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The successful applications of silicon carbide-ceramic matrix composites (SiC-CMCs) in aeronautical and aerospace industries require deeper understanding of their mechanical behaviors and failure mechanisms. The overview on tension and shear is then presented from meso-mechanics perspective, including matrix cracking, interface de-bonding and sliding, matrix crack propagation as well as fiber bridging. The results reveal that the matrix cracking stress is proportional to the interface sliding stress and the matrix fracture energy. The ratio of tensile to shear stress of the matrix cracking remains constant both in tension and in shear. In addition, the deflection of matrix cracks in the interface depends on the elastic modulus matching parameter, the angle between matrix cracks and interface, as well as the residual thermal stress. The matrix cracks propagate in a random or periodic pattern, which are proportional to the sliding length at the matrix cracking stress. The fiber bridging mechanism, related to the Weibull distribution of the fiber strength, determines the tensile and shear behaviors after the saturation of matrix cracks.

The aggregation in high-content carbon nanotube reinforced silica carbide composites (CNT/SiC) imposed constraints for further large-scale industrial applications. This study established a synergistic micro-nano pore structure by assembling CNT bundles to fabricate the CNT sponge preform, and then the SiC matrix was in-situ deposited by chemical vapor infiltration method, which facilitates composites with high density and exceptional properties. The pore size distribution and pore area can be regulated by simply adjusting the compression ratios (CRs) of the as-assembled CNT sponge. Samples with CR of 50 % exhibited noteworthy densification, significantly reduced porosity, and a remarkable 163.54 % extra increase in compression strength compared to uncompressed ones. Additionally, the CNT/SiC composites displayed excellent oxidation resistance and demonstrated improved electromagnetic interference (EMI) shielding performance, which exhibited a substantial increase with higher CRs. These findings underscore the significance of employing appropriate multi-level porosity in CNT preforms to fabricate advanced ceramic matrix composites with superior EMI shielding capabilities.

To enhance the resistance of SiCf/SiC to hydrothermal corrosion in the pressurized water reactor (PWR) environment, structurally tunable Ti3SiC2-based corrosion mitigation coatings for SiCf/SiC were prepared using molten salt synthesis. The influence of various process parameters, such as Si/Ti molar ratio in raw materials, annealing time, and annealing temperature, on the phase composition and the structure of the coatings was explored. Through the process control, the fabricated coatings can be either Ti3SiC2 monolithic structure or TiC/Ti3SiC2 and TiC/Ti3SiC2/Ti5Si3Cx multi-layered structures. The coatings demonstrate strong bonding to the substrate due to in-situ reaction, exhibiting tensile and shear strength of at least 26.9 and 30.8 MPa, respectively. Incorporating TiC as a transition layer further enhances the tensile and shear strength to 41.3 and 51.4 MPa, respectively. Monolithic Ti3SiC2 coatings enhance the thermal conductivity of SiCf/SiC by 10%–12%. Notably, Ti3SiC2 coatings effectively protect SiCf/SiC from hydrothermal corrosion, demonstrating an 83% strength retention rate compared to 71% in the control group after corrosion. However, the Ti5Si3Cx layer exhibits unsatisfactory corrosion mitigation. The Ti3SiC2 monolithic coating has higher thermal conductivity, TiC/Ti3SiC2 multi-layered coating has higher bonding strength, and both have desirable resistance to the hydrothermal corrosion.

In this work, the effects of carbon nanotubes (CNTs) on the microstructure evolution, thermal conductivity, and mechanical properties of Cf/SiC composites during chemical vapor infiltration (CVI) densification were investigated in detail. Compared with composites without CNTs, the thermal conductivity, flexural strength, flexural modulus, fracture toughness, interfacial shear strength, and proportional limit stress of specimens with CNTs of 4.94 wt% were improved by 117%, 21.8%, 67.4%, 10.3%, 36.4%, and 71.1%, respectively. This improvement was attributed to the role of CNTs in the division of inter-layer pores, which provided abundant vapor growth sites for the ceramic matrix and promoted densification of the whole composite. In addition, the high thermal conductivity network formed by the overlap of CNTs and the rivet strengthening effect of CNTs were beneficial for synergistic improvement of thermal conductivity and mechanical properties of the composites. Therefore, this study has practical significance for the development of thermal protection composite components with enhanced thermal conductivity and mechanical characteristics.

