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  • 1
    Electronic Resource
    Electronic Resource
    Stress Relaxation of Compression Loaded Plasma-Sprayed 7 Wt% Y2O3–ZrO2 Stand-Alone Coatings (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: Stand-alone plasma-sprayed tubes of 7 wt% Y2O3–ZrO2 made from the same starting powder but at two different sites were subject to stress-relaxation testing in axial compression at temperatures of 25°, 1000°, 1050°, 1100°, and 1200°C and at an initial stress of 10–80 MPa. A time-dependent stress response was observed for both coatings at all temperatures. For example, a 20 MPa stress applied at 1050°C relaxed to ∼3 MPa in 180 min. When the same initial stress was applied at 1200°C, the coating fully relaxed in 32 min. For all experimental conditions evaluated, an initial fast stress-relaxation regime was observed (〈10 min), followed by a slower second stress-relaxation regime at later times (〉10 min). Coatings with higher as-sprayed densities exhibited a lengthened fast relaxation regime as compared with less dense coatings. A Maxwell model was modified in order to provide an accurate fit to the experimental stress-relaxation curves. From scanning electron microscopy experiments and mechanical data, the mechanism for stress relaxation from 25°C through 1200°C, particularly during fast relaxation, was proposed to be the formation of cracks parallel with respect to the applied load. In addition to this mechanism, stress relaxation that occurred in specimens tested at 1000°C through 1200°C was proposed to be due to partial or complete closure of cracks oriented perpendicular to the applied stress.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2005.00407.x
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  • 2
    Electronic Resource
    Electronic Resource
    Role of Lamellae Morphology on the Microstructural Development and Mechanical Properties of Small-Particle Plasma-Sprayed Alumina (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 influence of spray parameters on the microstructure and flexural strength of plasma-sprayed alumina was investigated. Coatings were applied using a small-particle plasma spray (SPPS) method, which is a recently patented process that allows submicrometer-sized powders to be sprayed. Using identical starting powders, coatings that were produced using two distinctly different spray conditions exhibited significant differences in both microstructure and strength. Scanning electron microscopy investigations of single lamellae (or splats) revealed that, for one spray condition, melted alumina particles will splash when they contact the substrate. The morphology of the splats that comprised the subsequent layers of the coating also were highly fragmented and thinner than lamellae formed under “nonsplashing” spray conditions. The surface roughness was strongly dependent on the morphology of the lamellae; increased roughness was noted for fragmented splats. Thick coatings that were comprised of splashed splats developed a unique microstructural feature that was responsible for the observed increase in roughness. These microstructural differences greatly influenced the flexure strength, which varied from 75 ± 21 MPa for the nonsplashing spray condition to 17 ± 2.4 MPa for the “splashing” condition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2000.tb01290.x
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  • 3
    Electronic Resource
    Electronic Resource
    Investigation of the Physical and Mechanical Properties of Hot-Pressed Boron Nitride/Oxide Ceramic Composites (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: Billets of hexagonal boron nitride powders (h-BN) were hot-pressed, varying the alignment of the platelike particles and the amount of oxide additives. Increasing either alignment of individual grains or the amount of additives was shown to increase flexural strength, to approximately 120 MPa at ambient temperatures. h-BN was shown to deflect cracks initially propagating normal to its basal planes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb02123.x
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  • 4
    Electronic Resource
    Electronic Resource
