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1.
The energetics of martensitic transformation in ZrO2 is studied using a thermodynamic approach, with particular reference to Al2 O3 –ZrO2 composites. The different characters of three types of transformation-toughened ceramics are analyzed, and several factors affecting the t → m transformation in Al2 O3 –ZrO2 composites are discussed. The expression of transformation temperature dependence on particle size is derived and has good agreement with experimental results. The energetics concerned with nucleation of martensitic transformation is also discussed. 相似文献
2.
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
3.
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
4.
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
5.
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
6.
Alex Spring Wei-Ming Guo Guo-Jun Zhang Pei-Ling Wang Vladimir D. Krstic 《Journal of the American Ceramic Society》2008,91(8):2763-2765
ZrB2 –LaB6 powder was obtained by reactive synthesis using ZrO2 , La2 O3 , B4 C, and carbon powders. Then ZrB2 –20 vol% SiC–10 vol% LaB6 (ZSL) ceramics were prepared from commercially available SiC and the synthesized ZrB2 –LaB6 powder via hot pressing at 2000°C. The phase composition, microstructure, and mechanical properties were characterized. Results showed that both LaB6 and SiC were uniformly distributed in the ZrB2 matrix. The hardness and bending strength of ZSL were 17.06±0.52 GPa and 505.8±17.9 MPa, respectively. Fracture toughness was 5.7±0.39 MPa·m1/2 , which is significantly higher than that reported for ZrB2 –20 vol% SiC ceramics, due to enhanced crack deflection and crack bridging near SiC particles. 相似文献
7.
Philippe Boch Thierry Chartier Muriel Huttepain 《Journal of the American Ceramic Society》1986,69(8):191-C
Fracture toughness of ZrO2 -toughened alumina could he increased by macroscopic interfaces, such as those existing in laminated composites. In this work, tape casting was used to produce A/A or A/B laminates, where A and B can be Al2 O3 , Al2 O3 /5 vol% ZrO2 , and Al2 O3 /l0 vol% ZrO2 . An increase of toughness is observed, even in the Al2 O3 /Al2 O3 laminates. 相似文献
8.
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
9.
Yu Jia Yuji Hotta Kimiyasu Sato Koji Watari 《Journal of the American Ceramic Society》2006,89(3):1103-1106
ZrO2 –Al2 O3 nanocomposite particles were synthesized by coating nano-ZrO2 particles on the surface of Al2 O3 particles via the layer-by-layer (LBL) method. Polyacrylic acid (PAA) adsorption successfully modified the Al2 O3 surface charge. Multilayer coating was successfully implemented, which was characterized by ξ potential, particle size. X-ray diffraction patterns showed that the content of ZrO2 in the final powders could be well controlled by the LBL method. The powders coated with three layers of nano-ZrO2 particles, which contained about 12 wt% ZrO2 , were compacted by dry press and cold isostatically pressed methods. After sintering the compact at 1450°C for 2 h under atmosphere, a sintered body with a low pore microstructure was obtained. Scanning electron microscopy micrographs of the sintered body indicated that ZrO2 was well dispersed in the Al2 O3 matrix. 相似文献
10.
Ana M. Espino Luis A. Díaz Adolfo Fernández Ramón Torrecillas José S. Moya 《Journal of the American Ceramic Society》2005,88(4):1000-1003
The wettability of binary and ternary glasses belonging to SiO2 –Al2 O3 –ZrO2 diagram has been studied using the sessile drop technique at 1750° and 1800°C. The ternary SiO2 –Al2 O3 –ZrO2 (90–5–5 wt%) glass has proved to be well appropriated as a molybdenum oxidation barrier coating. The addition of 5 wt% of MoO2 slightly improves its wettablity at higher temperatures without affecting its oxidation barrier properties. The Mo comes into the glass network as a mixture of Mo5+ , Mo4+ , and Mo6+ . After oxidation at 1000°C in oxygen atmosphere, the molybdenum remains in the glass network as Mo6+ . 相似文献
11.
