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1.
Detailed microstructural analysis of a 10 mol% Y2 O3 fluxed hot-pressed silicon nitride reveals that, in addition to the yttrium-silicon oxynitride phase located at the multiple Si3 N4 grain junctions, there is a thin boundary phase 10 to 80 Å wide separating the silicon nitride and the oxynitride grains. Also, X-ray microanalysis from regions as small as 200 Å across demonstrates that the yttrium-silicon oxynitride, Y2 Si(Si2 O3 N4 ), phase can accommodate appreciable quantities of Ti, W, Fe, Ni, Co, Ca, Mg, Al, and Zn in solid solution. This finding, together with observations of highly prismatic Si3 N4 grains enveloped by Y2 Si(Si2 O3 N4 ), suggests that densification occurred by a liquid-phase "solution-reprecipitation" process. 相似文献
2.
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
3.
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
4.
Influence of Planetary High-Energy Ball Milling on Microstructure and Mechanical Properties of Silicon Nitride Ceramics 总被引:1,自引:0,他引:1
Xue-Jian Liu Zhi-Yong Huang Xi-Peng Pu Xing-Wei Sun Li-Ping Huang 《Journal of the American Ceramic Society》2005,88(5):1323-1326
The influence of ball-milling methods on microstructure and mechanical properties of silicon nitride (Si3 N4 ) ceramics produced by pressureless sintering for a sintering additive from MgO–Al2 O3 –SiO2 system was investigated. For planetary high-energy ball milling, the mechanical properties of Si3 N4 ceramics were evidently improved and a homogeneous microstructure developed. In contrast, some exaggerated elongated grains were developed due to the local enrichment of sintering additives in the specimen prepared by general ball milling. For Si3 N4 ceramics produced by planetary ball milling, flexure strength of 1.06 GPa, Vickers hardness of 14.2 GPa, and fracture toughness of 6.6 MPa·m0.5 were achieved. The differences in the mechanical properties of Si3 N4 ceramics produced by different processing seem to arise mainly from the changes in microstructural homogenization and sinterability. The planetary high-energy ball-milling process provides a good route to mix starting powders for developing ceramics with uniform microstructure and promising mechanical properties. 相似文献
5.
The microstructure of silicon nitride containing different percentages of β-seeds was investigated. The average grain size and volume fraction of large grains increased with the incorporation of β-seeds. The length and aspect ratio of large grains in sintered Si3 N4 initially increased by incorporating β-seeds, and then decreased. Similar trends were observed in the fracture toughness. The toughening mechanisms and fracture behaviors were correlated with the grain morphology measured from image analysis. Plots of measured toughness versus volume fraction of large grains fit very well with the equation derived by Becher and Budiansky, which strongly suggested the essential role of debonding length in the toughness of silicon nitride. Further improvement of fracture toughness in silicon nitride may be possible by tailoring the amount of incorporated β-phase seeds and leading to optimize the volume fraction, grain size, and aspect ratio of the elongated grains. 相似文献
6.
Takafumi Kusunose Tohru Sekino Koichi Niihara 《Journal of the American Ceramic Society》2007,90(10):3341-3344
To investigate the deformation mechanism of silicon carbide (SiC)/boron nitride (BN) nanocomposites, Hertzian contact tests were performed on monolithic SiC, and nanocomposite and microcomposite SiC/BN. Monolithic SiC had the typical microstructure of hot-pressed SiC with Y2 O3 and Al2 O3 additives, composed of slightly large grains in small matrix grains. The microcomposite comprised large BN grains dispersed along the grain boundaries of elongated SiC grains, while the nanocomposite showed a finer microstructure with fine BN particles and small matrix grains. These microstructural differences led to differences in the mechanism of contact damage. The damage of the monolithic SiC and the SiC/BN microcomposite exhibited classical Hertzian cone fracture and many large cracks, whereas the damage observed in the nanocomposites appeared to be quasi-plastic deformation. 相似文献
7.
Microstructure and Grain-Boundary Composition of Hot-Pressed Silicon Nitride With Yttria and Alumina
The microstructure of two hot-pressed silicon nitrides containing Y2 O3 and Al2 O3 was examined by electron microscopy, electron diffraction, and quantitative, energy-dispersive X-ray microanalysis. A crystalline second phase was identified in the material with additives of 5 wt% Y2 O3 +2 wt% Al2 O3 , as a solid solution of nitrogen mellilite and alumina. An amorphous third phase as narrow as 2 nm is discerned at all grain boundaries of this material by high-resolution dark-field and lattice imaging. The second phase in a material with additives of S wt% Y2 O3 +5 wt% Al2 O3 was found to be amorphous. Some of the additional alumina additive appears in solid solution with silicon nitride. In situ hot-stage experiments in a high-voltage electron microscope show that the amorphous phase volatilizes above 1200°C, leaving a skeleton of Si3 N4 grains linked by the mellilite crystals at triple points. The results show that intergranular glassy phases cannot be eliminated by the Y2 O3 /Al2 O3 fluxing. 相似文献
8.
