共查询到20条相似文献,搜索用时 15 毫秒
1.
Juergen Heinrich Eberhard Backer Manfred Böhmer 《Journal of the American Ceramic Society》1988,71(1):28-C-
Hot isostatically pressed silicon nitride was produced by densifying Si3 N4 powder compacts and reaction-bonded Si3 N4 (RBSN) parts with yttria as a sintering additive. The microstructure was analyzed using scanning electron microscopy, X-ray diffraction, and density measurements. The influence of the microstructure on fracture strength, creep, and oxidation behavior was investigated. It is assumed that the higher amount of oxygen in the Si3 N4 starting powder compared with the RBSN starting material leads to an increased amount of liquid phase during densification. This results in grain growth and in a larger amount of grain boundary phase in the hot isostatically pressed material. Compared with the hot isostatically pressed RBSN samples therefore, strength decreases whereas the creep rate and the weight gain during oxidation increase. 相似文献
2.
Cha-Yang Chu Jitendra P. Singh Jules L. Routbort 《Journal of the American Ceramic Society》1993,76(5):1349-1353
The high-temperature flexural strength of hot-pressed silicon nitride (Si3 N4 ) and Si3 N4 -whisker-reinforced Si3 N4 -matrix composites has been measured at a crosshead speed of 1.27 mm/min and temperatures up to 1400°C in a nitrogen atmosphere. Load–displacement curves for whisker-reinforced composites showed nonelastic fracture behavior at 1400°C. In contrast, such behavior was not observed for monolithic Si3 N4 . Microstructures of both materials have been examined by scanning and transmission electron microscopy. The results indicate that grain-boundary sliding could be responsible for strength degradation in both monolithic Si3 N4 and its whisker composites. The origin of the nonelastic failure behavior of Si3 N4 -whisker composite at 1400°C was not positively identified but several possibilities are discussed. 相似文献
3.
C. James Hwang†¶ David W. Susnitzky‡ Robert A. Newman‡ Donald R. Beaman‡ Aleksander J. Pyzik§ 《Journal of the American Ceramic Society》1995,78(11):3072-3080
The controlled crystallization of the amorphous grain boundary phase has been examined in a series of self-reinforced Si3 N4 materials with added Y2 O3 , SrO, and CaO. The effects of time, temperature, atmosphere, glass content, glass chemistry, and matrix Si3 N4 on the crystallization have been investigated. The stability of the crystallized product, the crystallization kinetics ( T-T-T curve), and crystallization mechanisms have also been examined. Crystallization produced an oxynitroapatite containing Y, Sr, and Ca over a broad range of heat-treatment conditions and glass compositions. The oxynitroapatite was compatible with Si3 N4 and remained stable up to 1600°C. At low temperatures (<1350°C), the rate-limiting crystallization mechanism was oxygen diffuson in the glass, and at higher temperatures (>1350°C) the rate-limiting crystallization step changed to either the formation of new Si3 N4 grains or solute diffusion in the glass. 相似文献
4.
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
5.
Delayed failure and creep behavior of high-purity Si3 N4 sintered without additives with a mean grain size of 1 μm has been measured at 1400°C. Lifetime under 300 MPa was >240 h, which showed good agreement with the value predicted in our previous report. Creep strain rate ranged from 1 × 10−5 to 3 × 10−5 h−1 between 200 and 360 MPa. These values demonstrate the excellent potential of high-purity Si3 N4 materials for structural application up to 1400°C. 相似文献
6.
C. Greskovich 《Journal of the American Ceramic Society》1981,64(2):31-C-
The development of microstructure in hot-pressed Sia N4 was studiehd for a typical Si3 N4 powder with and without BeSiN2 as a densification aid. The effect of hot-pressing temperature on density, α- to β-Si3 N4 conversion and specific surface area showed that BeSiN2 appears to increase the mobility of the system by enhancing densification, α- to β-Si3 N4 transformation, and grain growth at temperatures between 1450° and 1800°. These processes appear to occur in the presence of a liquid phase. 相似文献
7.
