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  • 1
    Electronic Resource
    Electronic Resource
    Fracture and Fatigue Behavior at Ambient and Elevated Temperatures of Alumina Bonded with Copper/Niobium/Copper Interlayers (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: Interfacial fracture toughness and cyclic fatigue-crack growth properties of joints made from 99.5% pure alumina partially transient liquid-phase bonded using copper/niobium/copper interlayers have been investigated at both room and elevated temperatures, and assessed in terms of interfacial chemistry and microstructure. The mean interfacial fracture toughness, Gc, was found to decrease from 39 to 21 J/m2 as temperature was raised from 25° to 1000°C, with failure primarily at the alumina/niobium interfaces. At room temperature, cyclic fatigue-crack propagation occurred both at the niobium/alumina interface and in the alumina adjacent to the interface, with the fatigue threshold, ΔGTH, ranging from 20 to 30 J/m2; the higher threshold values in that range resulted from a predominantly near-interfacial (alumina) crack path. During both fracture and fatigue failure, residual copper at the interface deformed and remained adhered to both sides of the fracture surface, acting as a ductile second phase, while separation of the niobium/alumina interface appeared relatively brittle in both cases. The observed fracture and fatigue behavior is considered in terms of the respective roles of the presence of ductile copper regions at the interface which provide toughening, extrinsic toughening due to grain bridging during crack propagation in the alumina, and the relative crack propagation resistance of each crack path, including the effects of segregation at the interfaces found by Auger spectroscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00491.x
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  • 2
    Electronic Resource
    Electronic Resource
    Effects of Moisture on Grain-Boundary Strength, Fracture, and Fatigue Properties of Alumina (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 role of moisture in affecting both intrinsic and extrinsic aspects of the fracture and fatigue-crack growth resistance of a polycrystalline alumina (99.5% pure, 25 μm grain size) has been examined in both moist and dry environments at ambient temperature. The intrinsic (crack-tip) toughness, deduced from measured crack-opening profiles, is found to be less than for a single crystal and is 30% lower (∼0.6 MPa·m1/2) in moist air versus in dry N2, implying that the grain-boundary theoretical strength is higher in a dry environment. Despite this, in dry atmospheres, the R-curves (which derive from crack deflection and grain bridging) initially rose more steeply and nominal fatigue-crack growth thresholds for short crack sizes (20–60 μm) were more than 1.3 MPa·m1/2 higher. Owing to this quicker crack bridging development, strengths for natural flaws could be more than doubled in dry atmospheres, a difference that well exceeds the effect solely due to the intrinsic toughness change. After ∼2 mm of crack growth, however, the R-curve and steady-state fatigue behavior appeared similar in both environments, although altering the atmosphere for such fatigue cracks in situ induced large, abrupt changes in transient growth rates. The environment influences the nature of the bridging zones, with uncracked-ligament bridges playing a larger role in dry atmospheres, while frictional bridges are predominant in moist air. Evidently, to achieve optimal toughness in bridging ceramics, the window for the requisite grain-boundary strength may be small; whereas weak boundaries are required to induce the necessary intergranular fracture, if too weak, shallower R-curves, less strengthening, and poorer fatigue resistance all follow.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2005.00434.x
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  • 3
    Electronic Resource
    Electronic Resource
    Crack-Size Effects on Cyclic and Monotonic Crack Growth in Polycrystalline Alumina: Quantification of the Role of Grain Bridging (2004)
    Oxford, UK : Blackwell Publishing Ltd
    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 role of grain bridging in affecting the initial rising portion of the R-curve and the transient, non-steady-state behavior of short cracks during (cyclic) fatigue-crack propagation has been quantitatively examined in a 99.5% pure alumina. Fatigue-crack growth properties for both long and short (Δaf 〈 2 mm) cracks emanating from machined notches (root radius, ∼ 15–150 μm) were investigated, where Δaf is the extension of the fatigue crack from the notch. Growth rates (da/dN) were far higher at the same applied stress-intensity range (ΔK) and fatigue thresholds, ΔKTH, were markedly lower for short cracks than for corresponding long cracks. Crack extension was measured at the lowest driving forces for short cracks emanating from razor micronotches with ∼ 15 μm. For growth rates 〈10-8 m/cycle, da/dN vs ΔK curves for short cracks merged with the demonstrably steady-state curve for long cracks after ∼2 mm of crack extension. This length corresponds well to the extent of the measured crack-bridging zone for a near-threshold steady-state fatigue crack. For da/dN 〉 10-8 m/cycle, however, non-steady-state behavior was observed at all crack sizes, indicating that achieving steady state at each ΔK level is difficult. The crack-tip shielding contribution due to such grain bridging was determined using both direct compliance and the more accurate multi-cutting/crack-opening profile techniques. Bridging stress-intensity factors were computed and subtracted from the applied stress intensities to estimate an effective (near-tip) driving force, ΔKeff These results provided (i) a lower threshold (in terms of ΔKeff) below which both long and short fatigue cracks should not propagate, and (ii) an estimate of the intrinsic toughness, K0, for the start of the R-curve. Such results quantitatively affirm that the reduced role of grain bridging is a primary source of the transient behavior of short cracks in grain-bridging alumina-based ceramics under cyclic loading.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.00093.x
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  • 4
    Electronic Resource
    Electronic Resource