Ellen Y. Sun Paul F. Becher Kevin P. Plucknett Chun-Hway Hsueh Kathleen B. Alexander Shirley B. Waters Kiyoshi Hirao Manuel E. Brito 《Journal of the American Ceramic Society》1998,81(11):2831-2840
Significant improvements in the fracture resistance of self-reinforced silicon nitride ceramics have been obtained by tailoring the chemistry of the intergranular amorphous phase. First, the overall microstructure of the material was controlled by incorporation of a fixed amount of elongated ß-Si3 N4 seeds into the starting powder to regulate the size and fraction of the large reinforcing grains. With controlled microstructures, the interfacial debond strength between the reinforcement and the intergranular glass was optimized by varying the yttria-to-alumina ratio in the sintering additives. It was found that the steady-state fracture toughness value of these silicon nitrides increased with the Y:Al ratio of the oxide additives. The increased toughness was accompanied by a steeply rising R -curve and extensive interfacial debonding between the elongated ß-Si3 N4 grains and the intergranular glassy phase. Microstructural analyses indicate that the different fracture behavior is related to the Al (and O) content in the ß´-SiAlON growth layer formed on the elongated ß-Si3 N4 grains during densification. The results imply that the interfacial bond strength is a function of the extent of Al and Si bonding with N and O in the adjoining phases with an abrupt structural/chemical interface achieved by reducing the Al concentration in both the intergranular phase and the ß´-SiAlON growth layer. Analytical modeling revealed that the residual thermal expansion mismatch stress is not a dominant influence on the interfacial fracture behavior when a distinct ß´-SiAlON growth layer forms. It is concluded that the fracture resistance of self-reinforced silicon nitrides can be improved by optimizing the sintering additives employed. 相似文献
9.
Christos C. Agrafiotis Jerzy Lis Jan A. Puszynski Vladimir Hlavacek 《Journal of the American Ceramic Society》1990,73(11):3514-3517
The feasibility of synthesizing silicon nitride-silicon carbide composites by self-propagating high-temperature reactions is demonstrated. Various mixtures of silicon, silicon nitride, and carbon powders were ignited under a nitrogen pressure of 30 atm (∼ 3 MPa), to produce a wide composition range of Si3 N4 -SiC powder products. Products containing up to 17 vol% of SiC, after being attrition milled, could be hot-pressed to full density under 1700°C, 3000 psi (∼ 21 MPa) with 4 wt% of Y2 O3 . The microhardness and fracture toughness of these composites were superior to those of the pure β-Si3 N4 matrix material and compared very well with the properties of "traditionally" prepared composites. 相似文献
10.
Masateru Nakamura Kiyoshi Hirao Yukihiko Yamauchi Shuzo Kanzaki 《Journal of the American Ceramic Society》2001,84(11):2579-2584
A silicon nitride ceramic with unidirectionally aligned β-Si3 N4 elongated grains (UA-SN) was fabricated by sintering the extruded Si3 N4 green body with a small amount of rodlike β-Si3 N4 seed. The effect of anisotropy in microstructure on tribological properties was investigated, compared with a fine-grained Si3 N4 without seed. Block-on-ring tests without lubricant were conducted at sliding speeds of 0.15 and 1.5 m/s, with a normal load of 5 N and a sliding distance of 75 m, using the UA-SN and Si3 N4 without seeds as block specimens and commercially supplied Si3 N4 as ring specimens. For UA-SN, tribological properties were evaluated in three directions with respect to the grain alignment: the plane normal to the grain alignment, and in the direction parallel to or perpendicular to the grain alignment in the side plane. For both sliding speeds, the plane normal to the grain alignment exhibited the highest wear resistance, and the worn surface of this plane was quite smooth, in contrast to the other specimens whose surfaces were irregular owing to grain dropping. It is considered that the high wear resistance achieved in this plane is attributable to the inhibition of crack propagation along the sliding surface by the stacked elongated grains normal to the sliding surface. 相似文献
11.
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
12.
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
13.
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
14.
