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In this work, stacked SiC fibers paper‐reinforced SiC ceramic matrix composites (SiCnf/SiC CMCs) were prepared by nanoimpregnation and transient eutectic (NITE) process using ultra‐long single‐crystal SiC nanofibers. The effect of the SiCnf surface modification via boron nitride (BN) interphase deposition as well as the sintering additive (Al2O3–Y2O3) content on the density, microstructure, and mechanical properties of SiCnf/SiC CMCs has been investigated systematically. The results revealed that the laminated SiCnf/SiC CMCs feature a significant saw‐tooth‐like curve on the load–displacement test, which indicates that the obtained laminated structure with the weak interlayer binding owning to the BN coating treatment possesses significant toughening to the SiC ceramics. Specifically, the SiCnf/SiC CMCs with the sintering additive content of 12 wt% revealed a fracture toughness of over 10 MPa m1/2 after 60 min of BN interface deposition, which is 104.31% higher than that of the composites prepared without BN coating. [ABSTRACT FROM AUTHOR]

Composites are versatile materials that can be tailored to meet the specific needs of various industries, including aerospace, automotive, and construction. This study focuses on investigating how the amount of titanium-di-boride (TiB2) particles (0%, 3%, 6%, and 9%) affects the physical, mechanical, microstructural, and fracture properties of Al7075/TiB2 composites produced using a liquid-state stir-casting process. The addition of TiB2 particles increases the hardness and tensile strength of the Al7075 alloy. This has been confirmed by X-ray diffraction analysis, which showed that these particles are dispersed throughout the aluminum matrix. The hardness increases from 60 HV to 90 HV and the tensile strength increases from 140 MPa to 211 MPa. The significance of increased wettability brought about by the addition of magnesium powder and the preheating of a ceramic reinforcement before pouring molten metal was revealed by scanning electron micrographs of the cast composites, which showed an even dispersal of reinforcements in the aluminum matrix, establishing the strong connection between the matrix and the reinforcement agents. Fracture surface scanning electron microscopy revealed that micro-void formation and nucleation in Al7075/TiB2 composites resulted in ductile material paves a way for manufacturing innovation. [ABSTRACT FROM AUTHOR]

SiBCN ceramics based on SiC, BN and Si3N4 structures have good comprehensive properties such as high-temperature resistance, oxidation resistance, creep resistance and long life, which makes it one of the very promising ceramic material systems in military and aerospace fields, etc. In this study, SiBCN ceramics, as well as Si3N4f/BN/SiBCN microcomposites, were prepared by a polymer infiltration pyrolysis method using PBSZ as the polymer precursor. The PBSZ was completely ceramized by pyrolysis at 900 °C. The weight loss and elemental bonding forms of the products after the pyrolysis of the precursors hardly changed from 600 °C to 900 °C. After pyrolysis at 600 °C for 4 h and using the BN coating obtained from twice deposition as the interfacial phase, a more desirable weak interface of fiber/matrix with a binding strength of 21.96 ± 2.01 MPa can be obtained. Si3N4f/BN/SiBCN ceramic matrix microcomposites prepared under the same pyrolysis conditions have a relatively good tensile strength of 111.10 MPa while retaining a weak interface between the fibers and the matrix. The results of the study provide more theoretical and methodological support for the application of new composite structural ceramic material systems. [ABSTRACT FROM AUTHOR]

The present study investigates the influences of SiC incorporation on the microstructure and corrosion behavior of B4C–nSiC composites in molten FLiNaK salt at 800°C. The corrosion characteristics and mechanisms of B4C–nSiC composites in molten FLiNaK salt were thoroughly characterized and extensively discussed. The B4C–nSiC composites exhibited a more refined grain size and lowered apparent porosity as the SiC content increased. Additionally, the concentration of high‐angle grain boundaries (HAGBs) in B4C–nSiC composites increased as the SiC content increased. The incorporation of 10 wt.% SiC improved the corrosion resistance of B4C–nSiC composites against molten FLiNaK salt. However, the incorporation of excessive SiC (≥20 wt.%) did not improve the corrosion resistance. The best corrosion resistance of B4C–10% SiC ceramic composite was attributed, on the one hand, to its relatively low apparent porosity and the low concentration of HAGBs with high structural disorder. On the other hand, the selective corrosion of B4C in B4C–10% SiC ceramic composite rapidly formed a sufficiently thick and highly graphitized C‐rich layer on its surface during the initial stages of the corrosion test. The C‐rich layer maintained the integral structure of the ceramic and prevented subsequent corrosive medium from penetrating into the ceramic. [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]

SiBCN fiber reinforced SiBCNmatrixmini-composites (SiBCN/SiBCN) as a new type of the ceramic matrix composite were fabricated by precursor infiltration and pyrolysis (PIP) process. Various degumming methods for continuous SiBCN fibers resulted in different properties and surface conditions, further affecting the interfacial bonding strength (IFBS) and mechanical properties of the composites. The relationship between fiber degumming modes, fiber states, and properties of compositeswas discussed and the strengtheningmechanisms of the SiBCN/SiBCN mini-composites were explored. With a degumming treatment of N,N-dimethylformamide (DMF) soaking, the flexural strength and modulus of mini-SiBCN/SiBCN composites achieved 508 ± 68 MPa and 79 ± 12 GPa, respectively. The novel strengthening mechanism of the microcrystalline SiBCN fiber reinforced microcrystalline SiBCN matrix composites will enrich and be helpful to understand the strengthening and tougheningmechanisms of ceramic matrix composites. [ABSTRACT FROM AUTHOR]

