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1.
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
2.
Processing and Properties of Intermetallic/Ceramic Composites with Interpenetrating Microstructure 总被引:3,自引:0,他引:3
Thomas Klassen Robert Günther Birte Dickau Frank Gärtner Arno Bartels Rüdiger Bormann Heinrich Mecking 《Journal of the American Ceramic Society》1998,81(9):2504-2506
Intermetallic/ceramic composites represent an interesting class of materials for high-temperature structural and functional applications. These materials can be prepared via high-energy milling of pure metals with Al2 O3 as well as of aluminum with metal oxides. During subsequent compaction via pressureless sintering, the components react to form dense composites that consist of interpenetrating networks of the ceramic and intermetallic phases. Microstructural investigations, mechanical properties, and resistivity and wear resistance measurements of selected composites are presented. Improved fracture toughness and bending strength, with respect to monolithic Al2 O3 , have been achieved. 相似文献
3.
Yoshiyuki Yasutomi Akio Chiba Masahisa Sobue 《Journal of the American Ceramic Society》1991,74(5):950-957
Reaction-bonded Si3 N4 · TiN and Si3 N4 · Al2 O3 composites were successfully fabricated by heating mixed powder compacts of Si and TiN or Si and Al2 O3 in a nitrogen atmosphere. The former showed electrical conductivity, owing to the presence of TiN. An electrical resistivity of 2.6 × 10−5 Ω· m was obtained for the Si3 N4 · TiN composite with 70 vol% TiN. The composite with 20 vol% TiN showed an electrical resistivity of 0.22 Ω· m and a bending strength of 460 MPa. On the other hand, the Si3 N4 · Al2 O3 composite had insulating properties. The use of an appropriate amount of resin binder resulted in a higher green density and, consequently, a higher bending strength. Moreover, electroconductive Si3 N4 · TiN/resistive Si3 N4 · Al2 O3 complex ceramics could be fabricated by heating green compacts composed of two different portions, one composed of mixed powders of Si and TiN and the other of Si and Al2 O3 . Attainment of such complex ceramics was attributed to the small dimensional change at the nitriding stage, under 0.3% and the similarity of the thermal expansion coefficients of the two composites. 相似文献
4.
Phase relations in the system Na2 O· Al2 O3 -CaO· Al2 O3 -Al2 O3 at 1200°C in air were determined using the quenching method and high-temperature X-ray diffraction. The compound 2Na2 O · 3CaO · 5Al2 O3 , known from the literature, was reformulated as Na2 O · CaO · 2Al2 O3 . A new compound with the probable composition Na2 O · 3CaO · 8Al2 O3 was found. Cell parameters of both compounds were determined. The compound Na2 O · CaO-2Al2 O3 is tetragonal with a = 1.04348(24) and c = 0.72539(31) nm; it forms solid solutions with Na2 O · Al2 O3 up to 38 mol% Na2 O at 1200°C. The compound Na2 O · 3CaO · 8Al2 O3 is hexagonal with) a = 0.98436(4) and c = 0.69415(4) nm. The compound CaO · 6Al2 O3 is not initially formed from oxide components at 1200°C but behaves as an equilibrium phase when it is formed separately at higher temperatures. The very slow transformation kinetics between β and β "-Al2 O3 make it very difficult to determine equilibrium phase relations in the high-Al2 O3 part of the diagram. Conclusions as to lifetime processes in high-pressure sodium discharge lamps can be drawn from the phase diagram. 相似文献
5.
James J. Hansen Raymond A. Cutler Dinesh K. Shetty Anil V. Virkar 《Journal of the American Ceramic Society》1988,71(12):501-C
Indentation fracture behavior of three-layer Al2 O3 -ZrO2 composites with substantial compressive residual stresses was compared with the behaviors of monolithic Al2 O3 and Al2 O3 -ZrO2 ceramics without intentionally introduced residual stresses. The indentation cracks were smaller in the three-layer specimens relative to the monolithic specimens in agreement with the predictions of indentation fracture mechanics theory. Indentation and strength testing were used to show that a residual compressive stress of approximately 500 MPa exists in the outer layers of the three-layer composites. The three-layer specimens showed excellent damage resistance in that the strength differential between the three-layer and monolithic indented specimens was maintained at indentation loads up to 1000 N, the maximum indentation load used in the experiments. 相似文献
6.
