor deposition (CVD). The mechanical and electromagnetic performances were studied. The results show that the optimally-structured sandwich Si3N4 processes a flexural strength of 216.5 MPa and a microwave transmissivity of 80 % in 2–13.4 GHz, which are obviously higher than that of traditional Si3N4 ceramics. Besides, this sandwich-structured Si3N4 ceramics also shows excellent dielectric and mechanical stabilities after a high-temperature oxidization at 1600 °C for 2 h in air atmosphere. Our prepared Si3N4 ceramics achieves excellent mechanical strength, high microwave transmissivity, and good high temperature stability, indicating a great application potential as high-speed aircraft radome materials.

Ultrathin carbon layer coated MXene/PBO nanofiber films for excellent electromagnetic interference shielding and thermal stability

In this study, a carbon layer coated MXene/poly(p-phenylene-2,6-benzobisoxazole) nanofibers (PNFs) (MXene/PNF@C) EMI shielding composite film was obtained through polymer infiltration and pyrolysis (PIP) technique. The introduction of the carbon layer improved both the electrical and thermal conductive pathways of the film leading to the enhancement of its electrical conductivity(σ), thermal conductivity coefficient (λ) and EMI shielding effectiveness (SE). Meanwhile, thermal annealing reduced the defects of PBO molecular chains and improved the mechanical properties of the composite film. When the content of MXene is 50 wt% and the thickness of the film is only 37 μm, MP50@C-400 composite film has the best comprehensive properties, with the σ, λ, specific EMI SE (SEt) and tensile strength is 1760 S/m, 5.64 W/(m·K), 1108.1 dB/mm and 66.8 MPa, respectively, and its weight loss is only 24.1% at 800°C. The composite film provides important application prospects in 5G communication technology, wearable equipment and artificial intelligence.

Frequency Characteristics of High Strain Rate Compressions of Cf-MWCNTs/SiC Composites

The incorporation of ductile reinforcements into ceramics helps restrain crack deflection, which can enhance ceramics’ toughness and overcome the matrix’s brittleness. In this paper, we produced a ceramic composite reinforced by carbon fibers coated by multi-wall carbon nanotubes (shortened by Cf-MWCNT/SiC composites) for enhanced impact resistance at a high strain rate that commonly occurs in composite materials used in astronautics, marine, and other engineering fields. The fabrication process involves growing multi-wall carbon nanotubes (MWCNTs) on a carbon fiber woven fabric (Cf) to create the fibril/fabric hybrid reinforcement. It is then impregnated by polymer solution (precursor of the ceramics), forming composites after the pyrolysis process, known as the liquid polymer infiltration and pyrolysis (PIP) technique. To assess the impact resistance of the Cf-MWCNT/SiC under high-strain rate compressions, the split Hopkinson pressure bar (SHPB) technique is employed. Since the failure behavior of the Cf-MWCNT/SiC composites in the absence of the ductile phase is not well understood, the study employs the Hilbert–Huang transform (HHT) to analyze the stress–time curves obtained from the SHPB experiments. By applying the HHT, we obtained the frequency–time spectrum and the marginal Hilbert spectrum of the stress signals. These analyses reveal the frequency characteristics of the Cf-MWCNT/SiC composite and provide insights into the relationship between transformed signal frequency and fracture behavior. By understanding the dynamic fracture behavior and frequency response of the Cf-MWCNT/SiC, it becomes possible to enhance its impact resistance and tailor its performance for specific protective requirements. Therefore, the findings of this study can guide the future design and optimization of Cf-MWCNT/SiC structures for various protective applications, such as body armor, civil structures, and protections for vehicles and aircraft.

Residual stress and interface debonding behavior in Si3N4w reinforced SiCN composites prepared by the PIP process: A case study

Polymer infiltration and pyrolysis (PIP), as a preparation route for ceramic matrix composites, employs the polymer-to-ceramic transformation inside the preforms to gradually buildup the matrix. The effects of the structural transformation on the residual stress and on the interface debonding behavior of PIP derived Si3N4 whisker reinforced SiCN (Si3N4w/SiCN) composites are analyzed. Accordingly, the Si3N4w whisker in the composites are under residual compressive stress after the formation of the polymer-derived ceramic matrix. An increase in the pyrolysis heating rate from 1 to 10 ℃/min effectively lowers the residual stress from 195.8 to 91.3 MPa. Interface fracture energies of Si3N4w/SiCN derived from the debonding behavior significantly rise from <11.91 to 21.82 J/m2 with the annealing temperature from 900 to 1400 ℃. The residual stress and interfacial behavior are related to the in-situ densification/shrinkage and structural rearrangement during pyrolysis and annealing.

