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1.
《Journal of the European Ceramic Society》2017,37(8):3009-3014
Tantalum diboride – boron suboxide ceramic composites were densified by spark plasma sintering at 1900 °C. Strength and fracture toughness of these bulk composites at room temperature were 490 MPa and 4 MPa m1/2, respectively. Flexural strength of B6O–TaB2 ceramics increased up to 800 °C and remained unchanged up to 1600 °C. At 1800 °C a rapid decrease in strength down to 300 MPa was observed and was accompanied by change in fracture mechanisms suggestive of decomposition of boron suboxide grains. Fracture toughness of B6O–TaB2 composites showed a minimum at 800 °C, suggestive a relaxation of thermal stresses generated from the mismatch in coefficients of thermal expansion.Flexural strength at elevated temperatures for bulk TaB2 reference sample was also investigated.Results suggest that formation of composite provides additional strengthening/toughening as in all cases flexural strength and fracture toughness of the B6O–TaB2 ceramic composite was higher than that reported for B6O monoliths. 相似文献
2.
William G. Fahrenholtz 《Journal of the American Ceramic Society》2013,96(1):47-50
The strength of zirconium diboride (ZrB2) ceramics was measured up to 2300°C, which are the first reported measurements above 1500°C since 1970. ZrB2 ceramics were prepared from commercially available powder by hot pressing. A mechanical testing apparatus capable of testing material in the ultra‐high temperature regime with atmosphere control was built, evaluated, and used. Four‐point bend strength was measured as a function of temperature up to 1600°C in air and between 1500°C and 2300°C in argon. Strength between room temperature and 1200°C was ~390 MPa, decreasing to a minimum of ~170 MPa between 1400°C and 1500°C, with strength increasing to ~220 MPa between 1600°C and 2300°C. 相似文献
3.
High‐temperature strength and plastic deformation behavior of niobium diboride consolidated by spark plasma sintering
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Dmytro Demirskyi Ievgen Solodkyi Toshiyuki Nishimura Oleg Vasylkiv 《Journal of the American Ceramic Society》2017,100(11):5295-5305
Bulk niobium diboride ceramics were consolidated by spark plasma sintering (SPS) at 1900°C. SPS resulted in dense specimens with a density of 98% of the theoretical density and a mean grain size of 6 μm. During the SPS consolidation, the hexagonal boron nitride (h‐BN) was formed from B2O3 on the powder particle surface and residual adsorbed nitrogen in the raw diboride powder. The room‐temperature strength of these NbB2 bulks was 420 MPa. The flexural strength of the NbB2 ceramics remained unchanged up to 1600°C. At 1700°C an increase in strength to 450 MPa was observed, which was accompanied by the disappearance of the secondary h‐BN phase. Finally, at 1800°C signs of plastic deformation were observed. Fractographic analysis revealed a number of etching pits and steplike surfaces suggestive of high‐temperature deformation. The temperature dependence of the flexural strength of NbB2 bulks prepared by SPS was compared with data for monolithic TiB2, HfB2 and ZrB2. Our analysis suggested that the thermal stresses accumulated during SPS consolidation may lead to additional strengthening at elevated temperatures. 相似文献
4.
Haoyi Wang Delong Cai Zhihua Yang Xiaoming Duan Bingzhu Wang Bo Wang Daxin Li Dechang Jia Yu Zhou 《Journal of the American Ceramic Society》2022,105(5):3590-3600
A type of boron nitride–magnesium aluminum silicate (BN-MAS) composite ceramics was fabricated by hot-press sintering at different sintering temperatures. The relationship between the sintering temperature and microstructure was investigated by analyzing the interaction between hexagonal boron nitride (h-BN) and the MAS phase. The main MAS phase in the composite ceramics is the α-cordierite phase at a sintering temperature of 1300°C. At temperatures above 1400°C, the inhibitory effect of h-BN on the crystallization of the MAS system is significant, and MAS mainly exists in the form of an amorphous phase. The composite sintered at 1700°C exhibited the highest bending strength of 218MPa. h-BN and MAS were co-enhanced. MAS can be used as an effective liquid-phase sintering aid to assist in the sintering of h-BN, whereas h-BN can absorb the fracture energy of the composite ceramics through the pull-out and bridging effect of the particles. 相似文献
5.