The effect of SiC concentration on the liquid and solid oxide phases formed during oxidation of ZrB2 –SiC composites is investigated. Oxide-scale features called convection cells are formed from liquid and solid oxide reaction products upon oxidation of the ZrB2 –SiC composites. These convection cells form in the outermost borosilicate oxide film of the oxide scale formed on the ZrB2 –SiC during oxidation at high temperatures (≥1500°C). In this study, three ZrB2 –SiC composites with different amounts of SiC were tested at 1550°C for various durations of time to study the effect of the SiC concentration particularly on the formation of the convection cell features. A calculated ternary phase diagram of a ZrO2 –SiO2 –B2 O3 (BSZ) system was used for interpretation of the results. The convection cells formed during oxidation were fewer and less uniformly distributed for composites with a higher SiC concentration. This is because the convection cells are formed from ZrO2 precipitates from a BSZ oxide liquid that forms upon oxidation of the composite at 1550°C. Higher SiC-containing composites will have less dissolved ZrO2 because they have less B2 O3 , which results in a smaller amount of precipitated ZrO2 and consequently fewer convection cells. 相似文献
12.
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
13.
Ling-Feng He Yi-Wang Bao Yan-Chun Zhou 《Journal of the American Ceramic Society》2009,92(11):2751-2758
ZrO2 –Al2 O3 nanocrystalline powders have been synthesized by oxidizing ternary Zr2 Al3 C4 powders. The simultaneous oxidation of Al and Zr in Zr2 Al3 C4 results in homogeneous mixture of ZrO2 and Al2 O3 at nanoscale. Bulk nano- and submicro-composites were prepared by hot-pressing as-oxidized powders at 1100°–1500°C. The composition and microstructure evolution during sintering was investigated by XRD, Raman spectroscopy, SEM, and TEM. The crystallite size of ZrO2 in the composites increased from 7.5 nm for as-oxidized powders to about 0.5 μm at 1500°C, while the tetragonal polymorph gradually converted to monolithic one with increasing crystallite size. The Al2 O3 in the composites transformed from an amorphous phase in as oxidized powders to θ phase at 1100°C and α phase at higher temperatures. The hardness of the composite increased from 2.0 GPa at 1100°C to 13.5 GPa at 1400°C due to the increase of density. 相似文献
14.
William G. Fahrenholtz Donald T. Ellerby Ronald E. Loehman 《Journal of the American Ceramic Society》2000,83(5):1279-1280
Al2 O3 –Ni composites were prepared by the reactive hot pressing of Al and NiO. The composites had a two-phase, interpenetrating microstructure and contained ∼35 vol% Ni. They exhibited an impressively high combination of strength and toughness at room temperature; the four-point bending strength was in excess of 600 MPa with a fracture toughness of more than 12 MPa·m1/2 . Examination of fracture surfaces showed that Ni ligaments underwent ductile deformation during fracture. SEM analysis revealed knife-edged Ni ligaments with a limited amount of debonding around their periphery (i.e., at the Ni–Al2 O3 interface), indicating a strong Ni–Al2 O3 bond. 相似文献
15.
Khalil Abdelrazek Khalil Sug Won Kim 《International Journal of Applied Ceramic Technology》2006,3(4):322-330
High-frequency induction heat sintering (HFIHS) is a comparatively new technique that consolidates metals and ceramics very rapidly to full density. In this work, superfast densification behavior and the attendant microstructural features of Al2 O3 –(ZrO2 +8% mol Y2 O3 ) composites processed by HFIHS were investigated. The effects of processing parameters such as sintering temperatures, pressures, and heating rate, on the mechanical and microstructural properties were studied. The results indicated that HFIHS was effective in the preparation of fine-grained, nearly fully dense Al2 O3 –8YSZ ceramics from the powder with a smaller particle size by optimizing the overall processing parameters. 相似文献
16.