John J. Petrovic Maria I. Pena Ivar E. Reimanis Michael S. Sandlin Samuel D. Conzone H. Harriet Kung Darryl P. Butt 《Journal of the American Ceramic Society》1997,80(12):3070-3076
The mechanical behavior of MoSi2 reinforced–Si3 N4 matrix composites was investigated as a function of MoSi2 phase content, MoSi2 phase size, and amount of MgO densification aid for the Si3 N4 phase. Coarse-phase MoSi2 -Si3 N4 composites exhibited higher room-temperature fracture toughness than fine-phase composites, reaching values >8 MP·am1/2 . Composite fracture toughness levels increased at elevated temperature. Fine-phase composites were stronger and more creep resistant than coarse phase composites. Room-temperature strengths >1000 MPa and impression creep rates of ∼10−8 s−1 at 1200°C were observed. Increased MgO levels generally were deleterious to MoSi2 -Si3 N4 mechanical properties. Internal stresses due to MoSi2 and Si3 N4 thermal expansion coefficient mismatch appeared to contribute to fracture toughening in MoSi2 -Si3 N4 composites. 相似文献
8.
Branko Matovic Georg Rixecker Fritz Aldinger 《Journal of the American Ceramic Society》2004,87(4):546-549
This paper deals with the densification and phase transformation during pressureless sintering of Si3 N4 with LiYO2 as the sintering additive. The dilatometric shrinkage data show that the first Li2 O- rich liquid forms as low as 1250°C, resulting in a significant reduction of sintering temperature. On sintering at 1500°C the bulk density increases to more than 90% of the theoretical density with only minor phase transformation from α-Si3 N4 to β-Si3 N4 taking place. At 1600°C the secondary phase has been completely converted into a glassy phase and total conversion of α-Si3 N4 to β-Si3 N4 takes place. The grain growth is anisotropic, leading to a microstructure which has potential for enhanced fracture toughness. Li2 O evaporates during sintering. Thus, the liquid phase is transient and the final material might have promising mechanical properties as well as promising high-temperature properties despite the low sintering temperature. The results show that the Li2 O−Y2 O3 system can provide very effective low-temperature sintering additives for silicon nitride. 相似文献
9.
The compressive creep behavior and oxidation resistance of an Si3 N4 /Y2 Si2 O7 material (0.85Si3 N4 +0.10SiO2 +0.05Y2 O3 ) were determined at 1400°C. Creep re sistance was superior to that of other Si3 N4 materials and was significantly in creased by a preoxidation treatment (1600°C /120 h). An apparent parabolic rate constant of 4.2 × 10−11 kg2 ·m-4 ·s−1 indicates excellent oxidation resistance. 相似文献
10.
Fei Chen Qiang Shen Faqiang Yan Lianmeng Zhang 《Journal of the American Ceramic Society》2007,90(8):2379-2383
A new method for preparing high bending strength porous silicon nitride (Si3 N4 ) ceramics with controlled porosity has been developed by using pressureless sintering techniques and phosphoric acid (H3 PO4 ) as the pore-forming agent. The fabrication process is described in detail and the sintering mechanism of porous ceramics is analyzed by the X-ray diffraction method and thermal analysis. The microstructure and mechanical properties of the porous Si3 N4 ceramics are investigated, as a function of the content of H3 PO4 . The resultant high porous Si3 N4 ceramics sintered at 1000°–1200°C show a fine porous structure and a relative high bending strength. The porous structure is caused mainly by the volatilization of the H3 PO4 and by the continous reaction of SiP2 O7 binder, which could bond on to the Si3 N4 grains. Porous Si3 N4 ceramics with a porosity of 42%–63%, the bending strength of 50–120 MPa are obtained. 相似文献
11.
