共查询到20条相似文献,搜索用时 31 毫秒
1.
Guo-Jun Zhang Hideki Kita Naoki Kondo Tatsuki Ohji 《Journal of the American Ceramic Society》2005,88(8):2246-2248
The effect of Y2 O3 addition (0–5 wt%) on the densification and properties of reactive hot-pressed alumina (Al2 O3 )–boron nitride composites based on the reaction between aluminum borate (2Al2 O3 ·B2 O3 ) and aluminum nitride (AlN) was investigated. The densification process was very sensitive to the amount of Y2 O3 . Compared with a low relative density of 79.3 theoretical density (TD)% for material with no Y2 O3 addition, the material density reached 98.6 TD% with 0.25% Y2 O3 addition. High Y2 O3 additions resulted in the formation of a new phase Al5 Y3 O12 . The grain growth of the Al2 O3 matrix was promoted by the Y2 O3 addition. Owing to the high density and the small Al2 O3 particle size the sample with 0.25% Y2 O3 addition demonstrated the highest bending strength of 540 MPa. 相似文献
2.
Ki-Woong Chae Doh-Yeon Kim Byung-Chan Kim Kyung-Bae Kim 《Journal of the American Ceramic Society》1993,76(7):1857-1860
The densification of Al2 O3 –30TiC (in weight percent) composite is investigated as a function of Y2 O3 additions. It is observed that very small amounts of Y2 O3 are effective in aiding the densification. The density was observed to pass through a maximum at 0.35 wt% of Y2 O3 . The gas-generating reaction of Al2 O3 with TiC is likely to be suppressed by the addition of Y2 O3 . 相似文献
3.
Nithyanantham Thangamani Ashutosh S. Gandhi Vikram Jayaram Atul H. Chokshi 《Journal of the American Ceramic Society》2005,88(10):2696-2701
This study examined pressure consolidation of amorphous Al2 O3 –15 mol% Y2 O3 powders prepared by co-precipitation and spray pyrolysis. The two amorphous powders had similar true densities and crystallization sequences. Uniaxial hot pressing was carried out at 450°–600°C with a moderate pressure of 750 MPa. The co-precipitated powder could be hot pressed to a maximum relative density of 98% and remained amorphous. Pressure adversely affected the densification of the spray-pyrolyzed powder by favoring an early crystallization of γ-Al2 O3 phase at 580°C. Plastic deformation of the amorphous phase is believed to be responsible for the large densification of the amorphous powders. 相似文献
4.
J. LLorca José Y. Pastor Pedro Poza José I. Peña Isabel de Francisco Angel Larrea Victor M. Orera 《Journal of the American Ceramic Society》2004,87(4):633-639
The effect of Y2 O3 content on the flexure strength of melt-grown Al2 O3 –ZrO2 eutectics was studied in a temperature range of 25°–1427°C. The processing conditions were carefully controlled to obtain a constant microstructure independent of Y2 O3 content. The rod microstructure was made up of alternating bands of fine and coarse dispersions of irregular ZrO2 platelets oriented along the growth axis and embedded in the continuous Al2 O3 matrix. The highest flexure strength at ambient temperature was found in the material with 3 mol% Y2 O3 in relation to ZrO2 (Y2 O3 ). Higher Y2 O3 content did not substantially modify the mechanical response; however, materials with 0.5 mol% presented a significant degradation in the flexure strength because of the presence of large defects. They were nucleated at the Al2 O3 –ZrO2 interface during the martensitic transformation of ZrO2 on cooling and propagated into the Al2 O3 matrix driven by the tensile residual stresses generated by the transformation. The material with 3 mol% Y2 O3 retained 80% of the flexure strength at 1427°C, whereas the mechanical properties of the eutectic with 0.5 mol% Y2 O3 dropped rapidly with temperature as a result of extensive microcracking. 相似文献
5.