Fabrication and Microstructure of Al2 O3 –SiC–YAG Hybrid Composites Prepared by Particulate Dispersion
Stable Al2 O3 –SiC–YAG hybrid composites were successfully fabricated by reaction of Al2 O3 and Y2 O3 and incorporation of SiC. The hot-pressed bodies consisted of uniformly dispersed grains of microsized YAG particulates and nanosized SiC particulates in an Al2 O3 matrix. Although the grain size of monolithic A12 O3 increases markedly with increased temperature, the grain size of the Al2 O3 –SiC–YAG hybrid composites was effectively restrained due to grain-boundary pinning by the particulates. 相似文献
7.
Pressureless Sintering of Alumina-Titanium Carbide Composites 总被引:3,自引:0,他引:3
The densification of Al2 O3 -TiC composites is detrimentally affected by chemical reactions between Al2 O3 and TiC. These reactions must be suppressed in order to promote sintering. In this study, the specific reactions occurring in Al2 O3 -TiC composites were modeled, using thermodynamic calculations, and verified by experiments. The reaction between Al2 O3 and TiC was suppressed by the use of specially prepared embedding powders allowing pressureless sintering to closed porosity. The Al2 O3 -TiC composites were subsequently hot isostatically pressed to > 99% of theoretical density without encapsulation. Typical flexural strength and fracture toughness of Al2 O3 -30 wt% TiC composites were 690 MPa and 4.3 MPa · m1/2 , respectively. 相似文献
8.
An electroconductive TiN/Al2 O3 nanocomposite was prepared by a selective matrix grain growth method, using a powder mixture of submicrosized α-Al2 O3 , nanosized γ-Al2 O3 , and TiN nanoparticles synthesized through an in situ nitridation process. During sintering, a self-concentration of TiN nanoparticles at the matrix grain boundary occurred, as a result of the selective growth of large α-Al2 O3 matrix grains. Under suitable sintering conditions, a typical interlayer nanostructure with a continuous nanosized TiN interlayer was formed along the Al2 O3 matrix grain boundary, and the electroconducting behavior of the material was significantly improved. Twelve volume percent TiN/Al2 O3 nanocomposite with such an interlayer nanostructure showed an unprecedentedly low resistivity of 8 × 10−3 Ω·cm, which was more than two orders lower than the TiN/Al2 O3 nanocomposite without such an interlayer nanostructure. 相似文献
9.
The composite sol—gel (CSG) technology has been utilized to process SiC—Al2 O3 ceramic/ceramic particulate reinforced composites with a high content of SiC (up to 50 vol%). Alumina sol, resulting from hydrolysis of aluminum isopropoxide, has been utilized as a dispersant and sintering additive. Microstructures of the composites (investigated using TEM) show the sol-originating phase present at grain boundaries, in particular at triple junctions, irrespective of the type of grain (i.e., SiC or Al2 O3 ). It is hypothesized that the alumina film originating from the alumina sol reacts with SiO2 film on the surface of SiC grains to form mullite or alumina-rich mullite-glass mixed phase. Effectively, SiC particles interconnect through this phase, facilitating formation of a dense body even at very high SiC content. Comparative sinterability studies were performed on similar SiC—Al2 O3 compositions free of alumina sol. It appears that in these systems the large fraction of directly contacting SiC—SiC grains prevents full densification of the composite. The microhardness of SiC—Al2 O3 sol—gel composites has been measured as a function of the content of SiC and sintering temperature. The highest microhardness of 22.9 GPa has been obtained for the composition 50 vol% SiC—50 vol% Al2 O3 , sintered at 1850°C. 相似文献
10.
Influence of Residual Stresses on the Wear Behavior of Alumina/Alumina–Zirconia Laminated Composites
Francesco Toschi Cesare Melandri Paola Pinasco Edoardo Roncari Stefano Guicciardi Goffredo de Portu 《Journal of the American Ceramic Society》2003,86(9):1547-1553
Symmetric structures of laminated ceramic composites were produced by superimposing alternating layers of Al2 O3 and Al2 O3 /ZrO2 composite prepared by tape casting. The composites were designed to have an alumina surface layer on either side. This configuration caused residual compressive stresses to be induced on the surface due to the different thermal expansion coefficients of the various layers, leading to an increase in the apparent surface toughness. The amount of residual stress was determined using the indentation technique. The tribological behavior of these laminated structures was evaluated using the pin-on-disk method for different loads and sliding speeds. Comparison with the results obtained from stress-free alumina showed that, within the range of these experimental conditions, the improvement in surface toughness leads to a reduced friction coefficient and increased wear resistance of the composites. Possible wear mechanisms are proposed. 相似文献
11.
