Search

The fatigue damage of fiber-reinforced ceramic matrix composites is characterized by the occurrence of multiple mechanisms in sequence and their interactions. The nonlinear stress-strain behavior is caused by micro-fracture events such as matrix cracking, fiber/matrix debonding, and fiber fracture. Clarifying damage types and their evolution process is of great significance for the optimization design of materials and accurate prediction of their mechanical behavior. In this paper, the tension-tension fatigue damage behavior of a plain-woven SiC/SiC composite was investigated via acoustic emission (AE) at elevated temperatures, unsupervised classification method was used to classify the damage mechanism, and quantitative analysis was carried out. The results showed that: Compared with 1200℃, the fatigue strength at 1350℃ is significantly reduced, and the fatigue life of SiC/SiC at high temperature is sensitive to temperature and stress; The damage types of SiC/SiC can be effectively identified, classified and quantified by K-means algorithm combined with AE amplitude and ringing count parameters; Based on the damage type and damage degree of the material, AE technology can also identify the fatigue damage stage of SiC/SiC material. Under high-temperature fatigue loading, the presence of microcracks and prolonged exposure to an air environment result in significant oxidation features on the crack surfaces of the specimen, the fiber pull-out lengths are relatively short, and some regions of the matrix show clear signs of melting. [ABSTRACT FROM AUTHOR]

In this work, we studied the effects of protective boron nitride/silconaluminocarbide (BN/SiAlC) interphases on the structural and mechanical properties of fabricated stacked carbon fiber-reinforced SiC ceramic matrix composites (C f /SiC CMCs) via the hot-press sintering route. The structural analyses were carried out by X-ray diffraction and scanning electron microscopy (SEM), while mechanical properties were elucidated by employing universal testing machine. The observed sharp diffraction peaks indicate excellent crystallization, and the formation of 4 H -SiC polytype was attributed to the partial transition of β -SiC phase during high-temperature sintering. The composite with single BN interface layer revealed enhanced bending strength of up to 364 ± 39.46 MPa (↑40 %), while composite with double layered interface showed optimal strength of 436 ± 33.54 MPa, and toughness of 6.11 ± 0.74 MPa m1/2, with increments of 67.7 % and 128.8 %, respectively, compared to the composite without interphase layer. In the composite with duplex interfacial layer (3BN/SiAlC), the microcracks generated during fracture propagated into the BN layer, deflected through both the sublayers and at the fiber-BN interface, resulting in fiber pull out using fracture energy, leading to the enhanced strength and toughness of the composite. The load-displacement curve revealed that the stacking C f /SiC CMCs with weak interlayer binding owing to the BN/SiAlC coating treatment possesses significant toughness to the SiC ceramics. [ABSTRACT FROM AUTHOR]

Controlled shrinkage of hydrothermal carbon coating (HTCC) during its carbonization preparation process offers a novel strategy for optimizing the interfacial properties of fiber-reinforced ceramic matrix materials. In this study, the effect of volumetric shrinkage in monolayer or bilayer HTCC on the interface characteristics and mechanical properties of C f /ZrB 2 -SiC composites is investigated. The bilayer HTCC significantly enhances the crack deflection effect within the interphase compared to the monolayer HTCC. By precisely controlling the shrinkage of the layers of the bilayer HTCC, an innovative C/SiC/C trilayer interphase was synthesized in situ during the polymer infiltration process for preparing the C f /ZrB 2 -SiC composites, which synergistically enhances stress dispersion and load transfer efficiency within the interface. The work of fracture for C f /ZrB 2 -SiC composites modified by the trilayer interphase has been significantly elevated to 2258 J/m2, which far exceeds the 129 J/m2 measured for the composites lacking a HTCC interphase. [ABSTRACT FROM AUTHOR]

To solve rapid failure of SiC Fiber-reinforced SiC Ceramic Composites (SiC f /SiC) under water-oxygen corrosion environment, novel SiC f /Si-Y-C-B-Yb composites was prepared in this study by Slurry Impregnation (SI) combined with Reactive Melt Infiltration (RMI) methods. Effects under different infiltration temperature on microstructures and mechanical properties of SiC f /Si-Y-C-B-Yb composites were systematically studied. Results showed that as the melting temperature rose, no significant differences were recorded in apparent density of SiC f /Si-Y-C-B-Yb composites while the porosity gradually increased. However, the Y diffusion layer gradually became thicker and changed from one layer to two layers due to the high temperature promoting the migration rate of Y element. Moreover, it revealed good corrosion resistance of SiC f /Si-Y-C-B-Yb composites in 50 vol% H 2 O+50 vol% O 2 water-oxygen environment. At corrosion temperatures below 1250 °C, strength retention rate of SiC f /Si-Y-C-B-Yb composites significantly increased by 21.12 %, a value higher than that of SiC f /SiC composites. One hand, the formation of silicate phase on SiC f /Si-Y-C-B-Yb composites surface rose corrosion resistance, hindering further erosion from water-oxygen atmosphere. On the other hand, Oxidation activation energy of SiC f /SiC composites was estimated to be 131 kJ/mol while that of SiC f /Si-Y-C-B-Yb composites was 269 kJ/mol. Thus, SiC f /Si-Y-C-B-Yb possessed excellent performance in resisting water-oxygen corrosion. [ABSTRACT FROM AUTHOR]

Currently, the primary method for preparing alumina fiber-reinforced alumina ceramic (Al 2 O 3f /Al 2 O 3) composites is the slurry impregnation (SI) process. However, this technique is plagued by the challenge of necessitating a high sintering temperature. Hence, an attempt was initiated to prepare Al 2 O 3f /Al 2 O 3 composites through the polymer impregnation and pyrolysis (PIP) method, with the objective of reduce thermal damage to the fibers during the preparation process. The high-temperature inorganic processing of the Al 2 O 3 precursor was studied, ultimately leading to the selection of 900 °C as the optimal pyrolysis temperature for the PIP process. The microstructure and high-temperature mechanical properties of the obtained composites were studied. The results indicated that the composites maintained microstructure stability up to 1000 °C. The flexural strength almost unchanged (from 37.20 ± 4.09 MPa to 37.03 ± 2.01 MPa). At 1200 °C, the formation of mullite greatly increased the defect density in the matrix, leading to a decrease in the flexural strength (28.42 ± 5.50 MPa). After heat treatment at 1400 °C, some of the blocky matrix dissolved and filled partial pores, improving the flexural strength (42.60 ± 1.95) of the composites. The continuous increases in flexural modulus meant that the brittleness of the composites became stronger with increasing temperature. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Materials Engineering / Cailiao Gongcheng is the property of Journal of Materials Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Recently, SiC-continued fiber-reinforced ceramic matrix composites were widely used in high-temperature absorbing materials. However, the excessive carbon content indicated the deteriorative absorbing property. To solve the impedance mismatching of the SiC matrix and increase the charge accumulation at the multi-phase interface, SiCf/mullite composites were prepared in this paper by using the sol–gel method. The introduction of mullite matrix without free carbon improved impedance matching characteristics. The strong bonding between the in situ grown SiO2 layer and the mullite matrix caused by high temperature induced the Maxwell–Wagner effect, which effectively optimized the absorbing performance. The complex dielectric constant of the composite increased with higher sintering temperatures. The highest reflection loss reached − 23.1 dB at the sintering temperature of 1100 °C. With the two-step drying process, the porosity was reduced to 16.1% and the density increased. The crystallinity and density of the mullite matrix increased in the rising sintering temperatures, with the highest bending strength reaching 157.89 MPa for composites sintered at 1100 °C. [ABSTRACT FROM AUTHOR]