Three multi-phase tantalum carbide composites (TaC z -Ta 5 Si 3) were fabricated by Spark plasma Sintering (SPS) using Ta, TaC and SiC powders. SiC was added to control the C:Ta ratio (z = 0.6, 0.74, 1.0), regulating the phase composition and grain morphology while also serving as a deoxidizer. Composite TaC 0.6 -Ta 5 Si 3 had Ta 2 C as the major phase and contained Ta 4 C 3−x , TaC and Ta 5 Si 3. It exhibited an excellent combination of high flexure strength (714 ± 21 MPa) and toughness (13.9 ± 0.2 MPa·m1/2), despite a low Ta 4 C 3−x fraction, a phase known to have very high toughness. The outstanding performance was attributed to the elongated Ta 2 C grain morphology, highly laminated intra-granular Ta 4 C 3−x laths, and the refined Ta 2 C grain size. Composite TaC 0.74 -Ta 5 Si 3 , characterised by equiaxed grain morphology, exhibited good flexure strength (571 ± 36 Mpa) and toughness (7.6 ± 1.1 MPa·m1/2) due to the presence of Ta 4 C 3−x laths in the c-TaC. Lastly, composite TaC 1.0 -Ta 5 Si 3 , composed of c-TaC and Ta 5 Si 3 , exhibited moderate strength (545 ± 25 MPa) and toughness (5.3 ± 0.1 MPa·m1/2). • Ta 2 C-dominant and TaC-dominant composites (TaC z -Ta 5 Si 3) are fabricated using Ta, TaC and SiC. • SiC additives control the C:Ta and effectively promoted the sintering through oxide removal. • TaC 0.6 -Ta 5 Si 3 has the best toughness due to the elongated Ta 2 C grains and intra-granular laths. • TaC 0.74 -Ta 5 Si 3 with the equiaxed TaC has good toughness due to the intra-granular laths. • TaC 1.0 -Ta 5 Si 3 with the equiaxed TaC is free of intra-granular laths and has the lowest toughness. [ABSTRACT FROM AUTHOR]

In this study, ceramic particle (WC) reinforced AlCoCrFeNi 2.1 eutectic high entropy matrix composites (WC x /HEA 1-x , x = 0, 5, 10 wt%) were prepared by using laser powder bed fusion (LPBF) technology. The microstructure evolution and wear behavior of the printed WC x /HEA 1-x composites were analyzed, and the strengthening mechanism and anti-wear mechanism of the WC x /HEA 1-x composites were extensively studied. The results show that the reinforcement ceramic particles (WC) were uniformly distributed in the HEA matrix and a good metallurgical bonding layer between the reinforced phase WC and the HEA matrix were found. The maximum width of the bonding layer is about 330 nm. Under the strong irradiation of high-energy laser, WC was decomposed into W and C elements, and diffused into the HEA matrix. Its reaction with Co, Fe, Ni elements produced M x C (M = Co, Fe, Ni) carbides. Part of W and C elements were soluble in the HEA. The wear resistance of the printed composite is found affected by the content of added ceramic particle (WC). The ranking of the wear resistance of the printed composites was found to be WC 0.05 /HEA 0.95 > HEA ≈ WC 0.10 /HEA 0.90. The improvement of wear resistance by adding WC was found due to interfacial load transfer strengthening of WC particles, solution strengthening of W and C atoms; and the second phase strengthening of various carbides M x C (M = Co, Fe, Ni). [ABSTRACT FROM AUTHOR]

A study has been carried out to examine the impact of fibre architecture on the infiltration permeability, constituent phase volume fractions, and matrix porosity of the carbon fibre (C f)-ZrB 2 -20 vol% SiC ceramic matrix composites prepared through slurry infiltration, followed by hand lay-up and hot pressing. Unidirectional (UD) C f -fibres in 0/0° and 0/90° orientations, as well as 8H satin woven C f -fibres, have been utilized as reinforcement in the composites, which were subsequently densified through hot pressing after infiltration. Revelation of the 3D internal structure of the composites by X-ray microscopy has facilitated a thorough qualitative and quantitative evaluation of infiltration. The fraction of matrix (ZrB 2 - 20 vol% SiC) present along three orthogonal axes (X, Y and Z) of the scanned composite blocks has been calculated, with Z representing the direction of infiltration. This study has revealed that the composites processed from UD C f -fibre preform exhibits greater infiltration, because of higher intra-bundle infiltration compared to the 8H woven C f -fibre, and the accompanying analysis provides insight into the formation mechanisms of matrix porosities. [ABSTRACT FROM AUTHOR]

Cf‐ZrB2 and Cf‐ZrB2–SiC ultrahigh‐temperature ceramic matrix composites were produced using slurry infiltration in the 2D woven carbon fabric and hot pressing at 2000°C. The mixing time and amount of solid loading of the ZrB2–SiC slurry were found to have a significant effect on both microstructure and mechanical properties and were optimized to obtain an agglomerate‐free composite. The ZrB2–SiC slurry with a solid loading of 20%–30% was found to be effective for infiltration within the intra‐pore in carbon tows. The composites have a nearly completely dense matrix layer with a porous matrix within the fiber layers. The fabricated 2D woven Cf‐ZrB2 and Cf‐ZrB2–SiC composites were non‐brittle. [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]

In the present work, the microstructure and chemical behavior of TiC ceramic reinforced steel matrix composite material after stabilizing heat treatments have been studied. The composition of the naturally formed oxide layer on the surface of the composite and the potential natural oxidation mechanisms are also elucidated. The results showed that the naturally formed oxide layer contained mainly O, C, Fe and Ti, with small amounts of Cr and Mo. In the multi-metallic oxide layer, Fe3+, Mo6+, and Ti4+ species are enriched on the free external surface of the composite, the protective Fe2+ oxides were distributed in the relative inner part of the oxide layer, and Mo4+ was more uniformly distributed throughout the natural oxide film. The Cr oxides formed near the substrate acted as a diffusion barrier for iron and chromium ions, and the preferential oxidation of chromium formed a passivation film, which effectively improved the corrosion resistance of the material. Due to the interfacial evolution and complex stress changes in the composite during the stabilizing heat treatments, the XPS spectral peaks were shifted towards lower binding energies than in the annealed sample. The core level spectra of Mo 3d, Ti 2p, and Fe 2p were all shifted to lower binding energies due to the combination of ligand and strain effects after quenching, and there was no significant difference in the spectra of the tempered and thermal cooling cycling (TCC) treated composites, which suggested that the chemical state was relatively stable during the subsequent stabilizing heat treatments. [Display omitted] [ABSTRACT FROM AUTHOR]

A pore-free ceramic composite [88ZrO2–11CeO2–Y2O3]/La0.85Y0.15Al11O18/Al2O3, consisting of a matrix based on zirconium dioxide stabilized with cerium and yttrium oxides, loaded with layered particles of lanthanum hexaaluminate and reinforced with aluminum oxide nanofibers, was obtained. Sol-gel method was used for the synthesis of all the composite components, except for aluminum nanofibers that were obtained by the electric explosion method. The phase composition, microstructure, and properties of the composite were studied depending on the combined effect of the stabilizing additives and aluminum oxide nanofibers obtained by different methods. The composite is intended to be used as a ceramic material for structural and instrumental purposes. [ABSTRACT FROM AUTHOR]