The thermal shock protection of SiC/SiC composites have become pivotal challenges in promoting their application in a heat field environment. This study presents a borosilicate glass (BSG) coating was fabricated successively by slurry brushing-sintering for SiC/SiC composites. The results show that the coated SiC/SiC composites exhibit excellent thermal protective resistance with a rather light mass change (

In this study, work on modelling uncertainty in the tensile properties of two-dimensional plain woven silicon carbide fibre-reinforced silicon carbide matrix (2D SiC/SiC) composite and B-basis values of tensile strength was carried out in the following four aspects. First, the uncertainty law and formation mechanism of the tensile properties of 2D SiC/SiC composites were researched through microstructural analysis. Subsequently, three distribution function models were established for the tensile properties of 2D SiC/SiC composites with Weibull, normal, and log-normal distribution functions. The development of three functional models was based on 30 groups of valid tensile data, linear regression methods, and Kolmogorov hypothesis testing methods. Based on the application of the model validation method, the accuracy of the three functional models was quantitatively evaluated by employing the area index of model validation. B-basis values for the tensile strength of 2D SiC/SiC composites were calculated and finally discussed for three distribution functions. The results indicate that the distribution regularity of tensile properties of 2D SiC/SiC composites could be characterized by using the three function models, and the Weibull distribution function was the most accurate. Therefore, it was preferable to calculate the B-basis values by using the Weibull distribution, with a B-basis value of 266 MPa.

The thermos-structural materials with high strength and high temperature water-oxygen corrosion resistance are urgently needed in aero-space fields. SiC whisker reinforced SiC matrix (SiCw/SiC) composites are the ideal candidate materials for their excellent mechanical properties and thermostability. However, the poor resistance to water-oxygen corrosion ability of SiC matrix limits their further application. In this work, a novel SiCw/SiC–Si–Y composites were first prepared by infiltrating silicon-yttrium (Si–Y) alloy into SiCw/C preform via reactive melt infiltration method. The as-obtained composites not only show the excellent mechanical properties (σF = 363 MPa, KⅠC = 9.14 MPa m1/2), and more importantly after water-oxygen corrosion of 20 h at such temperature as high as 1500 °C, the strength and toughness retention of the composites can reach 106.1% and 103.6%, respectively. The SiCw/SiC–Si–Y composites developed in this paper have a great potential as a new high-performance thermos-structural material for aero-space applications.

An ultralight and high-strength Silicon nitride (Si3N4) foam ceramic with highly efficient wave-transparent and heat insulation properties was successfully prepared using the organic foam impregnation technique combined with chemical vapor infiltration (CVI) process. The microstructure of Si3N4 foam ceramic inherits the pore structure characteristics of the template, and the ceramic skeleton is formed by coupling the Si3N4 whiskers with the CVI Si3N4 matrix. The use of CVI process avoids the volume shrinkage problem during the ceramic formation process by traditional sintering method at high temperature, and ensures the near-net-shape preparation of ceramic. Meanwhile, CVI Si3N4 matrix has pure components without impurities like low melting point metal oxides by sintering method or free carbon by polymer-derived ceramic method, which is beneficial to the improvement of wave-transparent ability and thermal stability. The addition of whisker reinforcement greatly increases the compressive strength of ceramic through whisker pulling out, crack deflection and other strengthening and toughening mechanisms. Moreover, we discuss in detail the relationship between the structural parameters of Si3N4 foam ceramic, such as whiskers-matrix solid content ratio, open-closed porosity ratio, pore size and mechanical, wave-transparent as well as heat insulation properties. In this study, the compressive strength of 40PPI Si3N4 foam ceramic with total porosity of 91.97% is 1.06 MPa, the thermal conductivity is only 0.624 W/(m·K) at 25 °C and the dielectric constant and loss tangent are 1.40 (10 GHz) and 6.35 × 10−3 (10 GHz), respectively.

The fabrication of silicon nitride (Si3N4) fiber-reinforced boron nitride (BN) and Si3N4 matrix (Si3N4f/BN/Si3N4) composites with BN interphase through precursor infiltration and pyrolysis (PIP) process is reported. The effects of heating rate during PIP process on mechanical and dielectric properties of composites are analyzed. When the heating rate is 5 °C/min, the overall performance of Si3N4f/BN/Si3N4 composites is optimal, and the flexural strength and fracture toughness attain 138 MPa and 5.7 MPa m1/2, and the dielectric constant and dielectric loss are 3.90 and 0.008, respectively. The composites achieve a synergy combining structural with functional properties. The influence mechanism of the heating rate during PIP process on the Si3N4f/BN/Si3N4 composites disclose the following. First, the heating rate makes an effect on the carbon content in the Si3N4 matrix, and consequently the dielectric properties of the composites are changed. Second, at 8 °C/min, the modulus of Si3N4 matrix is the lowest due to the existence of nanopores. At 2 °C/min, the strong axial tensile stress results in severe cracking of the Si3N4 matrix, so the matrix modulus decrease. Third, the heating rate strongly affects the radial stress state at the interphase, which affects the interfacial shear strength of the composites. The matrix modulus and interfacial shear strength can be optimized at 5 °C/min to improve the mechanical properties of the composites.

