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1.
Xudong Sun Ji-Guang Li Shiwen Guo Zhimeng Xiu Kai Duan Xiao Zhi Hu 《Journal of the American Ceramic Society》2005,88(6):1536-1543
Al2 O3 /SiC ceramic nanocomposites were fabricated from nanocrystalline Al2 O3 (10 nm in diameter) and SiC (15 nm in diameter) powders, and a theoretical model of intragranular particle residual stress strengthening was investigated. The SiC nanoparticles in the Al2 O3 grains create a normal compressive stress at the grain boundaries and a tangential tensile stress in the Al2 O3 grains, resulting in the "strengthening" of the grain boundaries and "weakening" of the grains. The model gives a good explanation of the experimental results of the authors and others which are difficult to be explained by the existing strengthening models, i.e. the maximum strength is normally achieved at about 5 vol% of SiC particles in the Al2 O3 –SiC ceramic nanocomposites. According to the model, there exists an optimum amount of SiC for strengthening, below which the grain boundaries are not fully "strengthened" and the fracture is mainly intergranular, above which the grains are "weakened" too much and the fracture is mainly transgranular, and at which the fracture is a mixture of intergranular and transgranular. 相似文献
2.
The fracture behavior of Al2 O3 /SiC nanocomposites has been studied as a function of the SiC volume fraction and compared to that of the pure Al2 O3 matrix. A pronounced strengthening effect was only observed for materials with low SiC content (i.e., ≤10 vol%) although no evidence of concurrent toughening was found. Assessment of near-tip crack opening displacement (COD) could not experimentally substantiate significant occurrence of an elastic crack-bridging mechanism, in contrast with a recently proposed literature model. Quantitative fractography analysis indicated that transgranular crack propagation in Al2 O3 /SiC nanocomposites depends on the location of the SiC dispersoids within the matrix texture; the higher the fraction of transgranularly located dispersoids, the more transgranular the fracture mode. Experimental evidence of remarkably high residual stresses arising from thermal dilatation mismatch (upon cooling) between Al2 O3 and SiC phases were obtained by fluorescence and Raman spectroscopy. A strengthening mechanism is invoked which merely arises from residual stress through strengthening of Al2 O3 grain boundaries. 相似文献
3.
Stefano Guicciardi Diletta Sciti Cesare Melandri Alida Bellosi 《Journal of the American Ceramic Society》2005,88(1):179-183
The wear behavior of a pure alumina matrix and two Al2 O3 -based composites, one with 5 vol% SiC nanosized particles (mean size 52 nm) and the other with 5 vol% SiC sub-microsized particles (mean size 230 nm), was studied in two different experimental conditions corresponding to mild and severe wear regime, respectively. Whether considering the friction or the wear resistance, in the mild regime no difference was observed among the materials. In the severe regime, the composites performed much better than the matrix alone due to stronger grain boundaries. The SiC particle size had no influence on the mean wear resistance. 相似文献
4.
Electroconductive Al2 O3 –NbN ceramic composites were prepared by hot pressing. Dense sintered bodies of ball-milled Al2 O3 –NbN composite powders were obtained at 1550°C and 30 MPa for 1 h under a nitrogen atmosphere. The bending strength and fracture toughness of the composites were enhanced by incorporating niobium nitride (NbN) particles into the Al2 O3 matrix. The electrical resistivity of the composites decreased with increasing amount of NbN phase. For a 25 vol% NbN–Al2 O3 composite, the values of bending strength, fracture toughness, Vickers hardness, and electrical resistivity were 444.2 MPa, 4.59 MPa·m1/2 , 16.62 GPa, and 1.72 × 10−2 Ω·cm, respectively, making the composite suitable for electrical discharge machining. 相似文献
5.
