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1.
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
2.
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
3.
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
4.
Shao-Yun Shan Jian-Feng Yang Ji-Qiang Gao Wen-Hui Zhang Zhi-Hao Jin Rolf Janssen Tatsuki Ohji 《Journal of the American Ceramic Society》2005,88(9):2594-2596
A new method for preparing porous silicon nitride ceramics with high porosity had been developed by carbothermal reduction of die-pressed green bodies composed of silicon dioxide, carbon, sintering additives, and seeds. The resultant porous silicon nitride ceramics showed fine microstructure and uniform pore structure. The influence of SiO2 particle size and sintering process (sintering temperature and retaining time) on the microstructure of sintering bodies was analyzed. X-ray diffractometry demonstrated the formation of single-phase β-Si3 N4 via the reaction between silicon dioxide and carbon at high temperature. SEM analysis showed that pores were formed by the banding up of rod-like β-Si3 N4 grains. Porous Si3 N4 ceramics with a porosity of 70–75%, and a strength of 5–8 MPa, were obtained. 相似文献
5.
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
6.
Gui-hua Peng Min Liang Zhen-hua Liang Qing-yu Li Wen-lan Li Qian Liu 《Journal of the American Ceramic Society》2009,92(9):2122-2124
Silicon nitride ceramics were prepared by spark plasma sintering (SPS) at temperatures of 1450°–1600°C for 3–12 min, using α-Si3 N4 powders as raw materials and MgSiN2 as sintering additives. Almost full density of the sample was achieved after sintering at 1450°C for 6 min, while there was about 80 wt%α-Si3 N4 phase left in the sintered material. α-Si3 N4 was completely transformed to β-Si3 N4 after sintering at 1500°C for 12 min. The thermal conductivity of sintered materials increased with increasing sintering temperature or holding time. Thermal conductivity of 100 W·(m·K)−1 was achieved after sintering at 1600°C for 12 min. The results imply that SPS is an effective and fast method to fabricate β-Si3 N4 ceramics with high thermal conductivity when appropriate additives are used. 相似文献
7.
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
8.
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
9.
Thermal Conductivity of Gas-Pressure-Sintered Silicon Nitride 总被引:3,自引:0,他引:3
Naoto Hirosaki Yusuke Okamoto Motohide Ando Fumio Munakata Yoshio Akimune 《Journal of the American Ceramic Society》1996,79(11):2878-2882
Si3 N4 with high thermal conductivity (120 W/(m. K)) was developed by promoting grain growth and selecting a suitable additive system in terms of composition and amount. β-Si3 N4 doped with Y2 O3 -Nd2 O3 (YN system) or Y2 O3 -A12 O3 (YA system) was sintered at 1700°-2000°C. Thermal conductivity increased with increased sintering temperature because of decreased two-grain junctions, as a result of grain growth. The effect of the additive amount on thermal conductivity with the YN system was rather small because increased additive formed multigrain junctions. On the other hand, with the YA system, thermal conductivity considerably decreased with increased additive amount because the aluminum and oxygen in the YA system dissolved into β-Si3 N4 grains to form a β-SiAlON solid solution, which acted as a point defect for phonon scattering. The key processsing parameters for high thermal conductivity of Si3 N4 were the sintering temperature and additive composition. 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.
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
12.
β-Si3 N4 ceramics sintered with Yb2 O3 and ZrO2 were fabricated by gas-pressure sintering at 1950°C for 16 h changing the ratio of "fine" and "coarse" high-purity β-Si3 N4 raw powders, and their microstructures were quantitatively evaluated. It was found that the amount of large grains (greater than a few tens of micrometers) could be drastically reduced by mixing a small amount of "coarse" powder with a "fine" one, while maintaining high thermal conductivity (>140 W·(m·K)−1 ). Thus, this work demonstrates that it is possible for β-Si3 N4 ceramics to achieve high thermal conductivity and high strength simultaneously by optimizing the particle size distribution of raw powder. 相似文献
13.
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
14.
The mechanical properties of Si3 N4 materials depend mainly on the microstructure, which originates during the densification process. The microscopic evidence indicates that β-Si3 N4 seeds incorporated in the starting powders play an important role in microstructural development, especially in the heterogeneous grain growth of β-Si3 N4 grains during sintering. The growth of β-grains is initiated from the β-seeds, resulting in a core/shell microstructure. The presence of Moiré fringes and dislocations is attributed to misfit strain and compositional differences between the core and the shell. Coalescence can occur at the final stage of sintering. 相似文献
15.
