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1.
The melting behaviors of selected compositions in the Si3 N4 -AlN-Y2 O3 system were determined under 1 MPa of nitrogen. The phase diagrams of the ternary and their binary systems are presented. The lowest melting composition of the ternary system contains 15 mol % Si3 N4 , 25 mol % AIN, and 60 mol % Y2 O3 and has a melting temperature of 1650°C. The binary eutectic compositions and temperatures are 15 mol % Si3 N4 and 85 mol % Y2 O3 at 1720°C, and 20 mol % AIN and 80 mol% Y2 O3 at 1730°C. 相似文献
2.
Hot-pressed Si3 N4 doped with 10 wt% zvttrite as a sinterine aid was studied. An equiaxed, fine-grainid microstructure was predominant, with no apparent porosity. Bend strengths were determined at room temperature and high temperatures (up to 1370°C/2500°F). Oxidation was measured by weight gain at 1370°C in air. The resulting material exhibited very good room-temperature strength (755 MPa/110 ksi). The work showed that room-temperature strength can be improved significantly by using controlled Si3 N4 powder with 10 wt% zyttrite. High-temperature strength (514 MPd75 ksi) at 1370°C was nearly double that of hot-pressed Si3 N4 (NC-132). The oxidation resistance at 1370°C was also higher than that of NC-132. 相似文献
3.
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
4.
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
5.
Shuqi Guo Naoto Hirosaki Yoshinobu Yamamoto Toshiyuki Nishimura Mamoru Mitomo 《Journal of the American Ceramic Society》2002,85(6):1607-1609
The effect of oxidation exposure on room-temperature flexural strength was examined in 3.33- and 12.51-wt%-Lu2 O3 -containing hot-pressed Si3 N4 ceramics exposed to air at 1500°C for up to 1000 h. After oxidation exposure, the room-temperature strength of the ceramics was degraded, and strength retention decreased with time at temperature, dependent on the amount of additive. The retention in room-temperature strength displayed by the two compositions after 1000 h of oxidation exposure was 75%–80%. The degradation in strength was attributed to the formation of new defects at and/or near the interface between the oxide layer and the Si3 N4 bulk during oxidation exposure. 相似文献
6.
High-density Si3 N4 +6% CeO2 composites with 5 to 50% BN were fabricated by hot-pressing. BN remained as a discrete phase. Dielectric constants were 4 to 8 and loss tangents were 0.0008 to 0.06 for the room temperature to 1100°C range for compositions with 10 to 50% BN. Thermal-expansion values perpendicular to the hot-pressing direction were somewhat less than those of hot-pressed Si3 N4 +6% CeO2 . Flexure strengths at room temperature were considerably lower than those of hot-pressed Si3 N4 +6% CeO2 but values at 1000°, 1250°, and 1400°C in air were only slightly lower. Young's modulus values were found to decrease with increasing BN content at all temperatures. Better thermal shock resistance was found than for commercial hot-pressed Si3 N4 . 相似文献
7.
Sintering kinetics of the system Si3 N4-Y2O3 -Al2 O3 were determined from measurements of the linear shrinkage of pressed disks sintered isothermally at 1500° to 1700°C. Amorphous and crystalline Si3 N4 were studied with additions of 4 to 17 wt% Y2 O3 and 4 wt% A12 O3 . Sintering occurs by a liquid-phase mechanism in which the kinetics exhibit the three stages predicted by Kingery's model. However, the rates during the second stage of the process are higher for all compositions than predicted by the model. X-ray data show the presence of several transient phases which, with sufficient heating, disappear leaving mixtures of β ' -Si3 N4 and glass or β '-Si3 N4 , α '-Si3 N4 , and glass. The compositions and amounts of the residual glassy phases are estimated. 相似文献
8.
Shuqi Guo Naoto Hirosaki Toshiyuki Nishimura Yoshinobu Yamamoto Mamoru Mitomo 《Journal of the American Ceramic Society》2003,86(11):1900-1905
The oxidation behavior and effect of oxidation on room-temperature flexural strength were investigated for hot-pressed Si3 N4 ceramics, with 3.33 and 12.51 wt% Lu2 O3 additives, exposed to air at 1400° and 1500°C for up to 200 h. Parabolic oxidation behavior was observed for both compositions. The oxidation products consisted of Lu2 Si2 O7 and SiO2 . The Lu2 Si2 O7 grew out of the surface silicate in preferred orientations. The morphology of oxidized surfaces was dependent on the amount of additive; Lu2 Si2 O7 grains in the 3.33 wt% composition appeared partially in a needlelike type, compared with a more equiaxed type exhibited in the 12.51 wt% case. The high resistance to oxidation shown for both compositions was attributed to the extensive amounts of crystalline, refractory secondary phases formed during the sintering process. Moreover, after 200 h of oxidation at 1400° and 1500°C, the strength retention displayed by the two compositions was 93%–95% and 85%–87%, respectively. The strength decrease was associated with the formation of new defects at the interface between the oxide layer and the Si3 N4 bulk. 相似文献
9.