    Measurements of the orthogonal blade–vortex interaction using a particle image velocimetry technique (2000)
    Springer
    Experiments in fluids 29 (2000), S. 369-379 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract This paper describes the results of application of a particle image velocimetry (PIV) technique to an orthogonal blade–vortex interaction experiment. To help resolve the problem of vortex meander during the tests, two PIV systems were used, which produced two velocity vector maps closely separated in time. During the PIV analysis an image-based vector validation scheme was used, which was shown to reduce significantly the number of wild vectors reaching the vector map. Preliminary results from the tests showed that, close to the blade, a significant radial outflow was superimposed on the vortex flow field. The radial flow is thought to be due to the dispersion of the vortex axial core flow during vortex cutting, which distorts the vortex flow field and enlarges the vortex. Further away from the blade, no significant radial flow was detected and the vortex remained undisturbed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003489900096
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  • 5
    Electronic Resource
    Electronic Resource
    Yb2O3-fluxed sintered silicon nitride (1993)
    Springer
    Journal of materials science 28 (1993), S. 3529-3538 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Microstructural development and crystallization behaviour of Yb2O3-fluxed sintered silicon nitride materials was investigated using CTEM and HREM. The materials contained 5 and 10 vol% Yb2O3 as sintering additives. After densification, both compositions were subsequently heat treated to crystallize the residual amorphous secondary phases present at triple-grain regions. In the material doped with 5 vol% Yb2O3, only an amorphous secondary phase was observed after sintering, which was about 80% crystalline (Yb2Si2O7) after the post-sintering heat treatment. A metastable phase was formed in the material with 10 vol% additives after sintering, with about 70% crystallinity in the triple-point pockets. Upon postsintering heat treatment, the material could be completely crystallized. During heat treating, the metastable phase combined with the remaining glass to form Yb2SiO5 plus Yb2Si2O7 and a small amount of Si3N4 which deposited epitaxially on pre-existing Si3N4 grains in areas of low-energy within the triple-point pockets. All materials contained thin amorphous films separating the grains. The amorphous intergranular films along grain boundaries (homophase boundaries) revealed excess ytterbium and oxygen. The thickness of the intergranular films was about 1.0 and 2.5 nm for the grain boundaries and the phase boundaries, respectively, independent of additive content and heat-treatment history.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01159834
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  • 6
    Electronic Resource
    Electronic Resource
    Ceramic joining III bonding of alumina via Cu/Nb/Cu interlayers (1994)
    Springer
    Journal of materials science 29 (1994), S. 3678-3690 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A method of ceramic-ceramic joining that exploits a multilayer interlayer designed to form a thin, potentially transient layer of liquid phase has been used to join alumina to alumina. Microdesigned multilayer Cu/Nb interlayers were used to achieve bonding at 1150 °C. Flexure strengths of as-bonded samples ranged from 119 to 255 MPa, with an average of ≈ 181 MPa. The ability to form ‘strong’ ceramic/metal interfaces is also indicated by instances of ceramic failure. Microstructural and chemical characteristics of fracture surfaces were evaluated using SEM, EDS and microprobe. The impact of post-bonding anneals of 10 h duration at 1000 °C in gettered argon on room-temperature joint strength was assessed. High strengths (198 to 238 MPa) were obtained. The retention of strength following annealing in low oxygen partial pressure argon differs from the behaviour previously observed in Cu/Pt bonded alumina. Effects of the anneal on interfacial microstructure were determined, and an explanation for this difference in behaviour is proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00357335
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  • 7
    Electronic Resource
    Electronic Resource
    Near-interfacial crack trajectories in metal-ceramic layered structures (1994)
    Springer
    International journal of fracture 66 (1994), S. 227-240 
    Details
    ISSN: 1573-2673
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Experimental and theoretical analyses have been developed to analyze the path of a near-interfacial crack running nearly parallel to a ceramic/metal interface in a bimaterial layered structure. In the present study, the trajectories of cracks, initiated in the ceramic at varying distances from such interfaces, are investigated both experimentally and numerically. General trends in expected behavior, specifically that cracks propagate along a path defined by K π=0, and that cracks are attracted to or repelled from a layer if it is relatively more or less compliant, respectively, are confirmed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00042586
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  • 8
    Electronic Resource
    Electronic Resource
    Epitaxial deposition of silicon nitride during post-sintering heat treatment (1992)
    Springer
    Journal of materials science 11 (1992), S. 1249-1252 
    Details
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00729782
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  • 9
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    On the physics of moisture-induced cracking in metal-glass (copper-silica) interfaces (2007)
    American Institute of Physics
    Details
    Publication Date: 2007-09-01
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics
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  • 10
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    Yb2O3-fluxed sintered silicon nitride (1993)
    Springer
    Details
    Publication Date: 1993-01-01
    Print ISSN: 0022-2461
    Electronic ISSN: 1573-4803
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Springer
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