The AA7075 alloy and AA7075/SiC/Gr hybrid composite prepared by the stir-casting method have been further thermo-mechanically processed through unidirectional hot rolling and hot cross-rolling routes to eliminate casting defects like voids, blow holes etc. Three initial sample temperatures, that is, 350℃, 400℃, and 450℃, have been considered for the hot cross-rolling. The Al alloy and its hybrid composite prepared at different rolling temperatures are studied to investigate their micro-machining behavior through micro-electric discharge machining (µ-EDM). The micro-holes are made on the rolled samples along the rolling direction of the final rolling pass using a tool with twist drill bit geometry. Further, multi-objective optimization of the µ-EDM process parameters considering the response parameters viz. material removal rate (MRR) and tool wear rate (TWR) has been carried out using the gray relational analysis (GRA) technique. The µ-EDM parameters chosen to optimize in this study are voltage, pulse on time, and tool rotation. The obtained GRA results are further analyzed through normality and equal variance tests. The R-squared values of 95.02% and 95.53% for AA7075 alloy and hybrid composite, respectively, indicate that the data fit well with the statistical model. In material removal, the different electrical and thermal characteristics of the Al matrix and the reinforcements possibly generate sparks with a different characteristic that ultimately affects the MRR of the composite. Through scanning electron microscopy (SEM), the morphological study confirmed the presence of globules and voids on the machined surface. The formation of globules and voids is more significant in the AA7075 alloy than in the composite. [ABSTRACT FROM AUTHOR]

Carbon fiber-reinforced ceramic matrix composites have excellent heat resistance and wear resistance, making them extensively utilized in the aviation and aerospace industries. However, processing carbon ceramics is challenging due to the inherent difficulty. Traditional hole-making methods often result in issues such as delamination and tearing during the processing of carbon ceramics. Helical grinding has emerged as a novel processing technology that shows promise for difficult materials like carbon ceramics. To address the lack of clarity regarding the removal mechanism and formation mechanism of material damage during helical grinding of carbon ceramic materials, firstly, this study models the trajectory and maximum undeformed chip thickness for a single abrasive. Subsequently, this study analyzes the influence of fiber anisotropy on the removal mechanism during helical grinding of carbon ceramics. The study also investigates the mechanisms behind exit damage occurring during carbon ceramic helical grinding processes. Finally, this study examines helical grinding technological parameters that affect surface quality by analyzing their impact on undeformed chip thickness. The results indicate that the matrix occurs brittle fracture during helical grinding. Four typical removal mechanisms emerge for different fiber angles: debonding is predominant at 0°; fiber fracture occurs at 45°; fiber shear occurs at 90°; fiber pull-out occurs at 135°. Hole exit damage is influenced by fiber direction with minimal damage observed when shear fracture occurs at angles 45° and 90° while burrs phenomenon and tear phenomenon are prevalent at angles 0°and 135°, respectively. By increasing orbital rotation speed and spindle speed or decreasing feed pitch, surface quality improved. Grinding parameters significantly affect surface quality by changing undeformed chip thickness and surface residual height. [ABSTRACT FROM AUTHOR]

The biggest difficulty facing the grain growth (TGG) method is the compatibility between template and ceramic matrix. Different templates show great differences in texture degree. Consider the limitation of conventional single-template method, the strategy of dual-template textured ceramics and sintering aids were introduced in this work. With the addition of ST and NN templates into BNT system, the texture degree is higher than 90% and the electrostrain reach ∼ 0.5% with ultra-low hysteresis ∼ 15%, which cannot be realized in single template textured ceramics. The two templates and sintering aids play different roles in grain orientation growth, which is important for the compatibility among matrix and templates, leading to unique microstructures. Sintering processes clearly reveal the growth mechanism of textured ceramics under the joint action of two templates, and of course, the sintering aids are also indispensable. Regard to domain structure, the polar nanoregions can respond quickly under electric field, providing assistance for the realization of ultra-low hysteresis. [ABSTRACT FROM AUTHOR]

A novel approach to the utilization of (Ca, Mg)-Zr phosphate adsorbents saturated by Cs+, Sr2+, Co2+ ions was developed. The main stages include: (i) Cs+, Sr2+, Co2+ ions adsorption, (ii) the drying and shaping by cold pressing, (iii) the sintering. Metal ions leaching from the powder of the spent adsorbent were 0.2–26.5 % in distillation water (рН 4.0–10.0) and tap water, and increased to 6.4–68.2 % in seawater. Calcination of spent adsorbents at 1000 °C led to a decrease in Cs+, Sr2+, Co2+ ions leaching to less than 1.0 % in tap and seawater. The ceramic matrices with a Cs+, Sr2+, Co2+ content of 8.0–30.2 wt %, mechanical compressive strength of 2.9–260.9 MPa, leaching rate of 1.0×10−4 - 4.3×10−7 g/(cm2×day), density of 1.4–3.4 g/cm3 were obtained by cold pressing with subsequent sintering. The samples obtained at molar ratios Zr/(Ca+Mg) of 0.35 and 0.21 were characterized by the highest compressive strength and Cs+ and Sr2+, Co2+ leaching resistance, respectively. The obtained ceramic matrices fitted to the requirements of GOST R 50926–96 and NRC 1991 for solid high-level waste forms. • A novel approach to the utilization of spent (Ca, Mg)-Zr phosphates was proposed. • Thermal transformations of Cs-, Sr-, Co-saturated adsorbents were studied. • The mechanism of Cs+, Sr2+, Co2+ ions leaching from ceramics was proposed. • The NZP ceramic matrices for safe radionuclide immobilization were obtained. [ABSTRACT FROM AUTHOR]

