Ablation properties and mechanisms of BN-coated Cf-reinforced SiBCNZr ceramic composites under an oxyacetylene combustion torch

The ablation properties andmechanisms of BN-coated C_f-reinforced SiBCNZr composites under an oxyacetylene combustion torch were investigated. The mass and linear ablation rates of the C_f/SiBCNZr ceramic matrix composites were lower than those of C_f/SiBCN and SiC_f/SiBCN composites, reaching 0.0022 mg/s and 0.0136 mm/s, respectively. The ablation resistance of the SiBCN ceramics was enhanced by the addition of Zr, whereas the BN-coated C_f increased the thermal shock resistance of the SiBCNZr ceramics. No macrocracks were found on the ablation surface of the C_f/SiBCNZr specimen. The ablation mechanisms based on different ablation temperatures, phase evolution during ablation, and ablation morphologies in the different ablation regions consisted of oxidation of the carbon fibre and ceramic matrix, emission of various gases, the flow of high-viscosity SiO₂, and denudation of C_f under the erosion of the ablation flame.     

Preparation,mechanical properties and long-term ablation resistance of Cf/SiBCN–ZrB2 composites

The C_f/SiBCN–ZrB₂ composites were prepared by dipping and winding combined with reactive hot pressing. The flexural strength and fracture toughness reached 261 MPa and 11.96 MPa • m^1/2, respectively, through continuous carbon fibers debonding, pulling and bridging mechanisms. Excellent mechanical properties ensured that the C_f/SiBCN–ZrB₂ composites remained intact after exposure to a plasma flame with a heat flux of 9.37 MW/m² for 300 s, with the mass and linear ablation rates of 1.78 mg/s, 1.01 μm/s, respectively. The excellent ablation resistance was due to the formation of dense oxide layers separating the matrix from the plasma flame. The SiO₂ formed in the low-temperature areas away from the center was the main ablation-resistant barrier, while the ZrO₂/SiO₂ double oxide layer formed in the high-temperature region at the center was the major ablation-resistant barrier.     

Long-term oxidation and ablation behavior of Cf/ZrB2–SiC composites at 1500, 2000, and 2200°C

Although C_f/ZrB₂–SiC composites prepared via direct ink writing combined with low-temperature hot-pressing were shown to exhibit high relative density, high preparation efficiency, and excellent flexural strength and fracture toughness in our previous work, their oxidation and ablation resistance at high and ultrahigh temperatures had not been investigated. In this work, the oxidation and ablation resistance of C_f/ZrB₂–SiC composites were evaluated via static oxidation at high temperature (1500°C) and oxyacetylene ablation at ultrahigh temperatures (2080 and 2270°C), respectively. The thickness of the oxide layer of the C_f/ZrB₂–SiC composites is <40 μm after oxidizing at 1500°C for 1 h. The C_f/ZrB₂–SiC composites exhibit non-ablative properties after oxyacetylene ablation at 2080 and 2270°C for >600 s, with mass ablation rates of 3.77 × 10⁻³ and 5.53 × 10⁻³ mg/(cm² s), and linear ablation rates of −4.5 × 10⁻⁴ and −5.8 × 10⁻⁴ mm/s, respectively. Upon an increase in the ablation temperature from 2080 to 2270°C, the thickness of the total oxide layer increases from 360 to 570 μm, and the carbon fibers remain intact in the unaffected region. Moreover, the oxidation and ablation process of C_f/ZrB₂–SiC at various temperatures was analyzed and discussed.     

Thermal ablation behavior of SiBCN-Zr composites prepared by reactive spark plasma sintering

To meet the ultrahigh temperature requirements of a thermal protection system, an ultrahigh temperature phase of ZrB₂ was introduced into a SiBCN matrix that was fabricated using a reactive spark plasma sintering method. The thermal ablation behavior of SiBCN-Zr composites was investigated using an oxyacetylene flame test. The test results indicated that the ablation behavior of the modified ceramic composites was significantly improved over that of a monolithic SiBCN ceramic. The linear and mass ablation rates of the SiBCN-Zr material were found to be 0.004 mm/s and 4.75×10⁻⁴ g/s, which was indicative of excellent ablation resistance. Analysis of the material after thermal ablation testing showed that ablation products mainly consisted of the ZrSiO₄, SiO₂ and ZrO₂ phases. A reaction occurred between the SiO₂ and ZrO₂ phases in the central region of the ceramic forming ZrSiO₄ that protected the material from further thermal damage. A loose and porous oxidation layer was found from the matrix based on analysis of a cross-section image.     

