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A graphene nanosheet reinforced ZrB2-SiC ceramic composite (GNs/ZrB2-SiC) using graphene oxide (GO) was hot pressed at 1950°C and 30 MPa for 1 h. Raman and XPS analysis showed multilayer GNs structures were successfully introduced into the composite by in situ thermal reduction of GO during the hot pressing process. The homogeneous dispersion of GO...
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Context 1
... Here, almost fully dense composites were achieved aer hot pressing process. The rela- tive densities were 98.9% and 99.2% for ZS2G and ZS5G composites respectively, which were listed in Table 3. The calculated density was 2.2 g cm À3 for reduced GO, 6.09 g cm À3 for ZrB 2 and 3.21 g cm À3 for SiC. ...
Context 2
... calculated density was 2.2 g cm À3 for reduced GO, 6.09 g cm À3 for ZrB 2 and 3.21 g cm À3 for SiC. Mechanical properties of GNs/ ZrB 2 -SiC ceramic composite were also listed in Table 3. Although GNs/ZrB 2 -SiC composite exhibited highly relative density, no improvement in the hardness was observed. ...
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Citations
... The fracture toughness and work of fracture (WOF) were evaluated by Savari et al. [28] using the Single-Edge Notched Beam (SENB) technique. It was found that the fracture toughness and WOF were improved by the addition of graphite platelets and SiC to the monolithic ZrB 2 . ...
Carbon fibre-reinforced ultra-high temperature ceramics (UHTCs) are considered a class of promising materials for several applications, the most appealing ones being in the aerospace sector. Reinforcement is necessary to overcome the brittleness and low thermal shock resistance of ceramics and is often provided through the addition of carbon fibres or other carbon-based phases, such as nanotubes, graphene, and graphite. The present work is focused on the toughening of UHTCs through incorporation of 30−50 vol% thin, ordered graphite layers from conventional filter paper followed by hot pressing sintering. Cellulose filter paper was selected because it undergoes thermolysis with no melting stage forming a strong carbonaceous residue that can be used as toughener. Microstructure and mechanical properties of toughened composites were compared to those of other materials reinforced with short carbon fibres and the effect of different distribution of graphite was studied. Addition of graphite allowed toughness to be increased from 3−4 MPa·m1/2 (for un-reinforced materials) to 5.1−5.5 MPa·m1/2, similar to results obtained with short fibre reinforcement. The high-temperature properties, such as strength and toughness as well as oxidation resistance at 1500 ℃, were also examined.
... According to several reports [2,18,[23][24][25][26][27][28][29][30][31], carbon additives such as graphite, carbon nanotube, carbon black and graphene have positive effects on the sintering process. For instance, effect of graphene (0, 2.5, 5 and 7.5 wt%) on the fracture toughness of ZrB 2 -25 vol% SiC w composite was investigated and it was found that the presence of graphene continuously improved the fracture toughness from ~5 MPa.m½ in the graphene-free composite to ~6 MPa.m½ in the specimen containing 7.5 wt% nano-graphene. ...
... Microstructural evaluation of the crack path induced by micro-Vickers indentation revealed the crack deflection, bridging and arresting as the dominant toughening mechanisms [32]. In another study [29], effect of graphene nano sheet on the mechanical properties of ZrB 2 -SiC composite was investigated. It was found that nearly 5 vol% graphene nanosheets addition resulted to enhance fracture toughness of ZrB 2 -SiC up to 7.32 MPa m 0.5 , and the strength to 1055 MPa. ...
... Compared with particle toughening, the incorporation of a larger-aspect-ratio phase into the matrix normally improves the defect size tolerance of composite materials and consumes more crack growth energy during the cracking process of composite materials, making these materials show better fracture toughness. An effective strategy is to replace SiC particles with SiC fibers or whiskers [7], as well as the further addition of toughening phases such as graphite flakes [8], graphene [9], BN [10], carbon nanotubes [11], ZrO 2 fiber [12], and carbon fiber [13]. These toughening phases with relatively large lengths and diameters can greatly inhibit the volume effect of matrix defects and improve the toughness of the materials. ...
