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  • 1
    Electronic Resource
    Electronic Resource
    Effect of the Amount of Additives and Post-Heat Treatment on the Microstructure and Mechanical Properties of Yttrium–α-Sialon Ceramics (2003)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 86 (2003), 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 yttrium–sialon ceramics with the composition of Y0.333Si10Al2ON15 and an excess addition of Y2O3 (2 or 5 wt%) were fabricated by hot isostatic press (HIP) sintering at 1800°C for 1 h. The resulting materials were subsequently heat-treated in the temperature range 1300–1900°C to investigate its effect on the α→β-sialon phase transformation, the morphology of α-sialon grains, and mechanical properties. The results show that α-sialons stabilized by yttrium have high thermal stability. An adjustment of the α-sialon phase composition is the dominating reaction in the investigated Y–α-sialon ceramics during low-temperature annealing. Incorporation of excess Y2O3 could effectively promote the formation of elongated α-sialon grains during post-heat-treating at relatively higher temperature (1700° and 1900°C) and hence resulted in a high fracture toughness (KIC= 6.3 MPa·m1/2) via grain debonding and pullout effects. Although the addition of 5 wt% Y2O3 could promote the growth of elongated α grains with a higher aspect ratio, the higher liquid-phase content increased the interfacial bonding strength and therefore hindered interface debonding and crack deflection. The heat treatment at 1500°C significantly changed the morphology of α-sialon grains from elongated to equiaxed and hence decreased its toughness.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2003.tb03621.x
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  • 2
    Electronic Resource
    Electronic Resource
    Solubility of Si3N4 in Liquid SiO2 (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: The nitrogen solubility in the SiO2-rich liquid in the metastable binary SiO2-Si3N4 system has been determined by analytical TEM to be 1%–4% of N/(O + N) at 1973–2223 K. Analysis of the near edge structure of the electron energy loss peak indicates that nitrogen is incorporated into the silicate network rather than being present as molecular N2. A regular solution model with a positive enthalpy of mixing for the liquid was used to match the data for the metastable solubility of N in the presence of crystalline Si3N4 and to adjust the computed phase diagram. The solubility of Si3N4 in fused SiO2 is far less than reported in liquid silicates also containing Al, Mg, and/or Y. Apparently, these cations act as modifiers that break anion bridges in the silicate network and, thereby, allow further incorporation of Si3N4 without prohibitive amounts of network cross-linking. Finally, indications emerged regarding the diffuse nature of the Si3N4-SiO2 interface that leads to amorphous regions of higher N content.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00033.x
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  • 3
    Electronic Resource
    Electronic Resource
    Preparation of β-Silicon Nitride Seeds for Self-Reinforced Silicon Nitride Ceramics (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: This paper describes a method for the preparation of silicon nitride (Si3N4) seeds that have an average aspect ratio of ∼4. The seeds are prepared via heat treatment of a powder mixture that contains alpha-phase-rich Si3N4 and 0.5 wt% Y2O3 at a temperature of 1800°C and a nitrogen pressure of 35 kPa. A Y-Si-O-N liquid forms during heat treatment; this liquid acts as a flux for seed precipitation. During cooling, the Y-Si-O-N liquid transforms to a thin intergranular grain-boundary phase and causes strong agglomeration of the seeds. The seeds can be isolated by dissolving the grain-boundary phase in hot phosphoric acid, followed by an ultrasonic treatment (for 30 min). The method can be used to produce large quantities of seeds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb01969.x
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  • 4
    Electronic Resource
    Electronic Resource
    Correlation between Surface Texture and Chemical Composition in Undoped, Hard, and Soft Piezoelectric PZT 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: The electrical and mechanical properties of piezoelectric lead zirconate titanate (PZT) ceramics are strongly influenced by domain-wall motion, which can be tailored via the substitution of ions within the perovskite structure. Different domain mobilities are achieved by lead and/or oxygen vacancies, according to the valency and ionic radius of the dopants. To quantify the surface near domain mobility, hard (silver-doped), soft (lanthanum-doped), and undoped PZT ceramics have been prepared. An applied mechanical stress after sintering causes texturing near the surface, because of the ferroelastic behavior of the 90° domains. The texture is quantified via X-ray diffractometry (XRD) analysis of the tetragonal FT(002)- and FT(200)-peak intensities, using least-squares refinement with Gaussian profile functions. The samples are subsequently annealed to remove the surface texture and again characterized via XRD measurements. However, annealed samples still reveal a preferred domain orientation that can be removed only by a second annealing of the pulverized samples. A comparison of the tetragonal additive systems clearly reveals the greatest domain mobility for lanthanum-doped PZT ceramics, whereas the silver-doped and undoped samples have similar ferroelastic behavior. Furthermore, the surface texture of all the compositions is dependent on the applied mechanical stress and cannot be removed completely by heat treatment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1998.tb02397.x
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  • 5
    Electronic Resource
    Electronic Resource
    Influence of the Rare-Earth Element on the Mechanical Properties of RE–Mg-Bearing Silicon Nitride (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: Silicon nitride bulk ceramics with varying compositions of the grain boundary phase but similar grain sizes were developed, which allows to analyze the influence of the grain boundary chemistry on mechanical properties. Micrographs of the crack path reveal a much weaker interface when the rare-earth element in the grain boundary phase changes from a small to a large rare-earth cation (RE3+). Room temperature measurements of toughness and bending strength show that weaker grain boundaries result in a higher toughness, but in a decreased strength of the bulk material. This investigation demonstrates that the mechanical behavior of silicon nitride can be readily tuned by chemical composition changes of the grain boundary phase, but that a compromise between toughness and strength has to be found when designing the material.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2005.00421.x
