共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
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
3.
PAUL F. BECHER 《Journal of the American Ceramic Society》1983,66(7):485-488
Significant increases in the critical fracture toughness (K IC ) over that of alumina are obtained by the stress-induced phase transformation in partially stabilized ZrO2 particles which are dispersed in alumina. More importantly, improved slow crack growth resistance is observed in the alumina ceramics containing partially stabilized ZrO2 particles when the stress-induced phase transformation occurs. Thus, increasing the contribution of the ZrO2 phase transformation by tailoring the Y2 O3 stabilizer content not only increases the critical fracture toughness (KIC ) but also the K Ia to initiate slow crack growth. For example, crack velocities ( v )≥10–9 m/s are obtained only at K Ia ≥5 MPa.m1/2 in transformation-toughened ( K IC =8.5 MPa.m1/2 ) composites vs K Ia ≥2.7 MPa.m1/2 for comparable velocities in composites where the transformation does not occur ( K IC =4.5 MPa.m1/2 ). This behavior is a result of crack-tip shielding by the dissipation of strain energy in the transformation zone surrounding the crack. The stress corrosion parameter n is lower and A greater in these fine-grained composite materials than in fine-grained aluminas. This is a result of the residual tensile stresses associated with larger (≥1 μm) monoclinic ZrO2 particles which reside along the intergranular crack path. 相似文献
4.
The cubic ( c -ZrO2 ) and tetragonal zirconia ( t -ZrO2 ) phase stability regions in the system ZrO2 –Y2 O3 –Ta2 O5 were delineated. The c -ZrO2 solid solutions are formed with the fluorite structure. The t -ZrO2 solid solutions having a c/a axial ratio (tetragonality) smaller than 1.0203 display high fracture toughness (5 to 14 MPa · m1/2 ), and their instability/transformability to monoclinic zirconia ( m -ZrO2 ) increases with increasing tetragonality. On the other hand, the t -ZrO2 solid solutions stabilized at room temperature with tetragonality greater than 1.0203 have low toughness values (2 to 5 MPa · m1/2 ), and their transformability is not related to the tetragonality. 相似文献
5.
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
6.
Gan Feng Tu Zhi Tong Sui Qiang Huang Chang Zhen Wang 《Journal of the American Ceramic Society》1992,75(4):1032-1034
Y-PSZ ceramics with 5 wt% Al2 O3 were synthesized by a sol–gel route. Experimental results show that powders of metastable tetragonal zirconia with 2.7 mol% Y2 O3 and 5 wt% Al2 O3 can be fabricated by decomposing the dry gel powder at 500°C. Materials sintered in an air atmosphere at 1500°C for 3 have high density (5.685 g/cm3 ), high content of metastable tetragonal zirconia (>96%), and high fracture toughness (8.67 MPa.m1/2 ). Compared with the Y-PSZ ceramics, significant toughening was achieved by adding 5 wt% Al2 O3 . 相似文献
7.
Mathias Herrmann Hans-Joachim Kleebe Jan Raethel Kerstin Sempf Stefan Lauterbach Mathis M. Müller Iakovos Sigalas 《Journal of the American Ceramic Society》2009,92(10):2368-2372
B6 O is a possible candidate of superhard materials with a hardness of 45 GPa measured on single crystals. Up to now, densification of these materials was only possible at high pressure. However, recently it was found that Al2 O3 can be utilized as an effective sintering additive, similar to the addition of Y2 O3 /Al2 O3 that was used in this work. The densification behavior of the material as a function of applied pressure, its microstructure evolution, and the resulting mechanical properties were investigated. A strong dependence of the densification with increasing pressure was found. The material revealed characteristic triple junctions filled with amorphous residue composed of B2 O3 , Al2 O3 , and Y2 O3 , while no amorphous grain-boundary films were observed along internal interfaces. Mechanical testing revealed on average a hardness of 33 GPa, a fracture toughness of 4 MPa·m1/2 , and a strength value of 520 MPa. 相似文献
8.