Ken-ichi Tajima † Hae Jin Hwang Mutsuo Sando Koichi Niihara 《Journal of the American Ceramic Society》2000,83(3):651-653
Hard lead zirconate titanate (PZT) and PZT/Al2 O3 composites were prepared and the alternating-electric-field-induced crack growth behavior of a precrack above the coercive field was evaluated via optical and scanning electron microscopy. The crack extension in the 1.0 vol% Al2 O3 composite was significantly smaller than that in monolithic PZT and the 0.5 vol% Al2 O3 composite. Secondary-phase Al2 O3 dispersoids were found both at grain boundaries and within grains in the composites. A large number of dispersoids were observed at the grain boundaries in the 1.0 vol% Al2 O3 composite. It appears that the Al2 O3 dispersoids reinforce the grain boundaries of the PZT matrix as well as act as effective pins against microcrack propagation. 相似文献
12.
Crack Bifurcation in Laminar Ceramic Composites 总被引:2,自引:0,他引:2
Matthias Oechsner Craig Hillman Fred F. Lange 《Journal of the American Ceramic Society》1996,79(7):1834-1838
Crack bifurcation was observed in laminar ceramic composites when cracks entered thin Al2 O3 layers sandwiched between thicker layers of Zr(12Ce)O2 . The Al2 O3 layers contained a biaxial, residual, compressive stress of ∼2 GPa developed due to differential contraction upon cooling from the processing temperature. The Zr(12Ce)O2 layers were nearly free of residual, tensile stresses because they were much thicker than the Al2 O3 layers. The ceramic composites were fabricated by a green tape and codensification method. Different specimens were fabricated to examine the effect of the thickness of the Al2 O3 layer on the bifurcation phenomena. Bar specimens were fractured in four-point bending. When the propagating crack encountered the Al2 O3 layer, it bifurcated as it approached the Zr(12Ce)O2 / Al2 O3 interface. After the crack bifurcated, it continued to propagate close to the center line of the Al2 O3 layer. Fracture of the laminate continued after the primary crack reinitiated to propagate through the next Zr(12Ce)O2 layer, where it bifurcated again as it entered the next Al2 O3 layer. If the loading was stopped during bifurcation, the specimen could be unloaded prior to complete fracture. Although the residual stresses were nearly identical in all Al2 O3 layers, crack bifurcation was observed only when the layer thickness was greater than ∼70 μm. 相似文献
13.
Weizhong Gu John R. Porter Terence G. Langdon 《Journal of the American Ceramic Society》1994,77(6):1679-1681
Experiments were conducted on monolithic Al2 O3 and Al2 O3 composites reinforced with SiC-whiskers in which the load was removed during high-temperature creep. The monolithic material exhibited no anelastic recovery on load removal, but the composites showed a significant anelastic recovery which was reproducible and essentially independent of the total creep strain at which the load was removed. The results were consistent with the hypothesis that an interconnecting whisker network may develop during processing of the composites. 相似文献
14.
Kai Hui Zuo Dong Liang Jiang Qing Ling Lin 《Journal of the American Ceramic Society》2005,88(9):2659-2661
Tape casting and electroless plating were used to fabricate Al2 O3 /Ni laminar ceramic composites with close control of the thickness of the Al2 O3 and Ni layers. Ninety-seven percent relative density, macrodefect-free composites were obtained by spark plasma sintering. In electroless plating solutions, the stable potential of grain boundary led to the first deposition of nickel on the grain boundary of Al2 O3 . Scanning electron microscopy, energy-dispersive X-ray, and X-ray diffraction were used to analyze the structure, elements distribution, and phase composition of the Al2 O3 /Ni laminar composites. 相似文献
15.
Jun Yoshikawa Yuji Katsuda Naohito Yamada Chikashi Ihara Masaaki Masuda Hiroaki Sakai 《Journal of the American Ceramic Society》2005,88(12):3501-3506
The phase composition, microstructure, and electrical resistivity of hot-pressed AlN ceramics with 0–4.8 wt% Sm2 O3 additive were investigated. The phase composition was approximately consistent with that estimated from the Sm2 O3 –Al2 O3 phase diagram using the amount of added Sm2 O3 and oxygen content of the AlN raw material. When sintered at more than 1800°C, the AlN ceramics with 1.0–2.9 wt% Sm2 O3 additive contained an Sm-β-alumina phase wetting the grain boundaries, and their electrical resistivity considerably decreased to 1010 –1012 Ω·cm. This resistivity decrease was caused by the continuity of the Sm-β-alumina phase with a resistivity lower than that of bulk AlN. 相似文献
16.