Abstract Three strategies were proposed to prolong the service life of continuous fiber-reinforced silicon carbide ceramic matrix composite (CMC-SiC), which served as thermal-structure components of aeroengine at thermo-mechanical-oxygenic coupling environment. As for some thermal-structure components with low working stress, improving the degree of densification was crucial to prolong the service life, and the related process approaches were recited. If the thermal-structure components worked under moderate stress, the matrix cracking stress (σ mc) should be improved as far as possible. The fiber preform architecture, interface shear strength, residual thermal stress, and matrix strengthening were associated with σ mc in this review. Introducing self-healing components was quite significant with the appearance of matrix microcracks when CMC-SiC worked at more severe environment for hundreds of hours. The damage can be sealed by glass phase originating from the reaction between self-healing components and oxygen. The effective self-healing temperature range of different self-healing components was first summarized and distinguished. The structure, composition, and preparation process of CMC-SiC should be systematically designed and optimized to achieve long duration target.

In order to improve the dielectric thermal stability of polyvinylidene fluoride (PVDF)-based film, nano silicon nitride (Si3N4) was introduced, and hence the energy storage performance was improved. The introduction of nano Si3N4 fillers will induce a phase transition of P(VDF-HFP) from polar β to nonpolar α, which leads to the improved energy storage property. As such, the discharging energy density of Si3N4/P(VDF-HFP) composite films increased with the amount of doped Si3N4. After incorporating 10wt% Si3N4 in Si3N4/P(VDF-HFP) films, the discharging density increased to 1.2 J/cm3 under a relatively low electric field of 100 MV/m. Compared with a pure P(VDF-HFP) film, both the discharging energy density and thermal dielectric relaxor temperature of Si3N4/P(VDF-HFP) increased. The working temperature increased from 80 °C to 120 °C, which is significant for ensuring its adaptability in high-temperature energy storage areas. Thus, this result indicates that Si3N4 is a key filler that can improve the thermal stability of PVDF-based energy storage polymer films and may provide a reference for high-temperature capacitor materials.

Abstract Oxidation behaviors of carbon fiber reinforced SiC matrix composites (C/SiC) are one of the most noteworthy properties. For C/SiC, the oxidation behavior was controlled by matrix microcracks caused by the mismatch of coefficients of thermal expansion (CTEs) and elastic modulus between carbon fiber and SiC matrix. In order to improve the oxidation resistance, multilayer SiC-Si3N4 matrices were fabricated by chemical vapor infiltration (CVI) to alleviate the above two kinds of mismatch and change the local stress distribution. For the oxidation of C/SiC with multilayer matrices, matrix microcracks would be deflected at the transition layer between different layers of multilayer SiC-Si3N4 matrix to lengthen the oxygen diffusion channels, thereby improving the oxidation resistance of C/SiC, especially at 800 and 1000 °C. The strength retention ratio was increased from 61.9% (C/SiC-SiC/SiC) to 75.7% (C/SiC-Si3N4/SiC/SiC) and 67.8% (C/SiC-SiC/Si3N4/SiC) after oxidation at 800 °C for 10 h.

Abstract An efficient chamber‐induced activation method was applied for the preparation of holey graphene/cellulose nanofiber‐based film with high specific surface area (SSA) and multiple channels through the graphene nanosheets. With the cellulose nanofiber (CNF) simultaneously serving as “dispersing agent,” “spacer,” and “activating agent,” the graphene oxide (GO) nanosheets are perforated by the pyrolysis gas from CNF in the confined space inside the hybrid films, uniformly dispersed, and sandwiched between CNF networks with less agglomeration and restacking. Additionally, we have proved that H2O and H2 are primarily responsible for the activation and etching of GO/CNF film. As the CNF content increases, the mesoporosity of the activated reduced GO/CNF (A‐RGO/CNF) film increases, and the graphene nanosheets show more nanopore perforations. Benefitting from the high SSA, high density, moderate mesoporosity, and abundant channels for ion diffusion through the graphene nanosheets, the A‐RGO/CNF film exhibits the highest specific capacitance of 323 (236) F g−1 (F cm−3) at 1 A g−1. For the A‐RGO5/CNF5 film containing half CNF and half GO, an excellent comprehensive electrochemical performance including superior rate performance (208 (160) F g−1 (F cm−3) at 60 A g−1) is exhibited. Moreover, the A‐RGO5/CNF5 electrode in an all‐solid‐state flexible symmetric supercapacitor delivers a high specific capacitance of 250 (193) F g−1 (F cm−3) at 1 A g−1. This study provides a novel idea for the preparation of holey graphene‐based film for supercapacitor electrodes. The strategy of simultaneously employing CNF as “dispersing agent,” “spacer,” and “activating agent” also offers a new vision for the assembly of homogeneous nanohybrid material and the utilization of pyrolysis gas.

