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SiBCN and BN/SiBCN light-leakage-proof coatings were prepared on silica optical fibers for sensing applications at high temperatures. Scanning electron microscopy was used to characterize the surface morphology and microstructure of the coated fiber. Mechanical and optical properties of the coated fiber were characterized by Raman, optical and tensile tests. Compared with the original fiber, the tensile strength of SiBCN and BN/SiBCN coated fiber show an increase of about 60% and 90% at room temperature, respectively. In addition, the tensile strength of BN/SiBCN coated silica optical fiber was increased by about 42% at 700 °C. It has been found that the improvement of the strength of BN/SiBCN coated silica optical fiber is related to the healing of defects and residual compressive stress in fibers. From the light transmittance performance of the coated fiber, it was found that BN/SiBCN double coating could be an ideal total reflection solution to protect silica optical fiber from light leakage during high temperature sensing operation.

Polymer derived SiBCN ceramic was introduced into carbon fiber reinforced SiC composites to prepare C/SiC-SiBCN composites. Weight change and flexural strength of the samples after oxidation at different temperatures and in different atmospheres were tested up to 100 h to investigate their wet oxidation behavior. It was found that the stable silicoboron glassy self-healing phase formed from the oxidation of SiBCN had favorable oxidation resistance in wet oxygen atmosphere. And the SiC-SiBCN matrix can provide about 50 h of protection for carbon fiber in wet oxygen. Besides, the influence of temperature on the oxidation behavior of C/SiC-SiBCN composites were much related to the release speed of gas products (B2O3, HBO2 and Si(OH)4). And the oxidation mechanism of SiC/SiC-SiBCN composites were further explained by the comparation with C/SiC-SiBCN composites.

To further improve the oxidation resistance of C/SiC–SiBCN at temperatures over 1200 °C, C/SiC–SiHfCN and C/SiC–SiHfBCN composites were prepared by a new method called chemical vapor infiltration (CVI) combined with polymer infiltration and on-line pyrolysis (PIOP) process. The weight change behavior, mechanical properties, and microstructure of C/SiC–SiHf(B)CN before and after oxidation in wet oxygen were studied in detail. Through the replacement of B by Hf, the weight loss of the composite in high-temperature wet oxygen environment has been significantly reduced. The strength retention of C/SiC–SiHfBCN is up to 75% after oxidation in wet oxygen at 1400 °C and the strength retention of C/SiC–SiHfBCN can reach 85% after oxidation in an atmosphere with high oxygen and water vapor content at 1300 °C. In addition, microscopic analysis showed that after oxidation at 1400 °C, only the fibers in the near-surface matrix were oxidized to some extent and hafnium has been enriched at the composite surface. Our work provides a reference for the study of the oxidation resistance of C/SiC composites in harsh environments.

To further investigate the reinforcing factors on the adhesion strength of SiO2 and TiB2 modified SiBCN-based adhesives, the thermal stability analysis, microstructure observations and phase composition analysis were performed on four kinds of modified PSNB (Polyborosilazane) adhesives. With the different Si/B ratio and SiO2 content, the room temperature adhesion strength reach up to 18.95, 12.04, 32.44 and 13.69 MPa for PPT-1, PPT-2, PPTS and PST respectively, after synthesized at 1000 degrees C in air. And then, the high temperature adhesion strength reach up to 12.3 and 16.4 MPa for PPT-1 and PPTS at 1000 degrees C in vacuum, respectively. Interestingly, it has been found that temperature, PSO, solid content and SiO2 content all have a great influence on the adhesion performance of SiO2 and TiB2 modified SiBCN-based adhesives.

In order to further expand the application of SiC/SiC composites in the hot-end components for advanced aerospace engines, a self-healing SiC/(SiC-SiBCN)x composite prepared by CVI + PIOP has been tested for their creep behavior at 1200 °C with the partial pressure of 12 kPa H2O: 8 kPa O2: 80 kPa Ar. For the samples tested under low stresses, the load is borne by a load-bearing region, so that the secondary stage of creep curves can be subdivided into several small steps. Besides, it is found that the number of defects in SiC/(SiC-SiBCN)x composites is predominantly related to the stress level while the size of the defects is related to the creep time. Our findings provide important analytical data related to the creep behavior of the SiC/(SiC-SiBCN)x composite material and contribute to the further development of CMCs with outstanding mechanical properties and corrosion resistance even under harsh environments.