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  • 6
    Electronic Resource
    Electronic Resource
    Influence of Grain Size on the Tensile Creep Behavior of Ytterbium-Containing Silicon Nitride (2004)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), 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 effect of grain size on the tensile creep of silicon nitride was investigated on two materials, one containing 5% by volume Yb2O3, the other containing 5% by volume Yb2O3 and 0.5% by mass Al2O3. Annealing of the Al2O3-free silicon nitride for a longer period during processing increased the grain size by a factor of 2. This increase did not affect the tensile creep rate; the grain size exponent of the creep rate differed little from zero, p=−0.20 ± 1.37 (95% confidence level). This finding supports the more recent theories of tensile creep for which p= 0 or −1 and rejects the more classical theory of solution-precipitation. In compression, a more limited data set showed p=−1.89 ± 1.72 (95% confidence level). In contrast to the Al2O3-free material, a longer term anneal of the Al2O3-containing material during processing did not increase its grain size. Despite this, the longer-annealed Al2O3-containing material crept 10 to 100 times slower than the short-annealed material. The enhancement of creep resistance may be a consequence of SiAlON formation during the additional annealing, which reduces the Al content in the amorphous phase and increases its viscosity. Such changes in chemical composition of the grain boundaries are more effective in controlling tensile creep rate than is the grain size.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.00421.x
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  • 7
    Electronic Resource
    Electronic Resource
    Contribution from Ferroelastic Domain Switching Detected Using X-ray Diffraction to R-Curves in Lead Zirconate Titanate Ceramics (2001)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 84 (2001), 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: In Pb(Zr,Ti)O3 ceramics, which are characterized by different magnitudes of coercive tensile stress, the ferroelastic domain switching induced during crack growth was measured using X-ray diffraction, and was compared with the R-curve behavior. The following correlation was established: material with smaller coercive stress has a larger amount of domain switching, and a higher toughness increment in the R-curve. The half-width of the process zone was determined for one of the four studied compositions from the spatial distribution of domain switching measured using X-ray diffraction from synchrotron source. Its value, 60–80 μm, was in good agreement with the estimate from fracture mechanics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2001.tb01116.x
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  • 8
    Electronic Resource
    Electronic Resource
    Long-Term Behavior and Application Limits of Plasma-Sprayed Zirconia Thermal Barrier Coatings (2001)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 84 (2001), 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: Investigations of changes in phase composition, mechanical properties, and microstructure of ZrO2-based plasma-sprayed thermal barrier coatings (TBCs) with 8 mol% CeO2, 19.5 mol% CeO2/1.5 mol% Y2O3, 35 mol% CeO2, and 4.5 mol% Y2O3 after long-term heat treatments at typical operation temperatures (1000°–1400°C) are presented. Experimental studies include X-ray diffractometry, mechanical testing, and scanning electron microscopy. Thermal cycling experiments also have been performed. TBCs with 8 mol% CeO2 contain mainly the tetragonal equilibrium phase and, therefore, show rapid failure because of the high amount of tetragonal → monoclinic phase transformation, even after relatively short heat treatments (1250°C/1 h). In the case of the other systems that consist mainly of the tetragonal or cubic nonequilibrium phases, TBCs with 19.5 mol% CeO2/1.5 mol% Y2O3 or 35 mol% CeO2 reveal a smaller amount of monoclinic phase after long-term heat treatments (1250°C/1000 h) compared with TBCs containing 4.5 mol% Y2O3. TBCs containing 35 mol% CeO2 show a higher degree of sintering than the TBCs with 19.5 mol% CeO2/1.5 mol% Y2O3 and, therefore, a greater increase of the elastic modulus. Among the systems investigated, TBCs containing 4.5 mol% Y2O3 exhibit the highest resistance to failure in thermal-cycling experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2001.tb00833.x
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  • 9
    Electronic Resource
    Electronic Resource
    Thermodynamic Analysis of Grain Aspect Ratio in Fibrous Microstructures of Silicon Nitride (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: Needlelike, free-floating ß-crystals of silicon nitride, precipitated within a supersaturated Y-Si-Al-O-N oxynitride glass, apparently approach an equilibrium value of the aspect ratio. An expression that relates this aspect ratio to the anisotropy in the interfacial energies of the longitudinal and transverse interfaces of the crystal is derived. The prediction agrees reasonably well with theoretical estimates of the interfacial energies. Kinetic and stearic effects that often lead to nonequilibrium values of the aspect ratio are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03262.x
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  • 10
    Electronic Resource
    Electronic Resource
    Preparation of Multiple-Cation alpha-SiAlON Ceramics Containing Lanthanum (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: Until recently, it was accepted that Ce3+ cations, with an ionic radius (r) of 1.03 Å, were too large to form an α-SiAlON structure. However, more-recent studies have shown that cerium cations can be incorporated into α-SiAlON via quenching at a rate of 600°C/min, after sintering at 1800°C. Thus far, no α-SiAlON formation has been observed for La3+ cations with r= 1.06 Å. In the present work, the possibility of having the La3+ species as a dopant cation in α-SiAlON has been investigated by using La2O3 alone or in equimolar mixtures with CaO or Yb2O3. The resulting materials have been heat-treated at a temperature of 1450°C for up to 720 h to devitrify the grain-boundary glass into crystalline phases and also to observe the α→β SiAlON transformation. X-ray diffractometry on samples that were densified with single cations revealed that the La3+ cation alone does not form an α-SiAlON; rather, it forms the N-phase (La3Si8O4N11) with a ß-SiAlON phase. In the case of multiple cations, α-SiAlON was observed only as a matrix phase. Energy-dispersive X-ray measurements have proven that La3+ cations can be accommodated into the α-SiAlON structure and this structure also does not transform to β-SiAlON at lower temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb01750.x
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