Pradeep Vallachira Warriam Sasikumar Gurdial Blugan Nicola Casati Eirini Kakkava Giulia Panusa Demetri Psaltis Jakob Kuebler 《Ceramics International》2018,44(17):20961-20967
Polymer derived SiOC and SiCN ceramics (PDCs) are interesting candidates for additive manufacturing techniques to develop micro sized ceramics with the highest precision. PDCs are obtained by the pyrolysis of crosslinked polymer precursors at elevated temperatures. Within this work, we are investigating PDC SiOC ceramic monoliths synthesized from liquid polysiloxane precursor crosslinked with divinylbenzene for fabrication of conductive electromechanical devices. Microstructure of the final ceramics was found to be greatly influenced by the pyrolysis temperature. Crystallization in SiOC ceramics starts above 1200?°C due to the onset of carbothermal reduction leading to the formation of SiC and SiO2 rich phases. Microstructural characterisation using ex-situ X-ray diffraction, FTIR, Raman spectra and microscopy imaging confirms the formation of nano crystalline SiC ceramics at 1400?°C. The electrical and mechanical properties of the ceramics are found to be significantly influenced by the phase separation with samples becoming more electrically conducting but with reduced strength at 1400?°C. A maximum electrical conductivity of 101 S?cm?1 is observed for the 1400?°C samples due to enhancement in the ordering of the free carbon network. Mechanical testing using the ball on 3 balls (B3B) method revealed a characteristic flexural strength of 922?MPa for 1000?°C amorphous samples and at a higher pyrolysis temperature, materials become weaker with reduced strength. 相似文献
6.
Highly porous Si3N4 ceramics have been fabricated via freeze casting and sintering. The as-sintered samples were pre-oxidized at 1200–1400 °C for 15 min. The effect of pre-oxidation temperature on the microstructure, flexural strength, and dielectric properties of porous Si3N4 ceramics were investigated. As the pre-oxidation temperature increased from 1200 °C to 1400 °C, firstly, the flexural strength of the pre-oxidized specimens remained almost constant at 1200 °C, and then decreased to 14.2 MPa at 1300 °C, but finally increased to 25.6 MPa at 1400 °C, while the dielectric constant decreased gradually over the frequencies ranging from 8.2 GHz to 12.4 GHz. This simple process allows porous Si3N4 ceramics to have ultra-low dielectric constant and moderate strength, which will be feasible in broadband radome applications at high temperatures. 相似文献
7.
Elevated Temperature Strength Enhancement of ZrB2–30 vol% SiC Ceramics by Postsintering Thermal Annealing
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William G. Fahrenholtz 《Journal of the American Ceramic Society》2016,99(3):962-970
The mechanical properties of dense, hot‐pressed ZrB2–30 vol% SiC ceramics were characterized from room temperature up to 1600°C in air. Specimens were tested as hot‐pressed or after hot‐pressing followed by heat treatment at 1400°C, 1500°C, 1600°C, or 1800°C for 10 h. Annealing at 1400°C resulted in the largest increases in flexure strengths at the highest test temperatures, with strengths of 470 MPa at 1400°C, 385 MPa at 1500°C, and 425 MPa at 1600°C, corresponding to increases of 7%, 8%, and 12% compared to as hot‐pressed ZrB2–SiC tested at the same temperatures. Thermal treatment at 1500°C resulted in the largest increase in elastic modulus, with values of 270 GPa at 1400°C, 240 GPa at 1500°C, and 120 GPa at 1600°C, which were increases of 6%, 12%, and 18% compared to as hot‐pressed ZrB2–SiC. Neither ZrB2 grain size nor SiC cluster size changed for these heat‐treatment temperatures. Microstructural analysis suggested additional phases may have formed during heat treatment and/or dislocation density may have changed. This study demonstrated that thermal annealing may be a useful method for improving the elevated temperature mechanical properties of ZrB2‐based ceramics. 相似文献
8.
《Journal of the European Ceramic Society》2002,22(4):559-566
In order to improve the elevated strength and thermal shock resistance of TiC materials, 20vol% short carbon fiber-reinforced TiC composite (Cf/TiC) was produced by hot pressing. With carbon fiber addition, the strength and fracture toughness of TiC is increased remarkably, and the elastic modulus and thermal expansion coefficient are decreased. The strength value of Cf/TiC composite is 593 MPa at room temperature and 439 MPa at 1400°C, and the fracture toughness value at room temperature is 6.87 MPa m1/2. The thermal stress fracture resistance parameter, R, thermal stress damage resistance parameter, RIV, and thermal stress crack stability parameter, Rst, are all increased. The residual strength decreases significantly when the thermal shock temperature difference, ΔT, is higher than 900°C, and the residual strength is 252 MPa when ΔT is 1400°C. Carbon fiber reinforced-TiC composite exhibits superior resistance to thermal shock damage compared with monolithic TiC. The catastrophic failure induced by severe thermal stresses can be prevented in Cf/TiC composite. 相似文献
9.