Groups of carbon/carbon (C/C) and tantalum carbide (TaC)-coated C/C composite specimens were studied under exposure to atomic oxygen (AO). Low earth orbit ground-based simulator was employed. Degradation mechanisms were investigated by scanning electron microscopy, X-ray photoelectron spectroscopy, and energy dispersive spectrometry. The results indicated that compared to C/C composite, TaC-coated C/C composite exhibited improvements in resistance properties against AO flux, such as 16.7% better strength retention ratio and 57% less mass ablation than non-coated C/C after 40 h of AO exposure. Moreover, AO preferentially consumed tantalum (Ta) atoms than carbon atoms of TaCx till atomic ratio was in the same proportion. Production of swollen tantalum oxide and crack healing components were obtained under the oxidation effect of high-speed AO. Swelling textures due to exposure were developed following an apical dominance growth behavior. The damage mechanisms of AO on TaC-coated C/C were revealed as chemical reaction first followed by mechanical effect.

Zirconium carbide (ZrC) components were induced as coating modification on carbon/carbon (C/C). These ZrC–C/C specimens were investigated after atomic oxygen (AO) exposure for different assessment times, low earth orbit (LEO) ground-based environmental simulator was employed. The results indicate that ZrO2 is the major production generated by the AO chemical reaction with the ZrC coating. Upon further exposure to AO, the production of ZrO2 would drop off, then exfoliate easily, due to the mechanical impacting effect. Then the exposed graphite matrix and carbon fiber get corroded. Amorphous diamond-like carbon (DLC) is detected by X-ray photoelectron spectroscopy during AO exposure. Bending strength performance increased by 25% under AO exposure at first 10 h, then dropped by 52.1% from 10 h to 30 h of AO exposure. The AO damage mechanisms of ZrC–C/C composites are revealed.

An adhesive of the SiBCN ceramic was synthesized through the polymer derived ceramics (PDC) route. Meanwhile with higher adhesion strength and simpler process condition, the polyborosilazane (PSNB) was modified by E-44 epoxy resin. The E-44 epoxy resin was used to promote the oxidation process of SiBCN, in other words, to produce more amount of SiO2-B2O3 glasses. The phase composition, elemental analysis, chemical bonds and microstructure were investigated by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM) measurements. The E-44 modified adhesives were cured at 120 °C in air for 2 h, and were pyrolyzed at 1 200, 1 400, and 1 500 °C for 2 h in air, respectively. The highest adhesion strength of the modified adhesive was up to 5.33, 12.23, and 12.50 MPa after being heat treated at 1 200, 1 400, and 1 500 °C, respectively. Finally, we proposed an adhesion model and revealed the adhesion mechanism of SiBCN ceramic.

In this work, samples of carbon/carbon (C/C) and chemical vapor deposited (CVD) SiC-coated C/C samples were investigated to understand the AO damage mechanism in low Earth orbit (LEO) environment. The ground-based simulated atomic oxygen (AO) generator was employed. Results indicate that the CVD SiC coating exhibited improved radiation resistance properties against AO radiation as evidenced by a 16% better strength retention ratio, 60% less mass ablation, and increased strength stability. The magnitude of these influences affected the surface morphology, as observed by scanning electron microscopy (SEM) and surface resistance meter test results. The variations in the surface constituents were confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results. The main products left on surface after AO exposure are SiO2 and SiCxOy film. Additionally, Si atoms are found to be the preferential reacting element in the SiC coating, and this process is accompanied by graphite precipitation, grain growth, and crack necking. Also, the damage mechanism of the AO-exposed SiC coating was revealed and is discussed.