Abstract Solar‐thermal conversion is considered as a green and simple means to improve the performance of energy storage materials, but often limited by the intrinsic photothermal properties of materials and crude structure design. Herein, inspired by the unique light trapping effect of wide leaf spiral grass during photosynthesis, a biomimetic structural photothermal energy storage system is developed, to further promote the solar thermal‐driven pseudo capacitance improvement. In this system, three‐dimensional printed tortional Kelvin cell arrays structure with interesting light trapping property functions as “spiral leaf blades” to improve the efficiency of light absorption, while graphene quantum dots/MXene nanohybrids with wide photothermal response range and strong electrochemical activity serve as “chloroplast” for photothermal conversion and energy storage. As expected, the biomimetic structure‐enhanced photothermal supercapacitor achieves an ideal solar thermal‐driven pseudo capacitance enhancement (up to 304%), an ultrahigh areal capacitance of 10.47 F cm−2, remarkable photothermal response (surface temperature change of 50.1 °C), excellent energy density (1.18 mWh cm−2) and cycling stability (10000 cycles). This work not only offers a novel enhancement strategy for photothermal applications, but also inspires new structure designs for multifunctional energy storage and conversion devices.

Abstract The SiBCN matrix via chemical vapor infiltration (CVI) or/and polymer infiltration pyrolysis (PIP) technologies was orderly introduced to SiCf/SiC composites to optimize the mechanical property and electromagnetic (EM) shielding effectiveness simultaneously. The BN interface with the thickness of 350 nm was designed to obtain a little stronger interface bonding. The flexural strength of SiCf/SiC-SiBCN composites reached 545.45±29.59 MPa thanks to the crack deflection between the CVI SiC and CVI SiBCN, as well as CVI SiBCN and PIP SiBCN matrix because of the modulus difference between them. The fracture toughness (K IC) with the value of 16.02±0.94 MPa·m1/2 was obtained owing to the extension of crack propagation path. The adverse effect of stronger interface bonding was eliminated by the design of matrix microstructure for SiCf/SiC-SiBCN composites. The thermal conductivity in the thickness direction was 7.64 W·(m·K)−1 at 1200 °C and the electric resistivity decreased to 1.53×103 Ω·m. The tunable dielectric property was obtained with the coordination of wave-absorption CVI SiBCN matrix and impedance matching PIP SiBCN matrix, and the total shielding effectiveness (SE T) attained 30.01 dB. It indicates that the SiCf/SiC-SiBCN composites have great potential to be applied as structural and functional materials.

Abstract Heterogeneous interface design to boost interfacial polarization has become a feasible way to realize high electromagnetic wave absorbing (EMA) performance of dielectric materials. However, interfacial polarization in simple structures such as particles, rods, and flakes is weak and usually plays a secondary role. In order to enhance the interfacial polarization and simultaneously reduce the electronic conductivity to avoid reflection of electromagnetic wave, a more rational geometric structure for dielectric materials is desired. Herein, a Ti3C2Tx/MoS2 self‐rolling rod‐based foam is proposed to realize excellent interfacial polarization and achieve high EMA performance at ultralow density. Different surface tensions of Ti3C2Tx and ammonium tetrathiomolybdate are utilized to induce the self‐rolling of Ti3C2Tx sheets. The rods with a high aspect ratio not only remarkably improve the polarization loss but also are beneficial to the construction of Ti3C2Tx/MoS2 foam, leading to enhanced EMA capability. As a result, the effective absorption bandwidth of Ti3C2Tx/MoS2 foam covers the whole X band (8.2–12.4 GHz) with a density of only 0.009 g cm−3, at a thickness of 3.3 mm. The advantages of rod structures are verified through simulations in the CST microwave studio. This work inspires the rational geometric design of micro/nanostructures for new‐generation EMA materials.