The object of the research is electrically conductive ceramics. It aims to analyze the microstructure of electrically conductive ceramic composites based on silicon carbide and investigate the influence of silicon carbide content on their properties. This study is pivotal for enhancing materials used in high-tech applications, particularly in fields where distinct electrical insulation and mechanical characteristics are crucial. The microstructure analysis conducted through scanning electron microscopy confirmed the presence of silicon carbide in all examined ceramic samples, except in those where silicon carbide was not added. Special attention should be given to the sample with 30 % silicon carbide, distinguished by the lowest open porosity. These findings are corroborated by previous research where this sample exhibited superior properties: open porosity – 12.51 %, water absorption – 5.88 %, apparent density – 2.13 g/cm², specific resistance – 0.43·106 Ω·m. These characteristics indicate low porosity and high structural-physical property values. The results not only affirm the successful incorporation of silicon carbide into the ceramic matrix but also highlight the prospects for applying the researched ceramic materials in areas where electrical insulation and mechanical properties are crucial. Specifically, the sample with 30 % silicon carbide appears particularly promising due to its high characteristics and lower porosity, making it potentially interesting for applications in high-tech industries such as electronics and telecommunications. The conclusions suggest the potential use of these ceramic materials in various high-tech industries where both electrical and mechanical properties are essential. The sample with 30 % silicon carbide, with its exceptional characteristics, holds potential for applications in advanced technologies. Further research in this direction could lead to the development of new materials for effective radiofrequency absorption, finding broad applications in different technological fields. [ABSTRACT FROM AUTHOR]

Copyright of Science of Sintering is the property of National Library of Serbia 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.)

Modern aviation components have higher requirements for high temperature resistance, high strength and lightweight materials, and ceramic matrix composites have superior overall performance. However, its high brittleness and anisotropy lead to a challenge for manufacturing. In order to understand the formation conditions and the evolution of surface microstructures of the C f /SiC microgrooves processed by ultrafast laser comprehensively, we designed a single-factor experiment and performed sensitivity analysis. The experiment results showed that the pulse energy had great effects on the depth of the microgroove, and the intense ablation caused more active oxidation of SiC to occur, generating more SiO(g). However, too much pulse energy may cause the material removal mechanism to be more due to the photothermal effect rather than the plasma effect. Low repetition frequency caused a large number of laminated connections in the microgroove and the oxide gradually changed from lumpy to flocculent as the repetition frequency increased. The more scanning times, the more ablation products sputtered onto the sample surface, including unablated carbon fibers. Shallow depth and ablation residues remained in the microgroove occurred under few scanning times. Although too fast scanning speed leaded to a rapid decrease in the microgroove depth, too slow scanning speed also generated more unablated carbon fibers sputtering out of the microgrooves. The microgroove depth had the highest sensitivity to the repetition frequency, followed by the pulse energy and scanning speed. The pulse energy and scanning speed had a greater effect on the oxide layer height, the repetition frequency affected the oxide layer width, and the scanning speed affected the microgroove width significantly. According to the processing requirements and the hot spot map, the processing parameters that can be adjusted effectively will be able to be obtained. [ABSTRACT FROM AUTHOR]

Employing ceramic particles like hydroxyapatite to fabricate magnesium-based bio-composite has received incredible attention in orthopedic applications due to their bioactivity and biocompatibility. Besides, applying severe plastic deformation methods like equal channel angular pressing (ECAP), in addition to eliminating defects induced by casting, causes the metallurgical and mechanical behavior improvement of Mg/HA bio-composites. In this paper, the combined effects of HA particles and the ECAP process with B c route on the microstructure, mechanical properties, and fracture toughness behavior of Mg/HA bio-composite fabricated through the electromagnetic and mechanical stir casting method were evaluated. Furthermore, a non-contact digital image correlation (DIC) method was adopted to accurately assess the elastic and plastic parameters and crack propagation during the fracture toughness test. Microstructural observation demonstrated that the addition of HA particles and, subsequently, applying four passes of the ECAP process on the bio-composites not only decreased the grain size by a considerable amount of 92%, but also resulted in a homogenous microstructure. Moreover, according to the results of the mechanical tests, after four-pass ECAP, although the compressive yield stress of Mg/HA bio-composite did not significantly change, the highest tensile yield stress, ultimate tensile, and compressive strength were accomplished. Among all elastic and plastic parameters, the elastic modulus and strength coefficient have continuously risen with adding HA and increasing the number of ECAP passes. However, the strain hardening exponent has decreased noticeably with the addition of HA, and the ECAP process compensated for some of this reduction. In addition, reinforcing magnesium with HA particles and improving the dislocation density caused by increasing the number of ECAP passes has led to increased material resistance against crack growth, wasted energy, and, consequently, fracture toughness. In this case, the four-pass ECAPed bio-composite showed the highest fracture toughness, approximately 28 MPa m0.5, 70% more than the pure Mg. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department 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.)

Interphase plays an important role in the mechanical behavior of SiC/SiC ceramic-matrix composites (CMCs). In this paper, the microstructure and tensile behavior of multilayered (BN/SiC) n coated SiC fiber and SiC/SiC minicomposites were investigated. The surface roughness of the original SiC fiber and SiC fiber deposited with multilayered (BN/SiC), (BN/SiC) 2 , and (BN/SiC) 4 (BN/SiC) 8 interphase was analyzed through the scanning electronic microscope (SEM) and atomic force microscope (AFM) and X-ray diffraction (XRD) analysis. Monotonic tensile experiments were conducted for original SiC fiber, SiC fiber with different multilayered (BN/SiC) n interfaces, and SiC/SiC minicomposites. Considering multiple damage mechanisms, e.g., matrix cracking, interface debonding, and fibers failure, a damage-based micromechanical constitutive model was developed to predict the tensile stress-strain response curves. Multiple damage parameters (e.g., matrix cracking stress, saturation matrix crack stress, tensile strength and failure strain, and composite's tangent modulus) were used to characterize the tensile damage behavior in SiC/SiC minicomposites. Effects of multilayered interphase on the interface shear stress, fiber characteristic strength, tensile damage and fracture behavior, and strength distribution in SiC/SiC minicomposites were analyzed. The deposited multilayered (BN/SiC) n interphase protected the SiC fiber and increased the interface shear stress, fiber characteristic strength, leading to the higher matrix cracking stress, saturation matrix cracking stress, tensile strength and fracture strain. [ABSTRACT FROM AUTHOR]