Effect of Cu on the ablation properties of Cf/ZrC composites fabricated by infiltrating Cf/C preforms with Zr-Cu alloys

C_f/ZrC composites were fabricated by reactive melt infiltration at 1200 °C, Low melting Zr₇Cu₁₀, ZrCu and Zr₂Cu alloys were used as infiltrators and the effect of Cu on ablation properties of the composites was investigated. The results show that the C_f/ZrC composites exhibit excellent anti-ablative properties affected apparently by the Cu contents. With the increase of Cu in infiltrators, the linear recession rates decrease from 0.0019±0.0006 to −0.0006±0.0002 mm s⁻¹, whereas the mass loss rates increase from 0.0006±0.0003 to 0.0047±0.0009 g s⁻¹. The formation of a dense ZrO₂ protective layer and the evaporation of residual Cu are in favor of their ablation resistance.     

Ablation behavior and mechanism of SiCf/Cf/SiBCN ceramic composites with improved thermal shock resistance under oxyacetylene combustion flow

The ablation properties and mechanisms (under oxyacetylene combustion) together with thermal shock behavior of SiC_f/C_f/SiBCN ceramic composites were investigated. The solid ablation products are primarily amorphous SiO₂ and cristobalite. The primary ablation mechanisms include fiber and ceramic matrix oxidation, evaporation of B₂O₃ (l) and SiO₂ (l), and mechanical exfoliation. SiC_f/C_f/SiBCN has a significantly low mass ablation rate and a desirable linear ablation rate. The combination of crack deflection caused by SiC and carbon fibers, fiber pull-out and debonding improves thermal shock resistance and thus leads to the absence of surface macrocracks.     

Self-generating oxidation protective high-temperature glass-ceramic coatings for Cf/C‐SiC‐TiC‐TaC UHTC matrix composites

The ablation/oxidation resistance of a carbon fibre (C_f)/carbon matrix (C)-SiC-TiC-TaC ceramic matrix composite (CMC) produced by melt infiltration of alloy into a C_f/C preform and tested in severely oxidising conditions was quantitatively determined and discussed. An oxyacetylene flame shot of 7.5 s (4 MW/m² nominal heat flux), as well as oxidising conditions imposed by a radiant furnace in air at 1873 K up to 480 s were the selected testing conditions. Detailed post-test microstructure investigations of the oxidised/ablated infiltrated CMC samples, compared to unprotected CMCs tested in nominally identical conditions, enabled to establish an increase in ablation/oxidation resistance of one order of magnitude. The occurrence of a self-generating protective high-temperature glass-ceramic, disclosed by microstructure analyses, played a substantial role for that performance jump during oxidation/ablation. The C_f/C-SiC-TiC-TaC composite herein tested can be a valuable candidate for uses in severe aerospace applications (propulsion and hypersonic flight).     

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 C_f/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 C_f/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 C_f/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.     

Effect of processing parameters on microstructure and ablation behavior of SiC/ZrB2 coating for graphite

In this research, a SiC/ZrB₂ coating was produced on graphite by reactive melt infiltration and plasma spraying method. The coating characterization was performed using XRD analysis, electron microscopy equipped with energy dispersive spectrometer (EDS), and supersonic flame ablation test at 2073 K. The results indicated that the dense C/SiC coating with good ablation resistance can be obtained at 1873 K. The coating thickness decreased with increasing infiltration temperature. The results of ablation test showed that by increasing the infiltration temperature and holding time, weight loss and mass ablation rate decreased from 22.63% to 9.83% and 3.63 × 10⁻³ g cm⁻² s⁻¹ to 1.34 × 10⁻³ g cm⁻² s⁻¹, respectively. The results showed that by using the ZrB₂ as outer coating the ablation resistance improved remarkably. The weight loss and mass ablation rates for the SiC/ZrB₂ coating were 12.79% and 1.857 × 10⁻³ g cm⁻² s⁻¹, respectively.     