Mamoun Medraj Robert Hammond William T. Thompson Robin A. L. Drew 《Journal of the American Ceramic Society》2003,86(4):717-26
The importance of aluminum nitride (AlN) stems from its application in microelectronics as a substrate material due to high thermal conductivity, high electrical resistance, mechanical strength and hardness, thermal durability, and chemical stability. Yttria (Y2 O3 ) is the best additive for AlN sintering. AlN densifies by a liquid-phase mechanism, where the surface oxide, Al2 O3 , reacts with Y2 O3 to form an Y-Al-O-N liquid that promotes particle rearrangement and densification. Construction of the phase relations in this multicomponent system is essential for optimizing the properties of AlN. The ternary phase diagram of the AlN–Al2 O3 –Y2 O3 was developed by Gibbs energy minimization using interpolation procedures based on modeling the binary subsystems. This paper aims at testing the resultant understanding experimentally at selected compositions using in situ high-temperature neutron diffractometry. These experimental results agree with the thermodynamic calculations of AlN–Al2 O3 –Y2 O3 . The ternary phase diagram has been constructed for the first time in this work. High-temperature neutron diffractometry has permitted real time measurement of the reactions involved in this ternary system, especially to determine the temperature range for each reaction, which would have been difficult to establish by other means. 相似文献
6.
Kentaro Fukuda Teiichi Hanada Setsuhisa Tanabe Takeshi Yao 《Journal of the American Ceramic Society》2002,85(4):915-920
Amorphous films in the system Al2 O3 –Y2 O3 were prepared by the rf sputtering method in the range of 0–76 mol% Y2 O3 , and their density, refractive index, and elastic constants were measured. All of the physical properties of the amorphous Al2 O3 –Y2 O3 films had a similar compositional dependence; that is, they increased continuously, but not linearly with increasing Y2 O3 content. To confirm the coordination states of aluminum and yttrium ions in the amorphous Al2 O3 –Y2 O3 films, the Al K α X-ray emission spectra and the X-ray absorption near edge structures (XANES) were measured. The average coordination number of aluminum ions in the amorphous films containing up to about 40 mol% Y2 O3 content was 5, that is a mixture of 4-fold- and 6-fold-coordinated states. In the region of more than about 50 mol% Y2 O3 , the fraction of the 6-fold-coordinated aluminum ions increased with increasing Y2 O3 content, while the results led to the conclusion that the coordination number of yttrium ions was always 6, regardless of composition. These results indicate that, in amorphous films in the system Al2 O3 –Y2 O3 , the change of the coordination state of aluminum ions has an important effect on physical properties. 相似文献
7.
Masahide Okamoto Hironori Kodama Kazuo Shinozaki 《Journal of the American Ceramic Society》2008,91(4):1110-1114
The sintering of a composite of MgO–B2 O3 –Al2 O3 glass and Al2 O3 filler is terminated due to the crystallization of Al4 B2 O9 in the glass. The densification of a composite of MgO–B2 O3 –Al2 O3 glass and Al2 O3 filler using pressureless sintering was accomplished by lowering the sintering temperature of the composite. The sintering temperature was lowered by the addition of small amounts of alkali metal oxides to the MgO–B2 O3 –Al2 O3 glass system. The resultant composite has a four-point bending strength of 280 MPa, a coefficient of thermal expansion (RT—200°C) of 4.4 × 10−6 K−1 , a dielectric constant of 6.0 at 1 MHz, porosity of approximately 1%, and moisture resistance. 相似文献
8.
Hae-Won Kim Young-Hag Koh Hyoun-Ee Kim 《Journal of the American Ceramic Society》2000,83(11):2863-2865
The densification behavior and mechanical properties of B4 C hot-pressed at 2000°C for 1 h with additions of Al2 O3 up to 10 vol% were investigated. Sinterability was greatly improved by the addition of a small amount of Al2 O3 . The improvement was attributed to the enhanced mobility of elements through the Al2 O3 near the melting temperature or a reaction product formed at the grain boundaries. As a result of this improvement in the density, mechanical properties, such as hardness, elastic modulus, strength, and fracture toughness, increased remarkably. However, when the amount of Al2 O3 exceeded 5 vol%, the level of improvement in the mechanical properties, except for fracture toughness, was reduced presumably because of the high thermal mismatch between B4 C and Al2 O3 . 相似文献
9.
Jun-Youp Choi Suk-Joong L. Kang O. Fukunaga Jong-Ku Park K. Y. Eun 《Journal of the American Ceramic Society》1993,76(10):2525-2528
Four kinds of BN powders—amorphous BN with B2 O3 , partially crystallized BN without B2 O3 , well-crystallized hBN with B2 O3 , and well-crystallized hBN without B2 O3 —were prepared to determine the effect of B2 O3 on the crystallization of amorphous BN and the effect of BN crystallinity on the formation of cBN under high pressure (4–5 GPa) and at high temperature (1350–1450°C). The amorphous BN with B2 O3 easily crystallized and transformed to cBN in the presence of A1N catalyst, while the partially crystallized BN without B2 O3 did not. The well-crystallized hBN transformed very slowly to cBN without B2 O3 , in contrast to fast transformation with B2 O3 . It is thus found that the transformation from hBN to cBN in the presence of AIN catalyst is determined by the degree of BN crystallinity as well as the presence of B2 O3 . Cubic BN can be synthesized only from crystallized hBN under the experimental conditions used. The formation of cBN from amorphous BN is possible through its prior crystallization, which can occur in the presence of B2 O3 . 相似文献
10.