    Fibrous Monolithic Ceramics (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: Fibrous monolithic ceramics are an example of a laminate in which a controlled, three-dimensional structure has been introduced on a submillimeter scale. This unique structure allows this all-ceramic material to fail in a nonbrittle manner. Materials have been fabricated and tested with a variety of architectures. The influence on mechanical properties at room temperature and at high temperature of the structure of the constituent phases and the architecture in which they are arranged are discussed. The elastic properties of these materials can be effectively predicted using existing models. These models also can be extended to predict the strength of fibrous monoliths with an arbitrary orientation and architecture. However, the mechanisms that govern the energy absorption capacity of fibrous monoliths are unique, and experimental results do not follow existing models. Energy dissipation occurs through two dominant mechanisms—delamination of the weak interphases and then frictional sliding after cracking occurs. The properties of the constituent phases that maximize energy absorption are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03148.x
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  • 5
    Electronic Resource
    Electronic Resource
    Co-Doping of Air Plasma-Sprayed Yttria- and Ceria-Stabilized Zirconia for Thermal Barrier Applications (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: Co-dopants of either Yb3+ or Ca2+ were incorporated into 7.6 mol% YO1.5–ZrO2 (7.6YSZ) and 12 mol% CeO2–ZrO2 (12CeSZ) coatings by infiltrating porous spray-dried powders with salt solutions containing the appropriate co-dopant species prior to plasma spraying. Co-dopant concentration was varied from 2 to 5 mol%. Using a combination of transmission electron microscopy and energy-dispersive analysis, no secondary phase or Yb3+ segregation was detected at the grain boundary of either as-sprayed 2Yb/7.6YSZ or 2Yb/12CeSZ coatings. Dilatometer measurements showed that 2 mol% Yb3+ co-doped 7.6YSZ and 12CeSZ coatings shrank ∼0.6% during a 5 h soak at 1400°C, approximately the same contraction as the baseline coatings (i.e. not co-doped). X-ray diffraction results show that the as-sprayed 7.6YSZ, 2Ca/7.6YSZ, and 2Yb/7.6YSZ coatings comprised of non-transformable, non-equilibrium composition tetragonal ZrO2 (identified presently as t′-ZrO2), while the 5Ca/7.6YSZ coating was a non-equilibrium composition of cubic ZrO2. After a heat treatment of 100 h at 1200°C, the 2Yb/7.6YSZ coating was completely t′-ZrO2, while the baseline and Ca2+ co-doped 7.6YSZ coatings showed evidence of partitioning. Therefore, it appears that co-doping of 7.6YSZ with 2 mol% Yb3+ increases the stability of t′-ZrO2, whereas co-doping with 2 mol% Ca2+ decreases the stability of t′-ZrO2. The volume fraction of m-ZrO2 in the baseline 12CeSZ coatings was estimated to be 88% after a 100 h heat treatment at 1200°C. 2 mol% Yb3+ or Ca2+ co-doping limited the tetragonal to monoclinic phase transformation in 12CeSZ, with only 37% and 43% monoclinic phase observed, respectively, after a 100 h heat treatment at 1200°C; this was an improvement over the baseline 12CeSZ coating. As-sprayed 2Yb/7.6YSZ and 2Yb/12CeSZ coatings had slightly lower thermal conductivity than their baseline counterparts in the as-sprayed condition; after 100 h at 1200°C, their conductivity increased to that of the baseline coatings.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2005.00296.x
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  • 6
    Electronic Resource
    Electronic Resource
    In Situ Observation of Crack Behavior in Compressively Loaded Plasma-Sprayed 7-wt%-Yttria-Stabilized Zirconia (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: A plasma-sprayed 7-wt%-yttria-stabilized zirconia stand-alone tube was incrementally loaded in uniaxial compression inside a scanning electron microscope. Micrographs taken at each increment showed cracks perpendicular to the applied load to have partially closed and cracks parallel to the applied load to have opened. New cracks were observed to nucleate and then propagate in a direction parallel to the applied load.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.00960.x
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  • 7
    Electronic Resource
    Electronic Resource
    Elevated-Temperature Mechanical Properties of Silicon Nitride/Boron Nitride Fibrous Monolithic Ceramics (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: A unique, all-ceramic material capable of nonbrittle fracture via crack deflection and delamination has been mechanically characterized from 25° through 1400°C. This material, fibrous monoliths, was comprised of unidirectionally aligned 250 μm diameter silicon nitride cells surrounded by 10 to 20 μm thick boron nitride cell boundaries. The average flexure strengths of fibrous monoliths were 510 and 290 MPa for specimens tested at room temperature and 1300°C, respectively. Crack deflection in the BN cell boundaries was observed at all temperatures. Characteristic flexural responses were observed at temperatures between 25° and 1400°C. Changes in the flexural response at different temperatures were attributed to changes in the physical properties of either the silicon nitride cells or boron nitride cell boundary.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2000.tb01191.x