ZrB2-SiC-Zr2Al4C5 multi-phase ceramics with uniform structure and high density were successfully prepared through the introduction of in situ synthesized Zr2Al4C5 into ZrB2-SiC ceramic via SPS at 1800 °C. A systematic analysis and discussion of the experimental results and proposed mechanisms were carried out to demonstrate the composition-dependent sintering properties, mechanical properties and oxidation behavior. The results showed that the in situ synthesized Zr2Al4C5 could be evenly distributed in the ZrB2-SiC ceramic matrix and inhibited the growth of ZrB2 grains, which played a positive role in the sintering densification of the composite ceramics. With increasing Zr2Al4C5 content, the Vickers hardness and Young’s modulus of composite ceramics gradually decreased. The fracture toughness showed a trend that first increased and then decreased, and was increased by about 30% compared with ZrB2-SiC ceramics. The major phases resulting from the oxidation of samples were ZrO2, ZrSiO4, aluminosilicate and SiO2 glass. With increasing Zr2Al4C5 content, the oxidative weight showed a trend that first increased then decreased; the composite ceramic with 30 vol.% Zr2Al4C5 showed the smallest oxidative weight gain. We believe that the presence of Zr2Al4C5 results in the formation of Al2O3 during the oxidation process, subsequently resulting in a lowering of the viscosity of the glassy silica scale, which in turn intensifies the oxidation of the composite ceramics. This would also increase oxygen permeation through the scale, adversely affecting the oxidation resistance of the composites with high Zr2Al4C5 content.
... Zhang et al [5] and An et al [6] added graphene into ZrB2-SiC composites by thermal reduction of graphene oxide into multilayer graphene nanoplatelets. Under the synergistic effect of SiC whiskers and graphene nanoplatelets, the bending ability and fracture toughness of the composite are improved to varying degrees compared with those of pure ZrB2 ceramics. ...
As a two-dimensional nano-material with outstanding characteristics, graphene is mainly composed of carbon atoms organized in a honeycomb configuration. Numerous attempts have been made to produce substantial amounts of graphene using various chemical processes since the first isolation of graphene in 2004 by mechanical exfoliation from graphite. There is still a lot of potential applications remained undiscovered, particularly in strengthen heat resistance and toughness of the material. This paper summarized the preparation process of graphene, micro-morphology and macro performance of graphene in recent years. The mechanical properties, ways of toughening composites and mechanism of graphene on ultra-high temperature ceramic matrix were studied. In addition, the influence on thermal properties via different synthesis process, thermal shock resistance and oxidation resistance of graphene were explored.
... In recent years, the applications of GNPs and GONPs in ceramic matrix composites are gradually emerging. The ceramic matrix composites filled with graphene-family nanoplates [9,10] have attracted broad research interest, as reviewed in refs. [11][12][13][14][15]. Sun et al. [16] studied the reinforcing mechanisms of graphene and nano-TiC in Al 2 O 3 -based ceramic tool materials. ...
As nanoscale reinforcements, the graphene and graphene oxide nanoplates exhibit distinct mechanical and physical properties. The determination of the effective elasto-plastic behavior of nanoplate/ceramic nanocomposites and the different filling effects of graphene and graphene oxide nanoplate deserve systematic investigation. In this work, we intend to uncover how the graphene and graphene oxide nanoplates affect the macroscopic elasto-plastic characteristics of ceramic matrix nanocomposites and what differences in both nanoplates enhancements. A homogenization model is first utilized for determining the effective elastic parameters of nanoplate/ceramic composite with a perfect interface. Then the slightly weakened interface model is introduced to characterize the sliding effects of nanoplates in a ceramic matrix, and the effective elastic parameters of such nanoplates filled composites incorporating the interfacial sliding effects are explicitly formulated. Furthermore, a nonlinear micromechanics model is developed to investigate the macroscopic elastoplasticity and the yield behavior of graphene and graphene oxide nanoplate-filled ceramic nanocomposites subjected to confining pressure. The filling effects of the two kinds of nanoplates on the mechanical properties of such nanocomposite are comparatively examined. The calculated results demonstrate that types of the nanoplates and the imperfect interfaces between nanoplates and ceramic matrix have significant influences on the effective elasto-plastic behaviors of the nanoplate composites.
... The detailed fabrication process could be found in our early paper. 23 Sodium alginate (AR, Aladdin, China) was added into GO solution and stirred for 8 h to achieve a uniform solution. Commercial zirconium diboride (2 μm, >98%, Aladdin, China) and silicon carbide (0.5 μm, >98%, Aladdin, China) were poured into the uniform GO-sodium alginate solution, and the mixed solution was vigorously stirred for 8 h. ...
Biomimetic Bouligand architecture is constructed in the ceramic to improve its toughness. Firstly, unidirectional carbon fiber‐reinforced ZrB2‐SiC ceramic films are achieved through a vacuum‐assisted filtration method using graphene oxide. Then, ceramic films are helically assembled at a fixed angle of 30° in the graphite die based on the fiber orientation. Finally, the spark plasma sintering method was utilized to densify helical assembly carbon fiber/ceramic films. By constructing Bouligand structure, high fracture toughness (7.4 MPa·m0.5) and work of fracture (∼1055 J/m²) are achieved in ZrB2‐based ceramic. The toughening mechanisms mainly are crack deflection, twisting and branching, carbon fiber pulling out, and bridging.