Koji Tsukuma Kuniyoshi Ueda Masahiko Shimada 《Journal of the American Ceramic Society》1985,68(1):4-C-5
Composites of Al2 O3 and Y2 O3 partially-stabilized ZrO2 were isostatically hot-pressed using submicrometer powders as the starting material. The addition of Al2 O3 resulted in a large increase in bending strength. The average bending strength for a composite containing 20 wt% Al2 O3 was 2400 MPa, and its fracture toughness was 17 MN·w−3/2 相似文献
11.
Tai-Il Mah Kristin A. Keller Sankar Sambasivan Ronald J. Kerans 《Journal of the American Ceramic Society》1997,80(4):874-878
Heat treatments in several environments were performed on a series of compounds in the Al2 O3 and Y2 O3 system: Al2 O3 Y3 Al5 O12 eutectic, Y3 Al5 O12 , YAlO3 , Y4 Al2 O9 , and Y2 O3 . The yttrium aluminates were found to be stable at high temperatures under vacuum and in air. However, when they were heat-treated under vacuum in proximity to SiC, degradation was observed. This was found to be primarily a result of carbothermal reduction. In a similarly reducing environment without Si, the yttrium aluminates, and Al2 O3 and Y2 O3 , all exhibited degradation by carbothermal reduction. Based upon the experimental results, a degradation mechanism for yttrium aluminates was proposed. 相似文献
12.
Sintering, crystallization, microstructure, and thermal expansion of Li2 O·Al2 O3 ·4SiO2 glass-ceramics doped with B2 O3 , P2 O5 , or (B2 O3 + P2 O5 ) have been investigated. On heating the glass powder compacts, the glassy phase first crystallized into high-quartz s.s., which transformed into β-spodumene after the crystallization process was essentially complete. The effects of dopants on the crystallization of glass to high-quartz s.s. and the subsequent transformation of high-quartz s.s. to β-spodumene were discussed. The major densification occurred only in the early stage of sintering time due to the rapid crystallization. All dopants were found to promote the densification of the glass powders. The effect of doping on the densification can fairly well be explained by the crystallization tendency. All samples heated to 950°C exhibited a negative coefficient of thermal expansion ranging from about −4.7 × 10-6 to −0.1 × 10-6 K-1 . Codoping of B2 O3 and P2 O5 resulted in the highest densification and an extremely low coefficient of thermal expansion. 相似文献
13.
The eutectic composition between Y4 Al2 O9 and Y2 O3 was determined using electron probe microanalysis (EPMA) on directionally solidified specimens with hypo- and hypereutectic compositions. The microstructures of the specimens as a function of composition differ considerably with small deviation from the eutectic composition (70.5 mol% Y2 O3 and 29.5 mol% Al2 O3 ). Based on the current results and other published data, the pseudobinary system between Al2 O3 and Y2 O3 is revised. 相似文献
14.
Koji Tsukuma 《Journal of the American Ceramic Society》2000,83(12):3219-3221
Composites of β-Ce2 O3 ·11Al2 O3 and tetragonal ZrO2 were fabricated by a reductive atmosphere sintering of mixed powders of CeO2 , ZrO2 (2 mol% Y2 O3 ), and Al2 O3 . The composites had microstructures composed of elongated grains of β-Ce2 O3 ·11Al2 O3 in a Y-TZP matrix. The β-Ce2 O3 ·11Al2 O3 decomposed to α-Al2 O3 and CeO2 by annealing at 1500°C for 1 h in oxygen. The elongated single grain of β-Ce2 O3 ·11Al2 O3 divided into several grains of α-Al2 O3 and ZrO2 doped with Y2 O3 and CeO2 . High-temperature bending strength of the oxygen-annealed α-Al2 O3 composite was comparable to the β-Ce2 O3 ·11Al2 O3 composite before annealing. 相似文献
15.