Due to the anisotropic characteristic of carbon fiber-reinforced silicon carbide ceramics, the fiber orientation angle significantly affects the grinding force. Therefore, it is important to study the influence rule of different fiber orientations on the grinding force of 2.5D-Cf/SiC composites. To study the comprehensive influence of machine tool parameters and the anisotropy of carbon fiber-reinforced ceramic matrix composites on the grinding force, two-dimensional ultrasonic plane grinding was studied by orthogonal test and single-factor experiment. Based on the multi-exponential fitting analysis method of multiple linear regression equation, the empirical equations of power exponential grinding force prediction model of 2D ultrasonic-assisted grinding and conventional grinding 2.5D-Cf/SiC composites at 0°, 45°, and 90° fiber orientation and considering fiber orientation and ultrasonic amplitude were established, respectively. To verify the empirical formula model in predicting the grinding force of 2.5D-Cf/SiC composites under various fiber orientation angles, the regression equation and regression coefficient of the model were examined. The influence of 2.5D-Cf/SiC grinding parameters on the grinding force was analyzed. The parameters of the grinding force model were optimized based on range analysis and variance analysis, and the optimal process parameter combination was obtained. The results show that the grinding force is negatively correlated with the linear speed and positively correlated with the feed speed and grinding depth within the range of experimental parameters. The maximum reduction of the normal grinding force is 29.78% when the line speed is 10.48 m/s, the feed speed is 100 mm/min, the grinding depth is 50 μm, and along the 45° fiber direction. The optimal grinding parameter combination is a line speed of 23.60 m/s, feed speed of 5 mm/min, and grinding depth of 10 μm along the 0° fiber orientation. [ABSTRACT FROM AUTHOR]

Binderless WC matrix cemented carbide was considered a novel material with the potential to replace WC-Co cemented carbide. However, current research was insufficient to address the trade-off between strength, toughness, and strength in binderless WC matrix cemented carbide. In this work, the machine learning was employed to estimate mechanical property and optimize the composition of WC matrix cemented carbide. WC-MgO-ZrO 2 composites were successfully developed with uniform microstructure and excellent mechanical properties. The experimental results showed that the grain size of WC reached 1.05μm where the mass fraction of ZrO 2 was 2%. The WC-MgO-2 wt%ZrO 2 composite exhibited superior Vickers hardness, fracture toughness, and flexural fracture strength, which were 1851HV, 11.2 MPa·m1/2 and 1368 MPa, respectively. The fracture mode of WC-MgO-ZrO 2 composites was mainly a mixture of transgranular fracture and intergranular fracture. The main toughening mechanisms were crack deflection, crack bridging, grain pull out and phase transformation. The comprehensive mechanical properties of WC-MgO-2 wt%ZrO 2 composites rank at a superior level compared to similar binderless WC matrix composites reported in the current literature. Meanwhile, the wear behaviors of WC-MgO-ZrO 2 composites were examined under three different loads. And the wear behavior and mechanism of WC MgO-2 wt% ZrO 2 composite were revealed. [ABSTRACT FROM AUTHOR]

In order to improve the performance of polymer-derived ceramics and expand its application field, the formulation of the photosensitive resin was further optimized and on the basis of modification, the two-dimensional filler h -BN was introduced in this paper. It was found that both the content of PVSA in the photosensitive resin and the introduction of h -BN had remarkable impacts on the properties of the polymer-derived ceramics. When the h -BN content in the PVSA photosensitive resin was 1 wt%, the bending strength and fracture toughness of the ceramic sample after pyrolysis reached 252.4 ± 12.2 MPa and 2.7 ± 0.2 MPa·m1/2, respectively. With the increase of h -BN content, the thermal conductivity of the composite ceramics increased from 0.44 W·m−1·K−1 to 5.34 W·m−1·K−1. It is concluded that the thermal, electrical, and mechanical properties of precursor ceramics are improved by the introduction of two-dimensional fillers of h -BN. [ABSTRACT FROM AUTHOR]

In the aerospace industry, lightweight can reduce the weight of the engine and improve the thrust-weight ratio of the engine. Ceramic matrix composites have attracted widespread attention in the industry due to their much lower density compared to high-temperature alloys and excellent high-temperature performance. SiC fiber-reinforced SiC ceramic matrix composites are the most outstanding representatives, but their long manufacturing cycle and high manufacturing costs limit their widespread use. Ti 2 AlC is a new type of ceramic material with the characteristics of low density, high melting point, high-temperature resistance, oxidation resistance, and corrosion resistance of ceramic materials, as well as the conductivity and machinability of metals. However, its mechanical properties are slightly inadequate. The use of chopped fibers for toughening can compensate for these deficiencies to a certain extent and improve mechanical properties. This article first explored the influence of various process parameters on the mechanical properties of pure-phase Ti 2 AlC ceramic materials in SPS preparation technology and then prepared Ti 2 AlC composites reinforced with 10 vol%, 20 vol%, and 30 vol% Al 2 O 3 chopped fibers. The results showed that the samples prepared at 1300 °C, 40 MPa, and 10 min had a flexural strength of 697 MPa and a fracture toughness of 9.83 MPa m1/2 when the volume ratio of the reinforcement phase was only 10 vol%, which was the same as that of the continuously fiber-reinforced SiC f /SiC composites. This study showed that the MAX phase matrix composites reinforced with chopped fibers have the potential to become high-temperature structural materials by adjusting the composite composition and optimizing the preparation process. [ABSTRACT FROM AUTHOR]

Using citric acid, ethylene glycol, ZrOCl2·8H2O, HfOCl2·8H2O, TiCl4, NbCl5, and TaCl5 as raw materials, the (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C high‐entropy ceramic precursor was prepared by Pechini coordination polymerization method. The precursor and pyrolysis products were analyzed and characterized by different methods. The results showed that the precursor formed a chelate structure, which greatly improved the stability of the precursor, and was clear and transparent with moderate viscosity (30–50 mPa·s). At a low pyrolysis temperature of 1600°C, single‐phase (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C high‐entropy ceramic nanopowders with a ceramic yield of 50.8% can be obtained. The high‐entropy ceramic powder has high purity, a particle size of about 140–200 nm, and uniform element distribution. It is suitable for introduction into fiber‐reinforced ceramic matrix composite by precursor infiltration and pyrolysis (PIP) process. [ABSTRACT FROM AUTHOR]