C/HfC-ZrC-SiC composites were fabricated via reactive melt infiltration (RMI) of the mixed HfSi 2 and ZrSi 2 alloys. The microstructure, infiltration behavior of the hybrid silicide alloys infiltrating C/C composites, and flexural strength of C/HfC-ZrC-SiC composites was studied. Inside composites, there were more Hf-rich (Hf, Zr)C phases distributed in the exterior region, while more SiC and Zr-rich (Zr, Hf)Si 2 in the interior region. There was compositional segregation in (Hf, Zr)C, with the HfC content decreasing from the exterior region to interior region. The RMI process was performed at different temperatures to investigate the structural evolution, and a model for the reactive melt infiltration of the mixed HfSi 2 and ZrSi 2 alloys into C/C composites was established. Compared with C/HfC-SiC and C/ZrC-SiC prepared by same process, C/HfC-ZrC-SiC had the highest flexural strength of 247Mpa and 213Mpa after oxidation at 1200 ℃ for 15 min. Both the unoxidized and oxidized samples presented a pseudo-plastic fracture behavior. [ABSTRACT FROM AUTHOR]

A kind of multiscale β-sialon grain-reinforced Al2O3 matrix composite ceramic tool material, named ASN, was prepared and studied. For the ASN, β-sialon (molecular formula: Si4Al2O2N6) was synthesized in situ by a hot-pressing and solid-solution reaction process. A total of six samples were prepared at varying sintering temperatures and holding times under vacuum conditions. The solid solution reaction mechanism of β-sialon, the phase composition, mechanical properties, microstructure, and strengthening and toughening mechanisms of the composite ASN were investigated. As a result, within the experimental parameters, an optimal ASN tool material was obtained under a pressure of 32 MPa and at a temperature of 1550 °C for 20 min. The tested mechanical properties of the optimal sample were as follows: flexural strength 997 ± 59 MPa, fracture toughness 6.4 ± 0.3 MPa·m1/2, Vickers hardness 18.2 ± 0.4 GPa, and relative density 98.1 ± 0.2%. According to crystal defect theory, the solid solution reaction mechanism of in-situ-synthesized β-sialon in an Al2O3 matrix involves a double mechanism of unequivalence (or hetero-valence) and interstitial filling. The multiscale β-sialon grains mainly consisted of four grains, which were elongated β-sialon grains with a diameter of 0.3–0.4 μm and an aspect ratio of 6–9, elongated β-sialon grains with a diameter of 70 nm and an aspect ratio of 10, β-sialon whiskers with a diameter of 0.2 μm and an aspect ratio of 12–15, and intragranular β-sialon whiskers with a diameter of 70 nm. The mechanical properties were improved due to strengthening and toughening mechanisms, such as mixed structure mode (intergranular and transgranular), elongated grain pullout, interface bonding, crack reflection, pinning, and bridging. [ABSTRACT FROM AUTHOR]

Sr‐containing ceramic products produced from geopolymer, (Na, Sr)‐GP, have been reported as excellent candidate materials for the immobilization of radionuclide 90Sr, despite sintering temperature at 1200°C. In this work, the product possessing the best immobilization performance (leaching rate of 1.29% for Sr2+) can be produced at 1000°C in the method of liquid‐phase sintering via the addition of fluxing agent B2O3 at 2.0 wt% in the geopolymer precursor. The mechanical properties of the geopolymer precursor (Na, Sr)‐GP were also enhanced via the promotion role of B2O3 to geopolymerization. It was revealed that the overall anti‐leaching ability of the Sr‐containing ceramic product not only depends on the microstructure of the loading substrate but also can be affected by the chemical state of radioactive strontium retention in the loading matrix. [ABSTRACT FROM AUTHOR]

Monolithic TiB2 are known to have a good combination of densification and hardness, which are sometimes helpful but limited in application. However, their usage in service at elevated temperatures such as in thermal power plants, cutting tools, tribological purposes (mechanical seals, blast nozzles, wheel dressing tools), etc. leads to catastrophic failure. Hence, the introduction of sintering additives in the TiB2 matrix greatly influences the sinterability and properties (fracture toughness, wear resistance, etc.) of the resulting composite needed to meet the requirement for various industrial applications. In this study, the influence of SiC as sintering additives on the microstructure, densification, hardness and wear performance of TiB2 ceramic was observed. Hence, TiB2, TiB2–10wt%SiC and TiB2–20wt%SiC were sintered at 1850 °C for 10 min under 50 MPa. The impacts of SiC on the TiB2 were observed to improve the microstructure and correspondingly improve the densification and mechanical properties, most especially with the composite with 20wt% SiC. Combined excellent densification, hardness and fracture toughness of 99.5%, 25.5 GPa, 4.5 MPa.m1/2 were achieved, respectively, for TiB2–20wt%SiC. Diverse in-situ phase and microstructural alterations were detected in the sintered composites. It was discovered that the in-situ phase of TiC serves as the contributing factor to the enhanced features of the composites. Moreover, the coefficient of friction and wear performance outcomes of the synthesized composites described a decreased coefficient with an enhanced wear resistance via the increasing SiC particulate. However, applying the load from 10 to 20 N increased the wear rates. [ABSTRACT FROM AUTHOR]

TiB 2 -B 4 C composite has various outstanding properties and great potentials in versatile high-end application fields, and currently the preparation of its monolithic counterpart with arbitrarily-complex shape is eagerly demanded. However, due to the intrinsically strong covalent-bonding and poor laser absorption performances of its constituents, it is still highly-challenging to prepare TiB 2 -based composite by additive manufacturing method. Herein, by direct laser powder-bed fusion additive manufacturing (selective laser sintering) and the unique strategy of in-situ synthesizing/sintering, dense and complex-shaped TiB 2 -B 4 C composites were successfully additively manufactured for the first time. More importantly, benefiting from their ultrafine eutectic microstructures and high relative densities, the resultant TiB 2 -B 4 C composites exhibited outstanding Vickers hardness and fracture toughness respectively up to 35.6 GPa and 8.6 MPa·m1/2, which were remarkably higher even than those of the near-fully-dense counterparts prepared by various subtractive methodologies. This work offered a reliable approach to near-net-forming high-temperature ceramic-matrix composites with arbitrarily-complex shapes and superior mechanical performances. [Display omitted] [ABSTRACT FROM AUTHOR]

We report a novel route to produce high quality SiC/SiC ceramic-matrix composites. A SiC slurry with binders was prepared by mixing SiC nano- and submicron-powders with sintering additives in isopropanol, which was then used to impregnate SiC fibers and form green sheets without fibers. The prepreg sheets were placed between two SiC green sheets to form a sandwich structure and warm-pressed at 100 °C under low pressure. The de-binding was performed at 800 °C for 1 h, and the densification of the SiC matrix was conducted by pressure-sintering at 1850 °C for 1.5 h under 20 MPa. Sandwich prepreg sheets showed a more controllable sheet thickness and smoother fiber bundles, compared to prepreg sheets prepared by hand that caused broken fibers and irregular thickness. The SiC/SiC ceramic-matrix composites using sandwich prepreg sheets exhibited excellent bending strength and tensile properties. [ABSTRACT FROM AUTHOR]