In this work, the ZrC-SiC composite coatings were co-deposited by chemical vapor deposition (CVD) using ZrCl4, MTS, CH4 and H2 as raw materials. The morphologies, compositions and phases of the composite coatings were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The results indicated that the morphologies, compositions and phases of the composite coatings were related to the deposition temperature, the flow rate of the carrier H2 gas, and the ratio of C/Zr. Moreover, the co-deposition mechanism of the composite coatings was also studied. It was found that different deposition temperatures resulted in different deposition mechanisms. At temperatures in the range of 1150–1250 °C, the ZrC-SiC co-deposition was controlled by the surface kinetic process. At temperatures in the range of 1250–1400 °C, the ZrC-SiC co-deposition was controlled by the mass transport process.

Mosaic structure ZrC-SiC coatings were fabricated on low-density, porous C/C composites via thermal evaporation and an in-situ method. ZrC was packed in a typical lamellar mode, and the mosaic structure was formed by the deposition of Zr and Si atoms on the shallow surface of the porous C/C composites. Ablation analysis showed that the defects in the coatings originate from the boundary between the ZrC and holes created by the consumption of SiC at 2500 °C. After ablation for 200 s at 3000 °C, a dense ZrO2 layer formed on the coating surface, and the defects were sealed owing to the continuous supply of ablative components. The mass and line ablation rates of the ZrC-SiC coatings were −0.46 ± 0.15 mg cm−2·s−1 and −1.00± 0.04 μm s−1, respectively.

To understand the degradation behavior of Carbon/Carbon(C/C) composite in LEO radiation environment, groups of 2D-C/C composites samples were exposed to ground-based Low Earth Orbit(LEO) simulating facilities. The LEO radiating environment covers part of Van Allen inner belt, which contains atomic oxygen(AO) and high-energy proton radiating regions. These two kinds of radiating sources were arranged for simulating the real LEO radiating conditions regarding to the first orbit movement speed of serving space shuttles. Changes of micro-structure, mass loss, surface roughness, chemical construction and thermal physical properties after environmental assessment were analyzed and compared to understand the damage behavior of LEO radiation on C/C composite. It was found that AO is the main factor of mass loss in LEO radiating particles. The charged high-energy protons have an aggravating damage ability with energetic AO, damage situations of degree in orbit down process is more serious than in orbit rising process. The LEO radiation damage mechanisms of C/C composite are revealed and expounded either.

In order to improve the anti-oxidation performance of C/SiC composites at high temperature, C/SiC composites should be modified by self-healing components. SiBCN ceramic is an ideal self-healing component because of excellent oxidation resistance and thermal stability. C/SiC composites were modified by PDC SiBCN ceramic (C/SiC-SiBCN) by using CVI combined with polymer infiltration and on-line pyrolysis (PI-OP). The oxidation behaviors of C/SiC composites fabricated by CVI method and C/SiC-SiBCN composites fabricated by CVI + PI-OP method and CVI + PIP method at different temperatures in air were compared. The results showed that the strength retention ratios of the composites fabricated by the three methods decreased with the increase of temperature. Compared with the samples fabricated by the other two methods, the weight loss of the samples fabricated by CVI + PI-OP method was greater, but the strength retention ratio was higher.

Laser ablation test of SiHfC-based ceramic nanocomposites as well as ceramic matrix composites (CMCs) was conducted by exposure to a CO2 laser beam in air. Laser ablation behavior and possible degradation mechanisms of dense monolithic HfC/SiC ceramic nanocomposites as well as of Cf/SiHfC CMCs were investigated. Dense SiC monoliths and Cf/SiC CMCs were exposed to same laser ablation conditions and considered as reference materials. The evolution of microstructure and chemical/phase composition of the studied ceramics was addressed by scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDX) as well as by X-ray diffraction. The results reveal that from the center to the edge of the damaged region of the materials three sections with different surface morphologies and ablation mechanisms are identified. The comparation between the SiC-based monoliths and CMCs with and without Hf demonstrates the positive effects of Hf-incorporation on their laser ablation resistance.

