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1.
Fabrication and Characterization of Three-Dimensional Carbon Fiber Reinforced Silicon Carbide and Silicon Nitride Composites 总被引:4,自引:0,他引:4
Kikuo Nakano Akira Kamiya Yoichi Nishino Toru Imura Tsu-Wei Chou 《Journal of the American Ceramic Society》1995,78(10):2811-2814
Three-dimensional (3D) carbon fiber reinforced SiC and Si3 N4 composites have been fabricated using repeated infiltration of an organosilicon slurry under vacuum and pressure. Open porosity of the infiltrated body was reduced from 40% after the first infiltration to approximately 8% after the seventh cycle. Further reduction of open porosity to less than 3% was accomplished by hot-press densification. The maximum values of flexural strength and fracture toughness were, respectively, 260 MPa and 7.3 MPa·m1/2 for C/Si3 N4 composites, and 185 MPa and 6 MPa·m1/2 for C/SiC composite. 相似文献
2.
Measurements of threshold stress intensities for crack growth, K h , of three polycrystalline SiC materials were attempted using interrupted static fatigue tests at 1200°–1400°C. Weibull statistics were used to calculate conservative Kth values from test results. The K th of a chemically vapor deposited β-SiC could not be determined, as a result of its wide variations in strength. The Kth ≥ 3.3,2.2, and 1.7 MPa·m1/2 for an Al-doped sintered α-SiC; and Kth ≥ 3.1, 2.7, and 2.2 MPa·m1/2 for a hot isostatically pressed α-SiC, both at 1200°, 1300°, and 1400°C, respectively. A damage process concurrent with subcritical crack growth was apparent for the sintered SiC at 1400°C. The larger Kth 's for the HIPed SiC (compared to the sintered SiC) may be a result of enhanced viscous stress relaxation caused by the higher silica content and smaller grain size of this material. Values measured at 1300° and 1400°C were in good agreement with the Kth 's predicted by a diffusive crack growth model, while the measured Kth 's were greater than the predicted ones at 1200°C. 相似文献
3.
Boron carbide/titanium diboride composites with 20 and 40 vol% particulate TiB2 and various amounts of free carbon were investigated with respect to microcrack toughening. In agreement with previous work, the mere addition of TiB2 was found to raise the toughness from 2.2 MPa·m1/2 up to 3.0 and 3.5 MPa·m1/2 , respectively. A further and very significant increase of composite toughness up to 6.0 MPa·m1/2 was discovered upon the incorporation of free carbon. SEM and TEM observations reveal that this toughening is associated with microcracking at B4 C-TiB2 phase boundaries. Microcracking is triggered by thin carbon interlayers, which are located at hetero interfaces and supply a weak fracture path. 相似文献
4.
A strain-gauge procedure that enables determination of the crack-tip toughness ( K I0 ) from bending-strength tests is described. The procedure is applied to coarse-grained alumina and yields an average K I0 value of 2.51 MPa·m1/2 , with a standard deviation of 0.16 MPa·m1/2 . 相似文献
5.
Naoki Kondo Yoshikazu Suzuki Tatsuki Ohji 《Journal of the American Ceramic Society》2000,83(7):1816-1818
Silicon nitride–silicon carbide (Si3 N4 –SiC) nanocomposites were fabricated by a process involving reaction bonding followed by superplastic sinter-forging. The nanocomposites exhibited an anisotropic microstructure, in which rod-shaped, micrometer-sized Si3 N4 grains tended to align with their long axes along the material-flow direction. SiC particles, typically measuring several hundred nanometers, were located at the Si3 N4 grain boundaries, and nanosized particles were dispersed inside the Si3 N4 grains. A high bending strength of 1246 ± 119 MPa, as well as a high fracture toughness of 8.2 ± 0.9 MPa·m1/2 , was achieved when a stress was applied along the grain-alignment direction. 相似文献
6.