Selective laser sintering (SLS) combined with reaction melt infiltration was used to fabricate Si–SiC ceramic matrix composites, and the effects of different concentrations of phenolic resin (PF) on the properties of the SLS green body and carbonized and final Si–SiC samples were investigated. The results showed that the impregnation with PF can increase the bulk density, reduce the porosity of the samples at all stages, and improve the mechanical properties of the reactive bonded samples. The degree of densification and mechanical properties of the sample gradually enhanced with an increase in PF concentration. The main phases of the Si–SiC composites were free Si, α-SiC, β-SiC, plus an extremely small amount of Al–Si alloy, and the SiC and the Si phase contents increased and decreased, respectively, as the concentration of PF increased when measured using Rietveld refinement and image analysis software. The macroscopic properties of the samples improved greatly after precursor infiltration pyrolysis (PIP) treatment with 66.7%vol PF-ethanol solution twice. According to the crystal nucleation-growth theory, it was inferred that the infiltrated PF could provide a certain amount of pyrolytic carbon in the carbonized specimen. During the reaction bonded process, the carbon formed by carbonization pyrolysis first dissolves into the molten Si and reaches saturation. With the further dissolution of carbon, [C] and [Si] in the liquid phase contact each other to form β-SiC nuclei, the nuclei that precipitate at the pore wall position and gradually form a continuous interfacial layer of β-SiC. The β-SiC layer prevents the liquid Si from direct contact with C inside the prefabricated body, therefore, further reactants diffuse through the layer. Finally, the fine crystalline β-SiC grains were fabricated inside the specimen. [ABSTRACT FROM AUTHOR]

Particle reinforced MMC succeeds in developing the metallic matrix with ceramic particle reinforcements to result in improved strength, mainly at elevated temperatures but adversely affects the ductility of the matrix. The present study aims to disperse different weight % (3,6,9) of SiC and 3wt.% Al2O3 particles in aluminum melt and fabricated composite. The evolution of microstructure and morphology of composite are studied using FESEM, Optical Microscopy, EDAX and deformation characteristics of Al-SiC+Al2O3 composite at cold conditions was studied. Cast nd forged composite material was subjected to hardness test and tensile test. The results show that hardness and strength of fabricated Al-SiC composite improves and ductility declines as compared to Al alloy in both as-cast and hot forged conditions. [ABSTRACT FROM AUTHOR]

Continuous silicon carbide (SiC) fiber reinforced SiC ceramic matrix (SiC f /SiC) composites are widely studied for possible applications as hot sections in next-generation aeroengines because of their excellent thermo-structural properties. Their mechanical properties were comprehensively evaluated based on the interaction mechanisms among fiber, interphase, and matrix. Moreover, it was found that matrix cracking and fiber bridging mechanisms influenced the shear-dominated and tension-dominated properties, respectively, clearly indicating that the mechanical properties of the material should be correlated. In this study, mechanical properties of the two-dimensional SiC f /SiC composite were comprehensively evaluated, and the correlation laws were verified between tension and bending, tension and in-plane shear, and in-plane shear and interlaminar shear. Results showed that the ratio of shear to tensile matrix cracking stress was 0.68, while the ratio of flexural to tensile strength was 2.3, and the interlaminar shear strength was equal to the in-plane shear strength minus the fiber bridging stress. Fiber bridging is the key mechanism controlling the above-mentioned correlation by the established meso-mechanical formulas, and the interlaminar shear mechanism is controlled by matrix cracking and influenced by interlaminar pores. [ABSTRACT FROM AUTHOR]

In this work, a chemical vapor infiltration (CVI) combined with polymer impregnation and pyrolysis (PIP) technique was used to prepare high-performance SiC f /BN/SiC composites. Compared with the SiC f /BN/SiC composite fabricated by conventional PIP technique, the SiC f /BN/SiC composite fabricated by CVI + PIP hybrid technique showed the significantly improved flexural strength and toughness. The microstructures, macro-mechanical and micro-mechanical properties were systematically investigated and compared. By applying various micro-mechanical tests (fiber push-in, micropillar compression and micropillar splitting), the in-situ mechanical parameters of different micro-zones for SiC f /BN/SiC composites were obtained accurately. Based on the characterization results of microstructures and micro-mechanical properties, the corresponding toughening process was analyzed in combination of the classical He-Hutchinson criterion. The results indicate that the micro-mechanical test methods can provide accurate and effective data for the analysis of toughening and fracture process, presenting great potentials in the further understanding of the improvement in mechanical properties of ceramic matrix composites. [ABSTRACT FROM AUTHOR]

A simple self-assembly method was applied for the successful synthesis of reduced graphene oxide-encapsulated alumina (Al 2 O 3 @RGO) nanohybrids with core-shell structures which were then added as nanofiller into a matrix of Al 2 O 3 –TiC to fabricate corresponding ceramic composites. Microstructural analysis revealed that RGO sheets were homogeneously dispersed in the matrix and bonded to grains to form a 3D RGO network. The formed unique structure forced RGO sheets to closely bond and strongly attach to matrix grains, effectively increasing load transfer efficiency and contact surface area between matrix and RGO sheets. Analysis of interface characteristics revealed that the interfacial phase Al 2 OC was generated by a localized carbothermic reduction process. Based on first-principles calculations, Al 2 OC interfacial phase was found to contribute to the generation of weak and strong hybrid interfaces in composites. The weak and strong hybrid interfaces could not only effectively promote the transfer of loads from the matrix to RGO sheets but also induce conventional toughening mechanisms. In summary, addition of Al 2 O 3 @RGO nanohybrids effectively improved the dispersion level of RGO in ceramic as well as interfacial bonding strength between these sheets and matrix, thereby improving overall mechanical characteristics of Al 2 O 3 –TiC ceramic composites. [ABSTRACT FROM AUTHOR]

