共查询到20条相似文献,搜索用时 593 毫秒
1.
Fabrication and Mechanical Properties of Silicon Carbide-Silicon Nitride Composites with Oxynitride Glass 总被引:1,自引:0,他引:1
Young-Wook Kim Young-Il Lee Mamoru Mitomo Heon-Jin Choi June-Gunn Lee 《Journal of the American Ceramic Society》1999,82(4):1058-1060
A microstructure that consisted of uniformly distributed, elongated β-Si3 N4 grains, equiaxed β-SiC grains, and an amorphous grain-boundary phase was developed by using β-SiC and alpha-Si3 N4 powders. By hot pressing, elongated β-Si3 N4 grains were grown via alpha right arrow β phase transformation and equiaxed β-SiC grains were formed because of inhibited grain growth. The strength and fracture toughness of SiC have been improved by adding Si3 N4 particles, because of the reduced defect size and the enhanced bridging and crack deflection by the elongated β-Si3 N4 grains. Typical flexural-strength and fracture-toughness values of SiC-35-wt%-Si3 N4 composites were 1020 MPa and 5.1 MPam1/2 , respectively. 相似文献
2.
The microstructure, crystal structure, and chemical composition of reaction-sintered Si3 N4 containing iron were studied using conventional and scanning transmission electron microscopy. It was found that the grains of β -Si3 N4 were large and blocklike with well-developed facets, a series of voids along some grain boundaries, a subgrain of iron silicide near the periphery, and penetration of iron silicide into the three-grain junctions and grain boundaries. At some distance from each β -Si3 N4 grain was a region of small α-Si3 N4 grains, with no evidence of iron silicide. Between this region and the β -Si3 N4 grain was a zone containing both α- and β -Si3 N4 and iron silicide. These observations suggest that the large β -Si3 N4 grains grow in liquid iron silicide, that the smaller α-Si3 N4 grains grow from the vapor, and that the latter are converted to the β form by solution in, and reprecipitation from, liquid iron silicide. 相似文献
3.
Gas-pressure sintering of α-Si3 N4 was carried out at 1850 ° to 2000°C in 980-kPa N2 . The diameters and aspect ratios of hexagonal grains in the sintered materials were measured on polished and etched surfaces. The materials have a bimodal distribution of grain diameters. The average aspect ratio in the materials from α-Si3 N4 powder was similar to that in the materials from β-Si3 N4 powder. The aspect ratio of large and elongated grains was larger than that of the average for all grains. The development of elongated grains was related to the formation of large nuclei during the α-to-β phase transformation. The fracture toughness of gaspressure-sintered materials was not related to the α content in the starting powder or the aspect ratio of the grains, but to the diameter of the large grains. Crack bridging was the main toughening mechanism in gas-pressure-sintered Si3 N4 ceramics. 相似文献
4.
The abnormal grain growth of β-Si3 N4 was observed in a 70% Si3 N4 –30% barium aluminum silicate (70%-Si3 N4 –30%-BAS) self-reinforced composite that was pressureless-sintered at 1930°C; Si3 N4 starting powders with a wide particle-size distribution were used. The addition of coarse Si3 N4 powder encouraged the abnormal growth of β-Si3 N4 grains, which allowed microstructural modification through control of the content and size distribution of β-Si3 N4 nuclei. The mechanical response of different microstructures was characterized in terms of flexural strength, as well as indentation fracture resistance, at room temperature. The presence of even a small amount of abnormally grown β-Si3 N4 grains improved the fracture toughness and minimized the variability in flexural strength. 相似文献
5.
Silicon nitride (Si3 N4 ) and SiAlONs can be self-toughened through the growth of elongated β-Si3 N4 /β-SiAlON grains in sintering. α-SiAlONs usually retain an equiaxed grain morphology and have a higher hardness but lower toughness than β-SiAlONs. The present work has demonstrated that elongated alpha-SiAlON grains can also be developed through pressureless sintering. alpha-SiAlONs with high-aspect-ratio grains in the calcium SiAlON system have exhibited significant grain debonding and pull-out effects during fracture, which offers promise for in-situ -toughened α-SiAlON ceramics. 相似文献
6.
Rong-Jun Xie Mamoru Mitomo Wonjoong Kim Young-Wook Kim 《Journal of the American Ceramic Society》2000,83(12):3147-3152
Silicon nitride–silicon oxynitride (Si3 N4 –Si2 N2 O) in situ composites have been fabricated via either the annealing or the superplastic deformation of sintered Si3 N4 that has been doped with a silica-containing additive. In this study, quantitative texture measurements, including pole figures and X-ray diffraction patterns, are used in conjunction with scanning electron microscopy and transmission electron microscopy techniques to examine the degree of preferred orientation and texture-development mechanisms in these materials. The results indicate that (i) only superplastic deformation can produce strong textures in the β-Si3 N4 matrix, as well as Si2 N2 O grains that are formed in situ ; (ii) texture development in the β-Si3 N4 matrix mainly results from grain rotation via grain-boundary sliding; and (iii) for Si2 N2 O, a very strong strain-dependent texture occurs in two stages, namely, preferred nucleation and anisotropic grain growth. 相似文献
7.