Oleg N. Grigoriev Boris A. Galanov Valerii A. Kotenko Sergey M. Ivanov Alexandr V. Koroteev Nikolay P. Brodnikovsky 《Journal of the European Ceramic Society》2010,30(11):2173-2181
Mechanical properties of ZrB2–SiC and ZrB2–ZrSi2–SiC ceramics in the temperature range from 20 to 1400 °C were studied. It was found that the introduction of zirconium silicide resulted in pore-free ceramics having bending strengths of 400–500 MPa over a wide range of boride–carbide compositions. Zirconium silicide additive did not lead to significant strength and hardness changes at low temperature, but essentially increased Weibull modulus, and, therefore, the reliability of the ceramics. However, zirconium silicide additions resulted in noticeably reduced bending strength in ZrB2–SiC based composites at 1400 °C. 相似文献
10.
《Journal of the European Ceramic Society》2017,37(1):393-397
Spark plasma sintering of TiB2–boron ceramics using commercially available raw powders is reported. The B4C phase developed during reaction-driven consolidation at 1900 °C. The newly formed grains were located at the grain junctions and the triple point of TiB2 grains, forming a covalent and stiff skeleton of B4C. The flexural strength of the TiB2–10 wt.% boron ceramic composites reached 910 MPa at room temperature and 1105 MPa at 1600 °С. Which is the highest strength reported for non-oxide ceramics at 1600 °C. This was followed by a rapid decrease at 1800 °C to 480–620 MPa, which was confirmed by increased number of cavitated titanium diboride grains observed after flexural strength tests. 相似文献
11.
Teng-Teng Xu Su Cheng Lai-Zhen Jin Kun Zhang Tao Zeng 《International Journal of Applied Ceramic Technology》2020,17(2):438-448
Silicon carbide (SiC) ceramics, as a kind of candidate material for aero-engine, its high-temperature performance is a critical factor to determine its applicability. This investigation focuses on studying the high-temperature properties of SiC ceramics fabricated by using additive manufacturing technology. In this paper, SiC ceramics were prepared by combining selective laser sintering (SLS) with precursor infiltration and pyrolysis (PIP) technique. The microstructure, phase evolution, and failure mechanism after high-temperature tests were explored. SiC ceramic samples tested at room temperature (RT), 800°C, 1200°C, 1400°C, and 1600°C demonstrated bending strengths of 220.0, 226.1, 234.9, 215.5, and 203.7 MPa, respectively. The RT strength of this material can be maintained at 1400°C, but it decreased at 1600°C. The strength retention at 1400°C and 1600°C were 98% and 92%, respectively. The results indicate that the mechanical properties of SiC ceramics prepared using this method have excellent stability. As the temperature increases, the bending strength of the specimens increased slightly and reached the peak value at 1200°C, and dropped to 203.7 MPa at 1600°C. Such an evolution could be mainly due to the crack healing, and the softening of the glassy phase. 相似文献
12.
《Journal of the European Ceramic Society》2000,20(12):2149-2152
Al2O3 ceramics were superfast densified using spark plasma sintering (SPS) by heating to a sintering temperature between 1350 and 1700°C at a heating rate of 600°C/min, without holding time, and then fast cooling to 600°C within 3 min. High-density Al2O3 ceramics could be achieved at lower sintering temperatures by SPS, as compared with that by conventional pressureless sintering (PLS). The bending strength of Al2O3 superfast densified by SPS in the range of sintering temperature between 1400 and 1550°C reached values as high as 800 MPa, almost twice that obtained by the PLS. SEM observations indicated that intragranular fracture was the preponderant fracture mode in these samples, resulting in these excellent bending strength values. 相似文献
13.
Fei Qi Xingxing Xu Jie Xu Yali Wang Jinlong Yang 《Journal of the American Ceramic Society》2014,97(10):3341-3347
Recent developments in the fabrication of hollow spheres have allowed our group to prepare a new type of macroporous ceramics: hollow sphere ceramics (HSCs). Alumina hollow spheres were first produced by centrifugal spray‐drying of particle‐stabilized foam slurry. The obtained hollow spheres were sintered together to form HSC at high temperatures. The effect of the sintering temperature on the linear shrinkage, porosity and compressive strength of HSC samples was investigated. When the sintering temperature was increased from 1400°C to 1600°C, the samples shrunk increasingly and the porosity decreased from 59% to 42%, which lead to an increase in the strength of the alumina foams from 6.9 (at 1400°C) to 100.0 MPa (at 1550°C). The mechanical strength of the HSC highly depends on the contact area between the hollow spheres, which could be increased by increasing the sintering temperature, decreasing the size of hollow spheres or by slurry infiltration. 相似文献
14.