The preparation of micro/nano periodic surface structures using femtosecond laser machining technology has been the academic frontier and hotspot in recent years. The formation and evolution of micro/nano periodic ripples were investigated on 2205 stainless steel machined by femtosecond laser. Using single spot irradiation with fixed laser fluences and various pulse numbers, typical ripples, including nano HSFLs (‖), nano LSFLs (⊥), nano HSFLs (⊥) and micro grooves (‖), were generated one after another in one test. The morphologies of the ripples were analyzed, and the underlying mechanisms were discussed. It was found that the nano holes/pits presented at all stages could have played a key role in the formation and evolution of micro/nano periodic ripples. A new kind of microstructure, named the pea pod-like structure here, was discovered, and it was suggested that the formation and evolution of the micro/nano periodic ripples could be well explained by the pea pod-like structure model.

Superwetting surfaces have the potential to address oil pollution in water, through their ability to separate the two. However, it remains a great challenge to fabricate stable and efficient separation structures using conventional manufacturing techniques. Furthermore, the materials traditionally used for oil-water separation are not stable at high temperature. Therefore, there is a need to develop stable, customizable structures to improve the performance of oil-water separation devices. In recent years, 3D printing technology has developed rapidly, and breakthroughs have been made in the fabrication of complicated ceramic structures using this technology. Here, a ceramic material with a gradient pore structure and superhydrophobic/superoleophilic properties was prepared using 3D printing for high-efficiency oil-water separation. The gradient pore structure developed here can support a flux of up to 25434 L/m2h, which is nearly 40% higher than that an analogous structure with straight pores. At 200 °C, the oil-water separation performance was maintained at 97.4%. Furthermore, samples of the material exhibited outstanding mechanical properties, and chemical stability in a variety of harsh environments. This study provides an efficient, simple, and reliable method for manufacturing oil-water separation materials using 3D printing, and may have broader implications for both fundamental research and industrial applications.

Abstract Porous Si3N4-Si3N4 composite ceramics were fabricated by 3D printing combined with low-pressure chemical vapor infiltration (CVI). This technique could effectively improve the designability of porous Si3N4 ceramics and optimize the mechanical and dielectric properties. The effects of process parameters including the deposition time and heat treatment on the microstructure and properties of porous Si3N4-Si3N4 composite ceramics were studied. The study highlights following: When CVI processing time was increased from 0 to 12 h, the porosity decreased from 68.65% to 26.07% and the density increased from 0.99 to 2.02 g/cm3. At the same time, the dielectric constant gradually increased from 1.72 to 3.60; however, the dielectric loss always remained less than 0.01, indicating the excellent electromagnetic (EM) wave-transparent performance of porous Si3N4-Si3N4 composite ceramics. The maximum flexural strength of 47±2 MPa was achieved when the deposition time attained 6 h. After heat treatment, the porosity increased from 26.07% to 36.02% and the dielectric constant got a slight increase from 3.60 to 3.70 with the dielectric loss still maintaining lower than 0.01. It has been demonstrated that the porous Si3N4-Si3N4 composite ceramics are a promising structural and EM wave-transparent material suitable for high temperature service.

The machining of micro/nano periodic surface structures using a femtosecond laser has been an academic frontier and hotspot in recent years. With an ultrahigh laser fluence and an ultrashort pulse duration, femtosecond laser machining shows unique advantages in material processing. It can process almost any material and can greatly improve the processing accuracy with a minimum machining size and heat-affected zone. Meanwhile, it can fabricate a variety of micro/nano periodic surface structures and then change a material’s surface performance dramatically, such as the material’s wetting performance, corrosive properties, friction properties, and optical properties, demonstrating great application potential in defense, medical, high-end manufacturing, and many other fields. In recent years, the research is gradually deepening from the basic theory to optimization design, intelligent control, and application technology. Nowadays, while focusing on metal structure materials, especially on stainless steel, research institutions in the field of micro and nano manufacturing have conducted systematic and in-depth experimental research using different experimental environments and laser-processing parameters. They have prepared various surface structures with different morphologies and periods with sound performance, and are one step closer to many civilian engineering applications. This paper reviews the study of micro/nano periodic surface structures and the performance of stainless steel machined using a femtosecond laser, obtains the general evolution law of surface structure and performance with the femtosecond laser parameters, points out several key technical challenges for future study, and provides a useful reference for the engineering research and application of femtosecond laser micro/nano processing technology.