Oxidation/ablation behaviors of hafnium carbide-silicon carbonitride systems at 1500 and 2500 C

The oxide scales of hafnium carbide (HfC) typically exhibit a porous structure after oxidation/ablation due to the release of gas oxidation products, which allows oxygen penetration to promote the rapid oxidation of the HfC matrices. Here, we report that the oxidation/ablation resistance of HfC was enhanced by the incorporation of amorphous silicon carbonitride (SiCN). HfC-SiCN ceramics with 10 vol % SiCN showed a significant improvement in the oxidation/ablation resistance compared with pure HfC. The HfC-10 vol % SiCN ceramic has a higher density with good mechanical properties. After being oxidized at 1500 °C for 2 h, a dense and homogeneous HfO₂-HfSiO₄ layer with low oxygen permeability is formed. The ablation resistance of the HfC-10 vol % SiCN ceramic is improved due to the formation of the triple-layer structure oxide with good thermal stability and mechanical scouring resistance. After ablation under an oxyacetylene flame for 60 s, the mass and linear ablation rates of HfC-10 vol % SiCN ceramic are −0.019 mg cm⁻² s⁻¹ and -0.156 μm s⁻¹, respectively.     

Effect of ZrC amount and distribution on the thermomechanical properties of Cf/SiC-ZrC composites

C_f/SiC-ZrC composites with different amounts and distributions of ZrC were fabricated by polymer impregnation and pyrolysis. The effects of the ZrC amount and distribution on the microstructural, mechanical, and ablation properties of C_f/SiC-ZrC composites were investigated. C_f/SiC-ZrC composites obtained by the alternating infiltration of ZrC organic precursors and polycarbosilane groups exhibit good tensile strength (240 ± 17.7 MPa) because the ZrC and SiC matrix can mix evenly. However, C_f/SiC-ZrC composites using only ZrC organic precursor infiltration show a low tensile strength (191 ± 16.6 MPa) because more defects can be introduced into the composites. Ablation characterization by a 30 kW plasma wind tunnel for 60 seconds showed that the C_f/SiC-ZrC composites with the highest amount of ZrC matrix (67.8 wt.%) possessed the lowest linear erosion rate of 4 μm/s because liquid SiO₂ could fill the porous ZrO₂ to form a homogenous protective layer. Nevertheless, the C_f/SiC-ZrC composites with a relatively high ZrC amount (55.3 wt.%) exhibited a poorer ablation performance compared to that of C_f/SiC-ZrC composites with a low ZrC amount (38.7 wt.%).     

SiBCN ceramic aerogel/graphene composites prepared via sol-gel infiltration process and polymer-derived ceramics (PDCs) route

The SiBCN ceramic aerogel/graphene composites were synthesized by combining a simple sol-gel infiltration process with CO₂ supercritical drying technology and polymer-derived ceramics route. In order to select the best preceramic sample for sintering, the micromorphology of PSNB aerogel/graphene composites fabricated with different graphene oxide solution concentrations were investigated. The microstructure evolution of the prepared SiBCN ceramic aerogel/graphene composites and phase composition were studied by SEM, TEM and XRD, the pore structure of the preceramic composites pyrolyzed at 1200 °C was tested by specific surface area and pore size analyzer. Furthermore, the compressive strain-stress curve and toughening mechanisms of composites were also investigated in detail. The results showed that all the preceramic composites and obtained ceramic aerogel composites possessed the mesoporous structure. The basic structure of SiBCN aerogel network changed from the initial spherical particles accumulation to the nanowires lapping with the sintering temperature increased from 800 °C to 1200 °C. After pyrolyzing at 1200 °C, the specific surface area and pore volume for the sample were 101.61 m² g⁻¹ and 1.43 cm³ g⁻¹, respectively, and a small amount of β-SiC crystalline phases were formed in amorphous ceramic matrix and had an relatively uniform distribution. Moreover, the paepared ceramic aerogel composites possessed a certain degree of toughness, the toughening mechanisms of composite samples mainly included the crack deflection, graphene pull-out, graphene bridging and graphene crumpling.     