Naoto Hirosaki Yoshinobu Yamamoto Toshiyuki Nishimura Mamoru Mitomo Junichi Takahashi Hisanori Yamane Masahiko Shimada 《Journal of the American Ceramic Society》2002,85(11):2861-2863
Phase relationships in the Si3 N4 –SiO2 –Lu2 O3 system were investigated at 1850°C in 1 MPa N2 . Only J-phase, Lu4 Si2 O7 N2 (monoclinic, space group P 21 / c , a = 0.74235(8) nm, b = 1.02649(10) nm, c = 1.06595(12) nm, and β= 109.793(6)°) exists as a lutetium silicon oxynitride phase in the Si3 N4 –SiO2 –Lu2 O3 system. The Si3 N4 /Lu2 O3 ratio is 1, corresponding to the M-phase composition, resulted in a mixture of Lu–J-phase, β-Si3 N4 , and a new phase of Lu3 Si5 ON9 , having orthorhombic symmetry, space group Pbcm (No. 57), with a = 0.49361(5) nm, b = 1.60622(16) nm, and c = 1.05143(11) nm. The new phase is best represented in the new Si3 N4 –LuN–Lu2 O3 system. The phase diagram suggests that Lu4 Si2 O7 N2 is an excellent grain-boundary phase of silicon nitride ceramics for high-temperature applications. 相似文献
10.
Hot isostatic pressing was studied for densification of reaction-bonded Si3 N4 containing various levels of Y2 O3 . Near-theoretical density was achieved for com positions containing 3 to 7 wt% Y2 O3 . An Si3 N4 -5 wt% Y2 O3 composition had a 4-point flexural strength at 1375°C of 628 MPa and survived 117 h of stress rupture testing at 1400°C and 345 MPa . 相似文献
11.
Siddharta Bandyopadhyay Michael J. Hoffmann † Günter Petzow 《Journal of the American Ceramic Society》1996,79(6):1537-1545
Different SiAION composites based on α'-SiAION are investigated, with respect to the phase relationships, densification behavior, and mechanical properties. The compositions are located on a phase-diagram line parallel to the Si3 N4 -Y2 O3 9AIN compound in the Si3 N4 -SiO2 -AlN-Al2 O3 -Y2 O3 -YN system. Analysis of the reaction sequences shows that the formation of the composites is associated with the transient appearance of Y4 A12 O9 (YAM), yttrium-aluminum-garnet (YAG), melilite, and a nitrogen-rich liquid phase. The small shift of compositions on the Si3 N4 -Y2 O3 -9AIN compound phase-diagram line toward the Al2 O3 -rich side offers the advantage of a higher sinterability and the removal of the melilite phase from a wide range of compositions containing α'-SiAlON and polytypes. The α'/β'-SiAlON composites show better mechanical properties in comparison to pure α'-SiAlON and composites of α'-SiAION and polytypes. A post-heat-treatment causes the crystallization of YAG as a grain-boundary phase and leads to excellent strength retention up to temperatures of 1350°C. 相似文献
12.
F. F. LANGE 《Journal of the American Ceramic Society》1978,61(1-2):53-56
Phase relation studies of Si3 N1 , SiO2 , and MgO have established three important subsolidus tie lines, viz. Si3 N4 -MgO, Si3 N4 -Mg2 SiO4 , and Si2 N2 O-Mg2 SiO4 for nonoxidizing fabrication conditions. Strength measurements at 1400°C show that optimum strengths are obtained for compositions approaching the Si3 N4 -MgO and Si3 N4 -Si2 N2 O tie lines and that inferior strengths are obtained for compositions approaching the Si3 N4 -Mg2 SiO4 tie line. Oxidation measurements at 1375°C show that the oxidation kinetics depend on the content of MgO and Mg2 SiO4 phases. Optimum oxidation resistance is observed for compositions approaching the Si3 N4 -Si2 N2 O tie line. Strength and oxidation results are discussed with regard to phase equilibrium considerations. 相似文献
13.
The effects of heat treatment in Ar-O2 and H2 -H2 O atmospheres on the flexural strength of hot isostatically pressed Si3 N4 were investigated. Increases in room-temperature strength, to values significantly above that of the aspolished material, were observed when the Si3 N4 was exposed at 1400°C to (1) H2 with water vapor pressure ( P H2O ) greater than 1 × 10−4 MPa or (2) Ar with oxygen partial pressure ( P O2 ) of between 7 × 10−6 and 1.5 × 10−5 MPa. However, the strength of the material was degraded when the P H2O in H2 was lower than 1 × 10−4 MPa, and essentially unaffected when the P O2 in Ar was higher than 1.5 × 10−5 MPa. We suggest that the observed strength increases are the result of strength-limiting surface flaws being healed by a Y2 Si2 O7 layer formed during exposure. 相似文献
14.