The mechanical behavior of silicon carbide (SiC) fiber used in ceramic matrix composites is valuable to permit the prediction of composite behavior and tailoring of composite properties. Herein, single‐fiber tensile tests of different SiC fibers are carried out and Weibull analysis is implemented to characterize its tensile property. To better understand its mechanical behavior, the surface and tensile fracture morphology of different fibers are observed by scanning electron microscopy (SEM) and the fiber elemental composition along the radial distribution is qualitatively analyzed by energy dispersive spectrometer (EDS). Also, the crystallinity and crystallite size of the fiber are analyzed by X‐ray diffraction (XRD). The results show that the tensile strength of SiC fiber conforms to the Weibull distribution, and its mechanical property is influenced by the surface morphology, elemental composition, crystallinity, and crystallite size. [ABSTRACT FROM AUTHOR]

Inverse Microstructure Design problems are ubiquitous in materials science; for example, property-driven microstructure design requires the inversion of a structure–property linkage. However, prior frameworks have struggled to address this problem's unique combination of challenges: the high dimensionality and stochasticity of microstructures, under sampled initial datasets, and ill-conditioning of the inversion. In this work, we propose a computational framework for Inverse Microstructure Design problems using a Bayesian methodology. We construct this framework from three modular components, enabling flexible extension and re-use. First, we define a low-dimensional, informative microstructure prior by integrating domain knowledge (i.e., statistical continuum mechanics) into a distributional learning scheme. This scheme includes multiple latent representations which address the challenges inherent to representing microstructures. Second, we define a property-specific likelihood using a multi-output Gaussian process regression surrogate model. Finally, we efficiently learn the conditional posterior density for a given target property, and generate samples using deep variational inference. We demonstrate our proposed method for solving stochastic microstructure design problems by identifying woven ceramic matrix composites matching target anisotropic thermal conductivities. Through this example, we analyze the integral role of each component in the inversion framework. [Display omitted] [ABSTRACT FROM AUTHOR]

Oxide fiber-reinforced oxide matrix composites (Ox/Ox-CMCs) were fabricated by vacuum-assisted impregnation and pressureless sintering using a high-yield alumina precursor. The Ox/Ox-CMCs were sintered at 1100 and 1200 °C for 2 h. SEM and X-ray CT revealed that in both cases the matrix formed successfully within and between the woven fabrics. Vickers hardness of the sintered matrix was independent of the location within each composite. In a three-point bending test, a bending fracture at the tensile side occurred prior to shear fracture, suggesting that the matrix achieved good adhesion between the woven fabrics. The Ox/Ox-CMC sintered at 1100 °C showed higher tensile strength than that sintered at 1200 °C. This strength difference was attributed to their microstructures; the specimen sintered at 1100 °C showed crack deflection at the fiber/matrix interface, while that sintered at 1200 °C had a strongly adherent interface. Both composites showed notch-insensitive behavior in double-edge notch tensile tests. [ABSTRACT FROM AUTHOR]

The unique physical and mechanical properties of SiC ceramics have led to extensive activities in recent years to improve these properties. The use of various additives can not only reduce the sintering temperature and improve the sinterability but also can change the properties of this ceramic. Graphene is one of these additives that has recently been paid attention by researchers. In this research, an attempt has been made to review the most important studies performed on the fabrication of SiC-graphene composites and the effect of parameters such as graphene type, size and amount, sintering temperature and time, and post-sintering heat treatment on the microstructure, crack propagation, densification, and mechanical properties such as hardness and fracture toughness and other important properties of this ceramic are discussed. [ABSTRACT FROM AUTHOR]

Adapting conventional sintering (CS) techniques of monolithic ceramics for the production of oxide ceramic matrix composites (Ox‐CMCs) comes along with a few drawbacks, such as fiber degradation. Thus, the applicability of two‐step sintering (TSS) for the production of Ox‐CMCs based on Nextel™ 610 fibers and porous alumina matrix is investigated in this study for the first time. Uniaxial tensile tests were performed to evaluate the performance of mini‐composites produced by TSS and compared with those produced by CS. Parameters known for influencing the mechanical behavior of the mini‐composites, such as grain size, porosity, shrinkage, as well as matrix properties, were analyzed. Both sintering techniques resulted in similar grain size distributions, whereas TSS showed higher total porosity and lower amount of sintering‐induced cracks. As a result, TSS samples showed a higher tensile strength of 230±27 MPa when compared to 133±8 MPa for CS. In general, it was observed that most of the densification happens during the first phase of TSS, while the matrix is slowly strengthened during the second step. Therefore, the reported TSS process is a very promising and easy‐to‐apply heat treatment for producing Ox‐CMCs with controlled microstructure. [ABSTRACT FROM AUTHOR]

Yttrium mono- and di-silicates are excellent candidate materials for Environmental Barrier Coatings (EBC), to protect Ceramic-Matrix Composites (CMC). A large distribution of microstructures can be generated by varying the duration of sintering, the particle size distribution of the precursor and/or the deposition method. In the present work, investigations of the corrosion resistance of yttrium silicate coatings with various microstructures in the high temperature range, under different oxidizing environments are reported. An original experimental methodology has allowed quantifying the influence of the microstructure (especially grain size and grain boundary surface area) on properties such as ionic conductivity, resistance to oxygen diffusion, volatilization rate and surface recession, and showing that they directly affect their protection efficiency against oxidation. Based on these results, guidelines for the design of an optimized yttrium silicate EBC featuring microstructural and compositional variations are proposed. [ABSTRACT FROM AUTHOR]

BxC-TiB2 ceramic composites were fabricated via reactive spark plasma sintering using TiC and B as the raw materials. The impact of B/TiC mole ratios on the phase compositions, densification behaviors, microstructure, and mechanical properties of the ceramic composites were investigated. The results showed that the stoichiometry of 'BxC' could be tailored by changing initial boron content and the obtained B4.5C, B6.5C and B8.5C phases have the same crystal structure (R-3 m). The excess of B enhanced the reaction between TiC and B, which released a large amount of hot energy and promoted the densification of the composites. The TB8.5 composite sintered at 1900°C had the best comprehensive mechanical properties, with hardness and flexural strength of 40.36 GPa and 551 MPa, respectively. The formation of nano-sized TiB2 grains induced by reaction were beneficial for improving the mechanical properties of these composites. [ABSTRACT FROM AUTHOR]

To improve the toughness and friction properties of carbon fiber reinforced ceramic matrix composite, a Cu alloy modified carbon fiber reinforced TiC based ceramic matrix composite was designed and prepared by TiCu alloy melt infiltration at low temperatures up to 1100 °C. The as-produced composite was mainly composed of carbon, TiC, Ti 3 Cu 4 , TiCu 4 and Cu phases. Due to the ductile Cu alloy introduced into the matrix, the composite showed good mechanical performance especially the fracture toughness. The flexural strength reached about 248.36 MPa while the fracture toughness was up to 15.78 MPa·m1/2. The high toughness of the composite was mainly attributed to the fiber bridging, fiber pull-out, interface debonding, crack propagation and deflection. The tribological performance of the as-produced composite was measured using SiC and 440C stainless steel balls as counterparts, respectively. The as-prepared composite exhibited good wear resistance and the wear mechanism was discussed based on the microstructural observations. [ABSTRACT FROM AUTHOR]