Functionally graded composites with fibre gradients were prepared with three different ceramic matrices: ZrB 2 -SiC-Y 2 O 3 , ZrB 2 -MoSi 2 and SiC-Y 2 O 3 , with short carbon fibres in amounts ranging from 0–50%. Short term oxidation tests at 1650 °C in air were carried out to study the influence of the graded architecture and fibre content on the structural stability and oxidation resistance. The composite layers were perfectly joined at the interface, with no visible defects. Even after oxidation testing, no spallation phenomena were observed. ZrB 2 -MoSi 2 matrix proved to be the most effective in protecting the composite from oxidation thanks to the formation of a compact ZrO 2 -SiO 2 scale. • Fibre gradient, ultra-refractory ceramic composites were produced by sintering. • Bulk ceramic layers and fibre reinforced layers were joined without cracks or spallation. • Oxidation tests at 1650 °C did not affect the structural integrity of the graded composites. • Out of the three ceramic matrices tested, ZrB 2 /MoSi 2 proved to be the most performing. [ABSTRACT FROM AUTHOR]

Ceramic aerogels are promising candidates for high-temperature thermal resistance and thermal insulation materials. However, their application can be restricted by their brittleness when exposed to harsh conditions. Herein, this study has developed a novel synthesis process based on a sol-gel method and carbothermal reduction-nitridation to produce a porous TiN composite aerogel from an organic/inorganic hybrid. The resulting TiN displays a polyhedral particle size of around 30–60 nm with nanoscale pores. In addition, the TiN aerogel demonstrates a high BET-specific surface area of 653.42 m2/g and a very low thermal conductivity of 0.046 W/(m·K). Furthermore, the TiN aerogel composite displays a good thermal difference with no shrinkage and cracks of the morphology during the butane blazing torch at 1300 °C for 10 min under air environment, demonstrating its excellent thermal insulation property and anti-oxidation characteristics. The gas-solid reaction mechanism of TiN aerogel based on the Gibbs free energy calculations is also proposed. [ABSTRACT FROM AUTHOR]

Covalently bonded silicon carbide (SiC) ceramics exhibit preeminent properties, yet their application scope is still challenged because the low self-diffusivity makes densification difficult. Herein, we use different sintering aids (TiO 2 , TiO 2 /Y 2 O 3 , and ZrO 2 /Y 2 O 3) to liquid-phase sinter SiC ceramics. The formation mechanism as well as the microstructure of the intergranular phase (IGP) and the interfacial relation between IGP and matrix grains on the densification and mechanical properties of the material were studied. The results showed that the formed IGP greatly differed in morphology, crystalline nature, and interface structure with the matrix grains. Particularly, fully dense SiC ceramic with a continuous network structure crystallized IGP was fabricated using ZrO 2 /Y 2 O 3. Benefiting from the proper bonding strength between the IGP and matrix grains, crack deflection took place at the interface between the two, which could enhance the flexural strength and fracture toughness of SiC ceramic up to 725 MPa and 7.27 MPa·m0.5, respectively. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced silicon carbide ceramic matrix composites (C f /SiC composites) have a wide range of applications in aerospace, nuclear energy, braking systems owing to its excellent mechanical performance. Nevertheless, the hardness, brittleness, heterogeneity, and anisotropy of C f /SiC composites give rise to difficulties in machining them. In addition, the characterization and formation mechanism of surface damage in the grinding of C f /SiC composites have not been fully elucidated. The purpose of this paper is to provide a characterization method for surface damage of C f /SiC composites and an evaluation index for surface edge chipping damage (SECD) through conventional scratching (CS) / ultrasonic vibration assisted scratching (UVAS) tests with single abrasive. Towards revealing the surface damage behavior of C f /SiC composites during scratching, as well as the impact of fiber orientation on surface damage. The findings indicate that main forms of surface damage of C f /SiC composites in single abrasive scratching are fiber breakage, fiber fracture-shedding, fiber fracture, fiber-matrix interface debonding, interface fragmentation, matrix cracking, and matrix microcracks. Further, ultrasonic vibration could help to suppress the SECD, and the SECD factor was smallest when scratching along the perpendicular fiber. Furthermore, the fiber orientation can significantly affect the scratching force and cross-sectional area of scratches on C f /SiC composites via single abrasive scratching. The tangential scratching force was usually smaller as compared to the normal scratching force, and the cross-sectional area of scratches in UVAS is smaller than that in CS. Based on the above findings, this study elucidates the formation and evolution of surface damage after scratching under different fiber orientations, filling the research gap in surface damage under ultrasonic assisted machining of C f /SiC composites and providing technical guidance for the machining. [Display omitted] [ABSTRACT FROM AUTHOR]

Strong, tough, and almost fully dense unidirectional SiC f /BSAS composites were obtained through the slurry infiltration and hot-pressing process. The 0.75BaO-0.25SrO-A1 2 O 3 -2SiO 2 mixed precursor synthesized by solid state reaction from metal oxides was utilized as the matrix slurry. SiC fibers with BN/C/SiN x /C coating served as reinforcements. During hot pressing, the monoclinic celsian phase in the matrix was produced in situ. The composite exhibited graceful failure in three-point bend tests at room temperature. The flexural strength and strain reached 315.37 MPa and 0.44 %, respectively. With the help of the BN/C/Si 3 N 4 /C coating, the SiC fibers occur debonding and pull-out, exhibiting outside debonding features. After annealing in O 2 at 850 °C for 10 h, the strength retention rate of the composites was 95.41 %, showing excellent stability for in thermal structural components. [ABSTRACT FROM AUTHOR]

Copyright of Gazi Üniversitesi Fen Bilimleri Dergisi Part C: Tasarım ve Teknoloji is the property of Gazi University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Ceramics / Taoci Xuebao is the property of Journal of Ceramics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

One of the enormous challenges of bio-composites is the improvement of the flexural and impact strength. Therefore, the optimization and parametric investigation of nanocomposites reinforced with natural hybrid fibers is the main focus of this study. Kenaf/basalt/nanographene fibers in polypropylene were used to reinforce bio-composite specimens. Response Surface Method (RSM) was applied to study and present a mathematical model for the performance of bio-composite according to a number of parameters including the basalt fiber weight percentage, kenaf fiber as well as nanographene. The performance of the specimens was discussed under the bending and impact tests and the outcomes were explained by the use of FESEM images. The optimal value of the parameters was set as a multi-objective according to the increase of the flexural strength and energy absorption, the reduction of the specimens' weight, and also a Pareto diagram was illustrated considering the design goals. The findings revealed that the composite specimen with the best flexural behavior had the flexural strength of 51.2558 MPa, which consisted of 0.8723 wt% of basalt fibers, 15% of kenaf fibers, and 0.76881% of graphene nanoparticles. In addition, the best specimen in terms of impact had 116,809 J / m energy absorption, which included 8.23% basalt fibers, 0.808% graphene nanoparticles, and 15% kenaf fibers. [ABSTRACT FROM AUTHOR]