Preparation and long-term ablation behavior of Cf-reinforced ZrC-SiC coated C/C-ZrC-SiC composite

To improve the long-term ablation resistance of the C/C composite, the Cf-reinforced ZrC-SiC coated C/C-ZrC-SiC composite is fabricated by thermal gradient chemical vapor infiltration (TGCVI) technology and the subsequent polymer infiltration and pyrolysis (PIP) process. The coating shares the same carbon fiber felt with the matrix, which can strengthen the bond between the coating and the matrix. Results show that the composite has excellent long-term anti-ablation performance (the linear ablation rate of the composite is −0.64 µm/s after ablated for 120 s (3 × 40 s), and the coating can withstand ablation for 160 s (4 × 40 s) without destruction). With the reinforcement of carbon fibers, the coating is peeled layer by layer rather than destructed in the whole coating, and the coating still works in the subsequent ablation cycles (the linear ablation rate of the composite is 2.40 µm/s after ablated for 280 s (7 × 40 s)).

Ablation behavior of C/C-ZrC-SiC composite with gradient distribution of ZrC-SiC ceramics along the thickness

A novel C/C-ZrC-SiC gradient composite (GGC/C-ZS) is prepared via thermal gradient chemical vapor infiltration (TGCVI) technology combined with polymer infiltration and pyrolysis (PIP). And ablation tests are carried out to evaluate the thermal shock and ablation resistance. Results show that the GGC/C-ZS exhibits excellent anti-ablation performance (linear ablation rate is −2.12 μm/s) after ablation for 2 × 40 s (under 2500 °C). The high ZrC-SiC content in the surface region of GGC/C-ZS ensures a dense ZrO2 scale of the ablation center and helps withstand the high thermal stress induced by the ablation. During the ablation, the compact ZrO2 scale can block heat transfer from the surface to the matrix of GGC/C-ZS because of its low thermal conductivity, which can relieve the thermal etching and the massive loss of SiO2 beneath the ZrO2 scale. Besides, the gradient structure can also reduce heat mismatch between the ZrC-SiC ceramics and the C/C matrix, which can avoid the peeling off of the ZrO2 scale after a second ablation process.

Effect of SiC on the anti-ablation resistance and flexural strength of (Hf-Ta-Zr)C-C/C composites

Recently, much attention has been drawn to the development of high temperature resistance of carbon-based composites due to their increasing demand in various applications. Herein, (Hf-Ta-Zr)C single-phase solid solution and SiC ceramic were incorporated into C/C by polymer infiltration and pyrolysis (PIP), forming (Hf-Ta-Zr)C-SiC-C/C composites. The findings reveal that the high yield of polycarbosilane facilitate enhanced compactness and interfacial debonding between the solid solution ceramic and the matrix. Notably, the composites with a mass ratio of (Hf-Ta-Zr)C: SiC= 3:1 exhibit a pseudo-plastic fracture model with flexural strength of 280.71 ± 7.52 MPa and modulus of 38.92 ± 3.62 GPa. Furthermore, the mass and linear ablation rates with only 0.328 mg/s and − 0.067 µm/s, respectively, are attributed to the sufficient healing defects such as cracks and pores within the inner layer by SiO2, along with enhanced adhesion of the Hf-Ta-Zr-O layer. This research contributes to the development of a rational design strategy for fabricating thermal structure components intended for ultra-high temperature environments.