Zongyun Shen Junxi Xie Kaichen Qian Qiangqiang Zhu Xiaojian Mao Minghui Feng Benxue Jiang Long Zhang Jintai Fan 《Journal of the American Ceramic Society》2021,104(12):6335-6344
In this study, fine Y2O3–MgO composite nanopowders were synthesized via the sol–gel method. Dense Y2O3–MgO composite ceramics were fabricated by pre-sintering the green body in air at different temperatures for 1 h and then subjecting the sintered bodies to hot isostatic pressing at 1300°C for 1 h. The effects of pre-sintering temperature on the microstructural, mechanical, and optical properties of the resulting ceramics were studied. The average grain size of the ceramics was increased, whereas their hardness and fracture toughness were decreased with increasing pre-sintering temperature. A maximum fracture toughness of 1.42 MPa·m1/2 and Vickers hardness of 10.4 GPa were obtained. The average flexural strength of the ceramics was 411 MPa at room temperature and reached 361 MPa at 600°C. A transmittance of 84% in the 3–5 µm region was obtained when the composite ceramics were sintered at 1400°C. Moreover, a transmittance of 76% in the 3–5 µm region was obtained at 500°C. 相似文献
15.
《Journal of the European Ceramic Society》1999,19(13-14):2359-2366
Silicon nitride ceramics were densified with the sintering additives Y2O3 and SiO2 by a two-step sinter-HIP-process. Three compositions with additive contents between 2 and 7 wt% Y2O3 were prepared to study the influence of the processing conditions on the mechanical properties. The minimum additive content required for nearly complete densification (>98.5%) was only 2 wt% Y2O3. However, densification was limited to certain Y2O3/SiO2 ratios. The additive-rich samples revealed a mean strength at room temperature up to 800 MPa which degrades at 1400°C. The material with only 2 wt% Y2O3 has a room temperature strength of ∼500 MPa, but no strength degradation up to 1400°C. The lower strength correlates with a pronounced increase in brittleness with a decreasing additive content indicated by a fracture toughness of only 2·5 MPam1/2 for composition 2/0. The investigated materials exhibit a relatively high creep resistance at 1400°C with creep rates down to 1·5×10−9 s−1. 相似文献
16.
Xin Wang Yazhong Chen Xiaozhao Han Jiarui Yu Kesong Xiao Xianlong Zhang Xueping Wu 《International Journal of Applied Ceramic Technology》2023,20(3):1442-1456
High-toughness mullite ceramics were fabricated through hot-press sintering (HPS) of pyrophyllite and AlOOH, which were wet-milled and well mixed using a planetary ball mill. The impacts of sintering temperatures and contents of AlOOH on mullite phase formation, densification, microstructure and mechanical properties in ceramic materials were investigated through XRD, SEM and mechanical properties determination. The results indicated that high-toughness mullite ceramics could be successfully prepared by HPS at temperatures higher than 1200°C for 120 min. Increasing the sintering temperature from 1000 to 1300°C significantly enhanced the flexural strength and fracture toughness of samples. The highest flexural strength of 297.97±25.32 MPa and fracture toughness of 4.64±0.11 MPa⋅m1/2 were obtained for samples sintered at 1300°C. Further increase of temperature to 1400°C resulted in slight decrease of flexural strength and fracture toughness. Compared with the mullite ceramics prepared only using pyrophyllite as raw material, incorporation of AlOOH into raw material significantly increased the mechanical properties of final mullite ceramics. And stoichiometric AlOOH and pyrophyllite as starting material gave the best performance in fracture toughness. The high-toughness of mullite ceramics were ascribed to the high mullite phase content, fine mullite whiskers and in situ formed, intertwined three-dimensional network structure obtained through HPS at a low temperature of 1300°C. 相似文献
17.
《Ceramics International》2019,45(13):16496-16503
Reduced graphene oxide (rGO) sheets were uniformly dispersed in boron carbide ceramics by a heterogeneous co-precipitation method. This approach was used to improve the fracture toughness of boron carbide ceramics and to address the problem of agglomeration of graphene in the boron carbide matrix. Cetyltrimethyl ammonium bromide was used as a heterogeneous co-precipitation reaction initiator to prepare a homogeneously dispersed graphene oxide/boron carbide (GO/B4C) mixture. Reduced graphene oxide/boron carbide (rGO/B4C) powder mixtures with good dispersion were obtained by high temperature heat treatment. Dense rGO/B4C composite ceramics were fabricated by spark plasma sintering at 1800 °C and 50 MPa. The fracture toughness and flexural strength of the rGO/B4C with an rGO content of 2 vol% composite increased by 42% (from 3.43 to 4.88 MPa·m1/2) and 28% (from 372 to 476 MPa) compared with those of pure B4C, respectively. The markedly improved fracture toughness and flexural strength of the boron carbide ceramics were attributed to the effect of crack bridging and crack deflection by graphene sheets, graphene interface sliding, and pulling out of graphene. 相似文献
18.