Long-term oxidation behaviors and strength retention properties of self-healing SiCf/SiC-SiBCN composites

The self-healing SiC_f/SiC-SiBCN composites with various boron contents in SiBCN were prepared, and their long-term oxidation behaviors and strength retention properties were investigated. The 100 h oxidation at 1200–1350 °C leads to parabolic mass gain of the obtained composites. With the oxidation temperature increased from 1200 °C to 1350 °C, the oxidation rate constants increase from 5.91 × 10^?8 mg²/(mm⁴ h) to 9.31 × 10^?7 mg²/(mm⁴ h) for the boron-lean (3.14%) composites, and from 2.57 × 10^?7 mg²/(mm⁴ h) to 6.04 × 10^?7 mg²/(mm⁴ h) for the boron-rich (7.18 wt%) composites. Correspondingly, the oxidation activation energy decreases from 363 kJ/mol to 112 kJ/mol due to the low initial oxidation temperature of boron-rich SiBCN. All the composites exhibit the higher strength retention rates after 1350 °C oxidation due to the enhanced self-healing performance. The boron-rich composites show a high strength retention rate of up to 104% due to the good self-healing capacity of the boron-rich SiBCN as well as the high CVI-SiC content.     

High-temperature oxidation behavior and oxidation mechanism of C/SiBCN composites in static air

On account of the excellent oxidation resistance of precursor-derived SiBCN ceramics, carbon-fiber-reinforced SiBCN (C/SiBCN) composites are increasingly being used in high-temperature aerospace applications. However, very few studies have investigated the high-temperature oxidation behavior of C/SiBCN composites for their application to high-heat engines. Herein, C/SiBCN composites prepared by precursor infiltration and pyrolysis were tested in static air up to an oxidation temperature of 1700 °C. The composites’ structural evolution after oxidation and their potential oxidation mechanisms were investigated in detail. The carbon fibers were preferentially oxidized at temperatures in the range of 1200–1500 °C and completely oxidized at 1500 °C. The oxidation of the fibers at 1500 °C resulted in the formation of abundant oxygen channels and consequently a high oxide scale growth rate of 5–7 μm² h⁻¹ and a large mass loss of 54.6 wt%. At elevated temperatures in the range of 1600–1700 °C, a dense SiO₂ oxide layer was formed by the sacrificial oxidation of the SiBCN matrix. The oxidation rate of the composites was therefore controlled by the diffusion rate of oxygen through the protective SiO₂ oxide layer and the weight loss of the composites decreased to 28.6% after oxidation at 1600 °C for 60 min. The structural integrity of the composites was maintained after long-term oxidation at 1600 °C.     

Improved electrical and thermal properties of silicon oxycarbide/spodumene composites

Novel bulk SiOC/spodumene composites have been developed by spark plasma sintering (SPS) at relatively low temperature (1200–1400 °C). Spodumene is a cheap and natural available lithium aluminosilicate mineral which acts as meltable/active filler. At 1300–1400 °C, the Al migrates toward the glassy matrix producing a Si-Al-O network and the crystallization of α-cristobalite. The C_free phase also experiences a deep transformation. The epitaxial growth of few-layered graphene over SiC particles occurs at 1400 °C. An increase in the phonon transport is observed (36%, 1.28 – 2.14 Wm⁻¹K⁻¹) associated to the reduction of the interface resistance between the partially crystallized SiO₂ matrix and the SiC nano-wires/graphene-like carbon conductive phase. The electrical conductivity increases (1.14 ×10⁻² – 8.1 Sm⁻¹) due to the densification reached and an increasing ordering degree of the tortuous C_free phase with a high quality of interconnection and crystallization. Raman parameters are determinant to understand the thermal and electrical response.     

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.     

Effect of interphase on mechanical properties and microstructures of 3D Cf/SiBCN composites at elevated temperatures

Interphase between the fibers and matrix plays a key role on the properties of fiber reinforced composites. In this work, the effect of interphase on mechanical properties and microstructures of 3D C_f/SiBCN composites at elevated temperatures was investigated. When PyC interphase is used, flexural strength and elastic modulus of the C_f/SiBCN composites decrease seriously at 1600°C (92 ± 15 MPa, 12 ± 2 GPa), compared with the properties at room temperature (371 ± 31 MPa, 31 ± 2 GPa). While, the flexural strength and elastic modulus of C_f/SiBCN composites with PyC/SiC multilayered interphase at 1600°C are as high as 330 ± 7 MPa and 30 ± 2 GPa, respectively, which are 97% and 73% of the values at room temperature (341 ± 20 MPa, 41 ± 2 GPa). To clarify the effect mechanism of the interphase on mechanical properties of the C_f/SiBCN composites at elevated temperature, interfacial bonding strength (IFBS) and microstructures of the composites were investigated in detail. It reveals that the PyC/SiC multilayered interphase can retard the SiBCN matrix degradation at elevated temperature, leading to the high strength retention of the composites at 1600°C.     