Shoichirou Taira Yasuyuki Yamasaki Kunihiko Nakashima Katsumi Mori 《Journal of the American Ceramic Society》1997,80(4):925-932
The dissolution rates of silicon nitride (Si3 N4 ) ceramics into CaOAl2 O3 SiO2 slags were investigated by using a rotating specimen method in the temperature range of 1773–1873 K. Dissolution rates in the present study increased as the revolution speed and temperature increased and decreased as the SiO2 content of the slags increased. The nitrogen content of the slags increased after the Si3 N4 ceramics had been immersed into them. The slags contained two types of nitrogen ions—N3− and CN- —because a graphite crucible was used for the experiment. N3− ions were confirmed in all the slags that were used in the present work; the CN- content was much lower than that of the N3− ions, except in the slag without SiO2 . Based on those results, Ficks law of diffusion was used to analyze the dissolution rates. The dissolution mechanism of the Si3 N4 ceramics into CaO–Al2 O3 SiO2 slags has been discussed in this paper. 相似文献
15.
Kiyoshi Hirao Koji Watari Manuel E. Brito Motohiro Toriyama Shuzo Kanzaki 《Journal of the American Ceramic Society》1996,79(9):2485-2488
Silicon nitride was fabricated by tape casting of α-Si3 N4 powder with 5 wt% Y2 O3 and 5 vol% rodlike β-Si3 N4 seed particles, followed by tape stacking, hot pressing under 40 MPa, and annealing at 1850°C for 2-66 h under a nitrogen pressure of 0.9 MPa. Silicon nitrides fabricated by this procedure exhibited a highly anisotropic microstructure with large elongated grains (developed from seed particles) uniaxially oriented parallel to the casting direction. Thermal conductivities parallel to the grain alignment were much higher than those measured in other directions and exhibited high values of up to 120 W/(m.K). The anisotropic thermal conductivity of the specimen could be explained by the rule of mixture, considering that large elongated grains developed from seeds have higher thermal conductivity than a small-grained matrix. 相似文献
16.
Microstructure and Properties of Self-Reinforced Silicon Nitride 总被引:3,自引:0,他引:3
Problems associated with manufacturing Si3 N4 /SiC-whisker composites have been overcome by developing selfreinforced Si3 N4 with elongated β-Si3 N4 grains formed in situ from oxynitride glass. This Si3 N4 –Y2 O3 –MgO–SiO2 –CaO-based material has a flexure strength >1000 MPa and fracture toughness >8 MPa·m½ . The optimum combination of mechanical properties has been obtained with Y2 O3 :MgO ratios ranging from 3:1 to 1:2, CaO contents ranging from 0.1 to 0.5 wt%, and Si3 N4 contents between 90 and 96 wt%. 相似文献
17.
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
18.
Xuguang Tong Jianbao Li Xiaozhan Yang Hong Lin Gangfeng Guo Mingsheng He 《Journal of the American Ceramic Society》2006,89(5):1730-1732
In this work, self-reinforced silicon nitrides with β-Si3 N4 seeds doped with Re2 O3 (Re=Yb, Lu) were investigated. Firstly, the two kinds of seeds were obtained by heating α-Si3 N4 powder with Yb2 O3 or Lu2 O3 , respectively. Then the self-reinforced silicon nitride ceramics were prepared by HP-sintering of α-Si3 N4 powder, Re2 O3 as additive, and the as-prepared seeds. Oxidation test was carried out at 1400°C in air for 100 h with thermogravimetry analysis (TGA) measurement. Mechanical properties, scanning electronic microscopy microstructures, and X-ray diffraction patterns were measured before and after oxidation. The results indicated that the introduction of the seeds doped with Re2 O3 (Re=Yb, Lu) could obviously increase the toughness and keep the room temperature and high-temperature strength of the ceramics at high values. After oxidation, the crystalline phase in grain boundary changed and the mechanical properties decreased. TGA showed a parabolic weight gain and the oxidation mechanism was discussed. 相似文献
19.
Eva Lidén Michael Persson Elis Carlström Roger Carlsson 《Journal of the American Ceramic Society》1991,74(6):1335-1339
Pressureless sintering of silicon nitride requires addition of sintering agents. The main part of this study was done in order to homogenize the distribution of sintering agents, in this case Y2 O3 , in a silicon nitride matrix. Colloidal 10-nm Y2 O3 Particles were electrostatically adsorbed on Si3 N4 particle surfaces. The adsorption was studied by X-ray fluorescence analysis and electrophoretic measurements. Addition of Y2 O3 sol to a Si3 N4 suspension decreased the viscosity of the suspension. The slip casting properties of Si3 N4 suspensions with added Y2 O3 sol were examined, and the homogeneity of Y2 O3 in the green compacts was compared with conventionally prepared samples. An improved microstructural homogeneity was obtained when Y2 O3 sol particles were adsorbed on the Si3 N4 particle surfaces. 相似文献
20.
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