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1.
Shi C. Zhang Greg E. Hilmas William G. Fahrenholtz 《Journal of the American Ceramic Society》2008,91(1):26-32
A pressureless sintering process was developed for the densification of zirconium diboride ceramics containing 10–30 vol% silicon carbide particles. Initially, boron carbide was evaluated as a sintering aid. However, the formation of a borosilicate glass led to significant coarsening, which inhibited densification. Based on thermodynamic calculations, a combination of carbon and boron carbide was added, which enabled densification (relative density >98%) by solid-state sintering at temperatures as low as 1950°C. Varying the size of the starting silicon carbide particles allowed the final silicon carbide particle morphology to be controlled from equiaxed to whisker-like. The mechanical properties of sintered ceramics were comparable with hot-pressed materials with Vickers hardness of 22 GPa, elastic modulus of 460 GPa, and fracture toughness of ∼4 MPa·m1/2 . Flexure strength was ∼460 MPa, which is at the low end of the range reported for similar materials, due to the relatively large size (∼13 μm long) of the silicon carbide inclusions. 相似文献
2.
Hui Zhang Yongjie Yan Zhengren Huang Xuejian Liu Dongliang Jiang 《Journal of the American Ceramic Society》2009,92(7):1599-1602
Pressureless sintering was used to densify ZrB2 –SiC ultra-high temperature ceramics. The physical, mechanical, thermal, electrical, and high temperature properties were investigated. This comprehensive set of properties was measured for ZrB2 containing 20 vol% SiC in which B4 C and C were used as the sintering aids. The three-point flexural strength was 361±44 MPa and the elastic modulus was 374±25 GPa. The Vickers hardness and fracture toughness were 14.7±0.2 GPa and 4.0±0.5 MPa·m1/2 respectively. Scanning electron microscopy studies of the microstructure of ZrB2 –SiC showed that SiC particles were distributed homogenously in the ZrB2 matrix with little residual porosity. 相似文献
3.
Yongjie Yan Hui Zhang Zhengren Huang Jianxue Liu Dongliang Jiang 《Journal of the American Ceramic Society》2008,91(4):1372-1376
Ultrafine ZrB2 –SiC composite powders have been synthesized in situ using carbothermal reduction reactions via the sol–gel method at 1500°C for 1 h. The powders synthesized had a relatively smaller average crystallite size (<200 nm), a larger specific surface area (∼20 m2 /g), and a lower oxygen content (∼1.0 wt %). Composites of ZrB2 +20 wt% SiC were pressureless sintered to ∼96.6% theoretical density at 2250°C for 2 h under an argon atmosphere using B4 C and Mo as sintering aids. Vickers hardness and flexural strength of the sintered ceramic composites were 13.9±0.3 GPa and 294±14 MPa, respectively. The microstructure of the composites revealed that elongated SiC grain dispersed uniformly in the ZrB2 matrix. Oxidation from 1100° to 1600°C for 30 min showed no decrease in strength below 1400°C but considerable decrease in strength with a rapid weight increment was observed above 1500°C. The formation of a protective borosilicate glassy coating appeared at 1400°C and was gradually destroyed in the form of bubble at higher temperatures. 相似文献
4.
Guo-Jun Zhang Zhen-Yan Deng Naoki Kondo Jian-Feng Yang Tatsuki Ohji 《Journal of the American Ceramic Society》2000,83(9):2330-2332
A ZrB2 –SiC composite was prepared from a mixture of zirconium, silicon, and B4 C via reactive hot pressing. The three-point bending strength was 506 ± 43 MPa, and the fracture toughness was 4.0 MPa·m1/2 . The microstructure of the composite was observed via scanning electron microscopy; the in-situ -formed ZrB2 and SiC were found in agglomerates with a size that was in the particle-size ranges of the zirconium and silicon starting powders, respectively. A model of the microstructure formation mechanism of the composite was proposed, to explain the features of the phase distributions. It is considered that, in the reactive hot-pressing process, the B and C atoms in B4 C will diffuse into the Zr and Si sites and form ZrB2 and SiC in situ , respectively. Because the diffusion of Zr and Si atoms is slow, the microstructure (phase distributions) of the obtained composite shows the features of the zirconium and silicon starting powders. 相似文献
5.