The fracture strengths of sintered Al2 O3 containing 20 and 40 vol% ZrO2 (12 mol% CeO2 )—zirconia-toughened alumina (ZTA)—composites along with the fracture resistance can be increased (e.g., to ∼900 MPa and >12 Mpa·m1/2 , respectively), by increasing the mean grain size of the t -ZrO2 (and the Al2 O3 ) from ∼0.5 μm to ∼3 μm. At these lower t -ZrO2 contents, the fracture strength-fracture resistance curves show a continuous rise as opposed to the strength maxima observed in polycrystalline t -ZrO2 (12 mol% CeO2 ), CeTZP, and ZrO2 (12 mol% CeO2 ) ceramics containing ≤20 vol% Al2 O3 . The toughened composites also exhibit excellent damage resistance with fracture strengths of 500 MPa retained with surfaces containing ∼150- N Vickers indentations which produce cracks of ∼160-μm radius. Greater damage resistance correlates with an increase in the apparent R -curve response of these composites. 相似文献
17.
DAVID J. GREEN 《Journal of the American Ceramic Society》1982,65(12):610-614
The internal strains asSociated with the martensitic phase transformation of zirconia were used to introduce microcracks into Al2 O3 /ZrO2 composites. The degree of transformation was found to be dependent on the volume fraction of ZrO2 and its size, the latter of which could be controlled by suitable heat treatments. The microstructural changes that occurred during the heat treatments were studied using quantitative microscopy and X-ray diffraction. For materials containing more than 7.5 vol% Zr02 , the ZrO2 particles were found to pin the Al2 O3 grain boundaries, thus limiting the Al2 O3 grain growth. The limiting grain size was found to be dependent on size and volume fraction of ZrO2 . Heat treatments for the higher volume fraction materials (>7.5 vol% ZrO2 ) caused micro-structural changes which resulted in increased amounts of monoclinic ZrO2 at room temperature; elastic modulus measurements indicated that this was occurring concurrently with microcracking. By combining the ZrO2 grain-size distributions with the X-ray analysis it was possible to calculate the critical ZrO2 size required for the transformation. The critical size was found to decrease with increasing amounts of ZrO2 . Hardness and indentation fracture toughness were measured on the composites. Grain fragmentation was observed at the edge of the indentations and microcracks were observed directly, using an AgNO3 decoration technique, near the indentations. 相似文献
18.
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
19.
Activity–composition relations of FeCr2 O4 –FeAl2 O4 and MnCr2 O4 –MnAl2 O4 solid solutions were derived from activity–composition relations of Cr2 O3 –Al2 O3 solid solutions and directions of conjugation lines between coexisting spinel and sesquioxide phases in the systems FeO–Cr2 O3 –Al2 O3 and MnO–Cr2 O3 –Al2 O3 . Moderate positive deviations from ideality were observed. 相似文献
20.
Mark I. Pownceby Keri K. Constanti-Carey Michael J. Fisher-White 《Journal of the American Ceramic Society》2003,86(6):975-980
Subsolidus phase equilibria in the system Fe2 O3 –Al2 O3 –TiO2 were investigated between 1000° and 1300°C. Quenched samples were examined using powder X-ray diffraction and electron probe microanalytical methods. The main features of the phase relations were: (a) the presence of an M3 O5 solid solution series between end members Fe2 TiO5 and Al2 TiO5 , (b) a miscibility gap along the Fe2 O3 –Al2 O3 binary, (c) an α-M2 O3 ( ss ) ternary solid-solution region based on mutual solubility between Fe2 O3 , Al2 O3 , and TiO2 , and (d) an extensive three-phase region characterized by the assemblage M3 O5 +α-M2 O3 ( ss ) + Cor( ss ). A comparison of results with previously established phase relations for the Fe2 O3 –Al2 O3 –TiO2 system shows considerable discrepancy. 相似文献