In the present work, SiBCNO-based ceramic as high temperature adhesives are fabricated by polymer derived ceramic route. The effect of polysiloxane (PSO) and TiB 2 on the microstructure and high temperature strength is studied, and the toughing effect of TiB 2 is discussed. The highest adhesion strength of the joint (S12) reached up to 18.95 MPa at room temperature and 12.3 MPa at 1000 °C in vacuum after pyrolysis at 1000 °C in air for 2 h. It is interesting to find that the crystallization of nano-SiO 2 reinforces the strength and thermal stability of glass phase with the addition of PSO, besides, the TiB 2 plays the important role in improving adhesion strength by bearing load and facilitating the formation of stable SiO 2 -B 2 O 3 -TiO 2 glass.

To avoid the leakage of laser at high temperature oxidative environment, sapphire optical fiber (SOF) was coated with boron nitride (BN) via chemical vapor deposition. The microstructures, mechanical properties and the optical properties of the coatings were characterized by scanning electron microscopy, Raman, optical and tensile tests. Compared with the uncoated fibers, the strength of the coated fibers was dramatically increased almost 3 times at room temperature. However, the tensile strength was decreased to about 500 MPa from about 700 MPa at 1200 °C. Thermal stresses in combination with surface defects seem to be responsible for the strength drop. From the light transmittance performance of the BN coated SOF, BN can work as a total reflection coating to protect SOF from light leakage.

For the first time, ZrC–ZrB2–SiC ceramic nanocomposites were successfully prepared by a single-source-precursor route, with allylhydridopolycarbosilane (AHPCS), triethylamine borane (TEAB), and bis(cyclopentadienyl) zirconium dichloride (Cp2ZrCl2) as starting materials. The polymer-to-ceramic transformation and thermal behavior of obtained single-source precursor were characterized by means of Fourier transform infrared spectroscopy (FT-IR) and thermal gravimetric analysis (TGA). The results show that the precursor possesses a high ceramic yield about 85% at 1000 °C. The phase composition and microstructure of formed ZrC–ZrB2–SiC ceramics were investigated by means of X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). Meanwhile, the weight loss and chemical composition of the resultant ZrC–ZrB2–SiC nanocomposites were investigated after annealing at high temperature up to 1800 °C. High temperature behavior with respect to decomposition as well as crystallization shows a promising high temperature stability of the formed ZrC–ZrB2–SiC nanocomposites.

Dynamic and quasi-static in-plane compression failure process of a 2D-SiC/SiC composite were explored in this paper. Specular Reflection Method (SRM) was introduced to capture the real-time high-resolution images of the SiC/SiC composite in tests. The fracture surfaces of the subject composite under dynamic and quasi-static loading show different angles with loading direction. Dynamic fracture surface results showed a larger angle with the loading direction, with fiber breakage without debonding. However, in the quasi-static tests fracture surface showed a small angle with the loading direction, with fiber debonding and fiber bundle buckling. Scanning electron microscope (SEM) characterization of fragments obtained after experiments were used to characterize the deformation mechanisms of the 2D-SiC/SiC composite. Although both shear deformation and delamination were found under quasi-static and dynamic loading, shear deformation dominated the failure process of specimens during dynamic compression. Two microscopic fracture modes were concluded from the failure process of quasi-static and dynamic loadings. The strength of the fiber-matrix interface significantly influenced the fracture modes. Finally, an effort was made to simulate the dynamic failure process of SiC/SiC composite using the topological structure of a full-size specimen.

An air stable high temperature adhesive synthesized via the polymer-derived-ceramic route had received increased attention in the last two decades. To improve the thermal stability and adhesion strength of a polysilazane (PSNB) adhesive, TiB2 was added as active filler to join SiC ceramic discs. The thermal stability, phase composition and microstructure were investigated by using TGA, XRD, FT-IR, BSE and SEM measurements. Effects of the pyrolysis temperature and active filler TiB2 on the microstructure and adhesion strength have been investigated. After curing and heat-treating at 120 degrees C and 1000 degrees C in air for 2 h, respectively, the adhesion strength of the modified adhesive reached up to 10.07 MPa (3 times higher than that of pure PSNB) at room temperature, and, more importantly, retained a strength of 8.0 MPa at 800 degrees C in air. It should be noted that the formation of a glass comprised of SiO2-B2O3-TiO2 and the emergence of the hexagonal and granular TiB2 in the adhesive layer are mainly responsible for the enhanced high temperature strength.