Koji Watari Kiyoshi Hirao Motohiro Toriyama Kozo Ishizaki 《Journal of the American Ceramic Society》1999,82(3):777-779
Polycrystalline Si3 N4 samples with different grain-size distributions and a nearly constant volume content of grain-boundary phase (6.3 vol%) were fabricated by hot-pressing at 1800°C and subsequent HIP sintering at 2400°C. The HIP treatment of hot-pressed Si3 N4 resulted in the formation of a large amount of ß-Si3 N4 grains ∼10 µm in diameter and ∼50 µm long, and the elimination of smaller matrix grains. The room-temperature thermal conductivities of the HIPed Si3 N4 materials were 80 and 102 Wm−1 K−1 , respectively, in the directions parallel and perpendicular to the hot-pressing axis. These values are slightly higher than those obtained for hot-pressed samples (78 and 93 Wm−1 K−1 ). The calculated phonon mean free path of sintered Si3 N4 was ∼20 nm at room temperature, which is very small as compared to the grain size. Experimental observations and theoretical calculations showed that the thermal conductivity of Si3 N4 at room temperature is independent of grain size, but is controlled by the internal defect structure of the grains such as point defects and dislocations. 相似文献
12.
Woo Y. Lee James R. Strife Richard D. Veltri 《Journal of the American Ceramic Society》1992,75(10):2803-2808
The crystal structure and surface morphology of Si3 N4 prepared by LPCVD were characterized as a function of processing conditions. Temperature was the most dominant variable which affected the coating microstructure. Strongly faceted crystalline Si3 N4 was deposited at temperatures above ∼ 1410°C. In the temperature range of 1300° to 1410°C, crystalline and amorphous phases were codeposited. The content of the crystalline phase rapidly decreased with decreased temperature. In this temperature range, the coating crystallinity was also influenced by kinetic factors such as deposition rate and reagent depletion. For example, Si3 N4 became more crystalline as the deposition rate was decreased by either decreasing the flow rate or increasing the NH3 /SiF4 molar ratio. At ∼ 1300°C, the coating surface appeared fully botryoidal, and the coatings were mostly amorphous. Changes in the orientation and size of Si3 N4 crystallites were parametrically documented. As the temperature was increased, the Si3 N4 grains generally became more preferentially oriented to the (102) and/or ( l 0 l ) where l = 1,2,3,., directions. The average facet size increased with coating thickness. 相似文献
13.
Linus U. J. T. Ogbuji 《Journal of the American Ceramic Society》1992,75(11):2995-3000
The results of two-step oxidation experiments on chemically-vapor-deposited Si3 N4 and SiC at 1350°C show that a correlation exists between the presence of a Si2 N2 O interphase and the strong oxidation resistance of Si3 N4 . During normal oxidation, k p for SiC was 15 times higher than that for Si3 N4 , and the oxide scale on Si3 N4 was found by SEM and TEM to contain a prominent Si2 N2 O inner layer. However, when oxidized samples are annealed in Ar for 1.5 h at 1500°C and reoxidized at 1350°C as before, three things happen: the oxidation k p increases over 55-fold for Si3 N4 , and 3.5-fold for SiC; the Si3 N4 and SiC oxidize with nearly equal k p 's; and, most significant, the oxide scale on Si3 N4 is found to be lacking an inner Si2 N2 O layer. The implications of this correlation for the competing models of Si3 N4 oxidation are discussed. 相似文献
14.
Subsolidus phase relations were established in the system Si3 N4 -SiO2 -Y2 O3 . Four ternary compounds were confirmed, with compositions of Y4 Si2 O7 N2 , Y2 Si3 O3 N4 , YSiO2 N, and Y10 (SiO4 )6 N2 . The eutectic in the triangle Si3 N4 -Y2 Si2 O7 -Y10 (SiO4 )6 N2 melts at 1500°C and that in the triangle Si2 N2 O-SiO2 -Y2 Si2 O7 at 1550°C. The eutectic temperature of the Si3 N4 -Y2 Si2 O7 join was ∼ 1520°C. 相似文献
15.
Woo Y. Lee Karren L. More David P. Stinton Yong W. Bae 《Journal of the American Ceramic Society》1996,79(9):2489-2492
Si3 N4 substrates coated with chemically-vapor-deposited, crystalline mullite (3Al2 O3 .2SiO2 ) were subjected to a corrosive environment containing Na2 SO4 and O2 at 1000°C for 100 h. The composition and microstructure of the as-deposited and corroded specimens were examined and compared. The coating appeared to be effective in preserving and therefore protecting the surface microstructure of the underlying Si3 N3 substrates. However, a small degree of Na penetration through mullite grain boundaries was observed to a coating depth of ∼1 μm. 相似文献
16.