Young-Hag Koh Hae-Won Kim Hyoun-Ee Kim John W. Halloran 《Journal of the American Ceramic Society》2002,85(12):3123-3125
The oxidation behavior and its effect on the mechanical properties of fibrous monolith Si3 N4 /BN after exposure to air at temperatures ranging from 1000° to 1400°C for up to 20 h were investigated. After exposure at 1000°C, only the BN cell boundary was oxidized, forming a B2 O3 liquid phase. With increasing exposure temperature, the Si3 N4 cells began to oxidize, forming crystalline Y2 Si2 O7 , SiO2 , and silicate glass. However, in this case, a weight loss was observed due to extensive vaporization of the B2 O3 liquid. After exposure at 1400°C, large Y2 Si2 O7 crystals with a glassy phase formed near the BN cell boundaries. The oxidation behavior significantly affected the mechanical properties of the fibrous monolith. The flexural strength and work-of-fracture decreased with increasing exposure temperature, while the noncatastrophic failure was maintained. 相似文献
15.
Shigeyuki Smiya Masahiro Yoshimura Shutaro Fujiwara Ken-Ichi Kondo Akira Sawaoka Takeo Haitori Jun-Ichi Mohri Masatada Araki 《Journal of the American Ceramic Society》1984,67(3):51-C-
To enhance the sinter ability of Si3 N4 , powders mixed with 0, 2, and 5 wt% Y2 O3 were explosively shock-treated. Compacts of these powders were encapsulated in 96% silica glass containers and isostatically hot-pressed. The shocked Si3 N4 with 5 wt% Y2 O3 was pressed to a density of 3.09 g/cm3 (95.4% of theoretical) at 1400°C under 430 MPa for 3 h, whereas the unshocked material attained only 82.4% of theoretical density under the same hot isostatic pressing conditions. 相似文献
16.
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
17.
IRVIN C. HUSEBY† HANS L. LUKAS GÜNTER PETZOW 《Journal of the American Ceramic Society》1975,58(9-10):377-380
The 1780°C isothermal section of the reciprocal quasiternary system Si3 N4 -SiO2 -BeO-Be3 N2 was investigated by the X-ray analysis of hot-pressed samples. The equilibrium relations shown involve previously known compounds and 8 newly found compounds: Be6 Si3 N8 , Be11 Si5 N14 , Be5 Si2 N6 , Be9 Si3 N10 , Be8 SiO4 N4 , Be6 O3 N2 , Be8 O5 N2 , and Be9 O6 N2 . Large solid solubility occurs in β-Si3 N4 , BeSiN2 , Be9 Si3 N10 , Be4 SiN4 , and β-Be3 N2 . Solid solubility in β-Si3 N4 extends toward Be2 SiO4 and decreases with increasing temperature from 19 mol% at 1770°C to 11.5 mol% Be2 SiO4 at 1880°C. A 4-phase isotherm, liquid +β-Si3 N4 ( ss )Si2 ON2 + BeO, exists at 1770°C. 相似文献
18.
A. J. KIEHLE L. K. HEUNG P. J. GIELISSE T. J. ROCKETT 《Journal of the American Ceramic Society》1975,58(1-2):17-20
The high-temperature chemical stability of hot-pressed Si3 N4 was studied between 600° and 1450°C. Reactions were followed by X-ray diffraction and scanning electron microscopy. In air, this material begins to oxidize at 700° to 750°C; a distinct amorphous siO2 surface layer results after 24 h at 750°C-Concomitant formation of cristobalite occurs, depending on exposure time, and is enhanced as temperature is Increased. Magnesium and calcium magnesium silicates form above 1000°C. The data suggest that impurities, e.g. Mg, Ca, and Fe, greatly lower the oxidation resistance of Si3 N4 in air. 相似文献
19.
Koichi Terao Yoshinari Miyamoto Mitsue Koizumi 《Journal of the American Ceramic Society》1988,71(3):167-C
Dense, ZrO2 -dispersed Si3 N4 composites without additives were fabricated at 180 MPa and ∼1850° to 1900°C for l h by hot isostatic pressing using a glass-encapsulation method; the densities reached >96% of theoretical. The dispersion of 20 wt% of 2.5YZrO2 (2.5 mol% Y2 O3 ) in Si3 N4 was advantageous to increase the room-temperature fracture toughness (∼7.5 MPa˙m1/2 ) without degradation of hardness (∼15 GPa) because of the high retention of tetragonal ZrO2 . The dependence of fracture toughness of Si3 N4 –2.5YZrO2 on ZrO2 content can be related to the formation of zirconium oxynitride because of the reaction between ZrO2 and Si3 N4 matrix in hot isostatic pressing. 相似文献
20.
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