Chemical vapor-infiltrated self-healing SiC(f)/BN(i)/[SiC-B4C](m) composite specimens were exposed at 1300 °C for 300 h at atmospheric pressure under two different oxidizing atmospheres (i.e., wet (12%H2O:8%O2:80%Ar) and dry (0.01%O2:99.99%Ar)) representative of rich and poor oxidizing conditions, respectively. Mechanical testing, microstructural observations, and element analyses were performed on the treated specimens. The flexural strength retentions of the specimens were 47.9 and 39.4% under wet and dry oxygen conditions, respectively. The SiC and B4C matrices were severely oxidized under wet oxygen conditions, whereas the BN interphase remained intact. The BN interphase and the B4C layered phase were both partially oxidized under dry oxygen conditions. Thus, the SiC(f)/BN(i)/[SiC-B4C](m) composites exhibited improved oxidation resistance under wet oxygen atmospheres as compared to dry oxygen conditions as a result of the formation of borosilicate glasses. In addition, two different degradation mechanisms for the composites during the oxidation process were discussed.

Pores and damages in the bulk of a two-dimensional plain woven C/SiC composite formed by chemical-vapor infiltration process are characterized in 3D by using X-ray Computed Tomography in order to validate the effectivity of X-ray Computed Tomography to establish the relations between pores and damage mechanisms in the following in-situ tests. An undamaged specimen is examined in order to characterize the pores, and a damaged specimen after a bending fatigue test under 500 °C is examined for the purpose of the characterization of damages. The morphologies of pores and damages are visualized in 3D through a series of 3D digital image processing and analysis. The pores in the undamaged specimen form a highly interconnected plain networks inside SiC matrix between laminates and even connect through several laminates to form a 3D interconnected network architecture. The SiC matrix enclosing the networks of pores could obstruct the contact between the air in the networks of pores and the fiber tows. However, once they are broken under mechanical loadings, the 3D interconnected network architecture may help the contact of air with fiber tows and thus accelerate the oxidations at high temperature. Fiber breaks and matrix breaks are both identified in the fractured area in the damaged specimen. Delaminations and matrix breaks are also observed in the bulk outside the fracture area. Oxidations of carbon fiber tows are not observed obviously under the current test temperature, i.e. 500 °C.

Self-healing functionality is an important issue of ceramics or ceramic matrix composites used in high temperature and oxidation environment. In this contribution, we reported the cross significant crack self-healing behaviors and mechanism of SiBCN ceramics derived from hyperbranched polyborosilazanes. The self-healing ability of cracks and indention cross sign are enhanced with the increase of oxidation time. And the temperature also influences the healing self-behaviors. The crack healing and indention sign occurred at 1000 °C in air atmosphere. The ceramics with high content of boron show much more obvious self-healing performance because the silicon and boron atoms can be reacted with the available oxygen at high temperature to form SiO2(l), B2O3(l), and B2O3.SiO2. The liquid-like products will fill the crack and prevents the destructive of substrates. The preceramic precursor-derived SiBCN ceramics show good self-healing performance and possess great potential in aeronautics, aerospace, and nuclear power industries.

The high temperature adhesives are required in most critical applications such as nuclear and aerospace technology. To obtain an adhesive with high temperature bond strength and low synthesis temperature, polysilazane (PSNB) was modified by PBSZ, PSO, nano-Al 2 O 3 additives. Effect of the SiO 2 to B 2 O 3 ratio and curing pressure on microstructure and high temperature bond strength has been investigated. After curing and heat-treating at comparatively lower temperatures, the bond strength of the modified adhesive reached up to 12.08 MPa, at room temperature, and, more significantly, retained the strength of 6.65 MPa at 1000 °C. The bond strength of modified adhesive is two-times higher than pure PSNB adhesive at elevated temperature. We demonstrate that optimum level of fluidity and applied pressure should be established in order to attain maximum bond strength. This paper open up avenues for further research in modifying existing adhesives for high temperature applications.