... % of GNP has shown to improve densification from ~83% to ~97% (shown in Figs. 14a-b [134,135]) for ZrB2 matrices, attributed to its higher electrical (106 Scm −1 [103]) and thermal conductivity (5300 Wm -1 K -1 [104]) which enables a uniform distribution of the current and heat during consolidation. Elsevier [134]. ...
Ultra-high temperature ceramics (UHTCs) have played a significant role in fulfilling demands for the thermal protection system (TPS) in the aerospace sector, however, a promising candidate has not emerged yet. This critical review provides typical inconsistencies and new perspectives related to UHTCs in terms of: (i) material and processing: i.e., sinterability, reinforcements, microstructural evolution, (ii) properties and performance correlation with the processing conditions and resulting microstructure, and (iii) outlook on the most promising ZrB2-HfB2-SiC-based composites as potential candidates for hypersonic leading edge and re-entry structures. An optimal selection of the content, size and reinforcing phase (such as silicides, refractory carbides, and carbon-based, etc.) is mandated in upgrading the thermo-mechanical performance of UHTCs to sustain elevated temperature (1700 °C), exhibiting flexural/fracture strength of >300 MPa, high thermal conductivity >14.5 Wm⁻¹K⁻¹, and high oxidation resistance (<80 gm⁻² over 2 hours at 1400 °C). From emphasis on the powder purity, and sintering additives on affecting the densification, mechanical properties and high temperature oxidation, improvements in the functional performance of UHTCs are carried forward with emphasis mainly on borides and carbides. Emergence of SiC as most promising sintering additive with optimal content of ∼20 vol.%, and with supplemented HfB2 addition in ZrB2-HfB2-SiC based UHTCs have exhibited higher oxidation resistance and may serve as conceivable entrants for hypersonic vehicles. Further, the review leads the reader to developing new materials (including silicides, MAX phases, and high entropy UHTCs), incorporating novel strategies like designing layered structures or functionally graded materials (FGM), and effective joining to allow the integration of smaller components into scaled up structures. On one hand, where plasma arc-jet exposure mimics high heat-flux exposures, the utilization of multi-length-scale computational modeling (such as finite element methods, density functional theory, ab initio etc.) allows assessing the material performance under dynamic changes (of variable partial pressure, temperatures, gradation, etc.) towards perceiving new insights into the structural stability and thermo-mechanical properties of UHTCs. This review critically underlines the present state of the art and guides the reader towards the futuristic development of new class of high-temperature materials for TPSs.
... Graphene, due to its high strength in the xy-plane, high thermal conductivity and specific surface area, attracts attention as a very promising strengthening component of ceramics [40][41][42][43][44][45][46][47][48][49], which, with a slight decrease in strength, can significantly increase fracture toughness and thermal shock resistance. Thus, in paper [40], 5 wt% graphene (G) was introduced to modify ZrB 2 -25 vol% SiC ceramics. ...
... In this case, the authors noted that graphene particles were strongly agglomerated [40]. To reduce the agglomeration problem for graphene particles when modifying UHTC of ZrB 2 -20 vol% SiC composition, the authors of [48] used graphene oxide (GO, containing the − OH, − COOH and =O groups in graphene layers), which was well stabilised in an aqueous and organic dispersion medium and was easily reduced to graphene (rGO) when heated in a vacuum or inert gas. For ceramics produced by adding 5 vol%GO, the best value of fracture toughness was stated (K IC GO = 7.32 ± 0.37 MPa⋅m 1/2 ), along with high strength and Vickers hardness (1055 MPa and 22.76 GPa, respectively) [48]. ...
... To reduce the agglomeration problem for graphene particles when modifying UHTC of ZrB 2 -20 vol% SiC composition, the authors of [48] used graphene oxide (GO, containing the − OH, − COOH and =O groups in graphene layers), which was well stabilised in an aqueous and organic dispersion medium and was easily reduced to graphene (rGO) when heated in a vacuum or inert gas. For ceramics produced by adding 5 vol%GO, the best value of fracture toughness was stated (K IC GO = 7.32 ± 0.37 MPa⋅m 1/2 ), along with high strength and Vickers hardness (1055 MPa and 22.76 GPa, respectively) [48]. In another study [46], SiC whiskers were used as a silicon-containing component to achieve a synergetic effect, and the GO content in the initial composite powders was increased to 5 and 10 vol%. ...