Hyun M. Jang Jong H. Moon Cheol W. Jang 《Journal of the American Ceramic Society》1992,75(12):3369-3376
Al2 O3 –ZrO2 –SiC whisker composites were prepared by surface-induced coating of the precursor for the ZrO2 phase on the kinetically stable colloid particles of Al2 O3 and SiC whisker. The fabricated composites were characterized by a uniform spatial distribution of ZrO2 and SiC whisker phases throughout the Al2 O3 matrix. The fracture toughness values of the Al2 O3 –15 vol% ZrO2 –20 vol% SiC whisker composites (∼12 MPa.m1/2 ) are substantially greater than those of comparable Al2 O3 –SiC whisker composites, indicating that both the toughening resulting from the process zone mechanism and that caused by the reinforced SiC whiskers work simultaneously in hot-pressed composites. 相似文献
6.
A. Mark Thompson Helen M. Chan Martin P. Harmer Robert E Cook 《Journal of the American Ceramic Society》1995,78(3):567-571
The crack-healing behavior of A12 O3 and Al2 O3 -SiC nanocomposite was studied using Vickers indentations to generate precracks. After annealing in argon for 2 h at 1300°C, radial cracks in the nanocomposite healed: The cracks closed and there was a small degree of rebonding in the vicinity of the crack tip. In contrast, radial cracks in alumina grew when exposed to the same annealing treatment. The different responses are attributed to the fracture mode and toughening mechanism in each material: In the nanocomposite, the cracks close as the residual stresses surrounding the indentations relax. Radial cracks open and grow in A12 O3 because microstructural toughening is diminished during heating to the annealing temperature. An implication is that strength-limiting machining flaws in these materials behave similarly, thereby accounting for the strengthening effect of annealing in this "nanocomposite" system. 相似文献
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8.
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
9.
Tanguy Rouxel Fumihiro Wakai Kansei Izaki 《Journal of the American Ceramic Society》1992,75(9):2363-2372
Si3 N4 /SiC composites are ceramic materials that exhibit excellent performance for high-temperature applications. Prepared from an ultrafine amorphous Si-C-N powder, sintered materials are constituted mainly of a β -Si3 N4 matrix with SiC inclusions and have a very small grain size (less than 1 μm). Such a microstructure is propitious for superplastic forming. Superplasticity has been studied in tension, from 1550° to 1650°C, under nitrogen atmosphere. Elongations over 100% have been achieved. In many cases, at the highest temperatures and slowest strain rates, materials are damaged by different processes, including microcracking, cavitation, and chemical decomposition. A map of the most suitable (strain-rate/temperature) domain has been established. It allows the prevention of any structural alteration by selecting carefully the testing conditions. Since specimens suffered considerable strain-induced hardening, sources for this phenomenon are examined. Although the experiments have involved high temperature and extensive strain, neither static nor dynamic grain growth has occurred. Crystallization of the amorphous grain-boundary phase, which is reported in most cases, may be invoked. However, based on microstructural observations, it is not the unique origin for flow hardening. 相似文献
10.
Subsolidus phase relationships in the Ga2 O3 –Al2 O3 –TiO2 system at 1400°C were studied using X-ray diffraction. Phases present in the pseudoternary system include TiO2 (rutile), Ga2−2 x Al2 x O3 ( x ≤0.78 β-gallia structure), Al2−2 y Ga2 y O3 ( y ≤0.12 corundum structure), Ga2−2 x Al2 x TiO5 (0≤ x ≤1 pseudobrookite structure), and several β-gallia rutile intergrowths that can be expressed as Ga4−4 x Al4 x Ti n −4 O2 n −2 ( x ≤0.3, 15≤ n ≤33). This study showed no evidence to confirm that aluminum substitution of gallium stabilizes the n =7 β-gallia–rutile intergrowth as has been mentioned in previous work. 相似文献
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12.