Mode I Fracture Toughness of a Small-Grained Silicon Nitride: Orientation, Temperature, and Crack Length Effects 总被引:1,自引:0,他引:1
The Mode I fracture toughness ( K I C ) of a small-grained Si3 N4 was determined as a function of hot-pressing orientation, temperature, testing atmosphere, and crack length using the single-edge precracked beam method. The diameter of the Si3 N4 grains was <0.4 µm, with aspect ratios of 2–8. K I C at 25°C was 6.6 ± 0.2 and 5.9 ± 0.1 MPa·m1/2 for the T–S and T–L orientations, respectively. This difference was attributed to the amount of elongated grains in the plane of crack growth. For both orientations, a continual decrease in K IC was observed through 1200°C, to ∼4.1 MPa·m1/2 , before increasing rapidly to 7.5–8 MPa·m1/2 at 1300°C. The decrease in K IC through 1200°C was a result of grain-boundary glassy phase softening. At 1300°C, reorientation of elongated grains in the direction of the applied load was suggested to explain the large increase in K IC . Crack healing was observed in specimens annealed in air. No R -curve behavior was observed for crack lengths as short as 300 µm at either 25° or 1000°C. 相似文献
7.
Yong Ming Luo Shu Qin Li Jian Chen Rui Gang Wang Jian Qiang Li Wei Pan 《Journal of the American Ceramic Society》2002,85(12):3099-3101
In the present study, the room-temperature properties of Al2 O3 -Ti3 SiC2 composites with different Ti3 SiC2 contents are determined. The composites are prepared by attrition milling Al2 O3 and Ti3 SiC2 mixture powders followed by spark plasma sintering (SPS) under vacuum. From a closer examination of the dependencies of the electrical conductivity on compositions in this system, we determined the percolation threshold at which an interconnected network of electrically conductive phase arises. Since the hardness of Ti3 SiC2 is lower than that of Al2 O3 , the Vickers hardness decreased with the increasing of Ti3 SiC2 content while the fracture toughness and the strength increased. The maximum strength (673 MPa) and the maximum toughness (9.3 MPa·m1/2 ) were reached in the pure Ti3 SiC2 material. 相似文献
8.
A procedure was used that made it possible to determine the R -curve for piezoelectric ceramics from tensile strength tests conducted with Knoop-damaged specimens. The resulting crack-tip toughness K I0 was 0.6 MPa·m1/2 , and the R -curve starting from this value increased to 1.4 MPa·m1/2 within a 0.7 mm crack extension. 相似文献
9.
Young-Wook Kim Mamoru Mitomo Toshiyuki Nishimura 《Journal of the American Ceramic Society》2001,84(9):2060-2064
Fully dense SiC ceramics with high strength at high temperature were obtained by hot-pressing and subsequent annealing under pressure, with AlN and Er2 O3 as sintering additives. The ceramics had a self-reinforced microstructure consisting of elongated SiC grains and a grain-boundary glassy phase. The strength of these ceramics was ∼550 MPa at 1600°C, and the fracture toughness was ∼6 MPa·m1/2 at room temperature. The beneficial effect of the new additive composition on high-temperature strength might be attributable to the introduction of aluminum from the liquid composition into the SiC lattice, resulting in a refractive grain-boundary glassy phase. 相似文献
10.
Tyrone Mitchell Jr. † ‡ Lutgard C. De Jonghe † ‡ Warren J. MoberlyChan Robert O. Ritchie† ‡ 《Journal of the American Ceramic Society》1995,78(1):97-103
α-silicon carbide platelet/β-silicon carbide composites have been produced in which the individual platelets were coated with an aluminum oxide layer. Hot-pressed composites showed a fracture toughness as high as 7.2 MPa·m1/2 . The experiments indicated that the significant increase in fracture toughness is mainly the result of crack deflection and accompanying platelet pullout. The coating on the platelets also served to prevent the platelets from acting as nucleation sites for the α- to β-phase transformation, so that the advantageous microstructure remains preserved during high-temperature processing. 相似文献
11.
Layered Silicon Nitride-Based Composites with Discontinuous Boron Nitride Interlayers 总被引:1,自引:0,他引:1
Zoltán Lené Kiyoshi Hirao Manuel E. Brito Motohiro Toriyama Shuzo Kanzaki 《Journal of the American Ceramic Society》2000,83(10):2503-2508
The influence of a strong/weak interface ratio on the mechanical properties of Si3 N4 /BN-based layered composites was studied. The ratio was controlled by the number of BN spots between the adjacent Si3 N4 layers. By increasing the BN interface area from 0% to 72%, fracture toughness increased from 7.7 to 10.9 MPa·m1/2 , and bending strength decreased from 1275 to 982 MPa. Fracture toughness was improved from 8.6 to 10.1 MPa·m1/2 by additional heat treatment of samples containing 2 vol%β-Si3 N4 seed particles. The bending strength of samples with 35% weak BN interfaces, measured perpendicular and parallel to layer alignment, was 1260 and 1240 MPa, respectively. This confirmed the two-directional isotropy of layered samples. 相似文献
12.