Shuqi Guo Yutaka Kagawa Toshiyuki Nishimura Hidehiko Tanaka 《Journal of the American Ceramic Society》2007,90(7):2255-2258
The thermal and electrical properties of MoSi2 and/or SiC-containing ZrB2 -based composites and the effects of MoSi2 and SiC contents were examined in hot-pressed ZrB2 –MoSi2 –SiC composites. The thermal conductivity and electrical conductivity of the ZrB2 –MoSi2 –SiC composites were measured at room temperature by a nanoflash technique and a current–voltage method, respectively. The results indicate that the thermal and electrical conductivities of ZrB2 –MoSi2 –SiC composites are dependent on the amount of MoSi2 and SiC. The thermal conductivities observed for all of the compositions were more than 75 W·(m·K)−1 . A maximum conductivity of 97.55 W·(m·K)−1 was measured for the 20 vol% MoSi2 -30 vol% SiC-containing ZrB2 composite. On the other hand, the electrical conductivities observed for all of the compositions were in the range from 4.07 × 10–8.11 × 10 Ω−1 ·cm−1 . 相似文献
6.
James W. Zimmermann Gregory E. Hilmas William G. Fahrenholtz Ralph B. Dinwiddie Wallace D. Porter Hsin Wang 《Journal of the American Ceramic Society》2008,91(5):1405-1411
Thermophysical properties were investigated for zirconium diboride (ZrB2 ) and ZrB2 –30 vol% silicon carbide (SiC) ceramics. Thermal conductivities were calculated from measured thermal diffusivities, heat capacities, and densities. The thermal conductivity of ZrB2 increased from 56 W (m K)−1 at room temperature to 67 W (m K)−1 at 1675 K, whereas the thermal conductivity of ZrB2 –SiC decreased from 62 to 56 W (m K)−1 over the same temperature range. Electron and phonon contributions to thermal conductivity were determined using electrical resistivity measurements and were used, along with grain size models, to explain the observed trends. The results are compared with previously reported thermal conductivities for ZrB2 and ZrB2 –SiC. 相似文献
7.
Hyung-Jong Kim Heon-Jin Choi June-Gunn Lee 《Journal of the American Ceramic Society》2002,85(4):1022-1024
TiB2 -AlN composites have been fabricated by the pressureless sintering of a mechanochemically processed Ti, Al, and BN powder mixture. TiB2 -AlN powder was obtained from the mixture of Ti, Al, and BN, which had a composition corresponding to 45.7 wt% TiB2 -54.3 wt% AlN, after mechanochemical processing for longer than 24 h. X-ray diffraction and transmission electron microscopy analysis showed that the powder subjected to mechanochemical processing for 60 h consisted of crystallites less than 300 nm in size with a disordered crystal structure. TiB2 -AlN composites with 95% relative density, a flexural strength of 172 MPa, a fracture toughness of 4.6 MPa·m1/2 , a hardness of 12.0 GPa, and an electrical resistivity of 1488 μΩ·cm were obtained by pressureless sintering at 1700°C for 2 h of the powder subjected to mechanochemical processing for 60 h. 相似文献
8.
Alex Spring Wei-Ming Guo Guo-Jun Zhang Pei-Ling Wang Vladimir D. Krstic 《Journal of the American Ceramic Society》2008,91(8):2763-2765
ZrB2 –LaB6 powder was obtained by reactive synthesis using ZrO2 , La2 O3 , B4 C, and carbon powders. Then ZrB2 –20 vol% SiC–10 vol% LaB6 (ZSL) ceramics were prepared from commercially available SiC and the synthesized ZrB2 –LaB6 powder via hot pressing at 2000°C. The phase composition, microstructure, and mechanical properties were characterized. Results showed that both LaB6 and SiC were uniformly distributed in the ZrB2 matrix. The hardness and bending strength of ZSL were 17.06±0.52 GPa and 505.8±17.9 MPa, respectively. Fracture toughness was 5.7±0.39 MPa·m1/2 , which is significantly higher than that reported for ZrB2 –20 vol% SiC ceramics, due to enhanced crack deflection and crack bridging near SiC particles. 相似文献
9.
Diletta Sciti Stefano Guicciardi Alida Bellosi Giuseppe Pezzotti 《Journal of the American Ceramic Society》2006,89(7):2320-2322
A ZrB2 -based composite was fully densified by pressureless sintering at 1850°C with addition of 20 vol% MoSi2 . The microstructure was very fine, with mean dimensions of ZrB2 grains around 2.5 μm. The four-point flexural strength in air was in excess of 500 MPa up to 1500°C. 相似文献
10.
