共查询到20条相似文献,搜索用时 15 毫秒
1.
《Ceramics International》2016,42(4):4984-4992
The nanocomposite was produced via phenolic resin infiltrating into a carbon nanotube (CNT) buckypaper preform containing B4C fillers and amorphous Si particles followed by an in-situ reaction between resin-derived carbon and Si to form SiC matrix. The buckypaper preform combined with the in-situ reaction avoided the phase segregation and increased significantly the volume fraction of CNTs. The nanocomposites prepared by this new process were dense with the open porosities less than 6%. A suitable CNT–SiC bonding was achieved by creating a B4C modified interphase layer between CNTs and SiC. The hardness increased from 2.83 to 8.58 GPa, and the indentation fracture toughness was estimated to increase from 2.80 to 9.96 MPa m1/2, respectively, by the reinforcing effect of B4C. These nanocomposites became much more electrically conductive with high loading level of CNTs. The in-plane electrical resistivity decreased from 124 to 74.4 μΩ m by introducing B4C fillers. 相似文献
2.
Non-oxide fiber tow reinforced silicon nitride matrix composite was fabricated by low temperature CVI process with PyC as interphase. The tensile strength of the C and SiC fiber tow composites were 547 MPa and 740 MPa, respectively. The difference in tensile strength was analyzed based on the length, amount of pull-out fiber and also interface bonding. The infiltration uniformity of CVI silicon nitride (SiN) matrix within SiC fiber tow was comparable with that of CVI SiC matrix. These results suggested that the low temperature CVI process is suitable for the fabrication of fiber reinforced SiN matrix composites with proper interface bonding and high strength. 相似文献
3.
Zhongqi Shi Shugang ChenJiping Wang Guanjun QiaoZhihao Jin 《Journal of the European Ceramic Society》2011,31(12):2137-2143
High density carbon nanofibers (CNFs) reinforced aluminum nitride (AlN) composites were successfully fabricated by plasma activated sintering (PAS) method. The effects of CNFs on the microstructure, mechanical and electrical properties of the AlN composites were investigated. The experimental results showed that the grain growth of AlN was significantly inhibited by the CNFs. With 2 wt.% CNFs added into the composites, the fracture toughness and flexural strength were increased, respectively to 5.03 MPa m1/2 and 354 MPa, which were 20.9% and 13.4% higher than those of monolithic AlN. The main toughening mechanisms were CNFs pullout and bridging, and the main reason for the improvements in strength should be the fine-grain-size effect caused by the CNFs. The DC conductivity of the composites was effectively enhanced through the addition of CNFs, and showed a typical percolation behavior with a very low percolation threshold at the CNFs content of about 0.93 wt.% (1.51 vol.%). 相似文献
4.
《Ceramics International》2015,41(7):8643-8649
Graphene nanosheet (GNS)/aluminum nitride (AlN) composites were prepared by hot-pressing and effects of GNSs on their microstructural, mechanical, thermal, and electrical properties were investigated. At 1.49 vol% GNSs content, the fracture toughness (5.09 MPa m1/2) and flexural strength (441 MPa) of the composite were significantly increased by 30.17% and 17.28%, respectively, compared to monolithic AlN. The electrical conductivity of the composites was effectively enhanced with the addition of GNSs, and showed a typical percolation behavior with a low percolation threshold of 2.50±0.4 vol%. The thermal conductivity of the composites decreased with the addition of GNSs. 相似文献
5.
《应用陶瓷进展》2013,112(5):249-259
A three-dimensional interpenetrated network structure composite was designed and prepared via a combination of phenolic resin infiltration-pyrolysis and MoSi2–Si–Ti alloy-activated melting infiltration processes to effectively merge the desirable properties of MoSi2 and RSiC. Influence of infiltration temperature on the microstructure, mechanical and electrical properties of the composites was examined. Almost dense MoSi2–RSiC composites with the designed structure were obtained at 1900°C. Formation of the gradient interface modified the interface combination and enhanced the mechanical and electrical properties of the composite. Flexural strength of the composites reached approximately 114.262?MPa (room temperature) and 128.392?MPa (1400°C), respectively, indicating corresponding increases of 37.08 and 35.69% compared with the RSiC matrix. Volume resistivity decreased to 57.63?mΩ?cm, nearly five orders of magnitude lower than that of RSiC. Influence of the interpenetrated network structure and interface combination on the electrical conductivity behaviour of the composites was discussed via a modified mixture rule. 相似文献
6.