New Strategies for Preparing NanoSized Silicon Nitride Ceramics 总被引:2,自引:0,他引:2
Xin Xu Toshiyuki Nishimura Naoto Hirosaki Rong-Jun Xie Yinchun Zhu Yoshinobu Yamamoto Hidehiko Tanaka 《Journal of the American Ceramic Society》2005,88(4):934-937
We report the preparation of nanosized silicon nitride (Si3 N4 ) ceramics via high-energy mechanical milling and subsequent spark plasma sintering. A starting powder mixture consisting of ultrafine β-Si3 N4 and sintering additives of 5-mol% Y2 O3 and 2-mol% Al2 O3 was prepared by high-energy mechanical milling. After milling, the powder mixture was mostly transformed into a non-equilibrium amorphous phase containing a large quantity of well-dispersed nanocrystalline β-Si3 N4 particles. This powder precursor was then consolidated by spark plasma sintering at a temperature as low as 1600°C for 5 min at a heating rate of 300°C/min. The fully densified sample consisted of homogeneous nano-Si3 N4 grains with an average diameter of about 70 nm, which led to noticeable high-temperature ductility and elevated hardness. 相似文献
16.
Byoung-Chan Bae Dong-Soo Park Young-Wook Kim Wonjoong Kim Byoung-Dong Han Hai-Doo Kim Chan Park 《Journal of the American Ceramic Society》2003,86(6):1008-1013
Silicon nitride ceramics seeded with 3 wt%β-Si3 N4 whiskers of two different sizes were prepared by a modified tape casting and gas pressure sintering. The fine whiskers had a higher aspect ratio than the coarse whiskers. Quantitative texture analysis including calculation of the orientation distribution function (ODF) was used for obtaining the degrees of preferred orientation of sintered samples. The maximum multiples of random distribution (mrd) values of samples seeded with the fine and coarse whiskers were large, greater than 15 and 9, respectively. Meanwhile, the mrd value of a sample seeded with fine whiskers was only 9 when it was prepared by conventional tape casting. The microstructures and the XRD data revealed that the well-aligned whiskers grew significantly after sintering and dominated the texture. Differences among the degrees of preferred orientation of the samples were explained using Jeffrey's model on rotation of elliptical particles carried by a viscous fluid. 相似文献
17.
Processing of a Novel Multilayered Silicon Nitride 总被引:1,自引:0,他引:1
Yasuhiro Shigegaki Manuel E. Brito Kiyoshi Hirao Motohiro Toriyama Shuzo Kanzaki 《Journal of the American Ceramic Society》1996,79(8):2197-2200
A new type of silicon nitride with a layered structure of alternating dense and porous layers was obtained by addition of β-Si3 N4 whiskers to the porous layers. The materials consisted of dense layers 60 μm thick and porous layers 40 μm thick with a final porosity of about 30%. Highly anisotropic shrinkage behavior was observed during sintering. A large addition of whiskers to the porous layers resulted in layers with well-oriented and tightly tangled elongated grains, where porosity is represented by anisotropic shaped pores. 相似文献
18.
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
19.
Silicon nitride (Si3 N4 ) ceramics, prepared with Y2 O3 and Al2 O3 sintering additives, have been densified in air at temperatures of up to 1750°C using a conventional MoSi2 element furnace. At the highest sintering temperatures, densities in excess of 98% of theoretical have been achieved for materials prepared with a combined sintering addition of 12 wt% Y2 O3 and 3 wt% Al2 O3 . Densification is accompanied by a small weight gain (typically <1–2 wt%), because of limited passive oxidation of the sample. Complete α- to β-Si3 N4 transformation can be achieved at temperatures above 1650°C, although a low volume fraction of Si2 N2 O is also observed to form below 1750°C. Partial crystallization of the residual grain-boundary glassy phase was also apparent, with β-Y2 Si2 O7 being noted in the majority of samples. The microstructures of the sintered materials exhibited typical β-Si3 N4 elongated grain morphologies, indicating potential for low-cost processing of in situ toughened Si3 N4 -based ceramics. 相似文献
20.
Tzer-Shin Sheu 《Journal of the American Ceramic Society》1994,77(9):2345-2353
The in situ β-Si3 N4 /α'-SiAlON composite was studied along the Si3 N4 –Y2 O3 : 9 AlN composition line. This two phase composite was fully densified at 1780°C by hot pressing Densification curves and phase developments of the β-Si3 N4 /α'-SiAlON composite were found to vary with composition. Because of the cooperative formation of α'-Si AlON and β-Si3 N4 during its phase development, this composite had equiaxed α'-SiAlON (∼0.2 μm) and elongated β-Si3 N4 fine grains. The optimum mechanical properties of this two-phase composite were in the sample with 30–40%α', which had a flexural strength of 1100 MPa at 25°C 800 MPa at 1400°C in air, and a fracture toughness 6 Mpa·m1/2 . α'-SiAlON grains were equiaxed under a sintering condition at 1780°C or lower temperatures. Morphologies of the α°-SiAlON grains were affected by the sintering conditions. 相似文献