Wei-Ming Guo Guo-Jun Zhang Pei-Ling Wang 《Journal of the American Ceramic Society》2009,92(11):2780-2783
This work reported the microstructural evolution and grain growth kinetics of ZrB2 –SiC composites containing 10, 20, and 30 vol% SiC during heat treatment at 2000°C. The coarsening of ZrB2 occurred in the three systems, whereas the obvious coarsening for SiC appeared only in the composite with 30 vol% SiC. The kinetics analysis showed the ZrB2 grain growth rate in the ZrB2 –30 vol% SiC was 25 times lower than that for ZrB2 –10 vol% SiC during heat treatment. Furthermore, the grain growth controlling mechanisms of ZrB2 and SiC were discussed. In addition, it was found that the heat treatment had little effect on Vickers hardness and fracture toughness of ZrB2 –SiC. 相似文献
11.
Jandhyala Subrahmanyam Renangi Mohan Rao 《Journal of the American Ceramic Society》1995,78(2):487-490
MoSi2 , SiC, and MoSi2 –SiC composites were prepared by the thermal explosion mode of self-propagating, high-temperature synthesis (SHS), from elemental powders Mo, Si, and carbon. The products were characterized using chemical analysis, X-ray diffraction, and scanning electron microscopy. The morphology of MoSi2 in the product points out that it is in the molten state at the combustion temperature. SiC in the composite shows a very fine particle morphology. These results are supported by the earlier thermochemical calculation carried out on this system. 相似文献
12.
Yanli Xie Thomas H. Sanders Jr. Robert F. Speyer 《Journal of the American Ceramic Society》2008,91(5):1469-1474
Zirconium diboride and a zirconium diboride/tantalum diboride mixture were synthesized by solution-based processing. Zirconium n -propoxide was refluxed with 2,4-pentanedione to form zirconium diketonate. This compound hydrolyzed in a controllable fashion to form a zirconia precursor. Boria and carbon precursors were formed via solution additions of phenol–formaldehyde and boric acid, respectively. Tantalum oxide precursors were formed similarly as zirconia precursors, in which tantalum ethoxide was used. Solutions were concentrated, dried, pyrolyzed (800°–1100°C, 2 h, flowing argon), and exposed to carbothermal reduction heat treatments (1150°–1800°C, 2 h, flowing argon). Spherical particles of 200–600 nm for pure ZrB2 and ZrB2 –TaB2 mixtures were formed. 相似文献
13.
Bikramjit Basu T. Venkateswaran Doh-Yeon Kim 《Journal of the American Ceramic Society》2006,89(8):2405-2412
In a recent work, 1 we have reported the optimization of the spark plasma sintering (SPS) parameters to obtain dense nanostructured 3Y-TZP ceramics. Following this, the present work attempts to answer some specific issues: (a) whether ZrO2 -based composites with ZrB2 reinforcements can be densified under the optimal SPS conditions for TZP matrix densification (b) whether improved hardness can be obtained in the composites, when 30 vol% ZrB2 is incorporated and (c) whether the toughness can be tailored by varying the ZrO2 –matrix stabilization as well as retaining finer ZrO2 grains. In the present contribution, the SPS experiments are carried out at 1200°C for 5 min under vacuum at a heating rate of 600 K/min. The SPS processing route enables retaining of the finer t -ZrO2 grains (100–300 nm) and the ZrO2 –ZrB2 composite developed exhibits optimum hardness up to 14 GPa. Careful analysis of the indentation data provides a range of toughness values in the composites (up to 11 MPa·m1/2 ), based on Y2 O3 stabilization in the ZrO2 matrix. The influence of varying yttria content, t -ZrO2 transformability, and microstructure on the properties obtained is discussed. In addition to active contribution from the transformation-toughening mechanism, crack deflection by hard second phase brings about appreciable increment in the toughness of the nanocomposites. 相似文献
14.
Sigrun N. Karlsdottir John W. Halloran Carl E. Henderson 《Journal of the American Ceramic Society》2007,90(9):2863-2867
During the high-temperature oxidation of ZrB2 –SiC composites, liquid boron oxide (B2 O3 ) is formed at the zirconium diboride–zirconium oxide interface and transported through the overlying layer of silica liquid by convection, forming distinct convection cells arranged like the petals of a flower. The convection cells are localized by a viscous fingering phenomenon, as the fluid B2 O3 rich liquid solution rises through the viscous silica layer. The upwelling B2 O3 rich liquid contains dissolved zirconium dioxide, which deposits in the center of the flower-like structure as the B2 O3 evaporates. The driving force for the B2 O3 liquid flow is the volume increase upon oxidation of ZrB2 . Convective transport of B2 O3 liquids suggests a novel mechanism for the high-temperature oxidation of these materials. 相似文献
15.