Marc Flinders Darin Ray Angela Anderson Raymond A. Cutler 《Journal of the American Ceramic Society》2005,88(8):2217-2226
Silicon carbide, with single-edge precracked beam (SEPB) toughness greater than 7 MPa·m1/2 , was made by hot-pressing using Al–B–C (ABC) or Al–Y2 O3 (YAG) as additives. The hardness of SiC processed with a liquid phase was always less than SiC densified without a liquid phase despite having a similar or finer grain size. With increasing Al content, the ABC system changed from trans- to intergranular fracture with a drop in hardness and a two- to threefold increase in SEPB toughness. Strength and Weibull modulus for materials processed with a liquid phase were higher than those of solid-state densified SiC. Ballistic testing, however, did not show any improvement over SiC densified with B and C additives. Depth of penetration was controlled by hardness of the SiC-based materials, while V 50 values for 14.5 mm WC–Co cored projectiles were in the range of 720–750 m/s for all materials tested. 相似文献
13.
Kjersti Kleveland Nina Orlovskaya Tor Grande Anne Marie Mardal Moe Mari-Ann Einarsrud Kristin Breder George Gogotsi 《Journal of the American Ceramic Society》2001,84(9):2029-2033
LaCoO3 and La0.8 Ca0.2 CoO3 ceramics show a nonelastic stress–strain behavior during four-point bending experiments where hysteresis loops are observed during loading–unloading cycles. Permanent strain is stored in the material after unloading, and a mechanism related to ferroelastic domain switching in the rhombohedral perovskite is proposed. Domain switching in the materials has been confirmed using X-ray diffractometry. Fracture toughnesses of La0.8 Ca0.2 CoO3 measured using single-edge notched beam and single-edge V-notched beam methods coincide and are equal to 2.2 MPa·m1/2 at room temperature and decrease to ∼1 MPa·m1/2 at temperatures >300°C. A decrease in fracture toughness is consistent with ferroelastic behavior, because the rhombohedral distortion decreases with increasing temperature. 相似文献
14.
Guo-Dong Zhan Joshua D. Kuntz Ren-Guan Duan Amiya K. Mukherjee 《Journal of the American Ceramic Society》2004,87(12):2297-2300
The combined effect of rapid sintering by spark-plasma-sintering (SPS) technique and mechanical milling of γ-Al2 O3 nanopowder via high-energy ball milling (HEBM) on the microstructural development and mechanical properties of nanocrystalline alumina matrix composites toughened by 20 vol% silicon carbide whiskers was investigated. SiCw /γ-Al2 O3 nanopowders processed by HEBM can be successfully consolidated to full density by SPS at a temperature as low as 1125°C and still retain a near-nanocrystalline matrix grain size (∼118 nm). However, to densify the same nanopowder mixture to full density without the benefit of HEBM procedure, the required temperature for sintering was higher than 1200°C, where one encountered excessive grain growth. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results indicated that HEBM did not lead to the transformation of γ-Al2 O3 to α-Al2 O3 of the starting powder but rather induced possible residual stress that enhances the densification at lower temperatures. The SiCw /HEBMγ-Al2 O3 nanocomposite with grain size of 118 nm has attractive mechanical properties, i.e., Vickers hardness of 26.1 GPa and fracture toughness of 6.2 MPa·m1/2 . 相似文献
15.
Matthew C. Osborne Jack C. Hay Lance L. Snead Don Steiner 《Journal of the American Ceramic Society》1999,82(9):2490-2496
Indentation and density measurements have revealed important changes in the mechanical and physical properties of silicon carbide (SiC) due to neutron irradiation. Specifically, the changes in the elastic modulus, hardness, fracture toughness, and density with irradiation have provided an understanding of the expected performance of SiC and SiC composites in nuclear applications. After the accumulated damage has saturated, these mechanical properties were affected primarily by the irradiation temperature. Chemical-vapor-deposited (CVD) SiC was irradiated above the saturation fluence and yielded volumetric swelling of 2.6% and 1.3% for irradiation temperatures of 100°-150°C and 500°-550°C, respectively. At the same respective temperatures, the elastic modulus decreased from an unirradiated value of 503 GPa to ∼420 and 450 GPa. Conversely, the hardness increased from 36 GPa for the unirradiated CVD SiC to 38 and 40 GPa for the samples irradiated at 100°-150°C and 500°-550°C, respectively. Interestingly, these two independent properties approached almost-constant levels after exposure to a fluence of 0.5 × 1025 n/m2 , E > 0.1 MeV. Indentation fracture toughness measurements, which were within the range of values in the literature for conventional fracture toughness procedures for SiC, increased from ∼2.8 MPa·m1/2 for the unirradiated samples to 3.7 and 4.2 MPa·m1/2 for the samples that were irradiated at 100°-150°C and 500°-550°C, respectively. 相似文献
16.
