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  • 11
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    An Insidious Mode of Oxidative Degradation in a SiC-SiC Composite (1997)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: The oxidative durability of a SiC-SiC composite with Hi-Nicalon fiber and BN interphase was investigated at 800 C (where pesting is known to occur in SiC-SiC composites) for exposure durations of up to 500 hours and in a variety of oxidant mixes and flow rates, ranging from quasi-stagnant room air, through slow flowing O2 containing 30-90% H2O, to the high-velocity flame of a burner rig. Degradation of the composite was determined from residual strength and fracture strain in post-exposure mechanical tests and correlated with microstructural evidence of damage to fiber and interphase. The severest degradation of composite behavior was found to occur in the bumer rig, and is shown to be connected with the high oxidant velocity and substantial moisture content, as well as a thin sublayer of carbon indicated to form between fiber and interphase during composite processing.
    Keywords: Composite Materials
    Type: Journal of the American Ceramic Society
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 12
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    Role of Si2N2O in the passive oxidation of chemically-vapor-deposited Si3N4 (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: The results of two-step oxidation experiments on chemically-vapor-deposited Si3N4 and SiC at 1350 C show that a correlation exists between the presence of a Si2N2O interphase and the strong oxidation resistance of Si3N4. During normal oxidation, k sub p for SiC was 15 times higher than that for Si3N4, and the oxide scale on Si3N4 was found by SEM and TEM to contain a prominent Si2N2O inner layer. However, when oxidized samples are annealed in Ar for 1.5 h at 1500 C and reoxidized at 1350 C as before, three things happen: the oxidation k sub p increases over 55-fold for Si3N4, and 3.5-fold for SiC; the Si3N4 and SiC oxidize with nearly equal k sub p's; and, most significantly, the oxide scale on Si3N4 is found to be lacking an inner Si2N2O layer. The implications of this correlation for the competing models of Si3N4 oxidation are discussed.
    Keywords: NONMETALLIC MATERIALS
    Type: American Ceramic Society, Journal (ISSN 0002-7820); 75; 11; p. 2995-3000.
    Format: text
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    NASA TECHNICAL REPORTS
  • 13
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    A Porous Ceramic Interphase for SiC/Si(sub 3)N(sub 4) Composites (1995)
    In:  CASI
    Details
    Publication Date: 2019-08-15
    Description: A suitable interphase material for non-oxide ceramic-matrix composites must be resistant to oxidation. This means it must exhibit a slow rate of oxidation, and its oxidation product must be such as to ensure that the system survives oxidation when it does occur. Because the current benchmark interphase materials, carbon and boron nitride, lack these qualities, a porous fiber coating was developed to satisfy both the mechanical and oxidative requirements of an interphase for the SiC/SiC and SiC/Si2N4 composites that are of interest to NASA. This report presents the interphase microstructure achieved and the resulting characteristics of fiber push-out from a matrix of reaction-bonded silicon nitride (RBSN), both as-fabricated and after substantial annealing and oxidation treatments.
    Keywords: NONMETALLIC MATERIALS
    Type: NASA-CR-198425 , NAS 1.26:198425 , E-10013 , NIPS-95-06250
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 14
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    Recent Developments in the Environmental Durability of Sic/sic Composites (2002)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Two types of pest behavior in SiC/BN/SiC composites are distinguished and illustrated: one intrinsic and progressive, the other extrinsic and catastrophic. Their similarities and differences are presented. Some recent remedies for SiC/BN/SiC pest are discussed.
    Keywords: Composite Materials
    Type: NASA/CR-2002-211687 , NAS 1.26:211687 , E-13416 , CIMTEC 2002 International Conferences on Modern Materials and Technologies; Jul 14, 2002 - Jul 19, 2002; Florence; Italy
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    NASA TECHNICAL REPORTS
  • 15
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    Pest Oxidation Regime in the Hi-Nicalon(Trademark)/BN/SiC Composite (1998)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: SiC-SiC composites are prone to pest degradation at intermediate temperatures where the formation of a protective scale of silica by direct oxidation of SiC is too slow to offer effective protection from attack by ambient gases. The attack results in the removal of the BN interphase and its replacement by a borosilicate liquid (which dissolves and weakens the fiber) and finally by SiO2, (which embrittles the composite by bonding fiber to fiber or to matrix). This paper reports a study aimed at mapping out the temperature range of such pest degradation and the severity of its effect.
    Keywords: Composite Materials
    Type: CIMTEC-9: World Ceramic Congress 1998; Jun 14, 1998 - Jun 19, 1998; Florence; Italy
    Format: text
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    NASA TECHNICAL REPORTS
  • 16
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    Precautions toward XTEM of Si3N4/SiO2 (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Severe difficulties are encountered in the preparation of oxidized Si3N4 specimens for XTEM transmission electromicroscopic inspection, in virtue of the extreme difference between Si3N4 and SiO2 mechanical properties. Attention is presently given to a preparation method in which an overlayer of the nitride is always occluded; this protects the oxide through most of the thinning that specimen preparation entails. An XTEM image of the oxide/nitride interface is presented.
    Keywords: NONMETALLIC MATERIALS
    Type: Annual Meeting of the Electron Microscopy Society of America; Aug 04, 1991 - Aug 09, 1991; San Jose, CA; United States
    Format: text
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    NASA TECHNICAL REPORTS
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