The implementation of SiC fiber reinforced SiC/SiC composites to aero-engine hot components has attracted wide attention, due to their many excellent properties. Along these lines, in order to predict the oxidation behavior of the material in extreme environments and to explore the effect of different preforms on the oxidative behavior of the composites, four SiC/SiC composites, with different preforms, were oxidized under environmental conditions of pressure of 12 kPa H2O:8 kPa O2:80 kPa Ar, at 1400 °C temperature. Moreover, the morphology and defect distribution of the samples were characterized by carrying out scanning electron microscopy, and micro-computed X-ray tomography measurements. Furthermore, the relation between the micro- and macro-scales was established, so as to be able to predict the oxidation behavior of the composites; not only the quantitative relationship between the mass change rate and the defect volume change rate, but also the combination of micro-computed X-ray images.

Impedance matching and attenuation principles are decisive for electromagnetic wave (EMW) absorption materials to achieve wider absorption bandwidth and higher strength absorption. By designing macrostructures to obtain metamaterials and tuning microstructures of absorption materials, impedance matching characteristic and absorption performance can be readily improved. In this paper, three-dimensional (3D) printing technology as well as precursor infiltration and pyrolysis (PIP) method were utilized to fabricate Al2O3/carbon nanotubes/SiC nanowires/SiOC composites with twisted cross metamaterial structures, where carbon nanotubes (CNTs) acted as a nucleating agent to obtain SiC nanowires (SiCnw) and as conductive phase to form conductive net structure, thus improving the dielectric and conductive loss of the composites. The Al2O3/CNT/SiCnw/SiOC composites achieved a minimum reflection coefficient (RCmin) value of −56.84 dB (99.999%) at 12.2 GHz with a thickness of 2.8 mm and the effective absorption bandwidth (EAB) ranges from 8.2–12.4 GHz with a thickness of 3.2 mm, covering the whole X-band. The excellent EMW absorption performance of the composite with metamaterial structure makes it possible to be practically applied.

Poor thermal conductivity of continuous fiber-reinforced silicon carbide (SiC) ceramic matrix (C/SiC) composites has become a huge obstacle to be widely used as thermal protection systems and hot structures for hypersonic vehicles. Herein, a high thermal conductivity of C/SiC composites modified with SiC whiskers (SiCw) was constructed by laser-assisted chemical vapor infiltration (LA-CVI). The inserted SiCw into the C/SiC composites were served as the second phase, yielding a unique three-dimensional network structure. Density, mechanical properties, and thermal conductivity of the prepared composites were systematically investigated. Results show that the bending strength (600 MPa) of the LA-CVI-C/SiC-SiCw composites is 27.6% higher than that of CVI-C/SiC composites (470 MPa). With the fiber debonded, fractured, and pulled out hierarchically, the failure crack propagated express Step-extension. Besides, the thermal conductivity (45.13 Wm−1K−1) of LA-CVI-C/SiC-SiCw composites is a factor 4 to 5 higher than that of CVI-C/SiC composites (10 Wm−1K−1). This work provides not only a facile method to construct high thermal conductivity C/SiC composites but an effective way to overcome the difficulties of improving the thermal conductivity of ceramic matrix composites (CMCs).

Various methods exist to improve the toughness and reduce the sensitivity to the defects in ceramic materials; however, the bionic laminated ceramics are the most promising ones. In this paper, we review preparation, sintering, properties and toughening mechanisms of laminated ceramics. Delamination cracks and crack deflection are the main sources of energy dissipation during the fracture of laminated ceramics with weak interfaces. The increasing fracture toughness is due to the residual compressive stress and is the mechanism of laminated ceramics toughness with strong interfaces. These extensively studied laminated ceramics with excellent comprehensive performances (such as high temperature resistance, ablation resistance, thermal shock resistance, high thermal conductivity and impact resistance) have broadened the scope of potential and useful engineering applications. This paper also predicts the feasibility of complex structural 3D designs for rapid prototyping as well as aid development of the new sintering technology, such as cold sintering process and liquid silicon infiltration process, for the preparation of laminated ceramics. Keywords: Laminated ceramics, Properties, Toughening mechanism, Application

The tensile behavior of a C/SiC minicomposite fabricated by chemical vapor infiltration was examined and the associated damage evolution was monitored by using acoustic emission (AE) technique. Both the tensile behavior and the associated AE evolution of the minicomposites can be well characterized by three regimes including matrix cracking emergence, multiplication followed by matrix cracking saturation. The grey Verhulst model and inverse Verhulst model were established for the evolution of the cumulative AE energy and the stress-strain behavior, respectively. Excellent agreement between predictions and experimental results was obtained for both the grey models, which indicates the nature of intraspecific competition for these matrix cracks in the minicomposites studied. Such robust relationships can be further applied to model the constitutive behavior of other ceramic composite systems.