High-temperature surface acoustic wave (SAW) sensors for multi-parameter simultaneous measurement are widely needed in the fields of aerospace and energy. For the SAW sensors that can be operated up to 1200 °C, high temperature conductive coatings are required to match with the YCa4O(BO3)3 (YCOB) single crystal, which is the only available piezoelectric ceramics now for use at 1200 °C. Promising high temperature conductive films comprised of SiBCN ceramics were coated via chemical vapor deposition (CVD), polymer-derived ceramic (PDC) route and PDC plus CVD method, respectively. The microstructure, morphology and electrical properties of the films were characterized in detail. It was found that a film with few defects and good conductive performance can be obtained at 1000 °C by PDC plus CVD route. However, a BN film has to be deposited on YCOB wafer first to suppress its decomposition in inert atmospheres around 1000 °C in the case of using CVD method. The overall conductivity change is primarily due to the increase in graphitization degree of free carbon in PDC-SiBCN.

Capability of a HfC-modified C/SiC (C/SiC-HfC) composite against high-speed atomic oxygen (AO) atoms was evaluated in a ground-based low Earth orbit simulating system. Energy Dispersive Spectrum, Scanning Electron Microscopy, X-Ray Diffraction and Raman spectroscopy were employeed to investigate the damage behaviors of the material. The results show that HfC was oxided by AO preferentially, while HfO2 and graphite films were its main products during AO exposure. The crystallization degree of the graphite film increased with the increasing of AO total flux. It's found that SiC areas had lower surface damage than HfC areas, and SiO2 was its main reacting product. Ascribed to the evolution of surface craters, three-point bending strength of the specimens increased within the first 10 h exposure of AO and decreased thereafter. The damage mechanisms of AO over C/SiC-HfC were revealed also.

SiBCN ceramic precursor, polyborosilazane, was synthesized through a novel method which used sodium borohydride as boron source. Vinyl silazane with Si Cl was converted to vinyl silazane with Si H structure, followed by hydroboration reaction and subsequent high-temperature reaction to form soluble polyborosilazane liquid. The process of precursor-to-ceramic conversion was almost completed before 800 °C and the cross-linked polyborosilazane precursor exhibited higher ceramic yield 75.6% at 1200 °C. The SiBCN ceramic annealed at 1400 °C contained B N, Si N and Si C bonds with smooth and dense surface and still retained principally amorphous structure up to 1600 °C. In addition, the viscosity of the polyborosilazane was 65 mPa.s, which can efficiently prepare ceramic matrix composite by means of precursor infiltration and pyrolysis (PIP). The density of as-obtained ceramic matrix composite (CMC) was 1.82 g/cm3, and the average bending strength, bending modulus and tensile strength were 265.2 MPa, 37.5 GPa and 158.6 MPa, respectively.

Boron nitride light-leakage-proof coating was prepared via chemical vapor deposition (CVD) process on silica optical fiber for sensing applications at high temperatures. Compared with the original fiber, the tensile strength of BN coated fiber was more than two times higher at both room temperature and 700 °C. It was found that the critical value of BN coating thickness at which the strength changes from fiber-controlled into fiber-matrix-controlled is 0.5 μm and that at which the strength changes from fiber-matrix-controlled into matrix-controlled is 1 μm. Moreover, BN coated silica optical fiber exhibited favorable creep resistance at 700 °C. Furthermore, BN coated silica optical fiber performed better compared with the uncoated fiber in terms of optical property. Hence, CVD BN is suitable as a light-leakage-proof coating of silica optical fiber.

The behavior of Cf/SiHfBCN composites upon laser ablation was investigated. The evolution of microstructure and phase composition of the composite was studied by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). It is found that the ablation mechanism and the microstructure evolution are mainly dependent on the local temperature which directly relies on the distance from the laser spot and the thermal conduction of the carbon fibers. Three regions with different ablation behavior are identified. In the center region, bubble-like structures consisting of HfO2, and SiHfxOy-based layers, cover the ends of the carbon fibers which retain their original shape despite their corrosion. Sheets consisting of HfCxOy and SiO2 as well as porous HfO2 and liquid SiO2 are generated in the transition region. The carbon fibers are well protected from oxidation in the two regions. SiO2 is produced and suppresses the further oxidation of the matrix in the fringe region.