In situ growth of SiC wires on CVI densification of SiC foam

AbstractSilicon carbide (SiC) foam prepared by polymer infiltration and pyrolysis (PIP) process was further densified with β‐SiC by chemical vapor infiltration (CVI) technique. Scanning electron microscopy and high‐resolution transmission electron microscopy images confirmed the presence of highly entangled and branched in situ grown SiC wires of uniform diameter (∼500 nm) over the struts of open‐cell SiC foam. A uniform rate increase in diameter from nanometer to micron range (∼11 μm) was observed with an increase in the CVI reaction period. X‐ray diffraction results showed the formation of highly crystalline β‐SiC structure along the &lt;111&gt; direction with stacking faults. The formation of SiC wires was explained by the vapor–liquid–solid mechanism and evenness of the surface and uniform growth rate of SiC confirmed the homogeneous concentration of gaseous species during CVI reaction. The compressive strength increased with relative density, with maximum values of 5.5 ± 1.26 MPa for ultimate SiC foam (ρ = 400 kg/m3) prepared by hybrid PIP/CVI technique. The thermo‐oxidative stability of the resultant foam was evaluated up to 1650°C under air and shows excellent thermal stability compared to SiC foam prepared by PIP route. The densified SiC foam can find potential applications in the field of hot gas filters, catalyst supports, microwave absorption properties, and heat insulation for high‐temperature applications.

Fracture characteristics and in-situ damage mechanism of PIP-C/SiC composites to various temperatures and loading velocities

C/SiC composites prepared by polymer infiltration and pyrolysis (PIP) are among the most promising materials for application in ultrahigh-temperature conditions. However, the mechanical properties and damage mechanisms of PIP-C/SiC composites at different loading velocities and temperatures have not been systematically studied. In this study, in-plane compression, bending, and in-plane shear experiments were systematically performed at different loading velocities and temperatures in an inert atmosphere. The ultimate strengths of the PIP-C/SiC composite were determined under different conditions, and the failure modes were revealed. In addition, in-situ X-ray microtomography tension experiments were conducted to study the failure mechanism of the PIP-C/SiC composite. The results showed that the ultimate strengths were considerably affected by the temperature and loading velocity, and the failure modes were dependent on experimental types. The fracture location of the PIP-C/SiC composite is affected by the defect. And the direction of crack propagation is toward the existing cracks and voids.

High performance SiC/SiOC composites with in situ carbon interface

A novel SiC/SiOC composite was prepared via the polymer infiltration and pyrolysis (PIP) process by using a low-cost poly-methyl-silsesquioxane resin as matrix precursor and continuous thin SiC fibers as reinforcements. A carbon coating is in situ formed on SiC fiber prior to the composite processing. The high yield of the resin resulted in a short period of the composites achieving densification. The composites exhibited pseudoplastic fracture with a high flexural strength of 315.10 MPa and a fracture toughness of 21.6 MPa m1/2. With the help of the in situ coating, the SiC fibers pulled out of the matrix independently, leading to optimization of the reinforcing effect and enhancement of the composite strength compared to chemical vapor deposition (CVD) fiber coatings. After annealing in N2 at 1000 °C for 10 h, the strength retention rate of the composites is 92.21%, showing excellent stability to be used in thermal structural components.

Structural evolution and properties of SiC/SiBCN composites at elevated temperatures

The SiC/SiBCN composites were prepared via polymer infiltration and pyrolysis (PIP) technique. The structural composition and property evolution behavior of the composites under inert high-temperature environment were investigated to reveal the failure mechanism of the composites. With the increase of the heat treatment temperature from 1500 °C to 1600 °C, the composite properties underwent a sharp decline. Among them, the weight loss rate gradually increased from 3% to 9% and the density decreased from 2.4 g/cm3 to 2.3 g/cm3. Especially, the room temperature flexural strength decreased from 267 ± 7 MPa to 179 ± 3 MPa and the strength retention were 46%. The degradation of SiC fiber properties is the main factor for the decrease in flexural strength of the composites at below 1500 °C. When heat treatment temperature above 1600 °C, the mechanical properties of SiC fiber dramatically decline, and the SiBCN ceramic matrix initially precipitated Si3N4 crystalline phase leading to a carbothermal reduction reaction. Hence, the mechanical properties of the composite at T > 1600 °C deteriorate sharply under the influences of the above two negative factors.