L. K. V. LOU T. E. MITCHELL A. H. HEUER 《Journal of the American Ceramic Society》1978,61(9-10):392-396
Impurity phases in commercial hot-pressed Si3 N4 were investigated using transmission electron microscopy. In addition to the dominant, β-Si3 N4 phase, small amounts of Si2 N2 O, SiC, and WC were found. Significantly, a continuous grain-boundary phase was observed in the ∼ 25 high-angle boundaries examined. This film is ∼ 10 Å thick between, β-Si3 N4 grains and ∼ 30 Å thick between Si2 N2 O and β-Si3 N4 grains. 相似文献
8.
Dong-Duk Lee Suk-Joong L. Kang Gunter Petzow Duk N. Yoon 《Journal of the American Ceramic Society》1990,73(3):767-769
By using α-Si3 N4 and β-Si3 N4 starting powders with similar particle size and distribution, the effect of α-β (β') phase transition on densification and microstructure is investigated during the liquid-phase sintering of 82Si3 N4 ·9Al2 O3 ·9Y2 O3 (wt%) and 80Si3 N4 ·13Al2 O3 ·5AIN·5AIN·2Y2 O3 . When α-Si3 N4 powder is used, the grains become elongated, apparently hindering the densification process. Hence, the phase transition does not enhance the densification. 相似文献
9.
Effect of Sintering Additives on Microstructure and Mechanical Properties of Porous Silicon Nitride Ceramics 总被引:2,自引:0,他引:2
Jun Yang Jian-Feng Yang Shao-Yun Shan Ji-Qiang Gao Tatsuki Ohji 《Journal of the American Ceramic Society》2006,89(12):3843-3845
Porous silicon nitride (Si3 N4 ) ceramics with about 50% porosity were fabricated by pressureless sintering of α-Si3 N4 powder with 5 wt% sintering additive. Four types of sintering aids were chosen to study their effect on the microstructure and mechanical properties of porous Si3 N4 ceramics. XRD analysis proved the complete formation of a single β-Si3 N4 phase. Microstructural evolution and mechanical properties were dependent mostly on the type of sintering additive. SEM analysis revealed the resultant porous Si3 N4 ceramics as having high aspect ratio, a rod-like microstructure, and a uniform pore structure. The sintered sample with Lu2 O3 sintering additive, having a porosity of about 50%, showed a high flexural strength of 188 MPa, a high fracture toughness of 3.1 MPa·m1/2 , due to fine β-Si3 N4 grains, and some large elongated grains. 相似文献
10.
Naoto Hirosaki Yoshio Akimune Mamoru Mitomo 《Journal of the American Ceramic Society》1993,76(7):1892-1894
β-Si3 N4 powder containing 1 mol% of equimolar Y2 O3 –Nd2 O3 was gas-pressure sintered at 2000°C for 2 h (SN2), 4 h (SN4), and 8 h (SN8) in 30-MPa nitrogen gas. These materials had a microstructure of " in-situ composites" as a result of exaggerated grain growth of some β Si3 N4 grains during firing. Growth of elongated grains was controlled by the sintering time, so that the desired microstructures were obtained. SN2 had a Weibull modulus as high as 53 because of the uniform size and spatial distribution of its large grains. SN4 had a fracture toughness of 10.3 MPa-m1/2 because of toughening provided by the bridging of elongated grains, whereas SN8 showed a lower fracture toughness, possibly caused by extensive microcracking resulting from excessively large grains. Gas-pressure sintering of β-Si3 N4 powder was shown to be effective in fostering selective grain growth for obtaining the desired composite microstructure. 相似文献
11.
Further Improvement in Mechanical Properties of Highly Anisotropic Silicon Nitride Ceramics 总被引:1,自引:0,他引:1
Hisayuki Imamura Kiyoshi Hirao Manuel E. Brito Motohiro Toriyama Shuzo Kanzaki 《Journal of the American Ceramic Society》2000,83(3):495-500
Si3 N4 ceramics were fabricated by tape casting of a raw-powder slurry seeded with three types of rodlike β-Si3 N4 particles. The effects of seed size on the microstructure and mechanical properties of the sintered specimens were investigated. All the seeded and tape-cast silicon nitrides presented an anisotropic microstructure, where the elongated grains grown from seeds were preferentially oriented parallel to the casting direction. The orientation degree of these grains, f 0 , was affected by seed size, and small-seed addition led to the highest f 0 value. This material exhibited high bending strength (∼1.4 GPa) and high fracture toughness (∼12 MPa. m1/2 ) in the direction normal to the grain alignment, which were attributed to the highly anisotropic and fine microstructure. 相似文献
12.