Dae-Joon Kim Paul F. Becher Camden R. Hubbard 《Journal of the American Ceramic Society》1993,76(11):2904-2908
Tetragonal ZrO2 ( t -ZrO2 ) solid solutions were prepared with addit ons of 2 mol% Y2 O3 plus up to 0.45 mol% Nb2 O5 . The thermal expansion coefficients in both the a- and c -axis lattice directions increased with Nb2 O5 alloying and the thermal expansion in the c -axis direction was greater than that in the a -axis direction over the entire composition range. This anisotropic thermal expansion behavior was related to the 4-fold coordination of Nb5+ with oxygen ions in t -ZrO2 solid solutions in the system ZrO2 –Y2 O3 –Nb2 O5 . The fracture toughness continuously increased with Nb2 O5 alloying and suggested that the c/a axial ratio is a more significant factor than the internal stress that arises from the thermal expansion anisotropy, in the determination of the transformability of t -ZrO2 in this system. 相似文献
9.
Gerhard W. Dransmann Rolf W. Steinbrech Antonia Pajares Fernando Guiberteau Arturo Dominguez-Rodriguez Arthur H. Heuer 《Journal of the American Ceramic Society》1994,77(5):1194-1201
Stable indentation cracks were grown in four-point bend tests to study the fracture toughness of two Y2 O3 -stabilized ZrO2 ceramics containing 3 and 4 mol% Y2 O3 . By combining microscopic in situ stable crack growth observations at discrete stresses with crack profile measurements, the dependence of toughness on crack extension was determined from crack extension plots, which graphically separate the crack driving residual stress intensity and applied stress intensity factors. Both materials exhibit steeply rising R -curves, with a plateau toughness of 4.5 and 3.1 Mpa·m1/2 for the 3- and 4-mol% materials, respectively. The magnitude of the plateau toughness reflects the fraction of tetragonal grains contributing to transformation toughening. 相似文献
10.
A. DOMINGUEZ-RODRIGUEZ K. P. D. LAGERLöF A. H. HEUER 《Journal of the American Ceramic Society》1986,69(3):281-284
Fully stabilized cubic ZrO2 single crystals containing various Y2 O3 concentrations were deformed at 1400°C in air. The orientation chosen favored (001)(110) slip, which was confirmed by slip-trace analysis and transmission electron microscopy; (111)(110) slip could also be activated. The yield and flow stresses increased with increasing Y2 O3 concentration, and stress-strain curves were dominated by a region of zero work hardening from very small strains for all compositions. 相似文献
11.
Sung R. Choi Dongming Zhu Robert A. Miller 《International Journal of Applied Ceramic Technology》2004,1(4):330-342
Mechanical behavior of free-standing, plasma-sprayed ZrO2 -8wt% Y2 O3 thermal barrier coatings, including strength, fracture toughness, fatigue, constitutive relation, elastic modulus, and directionality, have been determined under various loading-specimen configurations. This paper presents and describes a summary of mechanical properties of the plasma-sprayed coating material to provide them as a design database. 相似文献
12.
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
13.
Yoshikazu Suzuki Peter E. D. Morgan Koichi Niihara 《Journal of the American Ceramic Society》1998,81(12):3141-3149
Additions of 1-20 mol% Sc2 O3 or Y2 O3 to MoSi2 eliminate glassy SiO2 , which improves mechanical properties at both ambient and high temperatures. In particular, only 1 mol% ScO3 additions dramatically enhance three-point bending strength from 521 to 1081 MPa. Vickers hardness, Young's modulus, fracture toughness, and high-temperature strength are also improved by this low level of additive. The improvement of mechanical properties is attributed to the formation of crystalline silicates: Sc2 Si2 O7 , Y2 Si2 O7 , Y2 SiO5 , and Y4 Si3 O12 , which are analyzed by XRD, SEM-EDS, and TEM-EDS methods. 相似文献
14.
Up to 50 vol% of TiB2 , TiC0.5 N0.5 , TiN, or TiC was added to Y2 O3 -stabilized tetragonal ZrO2 polycrystals (Y-TZP) and hot pressed under vacuum. The influence of the type of secondary phase on the microstructure and mechanical properties was studied, as a function of the hot-pressing temperature. The influence of the secondary-phase content on the mechanical properties was studied by varying the TiB2 content up to 50 vol%. Fully dense Y-TZP-based composites with very high toughness (up to 10 MPa·m1/2 ), excellent bending strength (up to 1237 MPa), and increased hardness, with respect to ZrO2 (Vickers hardness up to 1450 kg/mm2 ), were obtained. 相似文献
15.