Within this study, the oxidation behavior of SiHfBCN ceramic powders and monoliths was studied at temperatures from 1200 to 1400 °C. Both powder and monolithic samples exhibited parabolic oxidation behavior characterized by very low rates (10−9–10−8 mg2 cm−4 h−1). The activation energy of 112.9 kJ mol−1, which was determined for the SiHfBCN powder, is comparable to that of other silica formers such as silicon or SiC and relates to the diffusion of molecular oxygen through silica scale. Whereas, the values determined for the SiHfBCN ceramic monoliths (174 and 140 kJ mol−1, depending on the Hf content) indicate the complex nature of their oxidation process, leading at temperatures below 1300 °C to a continuous oxide scale consisting of borosilicate, silica, m-and t-HfO2. At higher temperatures, the oxide scale consists of silica, HfSiO4 as well as m-and t-HfO2 and becomes discontinuous, probably due to the evaporation of boria.

To estimate the capability of SiC-BCx protecting carbon fibers under tensile stress, the creep behavior of 2D C/SiC-BCx Ceramic-matrix composites (CMCs) prepared by chemical vapor infiltration (CVI) has been tested and investigated in static wet oxygen atmosphere at 900 °C. Environmental degradation and Micro-mechanics of the composite was discussed according to the Microstructural analysis observed by scanning electron microscopy (SEM) and length change recorded by Instron material testing device. It is found the room temperature residual flexural strength increases with increasing creep stress. The strength improvement is attributed to the glass phase generation and local stress redistribution. The oxidative damage of 2D C/SiC-BC x composite is more and more serious with the increase of the creep stress. The steady creep speed and accelerated creep speed lay on the oxidation speed of carbon fiber. The oxidation of BC x layer and carbon fiber is controlled by gas diffusion.

High temperature adhesive using in air is extremely important for ceramic components. A novel adhesive for joining Al 2 O 3 ceramic was made using polyborosilazanes usually it was donated as PSNB. The ceramic joints were heat-treated at temperatures ranging from 1300 to 1500 °C in air surroundings. The bonding strength was tested at room temperature and high temperatures respectively. The best performance of bonding strength at room temperature was 15.73 MPa, which was heat-treated at 1500 °C, 1.5 KPa for 2 h with a heating rate of 2 °C/min. The formation of Al 2 O 3 ·B 2 O 3 means the reaction of adhesive and adhesion, and result in improving the bonding strength apparently. Compared to the bonding strength at room temperature, the bonding strength at 800 °C was 12.91 MPa, only decreased 18%. The thickness of bonding layer was about 5 μm, and the small thickness has the advantage of reducing thermal residual strain.

To prevent the oxidation of BN-coated sapphire optical fiber (SOF) at 800 °C, a SiBCN ceramic coating was used as an outer coating owing to its excellent high-temperature oxidation resistance. Compared with BN/SOF, the tensile strength of SiBCN/BN/SOF increases from 500 to 723 MPa at 1200 °C. The optical properties of double coating indicate that the addition of SiBCN does not diminish the total reflection of the BN coating. Furthermore, SiBCN-coated fibers indicate lower residual stress and performed better compared with other coated fibers in terms of mechanical and optical properties. Hence, SiBCN is highly suitable as an outer coating of SOF.

Cf/SiCN and Cf/SiHfBCN-based ceramic matrix composites (CMC) were fabricated using the precursor infiltration and pyrolysis technique (PIP). Their behavior in subcritical hydrothermal conditions was investigated at 150–250 °C using exposition times of 48, 96 and 240 h and shown to rely on active corrosion. The data of the mass loss as a function of the corrosion time and temperature at S/V of 0.075 were used to rationalize the corrosion kinetics of the CMCs. Both materials have been shown to exhibit excellent stability in subcritical hydrothermal conditions. The corrosion rates of Cf/SiHfBCN were lower than those determined for Cf/SiCN; furthermore, SEM investigation indicates that spallation occurred in the Cf/SiCN samples; whereas the ceramic matrix was still attached on the individual carbon fibers in Cf/SiHfBCN. The results indicate that the incorporation of Hf and B into SiCN matrix leads to a significant improvement of its hydrothermal corrosion performance.

