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  • 1
    Electronic Resource
    Electronic Resource
    Stress Corrosion Cracking of Single-Crystal Tetragonal ZrO2(Er2O3) (2005)
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The flexure strength of partially-stabilized tetragonal ZrO2(Er2O3) single-crystal monofilaments manufactured by the laser-heated floating zone method was measured as a function of the environment (air versus water) and temperature (from 25° to 800°C) at loading rates spanning three orders of magnitude to ascertain their susceptibility to the environmental conditions. These mechanical tests were completed with parallel tests on fully annealed monofilaments (to relieve the thermal residual stresses induced during growth) and by detailed analysis of the fracture surfaces using scanning electron microscopy and micro-Raman spectroscopy. While environmental susceptibility of ZrO2(Y2O3) in previous investigations was always associated with the destabilization of the tetragonal phase, monoclinic phase was not detected on the fracture surfaces of the ZrO2(Er2O3) monofilaments and it was concluded that slow crack growth in this material at high temperature or immersed in water was due to stress corrosion cracking.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2005.00573.x
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  • 2
    Electronic Resource
    Electronic Resource
    Phase Distribution and Residual Stresses in Melt-Grown Al2O3-ZrO2(Y2O3) Eutectics (2002)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 85 (2002), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Al2O3-ZrO2 eutectics containing 0 to 12.2 mol% Y2O3 (with respect to zirconia) were produced by directional solidification using the laser floating zone (LFZ) method. Processing variables were chosen to obtain homogeneous, colony-free, interpenetrating microstructure for all of the compositional range, optimum from the viewpoint of mechanical properties. The amount of cubic, tetragonal, or monoclinic zirconia phases was determined using a combination of Raman and X-ray diffraction techniques. Monoclinic zirconia was present up to concentrations of 3 mol% Y2O3, while the amount of tetragonal zirconia gradually increased with yttria content up to 3 mol%. Cubic zirconia was the only phase detected when the yttria content reached 12 mol%. The residual stresses in alumina were measured using the shift of the ruby R lines. Compressive stresses were isotropic when measured in the samples containing tetragonal and cubic zirconia, while higher tensile, anisotropic stresses were found when monoclinic zirconia was present. They were partially relieved in the eutectic sample without yttria. These results were compared with a thermoelastic analysis based on the self-consistent model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00399.x
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  • 3
    Electronic Resource
    Electronic Resource
    Piezospectroscopic Study of Residual Stresses in Al2O3–ZrO2 Directionally Solidified Eutectics (2000)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 83 (2000), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The residual thermoelastic stresses were studied in Al2O3–ZrO2 (monoclinic zirconia, m-ZrO2) and Al2O3–ZrO2(Y2O3) (tetragonal zirconia, t-ZrO2) fibrous eutectics that were produced via the laser floating zone method, using different piezospectrosocopic probes. The luminescence of the R-lines of ruby (Cr3+ in Al2O3 phase) was used to determine the stresses in the Al2O3 matrix, assuming that the stress state in the fibers was transversally isotropic. The sapphire matrix was subjected to tensile stresses in the Al2O3–m-ZrO2 eutectics. The hydrostatic stress component attained a value of 1.13 GPa in well-ordered regions. In contrast, sapphire was in compression in the Al2O3–ZrO2(Y2O3) fibers, and the hydrostatic stress was −0.37 GPa in both ordered and disordered regions. The influence of the microstructure in the residual stresses was explained through thermoelastic analyses, based on a self-consistent method. In addition, the Raman spectra of m-ZrO2 and the 417 cm−1 Raman mode of Al2O3 were measured in samples that showed different microstructures and thermoelastic stresses. An approximate linear dependence was observed in the tension–compression range between frequency shifts of the Al2O3R-lines and those of the 417 cm−1 Raman mode.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2000.tb01626.x
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  • 4
    Electronic Resource
    Electronic Resource
    Oxidation of BN/Nicalon Fiber Interfaces in Ceramic-Matrix Composites and Its Effect on Fiber Strength (1999)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 82 (1999), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Microstructural changes at the interface were analyzed in two Nicalon-fiber ceramic-matrix composites with a dual BN/SiC coating on the fibers after thermal exposure at different temperatures (in the range 800°-1400°C) and in different environments (air and argon). The outer SiC coating acted as a barrier to oxygen, which penetrated into the composite via pipeline diffusion along the BN/fiber interfaces. Oxygen penetration led to the formation of an SiO2 layer by oxidation of the fiber surfaces. The in situ fiber strength at different temperatures, as determined from the radius of the mirror region on the fiber fracture surface, indicated that this SiO2 layer severely degraded the fiber strength. Oxidation was highly dependent on the nature of the BN/fiber interface. The presence of a thin carbon-rich interlayer, which burned out rapidly at high temperature, favored the entry of oxygen and accelerated oxidation of the fibers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb02271.x
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  • 5
    Electronic Resource
    Electronic Resource