The use of monoclinic ZrO2 as an additive improves the mechanical properties of TiB2 -based composites without the use of stabilizers. In particular, TiB2 -30% ZrO2 compacts exhibited a transverse rupture strength of 800 MN/m2 , few pores, and a KI c of 5 MPa·m1/2 . The high strength and toughness are thought to result mainly from the presence of partially stabilized tetragonal ZrO2 and from solid solution of (TiZr)B2 formed in sintering. 相似文献
17.
Antonia Pajares Fernando Guiberteau Arturo Dominguez-Rodriguez Arthur H. Heuer 《Journal of the American Ceramic Society》1988,71(7):332-C
Vickers and Knoop indentation tests have been used to study the fracture and deformation characteristics of 9.4-mol%-Y2 O3 -stabilized ZrO2 single crystals. Kc is anisotropic, with values of 1.9 and 1.1 MPa·m1/2 for radial cracks propagating along (100) and (110), respectively. The toughness for these two orientations was also determined using the single-edge notched-beam geometry, and yielded values of 1.9 and 1.5 MPa·m1/2 . 相似文献
18.
Jia Li Yan-Sheng Yin Xun-Yan Tan Jin-De Zhang 《Journal of the American Ceramic Society》2005,88(1):235-238
Near fully dense ZrO2 (3Y)/Fe3 Al composites with significantly improved fracture toughness were synthesized by hot-press sintering at 1350°C. High fracture toughness and bending-strength values, 36 MPa·m1/2 and 1321 MPa, respectively, were achieved in 40 vol% Fe3 Al composite ceramics, whereas those same values for ZrO2 (3Y) alone were 10 MPa·m1/2 and 988 MPa, respectively. Microscopic observation of the crack path revealed that Fe3 Al particle uniformly dispersed in the matrix have obvious crack-bridging effect. Improved thermal-shock resistance was also obtained, which was attributed to higher toughness, thermal conductivity, and lower Young's modulus by adding of Fe3 Al particles. 相似文献
19.
A method for estimating the threshold stress intensity for crack growth is presented. The technique requires prior knowledge of the flaw population of a material and uses applied static loads followed by fast fracture to assess the effect of initial applied stress intensity on flaw behavior. The technique was applied to a hot-pressed Sic at 1200° and 1400°C in a nonoxidizing atmosphere. At 1400°C with a static load time of 4 h, the threshold stress intensity was determined to be ∼ 1.75 MPa·m1/2 with a slight tendency toward higher fracture stress with increasing initial stress intensity below the threshold. At 1200°C for a static load time of 4 h, apparent strengthening was observed below a threshold stress intensity of ∼2.25 MPa·m1/2 . This strengthening effect appears to result from stress relaxation in the crack-tip region, probably by plastic deformation which involves the oxide grain-boundary phase. 相似文献
20.
Kiyoshi Itatani Ryuji Tsukamoto Anne C. A. Delsing Hubertus T. Hintzen Isao Okada 《Journal of the American Ceramic Society》2002,85(7):1894-1896
Aluminum nitride (AlN)–silicon carbide (SiC) nanocomposite powders were prepared by the nitridation of aluminum-silicon carbide (Al4 SiC4 ) with the specific surface area of 15.5 m2 ·g−1 . The powders nitrided at and above 1400°C for 3 h contained the 2H-phases which consisted of AlN-rich and SiC-rich phases. The formation of homogeneous solid solution proceeded with increasing nitridation temperature from 1400° up to 1500°C. The specific surface area of the AlN–SiC powder nitrided at 1500°C for 3 h was 19.5 m2 ·g−1 , whereas the primary particle size (assuming spherical particles) was estimated to be ∼100 nm. 相似文献