Silicon carbide fiber reinforced silicon carbide ceramic matrix composite (CMC SiC f /SiC) has the advantages of high temperature resistance, corrosion resistance, high strength, low density, and oxidation resistance. It is a high-performance advanced material in aerospace, energy and other fields. However, due to its high hardness, brittleness and anisotropy of fiber structure, the research on application-oriented high-quality processing technology has become a hot issue. In this paper, a new process of rotational thirteen-beam coupling nanosecond laser processing of CMC-SiC f /SiC was studied. The rotational thirteen-beam coupling ablation experiments were carried out on CMC-SiC f /SiC workpiece. A laser beam is divided into thirteen beams and rotated around the beam center by using a beam splitter element. The morphology, structure and composition of ablation holes at different speeds were observed and analyzed by laser confocal microscope, scanning electron microscope, and X-ray energy dispersive spectrometer. It is found that the characteristics of rotational beam coupling have a significant effect on the laser ablation morphologies. The results show that the ablation region of CMC-SiC f /SiC is elliptical due to the fast heat transfer of fibers. The energy density distribution of the waist section of the Gaussian like beam after beam coupling is similar to the "W" shape, and the central energy is lower than the surrounding energy, and the ablation holes also show a similar "W" shape. With the increase of rotational speed, the hole depth first decreased and then increased, the hole diameter and roundness first increased and then decreased, and the hole section was "W" shaped. The ablation area can be divided into five parts: the white granular SiO 2 solid coverage area, the recast layer, the lower recast layer, the molten layer, and the heat affected zone. The rotational characteristics will make the reaction intensity of the whole ablation area more uniform in the circumferential direction. The formation mechanism and element distribution of each part were explored. The research work in this paper will provide a new technical way for the high-performance application of CMC-SiC f /SiC. [ABSTRACT FROM AUTHOR]

An additive manufacturing process and subsequent pyrolysis cycle were used to fabricate SiC matrix/carbon fiber hybrid composites. The matrix was fabricated using a mixture of preceramic polymer and acrylate monomers, while polyacrylonitrile (PAN) precursor was used to fabricate fibers via electrospinning. The precursor matrix and reinforcing fibers at 0, 2, 5, or 10 wt% were printed using digital light processing, and both were simultaneously pyrolyzed to yield the final ceramic matrix composite structure. After pyrolysis, XRD and SEAD analysis proved the existence of SiC nanocrystals and turbostratic carbon structure in the matrix, while the reinforcement phase was shown to have a turbostratic carbon structure similar to commercial carbon fibers. Thermogravimetric analysis (TGA) in air up to 1400 °C was used to evaluate the oxidation resistance of this material. TGA results showed some weight loss due to oxidation of SiC and/or carbon up to about 900 °C, followed by weight gain to about 1200 °C due to the formation of a protective SiO 2 layer. Although increasing carbon fiber content negatively impacted the total mass loss for the first heating cycle, exposure of the composite to second-run air revealed negligible weight loss. This is explained by SiO 2 layer formation which acts as a protective film that prevents oxygen diffusion. Oxidation of SiC and the formation of a glassy layer has been proven to protect the sample from further oxidation, as well as provide healing of surface cracks and defects as revealed by SEM analysis. [ABSTRACT FROM AUTHOR]

The long-term periodicity and uncontrollable interface properties during the preparation process for silicon carbide fiber reinforced silicon carbide-based composites (SiCf/SiC CMC) make it difficult to thoroughly investigate their mechanical damage behavior under complex loading conditions. To delve deeper into the influence of the interface strength and toughness on the mechanical response of microscopic representative volume element (RVE) models under complex loading conditions, in this work, based on numerical simulation methods, a microscale representative volume element (RVE) with periodic symmetric boundary conditions for the material is constructed. The phase-field fracture theory and cohesive zone model are coupled to capture the brittle cracking of the matrix and the debonding behavior at the fiber/matrix interface. Simulation analysis is conducted for tensile, compressive, and shear loading as well as combined loading, and the validity of the model is verified based on the Chamis theory. Further investigation is conducted into the mechanical response behavior of the microscale RVE model under complex loading conditions in relation to the interface strength and interface toughness. The results indicate that under uniaxial loading, increasing the interface strength leads to a tighter bond between the fiber and matrix, suppressing crack initiation and propagation, and significantly increasing the material's fracture strength. However, compared to the transverse compressive strength, increasing the interface strength does not continuously enhance the strength under other loading conditions. Meanwhile, under the condition of strong interface strength of 400 MPa, an increase in the interface toughness significantly increases the transverse compressive strength of the material. When it increases from 2 J/m2 to 20 J/m2, the transverse compressive strength increases by 28.49%. Under biaxial combined loading, increasing the interface strength significantly widens the failure envelope space under σ2-τ23 combined loading; with the transition from transverse compressive stress to tensile stress, the transverse shear strength shows a trend of first increasing and then decreasing, and when the ratio of transverse shear displacement to transverse tensile/compressive displacement is −1, it reaches the maximum. This study provides strong numerical support for the investigation of the interface properties and mechanical behavior of SiCf/SiC composites under complex loading conditions, offering important references for engineering design and material performance optimization. [ABSTRACT FROM AUTHOR]

Ultrasonic-assisted grinding (UAG) can effectively reduce the grinding force and improve the machining quality of carbon fiber-reinforced ceramic matrix composites (C/SiC) due to its excellent machining performance. Many researches have shown that the machining performance of UAG is closely related to the kinematic trajectory characteristics of the abrasive grains, so the surface morphology of diamond grinding wheels with various process preparations has an important influence on the grinding quality. In this paper, to investigate the performance of UAG of C/SiC composites with diamond grinding wheels prepared by different processes, UAG experiments were carried out on C/SiC composites using diamond grinding wheels prepared by brazing and electroplating processes. The trajectories of the abrasive grains and the maximum undeformed chip thicknesses with different abrasive grain protrusion heights were analyzed and the impact of the two diamond grinding wheels and the grain mesh size on the grinding force, surface roughness, and surface morphology were comparatively investigated. The results indicated that the grinding force and surface roughness obtained by brazed grinding wheels were reduced by 13 ~ 36.05% and 5.95 ~ 19.3% compared with electroplated diamond wheels at 240#, respectively. The brazed grinding wheels could improve the grinding surface morphology to a certain extent. However, the surface roughness value fluctuated with the increase of abrasive grain size. Additionally, the protrusion height of the abrasive grain of the brazed diamond wheels is more favorable for the UAG effect and the grinding wheels are less prone to clogging. [ABSTRACT FROM AUTHOR]

