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  • NONMETALLIC MATERIALS  (5)
  • Heat treatment  (1)
  • 1
    Digitale Medien
    Digitale Medien
    Preparation of cross-sectional specimens of ceramic thermal barrier coatings for transmission electron microscopy (1990)
    New York, NY : Wiley-Blackwell
    Journal of Electron Microscopy Technique 14 (1990), S. 307-312 
    Details
    ISSN: 0741-0581
    Schlagwort(e): Zirconia ; Metal - ceramic interface ; Superalloys ; Bonding ; Heat treatment ; Life and Medical Sciences ; Cell & Developmental Biology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Allgemeine Naturwissenschaft
    Notizen: During the microstructural examination of ceramic thermal barrier coatings by transmission electron microscopy (TEM), initial efforts for the preparation of cross-sectional thin foils from interface regions by conventional means were mostly failures. Delamination of the Y2O3-stabilized ZrO2 ceramic coating from the nickel-base alloy substrate sometimes occurred during fine polishing at around 80 μm thickness but mostly occurred during dimpling. Because of this sensitivity, special techniques for mechanical handling were developed so that ion milling could give thin enough regions of the metal-ceramic interface. TEM showed convincingly that the highly fragile nature of the coatings is in fact due to the extensive porosity at the interface developed as a result of heat treatment.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jemt.1060140404
    Standort Signatur Erwartet Verfügbarkeit
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    Artikel (Nationallizenzen)
    Volltext
  • 2
    facet.materialart.
    Unbekannt
    Microstructural aspects of zirconia thermal barrier coatings (1985)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: Various combination of plasma-sprayed bond coatings and zirconia ceramic coatings on a nickel-based superalloy substrate were tested by static thermal exposure at 1200 C and cyclic thermal exposure to 1000 C. The bond coats were based on Ni-Cr-Al alloys with additions of rare earth elements and Si. The ceramic coats were various ZrO2-Y2O3 compositions, of which the optimum was found to be ZrO2-8.9 wt percent Y2O3. Microstructural analysis showed that resistance to cracking during thermal exposure is strongly related to deleterious phase changes. Zones depleted of Al formed at the bond coat/ceramic coat interface due to oxidation and at the bond coat/substrate interface due to interdiffusion, leading eventually to breakdown of the bond coat. The 8.9 percent Y2O3 coating performed best because the as-sprayed metastable tetragonal phase converted slowly into the low-Y2O3 tetragonal plus high-Y2O3 cubic-phase mixture, so that the deleterious monoclinic phase was inhibited from forming. Failure appeared to start with the formation of circumferential cracks in the zirconia, probably due to compressive stresses during cooling, followed by the formation of radial cracks due to tensile stresses during heating. Cracks appeared to initiate at the Al2O3 scale/bond coat interface and propagate through the zirconia coating. Comparisons were made with the behavior of bulk ZrO2-Y2O3 and the relationship between the microstructure of the tetragonal phase and the phase diagram. A separate investigation was also made of the ZrO2-Al2O3 interface.
    Schlagwort(e): NONMETALLIC MATERIALS
    Materialart: NASA, Lewis Research Center, Thermal Barrier Coatings. Abstracts and Figures; p 59-76
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
    facet.materialart.
    Unbekannt
    Microstructure and mechanical properties of bulk yttria-partially-stabilized zirconia (1981)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: A commercially available bulk 4.5 mole percent yttria-(Y2O3) partially stabilized zirconia (PSZ) was studied by light microscopy, X-ray analysis, microhardness measurement, and fracture toughness testing. The growth of the precipitates and the phase transformations were studied as a function of aging in air at 1500 C. Aging curves were constructed for both the as received and the solution annealed and quenched materials; the curves showed hardness peaks at 1397 and 1517 Kg/sq mm respectively. The rectangular plate shaped tetragonal precipitates were found to have a 110 habit plane. A total of twelve different types of tetragonal precipitates were found. Grinding of the Y2O3 PSZ into powder did not cause a significant amount of metastable tetragonal precipitates to transform into the monoclinc phase, thus indicating that transformation toughening is not a significant mechanism for the material.
    Schlagwort(e): NONMETALLIC MATERIALS
    Materialart: NASA-CR-164438
    Format: application/pdf
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  • 4
    facet.materialart.
    Unbekannt
    Bubble formation in oxide scales on SiC (1984)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The oxidation of alpha-SiC single crystals and sintered alphaand beta-SiC polycrystals has been investigated at elevated temperatures. Bubble formation is commonly observed in oxide scales on polycrystalline SiC, but is rarely found on single-crystal scales; bubbles result from the preferential oxidation of C inclusions, which are abundant in SiC polycrystals. The absence of bubbles on single crystals, in fact, implies that diffusion of the gaseous species formed on oxidation, CO (or possibly SiO), controls the rate of oxidation of SiC.
    Schlagwort(e): NONMETALLIC MATERIALS
    Materialart: AD-A225456 , American Ceramic Society, Journal (ISSN 0002-7820); 67; C-17
    Format: text
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  • 5
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    TEM investigation of beta-SiC grown epitaxially on Si substrate by CVD (1987)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: A transmission electron microscopy study is being conducted on the microstructure of beta-SiC films grown epitaxially on 001-plane silicon by chemical vapor deposition. Observations have been made in plain view and in cross-section. A high density of stacking faults has been found in the bulk of the epilayer which are bounded by partials of the Shockley type with Burgers vectors 1/6 211-line. Cross-sectional high resolution electron microscopy of the interface has shown it to be semicoherent with misfit dislocations to accommodate the lattice parameter difference between the substrate and the epilayer. In addition to misfit dislocations, a high density of twins and some stacking faults are present in the SiC near the interface. Mechanisms for the nucleation and growth of these defects are discussed.
    Schlagwort(e): NONMETALLIC MATERIALS
    Format: text
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  • 6
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    Beta-to-alpha transformation in polycrystalline SiC. II - Interfacial energetics (1978)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-27
    Beschreibung: A phenomenological analysis of the energetics of the beta-to-alpha transformation in polycrystalline SiC is presented. It is found that the extreme anisotropy of the interfacial energy between alpha- and beta-SiC can account for the rapid growth of composite grains into the beta matrix during conventional sintering or hot-pressing processes. The composite grains consist of alpha-SiC plates 'sandwiched' between well-oriented and recrystallized beta-SiC 'envelopes'. The interfaces involving the 111 plane type of beta and (0001) of alpha have much lower energies than random beta/alpha interfaces.
    Schlagwort(e): NONMETALLIC MATERIALS
    Materialart: American Ceramic Society; vol. 61
    Format: text
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