Lianjun Wang Ting Wu Wan Jiang Jianlin Li Lidong Chen 《Journal of the American Ceramic Society》2006,89(5):1540-1543
A novel method for the preparation of Al2 O3 –TiN nanocomposites was developed. A mixture of TiO2 , AlN, and Ti powder was used as the starting material to synthesize the Al2 O3 –TiN nanocomposite under 60 MPa at 1400°C for 6 min using spark plasma sintering. X-ray diffractometry, scanning electron microscopy, and transmission electron microscopy were used for detailed microstructural analysis. Dense (up to 99%) nanostructured Al2 O3 –TiN composites were successfully fabricated, the average grain size being less than 400 nm. The fracture toughness ( K I C ) and bending strength (σb ) of the nanostructured Al2 O3 –TiN composites reached 4.22±0.20 MPa·m1/2 and 746±28 MPa, respectively. 相似文献
13.
Yung-Chao Ko 《Journal of the American Ceramic Society》2000,83(9):2333-2335
The XRD patterns at ambient temperature and at 1500°C showed that the spinel in the Al2 O3 –MgO castables fired at 1500°C for 3 h has the higher peak intensity, compared to those in Al2 O3 –spinel castables; the interplanar distance in the set (311) is 2.43 Å for the spinel in Al2 O3 –MgO castables as well as the spinels in Al2 O3 –spinel castables using spinels containing 73, 90, and 94 wt% Al2 O3 , respectively. The corresponding alumina contents of the spinels in these castables were estimated to be around 75 wt%. The smaller grain size of the spinel in Al2 O3 –MgO castables compared to that in Al2 O3 –spinel castables is evidenced by the recrystallization of the in situ spinel only occurring in Al2 O3 –MgO castables as revealed by the XRD patterns at ambient temperature and at 1500°C. The larger amount and smaller grain size of the in situ spinel in the matrix mostly account for the better slag resistance of Al2 O3 –MgO castables, compared to Al2 O3 –spinel castables. 相似文献
14.
Takayuki Nagano Hui Gu Kenji Kaneko Guo-Dong Zhan Mamoru Mitomo 《Journal of the American Ceramic Society》2001,84(9):2045-2050
Nanocrystalline β-SiC with additions of 7 wt% Al2 O3 , 2 wt% Y2 O3 , and 1 wt% CaO was subjected to tensile deformation to study its microstructural behavior under the dynamic process. The liquid-phase-sintered body had a relative density of >97% and an average grain size of 170 nm. Tension tests were conducted at initial strain rates ranging from 2 × 10−5 to 5 × 10−4 s−1 , in the temperature range 1973–2023 K, in both argon and N2 atmospheres. Although grain-boundary liquids formed by the additions vaporized concurrently with the decomposition of SiC and extensive grain growth, the maximum tensile elongation of 48% was achieved in argon. Annealing experiments under the same conditions revealed that vaporization and grain growth were both dependent on experimental time. Therefore, high strain rates suffered less from the hardening effect when cavitation damage was more severe. Testing in an N2 atmosphere brought about crystallization of the grain-boundary phase and prevented severe vaporization; however, fracture occurred at only 8% elongation. Grain-boundary sliding was still the dominant mechanism for deformation. 相似文献
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16.
Mikio Fukuhara 《Journal of the American Ceramic Society》1989,72(2):236-242
The effect of Al2 O3 and (Ti or Si)C additions on various properties of a (Y)TZP (yttria-stabilized tetragonal zirconia polycrystal)–Al2 O3 –(Ti or Si)C ternary composite ceramic were investigated for developing a zirconia-based ceramic stronger than SiC at high temperatures. Adding Al2 O3 to (Y)TZP improved transverse rupture strength and hardness but decreased fracture toughness. This binary composite ceramic revealed a rapid loss of strength with increasing temperature. Adding TiC to the binary ceramic suppressed the decrease in strength at temperatures above 1573 K. The residual tensile stress induced by the differential thermal expansion between ZrO2 and TiC therefore must have inhibited the t - → m -ZrO2 martensitic transformation. It was concluded that a continuous skeleton of TiC prevented grain-boundary sliding between ZrO2 and Al2 O3 . In contrast, for the ternary material containing β-SiC in place of TiC, the strength decreased substantially with increasing temperature because of incomplete formation of the SiC skeleton. 相似文献
17.