We report on the growth of SiC nanowires on a single crystal Si substrate by pyrolysis of polycarbosilane and using two catalyst (Al2O3 and Ni) films with different thickness (2, 4, and 6 nm). The catalyst films were deposited on the Si substrate, and the SiC nanowires were grown according to two mechanisms, i.e., the oxide-assisted growth mechanism and vapor- liquid-solid mechanism. As a result, pearl-chain-like SiC nanowires and straight SiC nanowires were obtained. The prepared nanowires exhibited excellent photoluminescence properties, emission spectra displaying two emission peaks at 395 and 465 nm, and have good thermal stability below 1000 °C. The experimental results revealed the importance of the catalyst in controlling the morphology and properties of SiC nanowires.

The thermodynamics and kinetics methods had been applied to study the effects of the deposition temperature, the reaction gas ratio and the dilution gas on Si _3 N _4 formation in the SiCl _4 -NH _3 -H _2 system. The studies revealed that raising the deposition temperature would accelerate the chemical reaction and increase Si _3 N _4 yield below 1400 K, higher temperature prompted the side reactions. With the increase of NH _3 concentration, the content of Si _3 N _4 in the reaction products also increased. As the diluent gas, H _2 could accelerate the reaction and the deposition of Si _3 N _4 . However, the excess dilution gas would carry away the reaction gas and inhibit the reaction. The comprehensive effect of temperature and gas ratio on Si _3 N _4 deposition were also analyzed by the three-dimensional figures. Finally, the optimal conditions for Si _3 N _4 preparation were suggested.

Abstract TiO2 is an ideal photocatalyst candidate except for its large bandgap and fast charge recombination. A novel laminated junction composed of defect‐controlled and sulfur‐doped TiO2 with carbon substrate (LDC‐S‐TiO2/C) is synthesized using the 2D transition metal carbides (MXenes) as a template to enhance light absorption and improve charge separation. The prepared LDC‐S‐TiO2/C catalyst delivers a high photocatalytic H2 evolution rate of 333 µmol g−1 h−1 with a high apparent quantum yield of 7.36% at 400 nm and it is also active even at 600 nm, resulting into a 48 time activity compared with L‐TiO2/C under visible light irradiation. Further theoretical modeling calculation indicates that such novel approach also reduces activation energy of hydrogen production apart from broadening the absorption wavelength, facilitating charge separation, and creating a large surface area substrate. This synergic effect can also be applied to other photocatalysts' modification. The study provides a novel approach for synthesis defective metal oxides based hybrids and broaden the applications of MXene family.

Short silicon nitride fibers were fabricated by direct nitridation of ferrosilicon in N2 atmosphere, and their structure and possible growth mechanism were characterized and investigated. The rod-like fibers which were α-Si3N4 with a low degree of crystallization and a high aspect ratio had a diameter of about 4 μm and a length close to a few millimeters. Belt-like fibers with a width about 5 μm and a thickness about 1 μm were also found in the nitrides. Scanning electron microscope (SEM), transmission electron microscope (TEM), high resolution transmission electron microscope (HRTEM), and selected area electron diffraction (SAED) investigations indicated that the fibers were single-crystalline α-Si3N4 with few amorphous distributed in the edge region, and the fibers grew by vapor–liquid–solid (VLS) mechanism.

A broadband microwave absorbing composite with a multi-scale layered structure is proposed, in which a reduced graphene oxide (RGO) film sandwiched between two layers of epoxy glass fiber laminates serves as the frequency selective surface (FSS). RGO films with the desired electrical properties were synthesized directly by hydrothermal reaction, vacuum filtration, and heat treatment without subsequent processing. With the novel layer-by-layer structure ranging from micro to macro scale, the optimized composite exhibits excellent microwave absorption performance with a total thickness of 3.2 mm. Its reflection coefficient (RC) is less than −10 dB in the entire X and Ku band, reaching a minimum value of −32 dB at 10.2 GHz and an average RC of −22.8 dB from 8 to 18 GHz. Enhanced microwave absorption of the composites is achieved through the optimization of layer thickness in the sandwich structure to promote destructive interference. Improved impedance matching by the introduction of FSS along with the polarization and conduction loss of layered graphene films also contribute to the increased absorption.

The mechanical and dielectric properties of two types of amorphous silicon nitride (Si3N4) fibers prior to and following annealing at 800 °C were studied. The tensile strengths of the Si3N4 fiber bundles were measured using unidirectional tensile experimentation at room temperature, whereas the permittivity values were measured at 8.2–12.4 GHz using the waveguide method. The results demonstrated that the tensile strength and dielectric properties of Si3N4 fibers were correlated to the corresponding composition, microstructure, and intrinsic performance of electrical resistance. The Si3N4 fibers with a lower content of amorphous SiNxOy presented an improved thermal stability, a higher tensile strength, a higher conductivity, and a significantly stable wave-transparent property. These were mainly attributed to the highly pure composition and decomposition of less amorphous SiNxOy.