Takeshi Satoh Shuji Sakaguchi Kiyoshi Hirao Motohiro Toriyama Shuzo Kanzaki 《Journal of the American Ceramic Society》2001,84(2):462-64
To investigate the influence of crystal structure and solid solutions of certain elements in Si3 N4 on aqueous tribological properties, seven specimens were fabricated. Solid solutions of aluminum and oxygen made the friction coefficient and wear increase in both α-type and β-type crystal structures. In particular, α-SiAlON, in which yttrium is also incorporated into the α-Si3 N4 lattice, showed a higher friction coefficient and wear than other specimens containing the same concentration of Al or O. 相似文献
13.
Rong-Jun Xie Mamoru Mitomo Guo-Dong Zhan Hideyuki Emoto 《Journal of the American Ceramic Society》2000,83(10):2529-2535
Starting with a mixture of ultrafine β-Si3 N4 and a SiO2 -containing additive, a superplastic Si3 N4 -based composite was developed, using the concept of a transient liquid phase. Significant deformation-induced phase and microstructure evolutions occurred in the nonequilibrium, fine-grained Si3 N4 material, which led to the in situ development of a Si3 N4 –22-vol%-Si2 N2 O composite and strong texture formation. The unusual ductility of the composites with elongated Si2 N2 O grains was attributed to the fine-grained microstructure, the presence of a transient liquid phase, and the alignment of the elongated Si2 N2 O grains. The mechanical properties of the resultant composite were enhanced rather than impaired by superplastic deformation and subsequent heat treatment; the resultant composite exhibited both high strength (957 MPa) and high fracture toughness (4.8 MPa·m1/2 ). 相似文献
14.
Satoshi Kitaoka Toshihide Tsuji Toshio Katoh Yoshimi Yamaguchi Kji Sato 《Journal of the American Ceramic Society》1994,77(2):580-588
The effects of sliding speed and dissolved oxygen on the tribological behavior of Si3 N4 sliding on itself in water were investigated at room temperature and at 120°C saturated vapor pressure. The friction coefficients and specific wear rates at 120°C were much larger than those at room temperature and had a minimum at about 0.4 m/s, whereats -the specific wear rate of the disk increased with increasing the sliding speed. The wear rate at lower sliding speeds in water at 120°C is considered to be primarily controlled by the increase of the contact stress on the asperities which are formed by the dissolution of grain boundaries of the Si3 N4 ceramic and the subsequent dissolution of the silica layer of the reaction product However, the wear rate at higher sliding speeds is governed by the direct oxidation and microfracture of the Si3 N4 substrate. The tribochemical reaction to produce NH3 mainly occurred at all sliding conditions in water at room temperature and 120°C, and the reaction to produce H2 gas appeared slightly only at the sliding speeds above 0.4 m/s at 120°C. The tribological behavior was independent of dissolved oxygen concentration for all sliding conditions in water at room temperature and 120°C. 相似文献
15.
Naoto Hirosaki Yoshio Akimune Mamoru Mitomo 《Journal of the American Ceramic Society》1994,77(4):1093-1097
Fine β-Si3 N4 powders with or without the addition of 5 wt% of large β-Si3 N4 particles (seeds) were gas-pressure sintered at 1900°C for 4 h using Y2 O3 and Al2 O3 as sintering aids. The microstructures were examined on polished and plasmaetched surfaces. These materials had a microstructure of in situ composites with similar small matrix grains and different elongated grains. The elongated grains in the materials with seeds had a larger diameter and a smaller aspect ratio than those in the materials without seeds. A core/rim structure was observed in the elongated grains; the core was pure β-Si3 N4 and the rim was β-SiAION. These results show that the large β-Si3 N4 particles acted as seeds for abnormal grain growth and the rim was formed by precipitation from the liquid containing aluminum. 相似文献
16.
Jianren Zeng Yoshinari Miyamoto Osamu Yamada 《Journal of the American Ceramic Society》1991,74(9):2197-2200
Fine Si3 N4 -SiC composite powders were synthesized in various SiC compositions to 46 vol% by nitriding combustion of silicon and carbon. The powders were composed of α-Si3 N4 , β-Si3 N4 , and β-SiC. The reaction analysis suggested that the SiC formation is assisted by the high reaction heat of Si nitridation. The sintered bodies consisted of uniformly dispersed grains of β-Si3 N4 , β-SiC, and a few Si2 N2 O. 相似文献
17.