Silicon carbide ceramic matrix composites (SiC CMC) have excellent properties for applications but is challenging to precisely process, in particular for curved surfaces and deep through-holes. A long interaction range of femtosecond laser filament with sufficiently high intensity may open the opportunity. In this work, femtosecond laser filament was used to ablate grooves on the surface of SiC CMC. The effects of different filament positions, pulse energies, scanning speeds and scanning times on filament ablated grooves were investigated. The plasma fluorescence from filament ablated SiC CMC was collected to monitor filament micro-grooving processes. The variation of fluorescence spectral lines of SiⅠ390.55 nm reflects the removal rate of material surface with different processing parameters, which helps understand the filament ablated grooves processes. Although using plasma fluorescence to monitor filament ablated SiC CMC was demonstrated by the intensity measurement, the method can be in principle extended for online imaging the laser ablation process. [ABSTRACT FROM AUTHOR]

Coated nuclear fuel particles, most commonly tri-structural isotropic (TRISO), are intended for use in advanced high temperature reactors. It is vital to understand the mechanical properties of each coating layer to accurately predict the performance of these fuel particles and how these might change at each stage of their lifecycle. This paper reports results of in-situ nanoindentation, with an emphasis on the structural SiC layer, along with microcantilever testing of the critical SiC-IPyC interface. At 1000 °C the hardness of the SiC layer is ∼75% lower than at room temperature implying significantly more plasticity at the reactor operating temperature. The elastic modulus was slightly lower at 1000 °C than at room temperature. Microcantilever fracture at the SiC-IPyC interface shows that failure occurs within the pyrolytic carbon layer rather than an interfacial "debonding" with a strength similar to that of bulk pyrolytic carbon. [ABSTRACT FROM AUTHOR]

Silicon carbide fiber‐reinforced SiC ceramic matrix composites (SiCf/SiC CMCs) based on a domestic KD‐SA SiC fiber were exposed to a wet oxygen atmosphere for 135 h at 800, 1100, and 1300°C. The evolution of the microstructure and mechanical properties of SiCf/SiC CMCs have been systematically investigated following oxidation. For weight change, CMC‐1300 showed the greatest gain (0.394%), followed by CMC‐1100 (0.356%) and CMC‐800 (0.149%). The volatilization of boron oxide (B2O3) combined with the slight oxidation of the SiC matrix at 800°C caused crack deflection and fiber pull‐out. The complete dissipation of the interphase could be found when the oxidation temperature increases to 1100°C, generated a fracture surface with brittle fracture characteristics. At 1300°C, crystalline SiO2 hindered oxygen diffusion, with evidence of fiber pull‐out. Based on thermodynamic calculations and microscopic observations, we propose a mechanism to explain the thermal degradation of SiCf/SiC CMCs. This work offers valuable guidance for the fabrication of SiCf/SiC CMCs that are suitable for high‐temperature applications. [ABSTRACT FROM AUTHOR]

The phenomenon caused by the competition between self‐healing and crack propagation of self‐healing fiber‐reinforced ceramics was succeeded to be quantified as a new mechanical function. To quantify, it was measured in detail that the creep deformation as time variation of the self‐healing composite under various stresses. In particular, a detailed analysis will be carried out focusing on the time variation of the creep rate. When the tensile stress of 100 MPa was applied to the self‐healing composite, the initially large creep rate decreased with time, eventually reaching zero. This behavior is considered to be achieved by self‐healing that suppresses crack propagation. The time when the creep rate reaches 0 is an important indicator of self‐healing ability and was defined as the crack arrest time. From the results of similar experiments in which the applied stress was varied, it was found that the crack arrest time increased with the applied stress. However, at 160 MPa, creep fracture occurred. From these results, it was confirmed that the maximum stress at which the competition behavior could be expressed was 153 MPa or less. Based on the obtained results, we propose a new mechanical function that utilizes the self‐healing function. [ABSTRACT FROM AUTHOR]

Introduction: Studies have established the benefits of horticultural therapy and activities for human health and well-being. Nonetheless, limited research has been conducted on the potential restorative advantages and distinctions between different types of horticultural activities in terms of stress reduction. Methods: This study employed a quantitative research method to investigate the stress recovery benefits of five horticultural activities (flower arrangement, sowing and transplanting seeds, kokedama crafting, pressed flower card making, and decorative bottle painting with dried flowers) and one reference activity (short composition writing) for children. The experiment was conducted in a children's activity center's multi-purpose classroom with 48 elementary students aged 9-12 years. The subjects first took a stress test to induce stress and then engaged in horticultural activities for 20 min. Physiological stress was assessed using electrocardiograms and electroencephalograms as feedback indicators. Psychological and emotional changes were determined using the Positive and Negative Affect Schedule for Children and Self-Assessment Manikin scales. Results: The results demonstrated that horticultural activities greatly reduced physiological fatigue, and their recovery benefits were significantly greater than those of the reference activity. The recovery effects from different horticultural activities were similar across physiological indicators, although flower arrangement and sowing and transplanting seeds exhibited relatively robust recovery benefits. The heart rate and a-EEG-based generalized estimating equation revealed that horticultural activities offered significantly better relative recovery at each time phase of operation than the reference activity, with girls showing a 3.68% higher relative recovery value than boys. Flower arrangement and kokedama crafting offered better physiological recovery for students with prior horticultural experience, and these two activities received the highest scores in terms of positive effects and the "pleasure" dimension. Students believed that participating in horticultural activities resulted in a noteworthy increase in personal confidence and a greater sense of achievement. Conclusion: The study suggests that horticultural activities that involve real and vibrant plants or natural materials and are more attractive have more stress-relieving benefits. We conclude that horticultural activities are beneficial leisure activities that aid in stress relief for children and that it is important to consider the attributes of activities when developing horticultural programs for elementary students. [ABSTRACT FROM AUTHOR]

C/C-ZrC-SiC composites with compact ceramic matrix were prepared by thermoset precursors with abundant active functional groups through precursor infiltration and pyrolysis. The mechanism of cross-linking and ceramization of precursor, and the effect of precursor structure on ceramic matrix, interface and mechanical properties of C/C-ZrC-SiC composites were studied. The compact structure of ZrC-SiC ceramics was ascribed to close cross-linked structure, and directly crystallized SiC without carbothermal reduction. The pyrolyzed precursor with more compact structure generated denser ceramic matrix and better interface bonding between the ceramic matrix and the carbon matrix. The composites with compact ZrC-SiC matrix and slightly defective interface performed ideal non-brittle fracture pattern, the flexural and compressive strength were 239 ± 21 MPa and 302 ± 24 MPa. The high mechanical properties could be ascribed to the considerable elastic modulus of ZrC-SiC matrix, and the apparent crack deflection and fiber pull-out caused by the moderate thermal residual stress damage and interface bonding. [ABSTRACT FROM AUTHOR]