Houbu Li Litong Zhang Laifei Cheng Yiguang Wang 《International Journal of Applied Ceramic Technology》2009,6(2):145-150
C/ZrB2 –SiC composites were fabricated by polymer infiltration and pyrolysis combined with slurry impregnation method. Three kinds of coating structures for these composites were applied in order to improve their ablation resistance: pure silicon carbide coatings, ZrB2 –SiC mixture coatings, and ZrC–SiC alternating multilayer coatings. The ablation experiments were carried out on an oxyacetylene torch flame with a temperature of about 3000°C. The ZrC–SiC alternating multilayer showed the best ablation resistance. The linear erosion rate for ZrC–SiC alternating multilayer coatings is half of that for ZrB2 –SiC mixture and pure SiC coatings. A model was put forward to account for such a result. 相似文献
16.
Yongsheng Zhang Litian Hu HaoKun Li Jianmin Chen 《Journal of the American Ceramic Society》2008,91(4):1332-1334
ZrO2 –Y2 O3 –CuO nanocrystalline powders have been synthesized using a chemical coprecipitation method. Nano-powders were compacted uniaxially and densified in a muffle furnace. Densification studies show that the presence of CuO accelerates the densification process of ZrO2 (3Y). A fully dense (>96%) pellet of ZrO2 (3Y)/5 mol% CuO was obtained after sintering at 900°C, with a very small grain size of 44 nm calculated by X-ray line broadening. 相似文献
17.
William G. Fahrenholtz 《Journal of the American Ceramic Society》2007,90(1):143-148
A thermodynamic model was developed to explain the formation of a SiC-depleted layer during ZrB2 –SiC oxidation in air at 1500°C. The proposed model suggests that a structure consisting of (1) a silica-rich layer, (2) a Zr-rich oxidized layer, and (3) a SiC-depleted zirconium diboride layer is thermodynamically stable. The SiC-depleted layer developed due to active oxidation of SiC. The oxygen partial pressure in the SiC-depleted layer was calculated to lie between 4.0 × 10−14 and 1.8 × 10−11 Pa. Even though SiC underwent active oxidation, the overall process was consistent with passive oxidation and the formation of a protective surface layer. 相似文献
18.
Sufang Tang Jingyi Deng Shijun Wang Wenchuan Liu 《Journal of the American Ceramic Society》2007,90(10):3320-3322
A novel carbon fiber-reinforced ZrB2 –SiC matrix composite was fabricated by heaterless chemical vapor infiltration through infiltration of SiC matrix into a carbon fiber-ZrB2 powder preform. The C/ZrB2 –SiC composite presented a flexural strength of 148 MPa, a fracture toughness of 5.6 MPa·m1/2 , and a good oxidation and ablation resistance. 相似文献
19.
The effect of SiC concentration on the liquid and solid oxide phases formed during oxidation of ZrB2 –SiC composites is investigated. Oxide-scale features called convection cells are formed from liquid and solid oxide reaction products upon oxidation of the ZrB2 –SiC composites. These convection cells form in the outermost borosilicate oxide film of the oxide scale formed on the ZrB2 –SiC during oxidation at high temperatures (≥1500°C). In this study, three ZrB2 –SiC composites with different amounts of SiC were tested at 1550°C for various durations of time to study the effect of the SiC concentration particularly on the formation of the convection cell features. A calculated ternary phase diagram of a ZrO2 –SiO2 –B2 O3 (BSZ) system was used for interpretation of the results. The convection cells formed during oxidation were fewer and less uniformly distributed for composites with a higher SiC concentration. This is because the convection cells are formed from ZrO2 precipitates from a BSZ oxide liquid that forms upon oxidation of the composite at 1550°C. Higher SiC-containing composites will have less dissolved ZrO2 because they have less B2 O3 , which results in a smaller amount of precipitated ZrO2 and consequently fewer convection cells. 相似文献
20.
Preliminary results about laser sintering of zirconium diboride (ZrB2 ), a good ultra high-temperature ceramics candidate, are presented. In order to evaluate a suitable sintering method, single pulsed laser and a concentric dual laser system were carried out. Two different ZrB2 powders having ∼15 and ∼2 μm particle size were assessed for sintering. Scanning electron microscopy images showed that the concentric dual laser sintered layer using ∼2 μm particle size of ZrB2 had relatively smooth surface morphology. X-ray diffraction results confirmed that the sintered layer mainly retained the crystalline phases as the starting powder. In addition, the rapid cooling rate of laser sintering enabled the formation of needle-like nanostructures at the sintered surface. 相似文献