Si3N4-Fe3Si composites were prepared using Fe-Si3N4 as the source of Fe3Si by gas-pressure sintering. By adding different amounts of Fe-Si3N4 into the starting powders, Si3N4-Fe3Si composites with various Fe3Si phase contents were obtained. The microstructure and mechanical properties of the composites were investigated. With the increase of Fe-Si3N4 contents, the content and particle size of Fe3Si both increased. When more than 60 wt. % Fe-Si3N4 were added, the abnormal growth of Fe3Si particles occurred and oversized Fe3Si particles appeared, leading to non-uniform microstructures and worse mechanical properties of the composites. It has been found that Fe3Si particles could toughen the composites through particle pull-out, interface debonding, crack deflection, and particle bridging. Uniform microstructure and improved mechanical properties (flexural strength of 354 MPa and fracture toughness of 8.4 MPa·m1/2) can be achieved for FSN40.

This study investigated the effects of CeO2 on structure and synthesis of boroaluminosilicate transparent glass ceramics containing CaF2 nanocrystals prepared through isothermal crystallization of the melt-quenched glasses with composition 54SiO2–10B2O3–13Al2O3–14Na2O–3ZnO–2Li2O–4CaF2 doped with 0–1.2 mol% CeO2. CeO2 in polyvalent states acting as network modifier leads to disruption of the silicate network and the conversion of [BO3] to [BO4] generating the nonlinear variations in crystallization, and thermodynamic and optical features. Glass transition temperature and the crystallization temperature decrease firstly and then increase with the increase of CeO2 content. Correspondingly, the size of CaF2 nanoscale crystals and the absorption coefficient of the glass ceramics are found to pass through a maximum and then decrease with increasing CeO2 addition. Increasing CeO2 concentration and elevating treating temperature lead to red-shift of absorption edge and transparency deterioration of glass ceramics.

SiBCN ceramics were introduced into porous Si3N4 ceramics via a low-pressure chemical vapor deposition and infiltration (LPCVD/CVI) technique, and then the composite ceramics were heat-treated from 1400 °C to 1700 °C in a N2 atmosphere. The effects of annealing temperatures on microstructure, phase evolution, dielectric properties of SiBCN ceramics were investigated. The results revealed that α-Si3N4 and free carbon were separated below 1700 °C, and then SiC grains formed in the SiBCN ceramic matrix after annealing at 1700 °C through a phase-reaction between free carbon and α-Si3N4. The average dielectric loss of composites increased from 0 to 0.03 due to the formation of dispersive SiC grains and the increase of grain boundaries.

To improve the thermal and mechanical stability of SiCf/SiC or C/SiC composites with SiBN interphase, SiBN coating was deposited by low pressure chemical vapor deposition (LPCVD) using SiCl4-BCl3-NH3-H2-Ar gas system. The effect of the SiCl4 flow rate on deposition kinetics was investigated. Results show that deposition rate increases at first and then decreases with the increase of the SiCl4 flow rate. The surface of the coating is a uniform cauliflower-like structure at the SiCl4 flow rate of 10 mL/min and 20 mL/min. The surface is covered with small spherical particles when the flow rate is 30 mL/min. The coatings deposited at various SiCl4 flow rates are all X-ray amorphous and contain Si, B, N, and O elements. The main bonding states are B-N, Si-N, and N-O. B element and B-N bonding decrease with the increase of SiCl4 flow rate, while Si element and Si-N bonding increase. The main deposition mechanism refers to two parallel reactions of BCl3+NH3 and SiCl4+NH3. The deposition process is mainly controlled by the reaction of BCl3+NH3.

The evolution of the thermal conductivities of the unidirectional, 2D woven and 3D braided composites during the CVI (chemical vapor infiltration) process have been numerically studied by the finite element method. The results show that the dual-scale pores play an important role in the thermal conduction of the CVI-densified composites. According to our results, two thermal conductivity models applicable for CVI process have been developed. The sensitivity analysis demonstrates the parameter with the most influence on the CVI-densified composites’ thermal conductivity is matrix cracking’s density, followed by volume fraction of the bundle and thermal conductance of the matrix cracks, finally by micro-porosity inside the bundles and macro-porosity between the bundles. The obtained results are well consistent with the reported data, thus our models could be useful for designing the processing and performance of the CVI-densified composites.