Three-dimensional characterization of the pore structures in SiC formed by binder jet 3D printing, polymer infiltration and pyrolysis (PIP)

Processing of binder jet printed refractory ceramics, including SiC, to high density remains a major challenge in additive manufacturing. Polymer Infiltration and Pyrolysis (PIP) has been applied to SiC made with large particle sizes and low sinterability, but the PIPed material struggles to reach high density even after many infiltration cycles. In this work, binder jetted α-SiC powders were PIPed up to 8 cycles and characterized after each cycle. By comparison with an exclude volume model, the infiltrated density showed a plateauing after 8 cycles. X-ray micro-computer tomography (μCT) was used to characterize the microstructure evolution in 3D. The reconstructed cross-sectional image indicated that large cracks, attributed to gas pressure build-up in burn-out, were formed as the number of infiltration cycles increased. Additionally, quantitative 3D data extracted from μCT images showed a large pore network existed in the interior of all samples and remained mostly open, even after 8 PIP cycles.

Simultaneous enhancement of mechanical and ablation properties of C/C composites modified by (Hf-Ta-Zr)C solid solution ceramics

In order to improve the mechanical and ablative resistance of C/C composites, (Hf-Ta-Zr)C single-phase solid solution ceramics were introduced into C/C composites by polymer infiltration and pyrolysis (PIP) to fabricate (Hf-Ta-Zr)C modified C/C composites (HTZ). Their mechanical property and ablation resistance were studied. The results showed that HTZ achieved simultaneous enhancement of mechanical property and ablative resistance. Their flexural strength and modulus could reach 219.34 MPa and 24.82 GPa, respectively. In addition, the mass and linear ablation rate of HTZ were 0.379 mg/s and 0.667 µm/s, respectively after the 90 s oxyacetylene ablation. A dense Hf-Ta-Zr-O multiphase oxide layer was formed on the surface of the HTZ during ablation process, which protected the interior modified C/C composites from ablation. Our work expands a rational design of modified C/C composites and broaden the application of solid solution ceramic in the field of ultra-high temperature ablation resistance for carbon or ceramic-based composites.

Preparation and properties of Ti3SiC2 preform reinforced SiC ceramic matrix composites

Ti3SiC2 preform reinforced SiC ceramic matrix composites (Ti3SiC2/SiC) were successfully fabricated through a novel near-net-shape process strategy combining molten salt synthesis with subsequent polymer infiltration and pyrolysis (PIP) for the first time. The effects of temperature and molten salt ratio on the phase composition, pore structure, and flexural strength of Ti3SiC2 preform were investigated in detail. The morphology and microstructure evolution of the composites during the PIP process were observed by SEM and TEM. The mechanical properties, electromagnetic interference shielding effectiveness (EMI SE) and thermal conductivity of Ti3SiC2/SiC were significantly improved compared to PDC-SiC, which benefits from the connected network skeleton of Ti3SiC2 preform. The flexural strength and fracture toughness of Ti3SiC2/SiC are 198.7 MPa and 4.5 MPa∙m1/2. The EMI SE remains above 30 dB covering the entire X-band and its average value is 46.92 dB. The thermal conductivity is 6–7 W/(m·k) (25–1000 °C).

Polymer infiltration and pyrolysis cycling for creating dense, conductive laser-induced graphene

Here we show that dense laser-induced graphene (LIG) structures can be synthesized using polymer infiltration and pyrolysis (PIP) cycles, providing a new avenue to polymer-derived carbon structures. LIG is a 3D porous graphene generated through the rapid process of laser writing on a precursor material, in contrast to conventional graphite-to-graphene processes; LIG properties are influenced by the choice of precursor material and the laser parameters such as speed and laser power. PIP has been used to densify composites by back-filling a porous matrix with a liquid Resorcinol Formaldehyde (Res-For) and then pyrolyzing the Res-For to a solid carbon structure. In this study, resorcinol formaldehyde is used as the LIG precursor material; by backfilling the LIG matrix with additional Res-For and lasing again, we demonstrate that the density, conductivity, and mechanical hardness are all increased via a PIP cycling process.