Paste samples of tricalcium aluminate alone, with CaCl2 , with gypsum, and with gypsum and CaCl2 were hydrated for up to 6 months and the hydration products characterized by SEM, XRD, and DTA. Tricalcium aluminate hydrated initially to a hexagonal hydroaluminate phase which then changed to the cubic form; the transformation rate depended on the size and shape of the sample and on temperature. The addition of CaCl2 to tricalcium aluminate resulted in the formation of 3CaO · Al2 O3 · CaCl2 ·10H2 O and 4CaO · Al2 O3 · 13H2 O, or a solid solution of the two. The chloride retarded the formation of the cubic phase 3CaO · Al2 O3 · 6H2 O; the addition of gypsum resulted in the formation of monosulfoaluminate with a minor amount of ettringite. When chloride was added to tricalcium aluminate and gypsum, more ettringite was formed, although 3CaO · Al2 O3 · CaSO4 · 12H2 O and 3CaO · Al2 O3 · CaCl2 · 10H2 O were the main hydration products. 相似文献
17.
Synthesis of Novel Niobium Aluminide-Based Composites 总被引:5,自引:0,他引:5
Daniel E. Garcia Silvia Schicker Jorn Bruhn Rolf Janssen Nils Claussen 《Journal of the American Ceramic Society》1997,80(9):2248-2252
A reactive sintering process has been used to produce almost fully dense composites with interpenetrating networks of NbAl3 and Al2 O3 . The process involves the reaction synthesis of niobium aluminides and Al2 O3 from compacts of intensively milled aluminum and Nb2 O5 powder mixtures. During carefully controlled heating under an inert atmosphere, the oxide reduction by aluminum to form niobium aluminides and Al2 O3 proceeds at temperatures below the melting point of aluminum. At temperatures of >1000°C, the reaction-formed niobium aluminides and Al2 O3 sinter. The present paper discusses processing parameters, such as attrition milling, the heating cycle, and the metal:ceramic ratio in the starting mixture, that control microstructure development and mechanical properties. 相似文献
18.
19.
Debonding in Multilayered Composites of Zirconia and LaPO4 总被引:4,自引:0,他引:4
David B. Marshall Peter E. D. Morgan Robert M. Housley 《Journal of the American Ceramic Society》1997,80(7):1677-1683
Multilayered composites consisting of LaPO4 (La-monazite) layers alternating with various ZrO2 -based materials were fabricated to investigate whether LaPO4 provides a weakly bonded interface suitable for promoting toughening, as previously observed in the system LaPO4 /Al2 O3 . The following ZrO2 -based materials were assessed: Y-ZrO2 , Y-ZrO2 /Al2 O3 , Ce-ZrO2 , and Ce-ZrO2 /Al2 O3 . Debonding was observed in all cases. The composites containing Y-ZrO2 and Y-ZrO2 /Al2 O3 were stable, with no reactions, at temperatures up to at least 1600°C. However, in the composites containing Ce-ZrO2 , interdiffusion of Ce and La occurred, resulting in formation of a pyrochlore-like phase and, in the case of the Ce-ZrO2 /Al2 O3 composite, a (Ce,La)Al11 O18 magnetoplumbite phase. 相似文献
20.
Jingguo Li Lian Gao Jingkun Guo Dongsheng Yan 《Journal of the American Ceramic Society》2002,85(3):724-726
A novel method for the preparation of TiN–Al2 O3 nanocomposites was developed. TiN–Al2 O3 nanocomposite powders were prepared by the direct nitridation of TiO2 –Al2 O3 nanocomposite powders that were derived from the simultaneous hydrolysis of tetra-butyl titanate and precipitation of aluminum nitrate. Dense sintered bodies of these TiN–Al2 O3 nanocomposite powders were obtained by hot pressing at 1450°–1650°C and 30 MPa for 60 min. The resistivity of nanocomposite reaches a minimum (1.5 × 10−3 Ω·cm) at 25 vol% TiN additions. The percolation concentration of nanocomposite is ∼10 vol% TiN. 相似文献