Reproducibility of indentation fracture resistance of three commercial silicon nitrides including bearing balls was evaluated by an international round robin with six laboratories. The between-laboratory standard deviations for indentations at 196 N on the perfectly mirror-finished surfaces were in the range of 0.2–0.5 MPa m1/2, demonstrating an excellent precession of the test results. The scatter in the fracture resistance increased as the indentation load decreased from 196 to 98 N. The errors in measuring crack lengths deduced from the deviation of each laboratory's readings from author's reading for the same indentations tended to increase with a decrease in the magnification of the lab's microscope, which suggested that finding exact crack tips with lower magnification was difficult especially for those samples with insufficiently mirror-finished surfaces indented at 98 N. Observation of indentations at the load of 196 N with powerful optics was advised to ensure the validity of the indentation technique which is used as the quality assessment of Si3N4 bearing balls. 相似文献
7.
Monika Michálková Zoltán Lenčéš Martin Michálek Peter Kocher Jakob Kuebler Pavol Šajgalík 《Journal of the European Ceramic Society》2013,33(13-14):2429-2434
In order to find out the influence of sintering additives on the electrical conductivity of Si3N4-based ceramics composites with dispersed carbon nano-fibers (CNFs) two different mixtures of sintering additives were tested – Al2O3/Yb2O3 and MgSiN2/Yb2O3, respectively. Optimization of hot-pressing conditions was performed for each mixture. The results show that the electrical conductivity can be effectively increased up to 1315 S/m by replacement of traditional sintering aid – alumina, with magnesium silicon nitride, while the mechanical properties remained on the same level. Other advantages of using MgSiN2 instead of alumina are the preservation of higher amounts of CNFs in the ceramic composite and lower densification temperature (1500 °C) compared to samples sintered with alumina-based sintering aids (1550 °C). 相似文献
8.
Silicon nitride based nanocomposites have been prepared with different amount (1 and 3 wt%) of multilayer graphene (MLG) as well as exfoliated graphite nanoplatelets (xGnP) and nano graphene platelets (Angstron) in comparison. The microstructure and mechanical properties of the graphene reinforced silicon nitride based composite materials have been investigated. Homogeneous distribution of the MLG additives have been observed on the fracture surface of the sintered material. The scanning electron microscopy examinations showed that graphene platelets are inducing porosity in matrix. The bending strength and elastic modulus of MLG/Si3N4 composites showed enhanced values compared to the other graphene added silicon nitride ceramic composites. These observations may be explained by the different type and quality of the starting materials and by the dispersion grade of graphene platelets having direct impact to the resulting density of the sintered samples. 相似文献
9.
Rasim CeylantekinCemail Aksel 《Ceramics International》2012,38(2):995-1002
Microstructural features and improvements on the mechanical properties and thermal shock behaviours of MgO-spinel composite refractories with ZrO2 addition were examined. ZrO2 incorporation into MgO-spinel led to improvements around ∼1.5-fold ratios on mechanical properties, Rst values and thermal shock results. The basic parameters improving mechanical properties and thermal shock resistance of MgO-spinel-ZrO2 composite refractories were determined as follows: (i) propagation of microcracks for a short distance by interlinking each other, (ii) stopping or deviation of microcracks when reaching pores or ZrO2 particles, (iii) concurrent occurrence of mostly intergranular and some transgranular cracks on fracture surfaces, and with the addition of ZrO2 (iv) the increase in bulk density, and (v) a significant decrease in MgO grain size. The improvements observed in thermo-mechanical properties confirmed that MgO-spinel-ZrO2 refractories showed a low strength loss and high thermal shock damage resistance at high temperatures, leading to longer service lives for using industrial applications. 相似文献
10.
11.