With the development of X-ray computed tomography over the last few decades, it is gradually considered to be a powerful tool in the field of materials research. This paper presents a comprehensive review of applications of CT imaging on fiber reinforced composites, from polymer composites to ceramic matrix composites. The principle of X-ray CT and experimental tomography setups was described firstly. Then, in situ experimental devices developed in recent years were illustrated. Furthermore, the applications of X-ray CT imaging on manufacturing process, modeling, mechanical damage, physical, and chemical behaviors were reviewed in detail. Besides, advantages and limitations of X-ray CT imaging were pointed out and the future development was prospected. [ABSTRACT FROM AUTHOR]

The ultrahigh temperature ceramic-matrix composites (UHTCMCs) are the core class of innovative materials. One of the key-features that such a new class of materials should exhibit is self-repair of damage without any external intervention. In the present work, a set of ZrB 2 -SiC ceramics (SiC from 5 to 15 vol.%) was produced by hot-pressing: besides SiC, also 5 vol.% Y 2 O 3 was added in the starting mixture to search for an improved self-healing capability (SH). Dedicated set-ups to thermally stimulate samples in severely oxidizing atmosphere up to 2278 K were designed and realized. To assess the SH capabilities, the retained flexural strengths were measured at room temperature using samples damaged by indentations and then heat treated from 1773 K to 2278 K. The strength recovery rates were measured and correlated to the SH efficiency. [ABSTRACT FROM AUTHOR]

Continuous carbon fiber reinforced SiOC composites (C/SiOC) show promise for high-temperature application. Whereas, the high temperature resistances of SiOC ceramic matrix and carbon fiber are mismatched, which significantly restricts the long-term application of C/SiOC composites at high temperatures above 1250 °C. In this paper, heterogeneous element Y was introduced in C/SiOC composite by taking Y-doped MK resin as raw material to modify the structure of the SiOC ceramic matrix. Characteristics and high temperature evolution behaviors of SiYOC ceramic matrix in the inert environment were investigated. The microstructure, mechanical properties and high-temperature evolution of C/SiYOC composites were analyzed. The density, flexural strength and fracture toughness of the as-fabricated C/SiYOC composites were 1.89 g/cm3, 261.7 MPa and 13.54 MPa•m1/2, respectively. In the process of high-temperature treatment, the mechanical properties of C/SiYOC composites decreased obviously at 1500 °C due to the decomposition of SiYOC ceramics matrix and the carbothermal reductions between matrix and fibers. [ABSTRACT FROM AUTHOR]

The incessant quest in fabricating enhanced ceramic materials for use in aerospace, chemical plants, as a cutting tool, and other industrial applications has opened the way for the fabrication of ceramic-based composites with sintering additives which have been experimented to influence sinterability, microstructure, densification, and mechanical properties. The current research practices for the consolidation of ceramic matrix composite (CMC) have been in the utilization of metallic and non-metallic additives as a reinforcement for the ceramic matrix. The use of additives has a promising influence in ensuring the achievement of good microstructures and excellent properties. The use of metallic additives enhances the sinterability of CMC but it has a debilitating effect on its intrinsic mechanical properties, especially at high-temperature applications. Hence, its uses in a high-temperature application environment under high impact load are limited. Thus, the types and amount of additives to be added to a ceramic-based matrix composite depends on the type of application and properties desired to be achieved from the composites. One of the critical issues that have affected the properties of CMC is the type of powder metallurgy (PM) used for consolidation. PM has been experimented with to be efficient in manufacturing ceramic-based composites. Although, past review works have pinpointed diverse PM methods, viz, hot press, pressureless sintering, hot isostatic press, and spark plasma sintering (SPS), for manufacturing ceramics-based composites. Amidst these diverse methods, SPS has progressively been applied for the consolidation of ceramics, owning to its possibility of achieving a good sintered compact in a relatively short time with enhanced properties. This review focuses on the synthesis of TiC reinforced with sintering additives, with more attention on carbides as sintering additives. Carbide additives have the potential to improve microstructure, densification, and mechanical properties. In addition, future works on the consolidation and characterization of TiC are included in this review. [ABSTRACT FROM AUTHOR]

Ceramic matrix composites are typically prepared by a costly, time-consuming process under severe conditions. Herein, a cost-effective C/SiC composite was fabricated from a silicon gel-derived source by Joule heating. The β-SiC phase was generated via carbothermal reduction, and the carbon fabric showed a well-developed graphitic structure, promoting its thermal and anti-oxidation stabilities. Owing to the excellent dielectric loss in carbon fabric, SiC and SiO 2 as well as the micropore structure of the ceramic matrix, the absolute electromagnetic interference shielding (EMI) effectiveness (SSE/t) reached 948.18 dB∙cm2∙g-1 in the X-band, exhibiting an excellent EMI SE. After oxidation at 1000 °C for 10 h in the air, the SSE/t of the composite was only reduced to 846.02 dB∙cm2∙g-1. The C/SiC composite promises the efficient fabrication of high-temperature resistant materials for electromagnetic shielding applications. [ABSTRACT FROM AUTHOR]

This review deals with the potential of combining self-propagating high-temperature synthesis (SHS) and spark plasma sintering (SPS) for obtaining single-phase ceramic materials and ceramic and metal matrix composites. The materials discussed in this review contain compounds produced by the SHS process: carbides, borides, and silicides of metals and intermetallics. Factors in the structure formation of materials obtained by sintering of SHS products and the influence of SPS conditions on the characteristics of the materials (relative density and grain size) are analyzed. Advantages of combining the SHS and SPS techniques, including the possibility of additional processing of SHS products (grinding and adding components) to modify the composition and properties of materials are discussed. [ABSTRACT FROM AUTHOR]