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  • 8
    Electronic Resource
    Electronic Resource
    Influence of Microstructure and Temperature on the Interfacial Fracture Energy of Silicon Nitride/Boron Nitride Fibrous Monolithic 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: The microstructure and interfacial fracture energy of silicon nitride/boron nitride fibrous monoliths, GammaBN, were determined as a function of starting silicon nitride composition and temperature using the method described by Charalambides. The glassy phase created by the sintering aids added to the silicon nitride cells was shown to migrate into the boron nitride cell boundaries during hot-pressing. The amount of glassy phase in the boron nitride cell boundaries was shown to strongly influence GammaBN at room temperature, increasing the fracture energy with increasing amounts of glass. Similar trends in the interfacial fracture energy as a function of temperature were demonstrated by both compositions of fibrous monoliths, with a large peak in GammaBN observed over a narrow temperature range. For silicon nitride cells densified with 6 wt% yttria and 2 wt% alumina, the room-temperature interfacial fracture energy was 37 J/m2, remaining constant through 950°C. A sharp increase in GammaBN, to 60 J/m2, was observed between 1000° and 1050°C. This increase was attributed to interactions of the crack tip with the glassy phase in the boron nitride cell boundary. Measurements at 1075°C indicated a marked decrease in GammaBN to 39 J/m2. The interfacial fracture energy decreased with increasing temperature in the 1200° to 1300°C regime, plateauing between 17 to 20 J/m2. A crack propagation model based on linkup of existing microcracks and peeling/cleaving boron nitride has been proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb02110.x
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  • 9
    Electronic Resource
    Electronic Resource
    Deformation Mechanisms in Compression-Loaded, Stand-Alone Plasma-Sprayed Alumina Coatings (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: Cylindrical, stand-alone tubes of plasma-sprayed alumina were tested in compression in the axial direction at room temperature, using strain gauges to monitor axial and circumferential strains. The primary compression-loading profile used was cyclic loading, with monotonically increased peak stresses. Hysteresis was observed in the stress–strain response on unloading, beginning at a peak stress of 50 MPa. The modulus decreased as the maximum applied stress increased. The stress–strain response was only linear at low stresses; the degree of nonlinearity at high stresses scaled with the stress applied. One-hour dwells at constant stress at room temperature revealed a time-dependent strain response. Using transmission electron microscopy and acoustic emission to investigate deformation mechanisms, the stress–strain response was correlated with crack pop-in, growth, and arrest. It is proposed that the numerous defects in plasma-sprayed coatings, including porosity and microcracks, serve as sites for crack nucleation and/or propagation. As these small, nucleated cracks extend under the applied stress, they propagate nearly parallel to the loading direction along interlamellae boundaries. With increasing stress, these cracks ultimately link, resulting in catastrophic failure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2000.tb01682.x
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  • 10
    Electronic Resource
    Electronic Resource
    Effect of Sintering Aid Composition on the Processing of Si3N4/BN Fibrous Monolithic 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: Si3N4/BN fibrous monoliths were prepared with 4 wt% Y2O3 added as a sintering aid to the Si3N4. Residual carbon, present in the billet before hot-pressing, was shown to influence the final microstructure. The sintering aid glass, known to migrate into the BN cell boundaries during hot-pressing, was not sufficient in quantity to prevent premature shear failure when samples were tested in flexure. Increasing the hot-pressing temperature alleviated this problem. For flexure samples tested at 1400°C, fibrous monoliths fabricated with 4 wt% Y2O3 demonstrated linear-elastic loading behavior at a greater stress than fibrous monoliths fabricated with 6-wt%-Y2O3/2-wt%-Al2O3 sintering aids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb02185.x
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