Eric W. Neuman Connor C. Wittmaier William G. Fahrenholtz Gregory E. Hilmas 《International Journal of Applied Ceramic Technology》2021,18(5):1845-1852
The mechanical response was studied for dense laminates containing layers of ZrB2 (~145 µm) and graphite—10 vol% ZrB2 (~20 µm). Individual layers were formulated by mixing starting powders with thermoplastic polymers and pressing into sheets. Laminates were produced by stacking and warm pressing the sheets, debinding, and hot pressing at 2050°C, 32 MPa, in Ar. The laminates were fractured at temperatures up to 2000°C in Ar. Laminates exhibited room temperature flexure strength of 260 MPa, increasing to 300 MPa at 1600°C, and then decreasing to 160 MPa at 2000°C. Inelastic work of fracture was 0.6 kJ/m2 at room temperature, reached a maximum of 1.3 kJ/m2 at 1400°C, and reverted to linear elastic failure at 2000°C. During fracture, cracks were deflected at the interfaces between the strong ZrB2 layers and the relatively weak C-ZrB2 layers, which led to an increased inelastic work of fracture by more than an order of magnitude compared to conventional ZrB2 ceramics. This study demonstrated that laminate architectures are a promising approach for improving the damage tolerance of ZrB2-based ceramics at elevated temperatures. 相似文献
19.
Xiaorong Zhang Zhixiao Zhang Bin Nie Huanyu Chen Yanming Wang Liyun Zheng Yongmei Bai Weimin Wang 《Ceramics International》2018,44(9):10766-10772
Dense and fine-grained boron carbide (B4C) ceramics were fabricated via high-pressure hot pressing (100?MPa) using powders, which are prepared by high-energy ball milling. These powders were sintered at a low temperature (1800?°C) without any sintering aid. The dense and fine-grained B4C ceramics demonstrate super high hardness, outstanding fracture toughness and modern flexure strength. The milled powders were characterised by disordered crystal structure and ultrafine particle size that ranges from a few nanometres to a few hundred nanometres. The combined contributions of high pressure and the characteristic of the milled powders guaranteed that the dense fine-grained microstructure was achieved at only 1800?°C. The grain size distribution of the ceramics was inhomogeneous and ranged from 70?nm to 1.6?µm. However, the average grain size was fine at only 430?nm, which partially contributed to the super high hardness of the B4C ceramics. The locally concentrated areas of the small grains changed the fracture mode of the B4C ceramics from the complete transgranular fracture to a mixture of transgranular and intergranular fractures, thereby enhancing the toughness of the B4C ceramics. The relative density, Vickers hardness, flexure strength and fracture toughness of the obtained B4C ceramics reached up to 99.5%, 41.3?GPa, 564?MPa and 4.41?MPa?m1/2, respectively. 相似文献
20.
Zhuang Lu Limeng Liu Guihong Geng Alexander M. Laptev Zhaoping Hou Yujin Wang 《Ceramics International》2019,45(6):6712-6717
TaC ceramics with 0.03–0.60?wt% of boron additions were prepared by hot pressing at 2100?°C for 1?h under a pressure of 40?MPa. Effects of boron content on densification, phase composition, microstructure, mechanical properties and oxidation resistance of the TaC ceramics were investigated. When the boron content was 0.12?wt% and above, full density was obtained due to reactions between boron and oxygen impurity at presence of TaC. Minor phases of TaB2 and C were formed in the 0.24 and 0.60?wt% B compositions after gas-out of the oxygen impurity. Microstructure of the TaC ceramics was refined with increasing in boron content. The TaC ceramic with 0.24?wt% of boron showed the best mechanical properties with a Vickers hardness, flexural strength and fracture toughness of 17.7?GPa, 534?MPa and 4.6?MPa?m1/2, respectively. When more boron was added, interfacial bonding of the TaC grains was strengthened causing a decrease in fracture toughness. Oxidation resistance of the TaC ceramics increased with boron content. Particularly, the 0.60?wt% B composition showed a weight gain of 0.0018?g/cm2 after oxidization at 800?°C in air for 3?h. 相似文献