Cf/Cu composite was prepared by vacuum melting infiltration. Ti and Cr were doped to the Cu alloy to improve the wettability between Cu and carbon. The microstructure was investigated by XRD, SEM and EDS. The arc erosion rate of Cf/Cu composite was investigated in vacuum. The results showed that the Ti and Cr could improve the wettability between Cu and C/C preform and the infiltration ability of Cu into C/C preform greatly. A TiC interface formed between the fibers and matrix. The good bonding between the fiber and matrix guaranteed that part of the Cu matrix can still be bonded on the fibers even when the material was exposed to the plasma. Consequently, the carbon fibers were protected from the erosion. In comparison, Cu was completely consumed by the arc erosion. Hence, the graphite was eroded and presented a cauliflower-like morphology. Therefore, the prepared Cf/Cu had better ability to resist the arc erosion, compared with common Cu-C material.

Before being densified by chemical vapor deposition, carbon preform was modified by boron. The mechanical property and resistance to atomic oxygen corrosion of carbon/carbon composites were investigated. The results show that fiber surface modification induces the deposition of high texture pyrocarbon and a moderate interfacial transition layer between carbon fibers and matrix carbon. After being modified by boron, the flexural and compressive strength of carbon/carbon composite is significantly increased. The bending curve has been adjusted with obvious pseudo-ductility phenomenon. The resistance ability to atomic oxygen corrosion is improved significantly. The mass loss and corrosion degree of the modified composite are lower than that of pure carbon/carbon composite.

Atomic oxygen (AO) is considered the most erosive particle to spacecraft materials in low earth orbit (LEO). Carbon fiber, carbon/carbon (C/C), and some modified C/C composites were exposed to a simulated AO environment to investigate their behaviors in LEO. Scanning electron microscopy (SEM), AO erosion rate calculation, and mechanical property testing were used to characterize the material properties. Results show that the carbon fiber and C/C specimens undergo significant degradation under the AO bombing. According to the effects of AO on C/C-SiC and CVD-SiC-coated C/C, a condensed CVD-SiC coat is a feasible approach to protect C/C composites from AO degradation.

Effects of processing on the microstructure and property of carbon fiber reinforced silicon carbide matrix composites, namely 2D C/SiC composites, have been investigated with respect to micro-crack evolution, strength change and mass loss, etc. Several 2D C/SiC materials prepared with different chemical vapour infiltration (CVI) cycles of SiC were studied. Raman spectroscopy was employed to measure the residual stress in the matrix of the C/SiC composite based on the shift of the position of the LO band of SiC. Two kinds of mircocracks were found during the preparation of C/SiC. One type of cracks originating from the corners of braided holes barely changes during the whole processing, the other type arising between the braided holes decreases with increasing matrix volume. The former is most responsible for carbon fibers oxidation at elevated temperature. The evaluation of the microstructure and properties of the material is discussed in terms of the internal stress changed with the deposition of the matrix.

One of the main features of SiBCN-based ceramics is their high temperature stability with respect to crystallization and decomposition in protective atmospheres. High temperature studies of a polyborosilazane in air up to 1500 degrees C show that the formation of coexisting nano-quartz and amorphous B2O3 is suitable for the application as adhesive for bonding advanced ceramics. Spectroscopic and X-ray studies combined with thermal analysis clearly demonstrate the strong influence of the presence of air on the cross-linking and pyrolysis behavior and, thus, finally on the ceramization process of the applied SiBCN preceramic polymer. Accordingly, cross-linking and subsequent pyrolysis of the SiBCN-precursor up to 1600 degrees C in air result in the formation of a network structure comprised of SiO2 and B2O3 with minor amounts of residual amorphous SiBCN. In contrast to the polymer-to-ceramic transformation of the used polyborosilazane in protective atmospheres like Ar or N-2, the ceramic yield at 1400 degrees C is high and amounts 85.6 wt%. Furthermore, the elemental composition of the resulting SiBCNO does not change significantly at T > 1200 degrees C even after heat-treatment at 1600 degrees C indicating the high temperature stability of the resulting SiBCNO material.