Polymer-metal slurry reactive melt infiltration: A flexible and controllable ceramic modification strategy for irregular C/C components

Herein, we investigate the applicability of the polycarbosilane (PCS)–metal slurry reactive melt infiltration (RMI) process to various metals. The slurry exhibiting the best ceramized ability was used to examine the relationship between the ceramic thickness and reactive time, ceramic thickness and reactive temperature, and infiltration depth and slurry-coating thickness. The results show that the thickness of the ceramic layer increases with reactive time and temperature and the infiltration depth increases with the coating thickness. PCS–Si₉₀Zr₁₀ slurry RMI was selected to modify cylindrical nozzle C/C preforms, and dense C/C–SiC–ZrC composites with a density of ~2.05 g cm⁻³ were obtained. Owing to the good control of the PCS–Si₉₀Zr₁₀ slurry RMI on the interface, matrix, and carbon fiber of the as-received cylindrical composites, the bending strength of the C/C–SiC–ZrC composites was as high as 306.4 MPa, which is considerably higher than that of a C/C preforms (70.4 MPa). Considering the ablation resistance, the mass and linear ablation rates of the C/C–SiC–ZrC composite (~0.29 mg s⁻¹ and ~2.48 × 10⁻³ mm s⁻¹, respectively) were similar to those of the composites prepared using traditional RMI (~0.23 mg s⁻¹ and ~2.29 × 10⁻³ mm s⁻¹). The proposed polymer–metal RMI is more suitable for the modification of C/C preforms with thin-wall structures owing to its advantages including precise control of infiltration dose and flexible operation of slurry coating. Furthermore, it is suitable for the local modification of C/C components.     

Mechanical properties and microstructure evolution of 3D Cf/SiBCN composites at elevated temperatures

3D C_f/SiBCN composites were fabricated by an efficient polymer impregnation and pyrolysis (PIP) method using liquid poly(methylvinyl)borosilazanes as precursor. Mechanical properties and microstructure evolution of the prepared 3D C_f/SiBCN composites at elevated temperatures in the range of 1500‐1700°C were investigated. As temperature increased from room temperature (371 ± 31 MPa, 31 ± 2 GPa) to 1500°C (316 ± 29 MPa, 27 ± 3 GPa), strength and elastic modulus of the composite decreased slightly, which degraded seriously as temperature further increased to 1600°C (92 ± 15 MPa, 12 ± 2 GPa) and 1700°C (84 ± 12 MPa, 11 ± 2GPa). To clarify the conversion of failure mechanisms, interfacial shear strength (IFSS) and microstructure evolution of the 3D C_f/SiBCN composites at different temperatures were investigated in detail. It reveals that the declines of the strength and changes of the IFSS of the composites are strongly related to the defects and SiC nano‐crystals formed in the composites at elevated temperatures.     

Ablation behavior of Cf/ZrC-SiC-based composites fabricated by an improved reactive melt infiltration

In this work, a highly dense C_f/ZrC-SiC-based composite is fabricated by an improved reactive melt infiltration (RMI). The ablation resistance of the composite is studied by air plasma test. The RMI-C_f/ZrC-SiC possesses a low porosity (3.49%) and high thermal conductivity. The dense microstructure can effectively retard oxygen from diffusing into the interior composite. Meanwhile, the high thermal conductivity makes the composite transfer heat timely during ablation, which reduces the heat accumulation on the ablation surface and weakens the thermal damage to the composite. Consequently, the as-fabricated composite exhibits an excellent ablation resistance. Compared to conventional PIP-C_f/ZrC-SiC composite, the linear and mass recession rates of the RMI-C_f/ZrC-SiC decline by 98.07% and 39.02% at a heat flux of 4.02 MW/m². Also, a continuous SiO₂-ZrO₂ layer forms on the sample surface, which isolates the sample surface from the plasma flame and protect the composites from further oxidation and ablation.