SiC f /SiC composites have emerged as a prominent research area in the field of structural materials for engine hot-end applications. However, SiC f /SiC composites exhibit susceptibility to oxidation and corrosion when exposed to oxygen and water vapor. The yttrium silicate ceramic in the SiC f /SiC composite (SiC f /SiC-YS composite) serves as corrosion-resistant matrix. The corrosion behavior of SiC f /SiC-YS composites was assessed by examining the phase composition, microstructure, and bending strength after exposure to different water and oxygen environments. The results show that SiC f /SiC-YS composites exhibit excellent resistance to water and oxygen at temperatures below 1300 °C. Above 1300 °C, the decomposition of yttrium disilicate affects the internal structure and bending strength of the composites. Temperature- and water vapor concentration-dependent crystal transformation of yttrium silicate is a crucial factor that influences the microstructure and water-oxygen corrosion resistance of SiC f /SiC-YS composites. [ABSTRACT FROM AUTHOR]

Optimizing the high‐temperature energy storage characteristics of energy storage dielectrics is of great significance for the development of pulsed power devices and power control systems. Selecting a polymer with a higher glass transition temperature (Tg) as the matrix is one of the effective ways to increase the upper limit of the polymer operating temperature. However, current high‐Tg polymers have limitations, and it is difficult to meet the demand for high‐temperature energy storage dielectrics with only one polymer. For example, polyetherimide has high‐energy storage efficiency, but low breakdown strength at high temperatures. Polyimide has high corona resistance, but low high‐temperature energy storage efficiency. In this work, combining the advantages of two polymer, a novel high‐Tg polymer fiber‐reinforced microstructure is designed. Polyimide is designed as extremely fine fibers distributed in the composite dielectric, which will facilitate the reduction of high‐temperature conductivity loss for polyimide. At the same time, due to the high‐temperature resistance and corona resistance of polyimide, the high‐temperature breakdown strength of the composite dielectric is enhanced. After the polyimide content with the best high‐temperature energy storage characteristics is determined, molecular semiconductors (ITIC) are blended into the polyimide fibers to further improve the high‐temperature efficiency. Ultimately, excellent high‐temperature energy storage properties are obtained. The 0.25 vol% ITIC‐polyimide/polyetherimide composite exhibits high‐energy density and high discharge efficiency at 150 °C (2.9 J cm−3, 90%) and 180 °C (2.16 J cm−3, 90%). This work provides a scalable design idea for high‐performance all‐organic high‐temperature energy storage dielectrics. [ABSTRACT FROM AUTHOR]

Woven silica fiber-reinforced ceramic silica matrix composites with 2.5 dimensionality (2.5D woven SiO2f/SiO2 CMCs) offer various advantages and are commonly utilized in the aerospace industry. The CMCs are primarily prepared using the sol–gel process including infiltration, drying, and sintering under a certain temperature for several cycles. The infiltration effect is influenced by the pore diameter distribution inside the silica matrix, the silica matrix geometry, porosity inside silica matrix, and the silica sol viscosity according to Washburn equation for capillary rise. The physical properties of fiber, matrix, and the interfacial properties are important factors for the mechanical performance of CMCs. The mechanical strength of the CMCs matrix can be enhanced by densification to increase the contact area between the silica fiber tows and silica matrix. Silica aerogels are prepared by proportioning different molar ratios of ethyl-cool orthosilicate, anhydrous ethanol, and deionized water. The porosity of CMCs specimens filled with silica aerogel is around 0.88-9.02%, which is lower than that of specimens without silica aerogel (20-25%). Therefore, woven SiO2f/SiO2 CMCs have a fill ratio of 90.98-99.12%. The compressive impact process was simulated with finite element analysis (FEA), and the split Hopkinson pressure bar (SHPB) compressive impact test for the CMCs specimens showed improvement in the anti-impact mechanical properties of CMCs. The densification effect on CMCs specimens filled with silica aerogel was examined and analyzed via SEM imaging. Upon comparison, the simulation results show good consistency with the experimental stress–strain curves and failure modes results, indicating that the compressive impact behaviors can be efficiently predicted with FEA. Kindly check and confirm whether the corresponding author and affiliation is correctly identified.it is ok [ABSTRACT FROM AUTHOR]

It is difficult to obtain X2-type rare-earth monosilicates that have the advantages of low thermal conductivity and a thermal expansion coefficient that matches that of ceramic matrix composites, and thus, the efficient use of these materials in extreme environments is challenging. In this study, we developed a novel component regulation method, which significantly reduced thermal conductivity and helped achieve a suitable thermal expansion coefficient for monosilicates. Monosilicates have low thermal diffusion coefficients mainly due to the effect of extrinsic phonon scattering mechanisms. We analyzed different extrinsic phonon scattering mechanisms associated with point defect, disorder, grain boundary, lattice distortion, dislocation, and symmetry. • A variety of monosilicates with suitable coefficients of thermal expansion were synthesized. • The thermal conductivity of monosilicates was significantly reduced. • The various extrinsic phonon scattering mechanisms related to point defect, disorder, and more were analyzed. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) has attractive properties for use in nuclear reactors. However, it is hampered by inherent brittleness that is overcome through a fiber-reinforced composite. A finite element model based on cohesive zone contact coupled to Coulomb friction is proposed to simulate the push-out response of isolated fibers in SiC/PyC fiber-reinforced composites. The model reproduces the measurements obtained during push-out experiments of isolated fibers in different configurations and predicts interfacial failure between the PyC interphase and fiber. The brittle properties predicted coincide with literature indicating that fiber–PyC interface could prevent the crack propagation through the fiber, fulfilling the function of the structure. [ABSTRACT FROM AUTHOR]

Carbon fiber–reinforced SiC ceramic matrix composites (C/C–SiC composites) with advantages of high wear resistance and corrosion resistance are of high application potential as ceramic bearings. In this study, the frictional and wear behaviors of C/C–SiC with different fiber orientations mating with Al2O3 and SiC balls, respectively, have been investigated. Results reveal that fiber orientation effectively affects the friction and wear properties of carbon–ceramic composites in paired friction experiments with ceramic balls. In comparison to C/C–SiC with unidirectional fiber orientation, C/C–SiC pads with randomly arranged fibers exhibited a more stable coefficient of friction and lower volume wear, presenting the best performance among the pads considered herein, which may have the potential to be applied to bearing materials. The factors affecting the formation of continuous tribo‐film, which influence the comprehensive performance, are researched. It is proposed that the amount of wear debris and the formation of SiC/SiC micro‐hard frictional pairs may inhibit or promote the formation of continuous friction film. The dominant wear mechanisms for friction pairs of C/C–SiC and ceramic are abrasive wear and oxidation wear. [ABSTRACT FROM AUTHOR]