《Ceramics International》2023,49(10):15442-15450
Carbon nanotubes (CNTs) are widely used in ceramic-matrix composites (CMC) as a filler. An individual carbon nanotube exhibits extremely high thermal conductivity, however, the influence of CNTs on the thermal conductivity of CMCs is moderate. In contrast, even a small quantity of CNTs significantly increases the electrical conductivity of CMCs. The present paper studies this contradictory influence for ZrO2-CNTs composites with 3, 5, 10 and 20 vol% multi-wall carbon nanotubes (MWCNTs). Their thermal and electrical conductivity was studied by the laser flash method and electrochemical impedance spectroscopy. The analysis reveals that the moderate influence of MWCNTs on the thermal conductivity of composites originates from the similar thermal conductivity of MWCNTs in a bundle and zirconia. On the other hand, the substantial difference in the electrical conductivity of MWCNTs and zirconia leads to an exponential increase in the electrical conductivity of the ZrO2-CNTs composite even with small additions of nanotubes. 相似文献
12.
Silicon nitride is used for demanding tasks due to its high stiffness, strength and, especially, its high fracture toughness. Examples include cutting tools, forming rolls and ball bearings. The microstructure is characterized by elongated β-Si3N4 grains of different size and shape, which lead to the increased fracture toughness. Consequently, the paper will present an algorithm for the generation of three-dimensional and periodic silicon nitride-like microstructures, which will be used for micromechanical finite element simulations. The structure generation algorithm enhances the sequential adsorption technique with growth of particles and steric hindrance, which are motivated by experimental results. Results of the structure generator, such as the pseudo-time evolution and its statistical geometric distributions are presented and compared to literature data. With the finite element simulations, using a periodic unit cell, a validation of the model with literature values for Young's modulus and Poisson's ratio was possible. 相似文献
13.
14.
Hiroyuki Miyazaki Hideki HyugaYu-ichi Yoshizawa Kiyoshi HiraoTatsuki Ohji 《Ceramics International》2009
The reliability of the Vickers indentation fracture (IF) method for various types of silicon nitride (Si3N4) ceramics was assessed by comparing the fracture resistance, KR obtained from the IF test with the fracture toughness, KIc from the surface crack in flexure (SCF) technique in the same crack depth region. The KR of a fine-grained and equiaxed Si3N4 matched with the KIc from the SCF test when Miyoshi's equation was used, while the KIc of a bearing-grade Si3N4 was found to lie between KR values calculated with Niihara's equation (higher side) and Miyoshi's equations (lower side). In the case of coarse Si3N4 with elongated grains, the KR determined using Niihara's equation gave the best fit with KIc. The inconsistent outcomes were explained by the probable mechanisms, indicating that the KR from the IF test cannot be correlated directly with the KIc unless the effective crack length for the IF test was clarified. 相似文献
15.
The mechanical and thermal properties of interply hybrid carbon fiber (continuous and spun fabric)/phenolic composite materials have been studied. Hybrid carbon/phenolic composites (hybrid CP) with continuous carbon fabric of high tensile, flexural strength and spun carbon fabric of better interlaminar shear strength and lower thermal conductivity are investigated in terms of mechanical properties as well as thermal properties.Through hybridization, tensile strength and modulus of spun type carbon fabric reinforced phenolic composites (spun CP) increased by approximately 28% and 20%, respectively. Hybrid CP also exhibits better interlaminar shear strength than continuous carbon fabric/phenolic composites (continuous CP).The in-plane thermal conductivity of hybrid CP is 4-8% lower than that of continuous CP. As continuous filament type carbon fiber volume fraction increases, the transversal thermal conductivity of hybrid CP decreases.The erosion rate and insulation index were examined using torch test. Spun CP has a higher insulation index than continuous CP and hybrid CP over the entire temperature range. Hybrid CP with higher content of spun fabric exhibits higher insulation index as well as lower erosion rate. 相似文献
16.
《Ceramics International》2023,49(7):11167-11177
Lanthanum cerate (LC: La2Ce2O7) is a potential material for thermal barrier coating, whose improved toughness is a crucial necessity for the pathway of its industrialization. Herein, we demonstrated a promising approach to develop graphene/carbon nanotube hybrid composite coating using a large throughput and atmospheric plasma spraying method. Graphene nanoplatelets (GNP: 1 wt %) and carbon nanotube (CNT: 0.5 wt %) reinforced lanthanum cerate (LCGC) hybrid composite coatings were deposited on the Inconel substrate. Addition of 1 wt % GNP and 0.5 wt % CNT in LC matrix has significantly increased its relative density, hardness, and elastic modulus up to 97.2%, 2–3 folds, 3–4 folds, respectively. An impressive improvement of indentation toughness (8.04 ± 0.2 MPa m0.5) was observed on LCGC coating, which is ~8 times higher comparing the LC coating. The toughening was attributed to the factors: such as the distribution of GNPs and CNTs in the LC matrix, synergistic toughening offered by the GNPs and CNTs; (i) GNP/CNT pull-out, (ii) crack bridging and arresting, (iii) splat sandwiching, mechanical interlocking, etc. Finally, this improved toughness offered an exceptional thermal shock performance up to 1721 cycles at 1800 °C, without any major failure on the coating. Therefore, the GNP and CNT-reinforced LC hybrid composite coating can be recommended to open a path for turbine industries. 相似文献
17.