Effect of Ta2 O5 , Nb2 O5 , and HfO2 Alloying on the Transformability of Y2 O3 -Stabilized Tetragonal ZrO2
Dae-Joon Kim 《Journal of the American Ceramic Society》1990,73(1):115-120
The addition of Ta2 O5 , Nb2 O5 , and HfO2 enhanced the transformability of Y2 O3 -stabilized tetragonal ZrO2 polycrystal (Y-TZP), which was indicated by an increase in phase transformation temperatures and fracture toughness of Y-TZP. Comparison of the alloying effects of these oxides on the transformability and crystal structure of Y-TZP suggested that an alloying oxide which increases the c/a axial ratio (tetragonality) of TZP also increases the transformability. Empirical equations to predict the tetragonality are proposed. Calculated tetragonalities showed good agreement with measured values in the systems ZrO2 -Y2 O3 -Ta2 O5 , -Nb2 O5 , and -HfO2 . 相似文献
16.
Composite ceramic materials based on Si3 N4 and ZrO2 stabilized by 3 mol% Y2 O3 have been formed using aluminum isopropoxide as a precursor for the Al2 O3 sintering aid. Densification was carred out by hot-pressing at temperatures in the range 1650° to 1800°C, and the resulting micro-structures were related to mechanical properties as well as to oxidation behavior at 1200°C. Densification at the higher temperatures resulted in a fibrous morphology of the Si3 N4 matrix with consequent high room-temperature toughness and strength. Decomposition of the ZrO2 grains below the oxidized surface during oxidation introduced radial stresses in the subscalar region, and from the oxidation experiments it is suggested that the ZrO2 incorporated some N during densification. 相似文献
17.
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
18.
Masahiro Yoshimura Manikpurage Jayaratna Shigeyuki Smiya 《Journal of the American Ceramic Society》1982,65(10):c166-c168
The pseudoternary system ZrO2 -Y2 O3 -Cr2 O3 was studied at 1600°C in air by the quenching method. Only one intermediate compound, YCrO3 , was observed on the Y2 O3 −Cr2 O3 join. ZrO2 and Y2 O3 formed solid solutions with solubility limits of 47 and 38 mol%, respectively. The apex of the compatibility triangle for the cubic ZrO2 , Cr2 O3 , and YCrO3 three-phase region was located at =17 mol% Y2 O3 (83 mol% ZrO2 ). Below 17 mol% Y2 O3 , ZrO2 solid solution coexisted with Cr2 O3 . Cr2 O3 appears to be slightly soluble in ZrO2 (ss). 相似文献
19.
Conventional ramp-and-hold sintering with a wide range of heating rates was conducted on submicrometer and nanocrystalline ZrO2 –3 mol% Y2 O3 powder compacts. Although rapid heating rates have been reported to produce high density/fine grain size products for many submicrometer and smaller starting powders, the application of this technique to ZrO2 –3 mol% Y2 O3 produced mixed results. In the case of submicrometer ZrO2 –3 mol% Y2 O3 , neither densification nor grain growth was affected by the heating rate used. In the case of nanocrystalline ZrO2 –3 mol% Y2 O3 , fast heating rates severely retarded densiflcation and had a minimal effect on grain growth. The large adverse effect of fast heating rates on the densification of the nanocrystalline powder was traced to a thermal gradient/differential densification effect. Microstructural evidence suggests that the rate of densification greatly exceeded the rate of heat transfer in this material; consequently, the sample interior was not able to densify before being geometrically constrained by a fully dense shell which formed at the sample exterior. This finding implies that rapid rate sintering will meet severe practical constraints in the manufacture of bulk nanocrystalline ZrO2 –3 mol% Y2 O3 specimens. 相似文献
20.
The tetragonal ( t ) and cubic ( c ) ZrO2 solid solutions in two-phase ZrO2 -8 wt% Y2 O3 ceramics have low and high solute content, respectively. Annealing samples sintered at 1600°C between 700° and 1400°C requires a change in the volume fraction of the coexisting phases, as well as their equilibrium Y2 O3 content. The enrichment in Y2 O3 content of the c -ZrO2 grains is accomplished by liquid-film migration involving the ubiquitous silicate grain-boundary phase, while the volume fraction of t -ZrO2 increases by the nucleation and growth of cap-shaped t -ZrO2 lenses. The interfaces between the c -ZrO2 matrix and the growing t -ZrO2 lenses are semicoherent. 相似文献