Koji Tsukuma Kuniyoshi Ueda Kenichi Matsushita Masahiko Shimada 《Journal of the American Ceramic Society》1985,68(2):56-C-
The temperature dependence of bending strength, fracture toughness, and Young's modulus of composite materials fabricated in the ZrO2 (Y2 O3 )-Al2 O3 system were examined. The addition of A1203 enhanced the high-temperature strength. Isostatically hot-pressed, 60 wt% ZrO2 (2 mol% Y2 O3 )/40 wt% Al2 O3 exhibited an extremely high strength, 1000 MPa, at 1000°C. 相似文献
16.
Refractory Y-α-SiAlON with elongated grain morphology was obtained by utilizing La2 O3 as a densification aid, which resulted in excellent room-temperature and high-temperature strength. Room-temperature strength of 1000 MPa was achieved when La2 O3 was augmented by adding Y2 O3 or removing AlN. With only La2 O3 , a temperature-independent strength of 800–950 MPa was maintained up to 1100°C, then gradually decreasing by 25% when reaching 1300°C. The R-curve measurements of fracture toughness showed relatively little dependence on microstructure, consistent with a strong interface that suppresses grain boundary decohesion. Compared with other densification aids such as SiO2 , Al2 O3 , Sc2 O3 , Y2 O3 , and Lu2 O3 , a finer microstructure was obtained by using La2 O3 . High nitrogen content in the residual La–Si–Al–O–N glass in equilibrium with the nitrogen-rich α-SiAlON is suggested to be the cause of these findings. 相似文献
17.
H.-J. Kleebe S. Lauterbach T. C. Shabalala M. Herrmann I. Sigalas 《Journal of the American Ceramic Society》2008,91(2):569-575
B6 O powders were hot pressed with and without Al2 O3 as a sintering additive at temperatures up to 1900°C and a pressure of 50 MPa. The microstructure of a doped and undoped sample was studied by transmission electron microscopy techniques. This paper aims at studying the correlation between micro/nanostructure evolution and the resulting mechanical properties; i.e., hardness and fracture toughness. The addition of alumina yields the formation of a secondary aluminum borate phase in addition to promoting grain growth strongly. While the addition of Al2 O3 slightly decreased the hardness of the B6 O polycrystals, the corresponding fracture toughness was strongly improved, as compared with the undoped material. 相似文献
18.
The fracture toughness of 3 mol% Y2 O3 -ZrO2 (3Y-PSZ) composites containing 10–30 vol% Al2 O3 with different particle sizes was investigated. It was found that Al2 O3 dispersion of up to 30 vol% increased the fracture toughness by 17% to 30%, and the toughness increase was more remarkable in the composite dispersed with Al2 O3 particles of larger sizes. By combining the effects of the dispersion toughening and phase transformation toughening, the toughness change in the present materials was theoretically predicted, which was in good agreement with the experimental data. 相似文献
19.
A. R. C. WESTWOOD N. H. MACMILLAN R. S. KALYONCU 《Journal of the American Ceramic Society》1973,56(5):258-262
The influences of water, toluene, and n -alcohols on the pendulum hardness of Al2 O3 monocrystals and on the ease of drilling of mono- and polycrystalline Al2 O3 were studied. Adsorption-induced increases in pendulum hardness were produced by certain alcohol environments; these increases resulted in rates of drilling with diamond-studded core bits of up to 10 times those measured under water. A correlation between pendulum hardness, machinability, and surface charge (as indicated by ζ-potential measurements) was established and revealed that Al2 O3 is hardest and most effectively drilled with a diamond core bit at its zero point of charge. The possible use of this correlation in developing more cost-effective and ecologically viable cutting fluids for the machining of Al2 O3 is discussed. 相似文献
20.
Yangyang Ji Jingkui Liang Zhan Chen Sishen Xie 《Journal of the American Ceramic Society》1991,74(2):444-446
The phase relations at a temperature below "subsolidus" in the system Al2 O3 –B2 O3 –Nd2 O3 are reported. Specimens were prepared from various compositions of Al2 O3 , B2 O3 , and Nd2 O3 of purity 99.5%, 99.99%, and 99.9%, respectively, and fired at 1100°C. There are six binary compounds and one ternary compound in this system. The ternary compound, NdAl3 (BO3 )4 (NAB), has a phase transition at 950°C ± 15°C. The high-temperature form of NAB has a second harmonic generation (SHG) efficiency of KH2 PO4 (KDP) of the order of magnitude of the form which has been used as a good self-activated laser material, and the low-temperature form of NAB has no SHG efficiency. 相似文献