Hideki Hyuga Mark I. Jones Kiyoshi Hirao Yukihiko Yamauchi 《Journal of the American Ceramic Society》2005,88(5):1239-1243
The friction and wear properties of silicon nitride/carbon fiber composites have been assessed and compared with monolithic Si3 N4 . Three different types of composites have been produced; one in which both the Si3 N4 grains and the carbon fibers were aligned, one in which only the fibers had alignment, and a third where both the grains and fibers had random orientation. The friction coefficients of all of the composites, following running in, were around 0.2–0.3, typically less than one-third of that of the monolithic material. However there was no significant difference in friction coefficient between the three different types of composite. The specific wear rates of all the materials decreased with sliding distance and those of the composites were lower than the monolithic material. Among the composites, the wear rate of the one with aligned fibers in a randomly oriented Si3 N4 matrix showed no dependence on sliding direction relative to the fiber alignment, and the specific wear rates of these samples were similar to that of the randomly oriented fiber composite, indicating little effect of fiber alignment alone on the wear properties under the present testing conditions. However, the specific wear rate of the composite with both fiber and grain alignment showed directional dependence. Grain cracking was observed perpendicular to the sliding direction, and the Spara specimen, in which the sliding direction was parallel to the Si3 N4 grain alignment, showed higher wear rates than the Sperp and N samples of this composite. Such cracks are perpendicular to the major axis of the grains in the Spara sample and are thought to lead to easier removal of grains following their cracking under the tensile stresses induced particularly during the running in period. 相似文献
18.
Gayle S. Painter Paul F. Becher Ellen Y. Sun 《Journal of the American Ceramic Society》2002,85(1):65-67
In Si3 N4 ceramics sintered with Al2 O3 , the interfacial strength between the intergranular glass and the reinforcing grains has been observed to increase with increases in the aluminum and oxygen content of the epitaxial β-Si6- z Al z O z N8– z layer that forms on the Si3 N4 grains. This has been attributed to the formation of a network of strong bonds (cross bonds) that span the glass-crystalline interface. This proposed mechanism is considered further in light of first-principles atomic cluster calculations of the relative stabilities of bridge and threefold-bonded atomic fragments chosen to represent compositional changes at the glass/Si3 N4 grain interface. Calculated binding energies indicate Al-N binding is favorable at the Si3 N4 grain surface, where aluminum occupancy can promote the growth of SiAlON, further enhancing the cross-bonding mechanism of interfacial strengthening. 相似文献
19.
Youren Xu Chao M. Huang Waltraud M. Kriven Avigdor Zangvil 《Journal of the American Ceramic Society》1994,77(8):2213-2216
The microstructure of a pressureless sintered (1605°C, 90 min) O'+β' SiAlON ceramic with CeO2 doping has been investigated. It is duplex in nature, consisting of very large, slablike elongated O' grains (20–30 μm long), and a continuous matrix of small rodlike β' grains (< 1.0 μm in length). Many α-Si3 N4 inclusions (0.1–0.5 μm in size) were found in the large O' grains. CeO2 -doping and its high doping level as well as the high Al2 O3 concentration were thought to be the main reasons for accelerating the reaction between the α-Si3 N4 and the Si-Al-O-N liquid to precipitate O'–SiAlON. This caused the supergrowth of O' grains. The rapid growth of O' crystals isolated the remnant α–Si3 N4 from the reacting liquid, resulting in a delay in the α→β-Si3 N4 transformation. The large O' grains and the α-Si3 N4 inclusions have a pronounced effect on the strength degradation of O'+β' ceramics. 相似文献
20.
Yu-Ping Zeng Jian-Feng Yang Naoki Kondo Tatsuki Ohji Hideki Kita Shuzo Kanzaki 《Journal of the American Ceramic Society》2005,88(6):1622-1624
The fracture energies of the tape-cast silicon nitride with and without 3 wt% rod-like β-Si3 N4 seed addition were investigated by a chevron-notched-beam technique. The material was doped with Lu2 O3 –SiO2 as sintering additives for giving rigid grain boundaries and good heat resistance. The seeded and tape-cast silicon nitride has anisotropic microstructure, where the fibrous grains grown from seeds were preferentially aligned parallel to the casting direction. When a stress was applied parallel to the fibrous grain alignment direction, the strength measured at 1500°C was 738 MPa, which was almost the same as room temperature strength 739 MPa. The fracture energy of the tape-cast Si3 N4 without seed addition was 109 and 454 J/m2 at room temperature and 1500°C, respectively. On the contrary, the fracture energy of the seeded and tape-cast Si3 N4 was 301 and 781 J/m2 at room temperature and 1500°C, respectively, when a stress was applied parallel to the fibrous gain alignment. The large fracture energies were attributable primarily to the unidirectional alignment fibrous Si3 N4 grains. 相似文献