《Ceramics International》2017,43(12):8873-8878
Film formed by carbon nanotubes is usually called carbon nanotube film (CNTf). In the present study, CNTf fabricated by floating catalyst method was used to prepare CNTf/SiC ceramic matrix composites by chemical vapor infiltration (CVI). Mechanical and electrical properties of the resulting CNTf/SiC composites with different CVI cycles were investigated and discussed, and the results revealed that the CNTf has a good adaptability to CVI method. Tensile test demonstrated an excellent mechanical performance of the composites with highest tensile strength of 646 MPa after 2 CVI cycles, and the strength has a decline after 3 CVI cycles for an excessively dense matrix. While, the elastic modulus of the composite increased with the CVI cycles and reached 301 GPa after 3 CVI cycles. Tensile fracture morphologies of the composites were analyzed by scanning electron microscope to study the performance change laws with the CVI cycles. With SiC ceramic matrix infiltrated into the CNTf, enhanced electrical conductivity of the CNTf/SiC composite compared to pure CNTf was also obtained, from 368 S/cm to 588 S/cm. Conductivity of the SiC matrix with free carbon forming in the CVI process was considered as the reason. 相似文献
18.
Interface of multiwalled carbon nanotube (MWCNT)/alumina (Al2O3) nanocomposites have been studied using TEM. At low sintering temperature (Tsin=1500 °C), a 3–5 nm thick amorphous interface region was noticed. Nanocomposite sintered at 1700 °C possessed a well-defined graphene layer coating on matrix grains as the interface between CNT and Al2O3. A mechanism of such layered interface formation has been proposed. No traceable chemical reaction product was observed at the interface even after sintering at 1700 °C. It was noticed that while DC electrical conductivity (σDC) of 1500 °C sintered 2.4 vol% MWCNT/Al2O3 nanocomposite was only~0.02 S/m, it raised to ~21 S/m when sintering was done at 1700 °C. Such 103 times increase in σDC of present nanocomposite at a constant CNT loading was not only resulted from the exceptionally high electron mobility of CNT but the well-crystallized graphene interface on insulating type Al2O3 grains also significantly contributed in the overall increase of electrical performance of the nanocomposite, especially, when sintering was done at 1700 °C. 相似文献
19.
In order to enhance the mechanical properties of B4C without density increase, the short carbon fibers M40, M55J and T700 reinforced B4C ceramic composites were fabricated by hot-pressing process. The addition of the carbon fibers accelerates the densification of the B4C, decreases their densities, and improves their strength and toughness. The enhancement effects of the three kinds of carbon fibers were studied by investigating the density, Vickers hardness and the mechanical properties such as flexural strength, flexural modulus and fracture toughness of the composites. The fiber type has a great influence on the mechanical properties and enhancement of the short carbon fiber reinforced B4C composites. The flexible carbon fiber with high strength and low modulus such as T700 is appropriate to reinforce the B4C matrix ceramic composites. 相似文献
20.
The gelcasting technique was employed to prepare Si3N4 green body. The monomers used in the research were acrylamide (AM) and N,N′-methylenebisacrylamide (MBAM). The influences of the monomer content (AM and MBAM) and the ratio of monomers (AM/MBAM) on the warpage rate, shrinkage rate, and the flexural strength of Si3N4 ceramics green body were investigated. Both warpage rate and shrinkage rate of green body were found to decrease with the increase of monomer content, and monotonically increase with the ratio of monomers after drying. The variation of warpage rate with the ratio of monomers is evident when monomer content is 20 wt.%, but the variations are not evident when monomer contents are 40 and 55 wt.%. The flexural strength of the green body is highest at an optimum value of the monomers ratio, and increases with increasing monomer content, reaching 50–90 MPa when monomer contents are 40 and 55 wt.%. 相似文献