The oxidation resistance of ultra-high-temperature ceramic material (HfB2-30 vol%SiC)-2 vol%rGO (rGO: reduced graphene oxide) under long-term exposure (2000s) to a supersonic air flow has been studied. The ceramics were obtained by reactive hot pressing of HfB2-(SiO2-C)-rGO composite powder at a temperature of 1800 °C (pressure 30 MPa, holding time 15 min, Ar). The surface temperature of graphene-modified ceramics under the influence of heating by high-enthalpy air flow (heat flow q reached 779 W⋅ cm–2) did not exceed 1700 °C, which is 650-700 °C less than for the HfB2-30 vol%SiC baseline ceramics. This may be related to an increase in the efficiency of heat transfer from the sample to the water-cooled module, due to the higher thermal conductivity of the rGO-containing material. Thereby, a decrease in the material degradation degree has been noted, i.e. decrease in the recession rate and decrease in the total thickness of the oxidised ceramic layer by tenth. The peculiarities of the oxidised surface and near-surface region microstructure upon aerodynamic heating of the graphene-modified ceramic material, have been shown.
... Graphene has the ability to affect the morphology of the TiO 2 through controlling the nucleation and the grain growth of TiO 2 , allowing the optimal chemical interaction and bonding between TiO 2 and graphene platelets [17]. Graphene nanosheets are found to be effective in strengthening and toughening ceramic composites, while the toughening mechanisms mainly are graphene pulling out, graphene bridging, and three-dimensional crack deflection [18]. ...
... Several studies confirmed the fabrication of the TiO 2 matrix composites reinforced by graphene through a variety of methods, such as solgel [19], electrodeposition, chemical vapor deposition (CVD), physical vapor deposition (PVD), ultrasonic spray pyrolysis technology, [20] and spark plasma sintering (SPS) technics [21,22]. Films of graphene/TiO 2 ceramic composites with 0.025 wt% graphene demonstrate the best tribological properties at 100 • C. Overall, graphene acts as an effective reinforcing and lubricating agent in graphene/TiO 2 ceramic composite films [17][18][19][20][21][22]. In the publication, Cheng Zhang et al. have synthesized TiO 2 − GNPs 1% composite by SPS technique and achieved a 25% of improvement in photocatalytic activity [21]. ...
This study reports the role of graphene in improving the mechanical and electrical properties of TiO2/graphene nanoplatelets (GNPs) composite. Graphene oxide (GO), as a precursor was used with varying concentrations of 0, 0.5, 1, and 2 wt%. The GO was being reduced simultaneously with the TiO2 matrix, providing uniform distribution of rGO nanoplatelets among the matrix particles. Spark plasma sintering technique (SPS) was used for sintering initial powder of the TiO2/rGO composite. Alongside the sintering of the powder, SPS induces rGO transformation to graphene nanoplatelets at high temperatures and provides the densification of TiO2/GNPs as a final composition. Morphology and microstructure of prepared samples were characterized by XRD and SEM. Density and microstructural studies were used to determine the sintering quality and compared to the theoretical density of TiO2 and TiO2/GNPs composites. Vickers microhardness method was used to calculate hardness and fracture toughness depending on the crack propagation alongside the indentations. The two-probe method was applied to study the electrical conductivity by resistance measurement. The results indicated that there was a significant change in the structural and physical properties of TiO2/GNPs composites. The rGO takes an important role as a grain growth inhibitor, acting as the barrier for crack propagation and leading to increased fracture toughness. Thus, GNPs can be considered as a good reinforcement for titanium dioxide ceramic in order to improve the material's brittleness and electrical conductivity without adversely affecting its microhardness.
... In order to acquire a homogeneous microstructure in the HS w G ceramic matrix, GO nanoplatelets were chosen instead of graphene nanoplatelets as a precursor to avoid the aggregation of graphene caused by the additional reduction process. 25,29 Thermal treatment during the sintering process is considered an effective method to reduce GO. The Raman spectra of raw GO powder and sintered HS w G matrix sheets illustrated the structural changes from GO to rGO during sintering ( Figure 2). ...
A multiscale structural design was innovatively adopted herein to increase the toughness of monolithic HfB2 ceramics. SiC whiskers (SiCw) and graphene oxide (GO) were used as fillers for the HfB2 matrix, whereas a ductile W foil was introduced as an interlayer to synthesize laminated HfB2‐SiCw‐rGO/W ceramics. Monolithic HfB2‐SiCp (particulate) and laminated HfB2‐SiCp/W ceramics were prepared using the same routes and used as controls. Following tape casting and spark plasma sintering at 1800°C, the toughness of the prepared laminated HfB2‐SiCw‐rGO/W samples was increased to 14.2 ± 0.6 MPa·m1/2, with minimal sacrifice in flexural strength (421 ± 16 MPa). Morphological analysis of the fracture surface revealed the synergistic effects of micro‐toughening (including bridging and pullout of whiskers and rGO) and macro‐toughening (including crack deflection, bifurcation, and delamination) mechanisms responsible for improving the fracture toughness of the laminated HfB2‐SiCw‐rGO/W composites.