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

The chopped carbon fiber reinforced SiC (Cf/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 Cf/SiC composites with high strength and low shrinkage. Five types of PDCs printing inks with different Cf 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 Cf/SiC composites were fabricated with different Cf contents. The results found that the Cf/SiC composite with 30 wt% Cf content has high bending strength (∼ 7.09 MPa) and negligible linear shrinkage (∼ 0.48%). After the PIP process, the defects on the Cf/SiC composite structures were sufficiently filled, and the bending strength of Cf/SiC composite can reach up to about 100 MPa, which was about 30 times greater than that of the pure SiC matrix without Cf. This work demonstrated that the printed Cf/SiC composites by using this method is beneficial to the development of the precision and complex high-temperature structural members.

Preparation of self-healing Cf/SiBCN(O) composite using a novel polyborosilazane

In this study, novel polyborosilazane-derived SiBCN(O) ceramic was used as self-healing component in self-healing Cf/SiBCN(O) composite, which was prepared by polymer infiltration and pyrolysis (PIP) process. Molecular-level structure design of boron-containing ceramic precursors was utilized to achieve uniform dispersion of boron-containing self-healing components in prepared composites. No elemental diffusion was observed at the interface of ceramic matrix and carbon fibers, which resulted in stable SiBCN(O) structure. In addition, boron was uniformly distributed in Cf/SiBCN(O) composite ceramic matrix, which was beneficial for self-healing of cracks. Cracks and indentations were able to heal at high temperatures in air. The best crack-healing behavior occurred in air atmosphere at 1000 °C, with nearly complete crack healing. This excellent self-healing behavior was achieved because silicon and boron atoms in SiBCN(O) ceramic reacted with available oxygen at high temperatures to form SiO2(l), B2O3(l), and B2O3·xSiO2 liquid phases, which effectively filled cracks. In general, as-prepared Cf/SiBCN(O) composite exhibited excellent self-healing properties and shows great application potential in high-temperature environment applications such as aviation, aerospace, and nuclear power.

C/C–SiC composites derived from single‐source poly(silylene–acetylene) precursors

AbstractCarbon‐fiber‐reinforced carbon–silicon carbide (C/C–SiC) composites were prepared by impregnating carbon fibers with ethynylphenyl‐terminated poly(silylene–acetylene) (EPTSA) as a single‐source precursor with subsequent hot pressing and pyrolysis. The structural evolution, crystallization behavior, and graphitization of bulk C–SiC ceramics, as well as their mechanical properties and ablation behavior, were investigated. The EPTSA precursor starts to transform into inorganic SiC ceramic materials at 800°C, which is characterized by an amorphous structure with weight loss, shrinkage, and densification between 800 and 1000°C. The formation of SiC crystals inhibited the growth of the graphitic structure between 1000 and 1200°C. As the temperature was raised, both graphite and SiC crystals continued to grow, and the crystalline forms became more complete. The carbon‐fiber cloth (T300CF)‐reinforced C–SiC composite (T300CF/C–SiC) prepared using polymer infiltration and pyrolysis (PIP) exhibited excellent mechanical properties. After five PIP cycles, the flexural strength, flexural modulus, and interlaminar shear strength of the T300CF/C–SiC composite reached 169 MPa, 32.5 GPa, and 9.38 MPa, respectively. In addition, the chopped‐carbon‐fiber‐reinforced C–SiC composite fabricated using the PIP process demonstrated good oxyacetylene‐torch ablation properties.

Fatigue behavior and damage analysis of PIP C/SiC composite

In this work, we study the fatigue behavior of a C/SiC composite produced by several cycles of polymer infiltration and pyrolysis (PIP). Fatigue tests were performed with maximum stresses corresponding to 60–90% of the tensile strength of the composite. During the fatigue tests, acoustic emission (AE) monitoring was performed and the measured AE energy was utilized to quantify the damage and distinguish possible damage mechanisms. Most of the fatigue damage in the form of matrix cracking, interface damage and fiber breakage occurs in the first cycle. As loading cycles proceeded, damage in form of matrix crack re-opening and interfacial friction constantly accumulates. Nevertheless, all samples survived the run-out of 1,000,000 cycles. After the fatigue tests, an increase of the tensile strength is observed. This phenomenon is associated with the relief of process-induced internal thermal stresses and the weakening of the fiber-matrix interface. In general, the studied material shows very high relative fatigue limit of 90% of its tensile strength.