To fabricate a C/C-SiC (Carbon fiber-reinforced Silicon Carbide) with favorable mechanical properties via the Liquid Silicon Infiltration process, it is crucial to focus on the first fabrication step, the creation of a CFRP (carbon fiber-reinforced plastic). Hence, the selection of a fitting polymer is essential. Besides thermosets, thermoplastics can be used as matrix material. Nevertheless, the high melt viscosity of thermoplastics leads to problems regarding the fiber bundle infiltration. This study shows for the first time that this problem can be avoided by using C/C-SiC based on a novel short fiber C f /PEEK fiber hybrid yarn. The yarn was warm pressed into a CFRP, pyrolyzed and infiltrated with C/C-SiC. The product of each processing step was characterized with a focus on the analysis of the microstructure. Additionally, for the C/C-SiC, three-point bending tests were conducted. Those results were simular compared to reference literature. [Display omitted] [ABSTRACT FROM AUTHOR]

In fabrication of metal-reinforced ceramics, metallic powders are used as one of the raw materials, however, they hinder obtaining nanometallic particles in the matrix. The use of metallic nanopowders is inefficient, because they are highly flammable and require special storage and handling conditions (cool, dry inert gas, tightly sealed). Replacing metallic powders with coordination complexes allows to obtain nanocomposites in harmless manufacturing processes. The use of coordination complex of molybdenum (molybdenyl acetylacetonate) allowed to fabricate ZrO 2 /Mo composites by slip casting and gelcasting. The increase in fracture toughness (ca. 25%) was observed with the little concentration of the metallic phase (up to 1.5 wt%) in a composite. It results from gaining fine metallic particles (ca. 62 nm) in the ceramic matrix. SEM analysis revealed that crack propagation is inhibited by nano-sized metallic particles according to three mechanisms: crack deflection, crack blocking by plastic deformation and interface debonding. [Display omitted] • Coordination complexes are good substitutes for metal powders in CMCs fabrication. • Molybdenyl acetylacetonate is the beneficial precursor of Mo phase in ZrO 2 matrix. • ZrO 2 -Mo composites showed increased fracture toughness (27%) at low Mo content (1.5%). • Precursors decompose to fine metallic grains (ca. 62 nm) visible in composite microstructure. [ABSTRACT FROM AUTHOR]

This article discusses a nonlocal elasticity theory used to model the static behavior of edge-cracked nanobeams. It focuses on 1D nanostructures, specifically nanobeams, and proposes a formulation to analyze the mechanical behavior of edge-cracked nanobeams under mixed-mode loading. The formulation is applied to simulate experimental tests and the accuracy of the results is compared to existing data. The article also includes three case studies on the mechanical behavior of different materials, including silicon, silicon microbeams, and FeAl single crystalline material. The studies compare experimental results to analytical solutions and explore the influence of various factors on the properties of these materials. The research aims to provide insights into the performance and potential applications of these materials in different industries. [Extracted from the article]

Strong fiber/matrix interface combination is a tricky problem for Si 3 N 4 f /SiO 2 composites to be applied as antenna windows in harsh thermal conditions. In this study, perhydropolysilazane derived silicon oxynitride coating was prepared on the surface of Si 3 N 4 fiber pre-coated with BN coating to generate a BN c /SiON c double-layer interface. The optimized SiON coating thickness is ∼140 nm, while the corresponding tensile strength of the Si 3 N 4 f /BN c /SiON c fiber is 1.21 GPa. The composites with optimised BN c /SiON c coatings possess improved bending strength (∼20% up) and fracture toughness. The double-layer coatings benefit to crack propagation and reduced the penetration crack along the fibers. In addition, good thermal stability and dielectric performance (ε = 3.24–3.28 at 12–18 GHz) are indicated. [ABSTRACT FROM AUTHOR]

Pyrolytic carbon (PyC) interphase plays a crucial role in the mechanical properties of fiber‐reinforced ceramic matrix composites. In this research, a novel micro‐stack PyC interphase with different PyC textures was designed and fabricated by changing the deposition parameters during the chemical vapor infiltration process. The growth mechanism of the micro‐stack PyC interphase with different texture were also studied by experimental characterizations and kinetic calculations, and the results show that the content ratio of (C2H2 + C2H4) to C6H6 gas intermediate is a key parameter to control the texture types of PyC interphase. Furthermore, the value of orientation angle (OA) value, thickness, and modulus of the micro‐stack PyC interphase were further characterized by high resolution TEM (HRTEM), scanning electronic microscopy, and nanoindentation. Finally, the tensile testing of mini‐Cf/PyC/SiC composites was conducted, and the results showed that the tensile strength of mini‐Cf/PyC/SiC composites with micro‐stack PyC interphase is approximately 40% higher than that containing single high texture PyC interphase. The improvements on the tensile strength of Cf/PyC/SiC composites prove the significant advantages of micro‐stack PyC interphase. [ABSTRACT FROM AUTHOR]

SiC f /SiC ceramic matrix composites have been widely applied in turbine engine aerospace components with high temperature resistance, high strength, and lightweight performances. Due to the high brittleness and anisotropy, laser-assisted machining acts as a feasible process to improve the machinability of the SiC f /SiC composites. A single-factor experiment was designed to understand the microstructure evolution and ablation behaviors of the microgrooves processed by pico-second laser in this study. The high pulse energy/scanning time and low scanning speed had positive impacts on the depth and width, but negative effect on the three-dimensional surface roughness Sa. Besides, the optimal parameter was 200 kHz repetition frequency. In addition, the microstructure evolution and ablation mechanism under different laser parameters were investigated by the HRSEM, EDS, and XRD analysis. These experimental results showed that the machined microgrooves were covered by a large amount flocculent composed of amorphous SiO 2 when the oxidation was weak, and the splashes with the form of amorphous SiO 2 and crystal SiO 2 under strong ablation conditions. This indicated that the plasma effect transformed to the photothermal effect with enough heat. Meanwhile, a condensate layer occurred in all experiments and a recrystallized SiC layer relied on the microgroove depth controlled by adjusting laser parameters. This work will provide a theoretical basis and practice guidance for laser-assisted machining of the SiC f /SiC composites. [ABSTRACT FROM AUTHOR]