    Mechanical Properties of Textured Bi2Sr2CaCu2O8+delta High-Temperature Superconductors (1999)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 82 (1999), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The mechanical properties of Bi2Sr2CaCu2O8+delta fibers produced via laser-induced directional solidification at different growth rates were determined through longitudinal and transverse tension tests, as well as flexure tests. In addition, polished sections of as-received fibers and the fracture surfaces of the broken samples were examined using scanning electron microscopy to elucidate the relationship between the microstructure and the mechanical properties. The fibers were anisotropic, and the transverse fiber strength was very low, because of early failure via cleavage of the grains perpendicular to the c-axis. The longitudinal strength and the degree of anisotropy increased as the fiber growth rate decreased, whereas the transverse strength followed the opposite trend. This behavior was due to changes in the porosity and the alignment of the crystals along the fiber axis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb02214.x
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  • 6
    Electronic Resource
    Electronic Resource
    Fatigue Crack Growth Behavior in Mullite/Alumina Functionally Graded Ceramics (1998)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Mullite/Al2O3 functionally graded ceramics (FGCs) have been obtained by sequential slip casting and subsequently firing at 1650°C in air. Functionally graded layered dense (similar/congruent99% of the theoretical density) compacts, with five different layers with thickness ranging from 670 to 850 µm, were obtained. The layer composition was gradually changed from 100% mullite to 80% mullite/20% alumina. The elastic modulus, the flexure strength, and the fatigue life of the monolithic (80% mullite/20% alumina) and mullite/alumina FGCs were measured by means of four-point bending tests. The mullite/alumina FGCs exhibited lower strength than the monolithic material but the fatigue resistance and reliability were improved in the high cycle fatigue regime. These results were rationalized in terms of the residual stress distribution in the FGCs, which was computed using a description of stresses and strains in the multilayer composite based on the simple beam analysis. The tensile residual stresses which developed in the surfaces were responsible for the lower strength, while the compressive residual stresses within the bulk arrested the fatigue crack and improved the fatigue life of the FGC material.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1998.tb02509.x
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  • 7
    Electronic Resource
    Electronic Resource
    Sliding Wear of Alumina/Silicon Carbide Nanocomposites (1999)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 82 (1999), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The wear resistance of four Al2O3/SiC nanocomposites that contained SiC particles of varying average size (40, 200, and 800 nm) was studied under dry sliding conditions and compared with the results obtained in unreinforced alumina. The wear rate of the alumina and the nanocomposites of equivalent grain size increased as the contact load increased; however, the nanocomposite wear resistance at high contact loads was better than that of the alumina by a factor of 3–5. The wear resistance of the nanocomposites of submicrometer grain size was fairly independent of the contact load, and their wear resistance at high contact loads was up to two orders of magnitude better than that of the alumina. The mechanisms responsible for these behaviors were discussed in terms of the microscopic wear mechanisms that were observed on the worn surfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb02071.x
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  • 8
    Electronic Resource
    Electronic Resource
    Mechanical Behavior at 20° and 1200°C of Nicalon-Silicon-Carbide-Fiber-Reinforced Alumina-Matrix Composites (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Tensile and fracture tests were conducted at 20° and 1200°C on a ceramic-matrix composite that was composed of an alumina (Al2O3) matrix that was bidirectionally reinforced with 37 vol% silicon carbide (SiC) Nicalon fibers. The composite presented nonlinear behavior at both temperatures; however, the strength and toughness were significantly reduced at 1200°C. In accordance with this behavior, matrix cracks were usually stopped or deflected at the fiber/matrix interface, and fiber pullout was observed on the fracture surfaces at 20° and 1200°C. The interfacial sliding resistance at ambient and elevated temperatures was estimated from quantitative microscopy analyses of the saturation crack spacing in the matrix. The in situ fiber strength was determined both from the defect morphology on the fibers and from the size of the mirror region on the fiber fracture surfaces. It was shown that composite degradation at elevated temperature was due to the growth of defects on the fiber surface during high-temperature exposure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03159.x
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  • 9
    Electronic Resource
    Electronic Resource
    Mechanical Properties of Melt-Grown Alumina–Yttrium Aluminum Garnet Eutectics up to 1900 K (2005)
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Alumina/yttrium aluminum garnet (YAG) eutectic rods of 1 mm in diameter were grown by the laser-heated floating zone method at different rates to obtain microstructures with the same morphology but of very different domain size. The mechanical properties of the rods (hardness, toughness, strength) were measured at ambient temperature in the longitudinal and transverse directions and, in addition, the longitudinal flexure strength was determined up to 1900 K. The fracture resistance and the hardness of the eutectics at ambient temperature were isotropic and independent of the domain size. On the contrary, the longitudinal strength was significantly higher than the transverse one and increased linearly with the growth rate, reaching almost 2 GPa in the rods grown at 750 mm/h, which presented a submicrometer homogeneous microstructure. The critical defect size was equivalent to that of Al2O3 and YAG domains in the microstructure, and the strength was proportional to the inverse of the square root of the domain size. In addition, the strength retention of the eutectics was remarkable, and the rods with the finest microstructure withstood 1.53 GPa at 1900 K. The moderate reduction in strength at very high temperature was induced by the homogeneous coarsening of the microstructure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2005.00265.x
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