To prepare a self-lubricating ceramic tool with excellent mechanical properties and crack healing ability, the h-BN@Al 2 O 3 solid lubricant with a core-shell structure was prepared by the heterogeneous nucleation method, and was added into Al 2 O 3 /TiC ceramic matrix together with TiB 2. Examination of the micro-morphology and phase composition of h-BN@Al 2 O 3 found that the surface of the solid lubricant h-BN was coated with Al(OH) 3 at first, and after calcination at 1200 °C, a dense and uniform Al 2 O 3 shell was formed. At the same time, the effects of the h-BN@Al 2 O 3 addition on the ceramic tool material were studied. The mechanical properties of the ceramic tool material with h-BN@Al 2 O 3 were improved relative to than those with h-BN. The optimal content of h-BN@Al 2 O 3 solid lubricant was 5 vol%. In the friction and wear test, h-BN in h-BN@Al 2 O 3 particles can be stripped to form a solid lubricating film on the material surface, which plays a good role in reducing wear and resisting wear. The crack healing ability of the self-lubricating ceramic tool material was studied by prefabricating cracks with a length of 400 μm on the surface. After a heat treatment at 700 °C for 60 min, the surface cracks of the ceramic tool material were completely healed, and the flexural strength was restored to 90% of that of the smooth samples. The oxidation of TiB 2 and h-BN in ceramic tool materials is the main reason for crack healing. [ABSTRACT FROM AUTHOR]

The properties of the laminated ceramic composites are known not only determined by the macro-laminated composite structure, but also highly dependent on their micro-polycrystalline structure. With the aim to investigate the competitive grain growth behavior during polycrystalline microstructure formation in laminated ceramic composites, a phase-field simulation for anisotropic grain growth is carried out in this study, and the effect of anisotropy in grain boundary energy on the grain coarsening and deformation near the interfaces is meticulously studied. Simulation results indicate that the polycrystalline microstructure is highly influenced by the competitive grain growth kinetics, and an oriented columnar grain layer is newly-formed near the interface. This abnormal grain growth phenomenon in the binary polycrystalline interface is attributed to the different grain boundary migrations in two layers, thereby leading to the interface migration in the laminated polycrystalline microstructures with an intermediate layer, which is consistent with experimental observations. Therefore, specifying the characteristics of the laminated polycrystalline microstructures could be an efficient way to improve the structure and performance design ability in laminated ceramics. [ABSTRACT FROM AUTHOR]

For high-temperature, sand-bearing, and high-pressure water injection pipelines, failure of commonly used organic epoxy coatings occurs frequently, which needs to be solved urgently. Ceramic coating is excellent alternative to solve this problem, attributed to its high hardness, high temperature resistance, and corrosion resistance. However, ceramic coatings prepared till date suffer from some problems, such as high porosity, and poor toughness. To improve overall performance of composite ceramic coating, herein, ceramic-lined composite steel pipes were synthesized by centrifugal self-propagating high-temperature synthesis (centrifugal-SHS), via doping different concentrations of SiO 2 in the Al/Fe 2 O 3 reaction system. The microstructure and phase of composite ceramic coatings after addition of SiO 2 were analyzed by optical microscopy with super depth of focus, scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. Effects of SiO 2 on the density and porosity, microhardness and fracture toughness, compression-shear strength and crushing strength of composite ceramic coatings were investigated by Archimedes method, Vickers indentation microfracture method, shearing test, and squeezing test, respectively. Results showed that the introduction of appropriate amount of SiO 2 reduced cooling rate of reaction system, thus improving the densification level and strength of coatings. Furthermore, in reaction system, FeAl 2 O 4 phase disappeared, owing to excessive Al, which could improve corrosion resistance of composite ceramic coatings. The optimum doping concentration of SiO 2 was found to be 4 wt%, in which composite ceramic coating showed excellent properties. [ABSTRACT FROM AUTHOR]

The paper describes the structure and properties of preceramic paper-derived Ti 3 Al(Si)C 2 -based composites fabricated by spark plasma sintering. The effect of sintering temperature and pressure on microstructure and mechanical properties of the composites was studied. The microstructure and phase composition were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. It was found that at 1150 °C the sintering of materials with the MAX-phase content above 84 vol% leads to nearly dense composites. The partial decomposition of the Ti 3 Al(Si)C 2 phase becomes stronger with the temperature increase from 1150 to 1350 °C. In this case, composite materials with more than 20 vol% of TiC were obtained. The paper-derived Ti 3 Al(Si)C 2 -based composites with the flexural strength > 900 MPa and fracture toughness of >5 MPa m1/2 were sintered at 1150 °C. The high values of flexural strength were attributed to fine microstructure and strengthening effect by secondary TiC and Al 2 O 3 phases. The flexural strength and fracture toughness decrease with increase of the sintering temperature that is caused by phase composition and porosity of the composites. The hardness of composites increases from ~9.7 GPa (at 1150 °C) to ~11.2 GPa (at 1350 °C) due to higher content of TiC and Al 2 O 3 phases. [ABSTRACT FROM AUTHOR]

This study deals with Al2O3-13wt.%TiO2-reinforced CoCrFeMnNi high-entropy alloy (HEA) composite coatings prepared by plasma spraying. The effect of the Al2O3-TiO2 ceramic phase on the microstructure, mechanical properties and high-temperature tribological performance of the as-sprayed composite coatings was investigated. The results showed that the composite coatings consisted of a HEA phase with a FCC (face-centered cubic) structure and an Al2O3-TiO2 ceramic phase with a three-dimensional network structure. The coatings presented a typical layered structure with less porosity than pure HEA coatings. The three-dimensional network structure was mainly due to partially melted Al2O3-13wt.%TiO2 particles during the spraying process. The composite coating with Al2O3-TiO2 ceramic phase had an improved plastic deformation resistance and a reduced elastic recovery resistance. Its wear rate was lower than that of the pure HEA coating. The main wear mechanisms included oxidation, wear and adhesive wear. The Al2O3-TiO2 ceramic phase reduced the adhesive wear and promoted the tribological behavior of the HEA composite coating at low temperature. The excellent wear resistance of the as-sprayed coating at high temperatures was mainly due to the formation of an oxide layer on the worn surface. [ABSTRACT FROM AUTHOR]

SiC-based fibers, a key component for the reinforcement of thermostructural ceramic matrix composites, are subjected to subcritical crack growth (SCG) causing their delayed failure. Stress exponents <10 were reported for various fiber types, standing out from other types of ceramic or glass. The continuum of silicon oxycarbide (SiCO) and carbon free phases is suspected to govern the environmentally assisted crack growth phenomenon, highlighted by relationships between SCG parameters and oxygen or carbon free contents. Metallic heteroelements (Ti or Zr, found in Tyranno® fibers) play a critical role on this sensitivity as well. The existence of 2 distinct groups of fiber types, possibly associated to different SCG mechanisms, is discussed. [ABSTRACT FROM AUTHOR]