A method is proposed to prepare Al2 O3 -AlN-Ni composites. The composites are prepared by sintering Al2 O3 /NiAl powder mixtures at 1600°C in a mixture of nitrogen and carbon monoxide. The presence of NiAl particles raises the green density of Al2 O3 /NiAl powder compacts. During sintering, NiAl reacts with nitrogen to form AlN and Ni inclusions. A volume expansion accompanies the reaction. Because of the high green density and the reaction, the volume shrinkage of the Al2 O3 -AlN-Ni composite decreases with the increase of added NiAl content. 相似文献
18.
Cristina Siligardi Luca Lusvarghi Monia Montorsi Cecilia Vernia 《Journal of the American Ceramic Society》2008,91(3):990-995
In this work several complementary techniques have been employed to carefully characterize the sintering and crystallization behavior of CaO–Al2 O3 –ZrO2 –SiO2 glass powder compacts after different heat treatments. The research started from a new base glass 33.69 CaO–1.00 Al2 O3 –7.68 ZrO2 –55.43SiO2 (mol%) to which 5 and 10 mol% Al2 O3 were added. The glasses with higher amounts of alumina sintered at higher temperatures (953°C [lower amount] vs. 987°C [higher amount]). A combination of the linear shrinkage and viscosity data allowed to easily find the viscosity values corresponding to the beginning and the end of the sintering process. Anorthite and wollastonite crystals formed in the sintered samples, especially at lower temperatures. At higher temperatures, a new crystalline phase containing ZrO2 (2CaO·4SiO2 ·ZrO2 ) appeared in all studied specimens. 相似文献
19.
Yury G. Gogotsi Franz Porz Viktor P. Yaroshenko 《Journal of the American Ceramic Society》1992,75(8):2251-2259
The study examines the effect which the composition of hot-pressed electroconductive ceramics has on their structure, mechanical properties, and oxidation behavior, for ceramics of the type AIN–Al2 O3 –42 wt% TiN, differing in the AIN/Al2 O3 ratio. The results are physico-mechanical property data, including density, hardness, strength, fracture toughness, and wear resistance. A correlation was found between the wear resistance and fracture toughness. The analysis of oxidation products revealed the formation of α-Al2 O3 and rutile in the temperature range from 600° to 1100°C and aluminum titanate above 1200°C. The spallation of the oxide layer caused low oxidation resistance of Al2 O3 -rich composites above 1250°C. The oxidation of composites was compared with the oxidation of pure TiN. The relationship is discussed between material properties, composition, phases, and processing parameters. 相似文献
20.
Daniele Mazza Mario Vallino Guido Busca 《Journal of the American Ceramic Society》1992,75(7):1929-1934
A morphous solids belonging to the systems Al2 O3 –Me2 O (Me = Na, K) and Al2 O3 –B2 O3 were prepared by nitrate decomposition, introducing boron in the form of boric acid. Crystalline metastable solids with pseudotetragonal symmetry were obtained from thermal treatment at 850° to 900°C for the compositions Al6 Mex O(9+0.5 x ) ( x ≅ 1; Me = Na, K) and Al6- x B x O9 (1 x 3). The resultant solids were stable only within a difinite temperature range and transformed, with further treatment increases, into stable equilibrium phases. The structures of the metastable phases were examined by X-ray diffraction and Fourier transform infrared spectroscopy, and both analyses showed a mullite type of framework, inside of which the atomic coordinates were refined in the Pbam (no. 55) space group. The present results indicate that these silica-free mullite structures are stabilized by two different mechanisms: (1) interstitial occupation of bulky cations (Na+ , K+ ) or (2) substitution of B for Al in some of the tetrahedral positions. 相似文献