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
17.
Hyoungjoon Park Hae-Won Kim Hyoun-Ee Kim 《Journal of the American Ceramic Society》1998,81(8):2130-2134
The oxidation behaviors of monolithic Si3 N4 and nanocomposite Si3 N4 -SiC with Yb2 O3 as a sintering aid were investigated. The specimens were exposed to air at temperatures between 1200° and 1500°C for up to 200 h. Parabolic weight gains with respect to exposure time were observed for both specimens. The oxidation products formed on the surface also were similar, i.e., a mixture of crystalline Yb2 Si2 O7 and SiO2 (cristobalite). However, strength retention after oxidation was much higher for the nanocomposite Si3 N4 -SiC compared to the monolithic Si3 N4 . The SiC particles of the nanocomposite at the grain boundary were effective in suppressing the migration of Yb3+ ions from the bulk grain-boundary region to the surface during the oxidation process. As a result, depletion of yttribium ions, which led to the formation of a damaged zone beneath the oxide layer, was prevented. 相似文献
18.
Full-density Si3 N4 -SiO2 -Ce2 O3 compositions were prepared by sintering with 2.5 MPa nitrogen pressure at temperatures of 1900° and 2090°C. Room-temperature flexural strengths near 700 MPa for sintered material compared favorably with the strength of hot-pressed material. At 1370°C, where flexural strengths as high as 363 MPa were obtained, it was observed that the coarsest structure was the strongest and the finest structure was the weakest. One of the compositions tested, Si3 N4 -8.7 wt% SiO2 -8.3 wt%-Ce2 O3 , was found to have excellent 200-h oxidation resistance at 700°, 1000°, and 1370°C, without incidence of 700° to 1000°C phase instability and cracking. 相似文献
19.
The tribological behavior of Mo5 Si3 -particle-reinforced silicon nitride (Si3 N4 ) composites was investigated by pin-on-plate wear testing under dry conditions. The friction coefficient of the Mo5 Si3 –Si3 N4 composites and Si3 N4 essentially decreased slowly with the sliding distance, but showed sudden increase for several times during the wear testing. The average friction coefficient of the Si3 N4 decreased with the incorporation of submicrometer-sized Mo5 Si3 particles and also as the content of Mo5 Si3 particles increased. When the Mo5 Si3 –Si3 N4 composites were oxidized at 700°C in air, solid-lubricant MoO3 particles were generated on the surface layer. Oxidized Mo5 Si3 –Si3 N4 composites showed self-lubricating behavior, and the average friction coefficient and wear rate of the oxidized 2.8 wt% Mo5 Si3 –Si3 N4 composite were 0.43 and 0.72 × 10−5 mm3 (N·m)−1 , respectively. Both values were ∼30% lower than those for the Si3 N4 tested in an identical manner. 相似文献
20.
Byung-Jin Choi Young-Hag Koh Hyoun-Ee Kim 《Journal of the American Ceramic Society》1998,81(10):2725-2728
The effects of microstructure and residual stress on the mechanical properties of Si3 N4 -based three-layer composite materials were investigated. The microstructure of each layer was controlled by the addition of two differently sized silicon carbides: fine SiC nanoparticles (∼200 nm) or relatively large SiC platelets (∼20 µm). When the SiC nanoparticles were added, the average grain size of Si3 N4 was reduced because of the inhibition of grain growth by the particles. On the other hand, when the SiC platelets were added, the microstructure of Si3 N4 was not much changed because of the large size of the platelets. Three-layer composites were fabricated by placing the Si3 N4 /SiC-nanoparticle layers on the surface of the Si3 N4 /SiC-platelet layer. The residual stress was controlled by varying the amount of SiC added. The mechanical properties of three-layer composites with various combinations of microstructure and residual stress level were investigated. 相似文献