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Crack healing behavior of hot pressed silicon nitride due to oxidationIt is shown that limited oxidation of an MgO-containing, hot-pressed silicon nitride ceramic at 800 deg C and above results in increased strength due to crack healing. Slight oxidation of the surface produces enstatite and cristobalite which fills in cracks. More extensive oxidation leads to strength degradation due to the formation of new flaws by the evolution of N2 gas at the surface. The apparent fracture toughness also increased at 800 deg C and above due to oxidation. Bonds formed between the two surfaces of the crack during oxidation leads to a reduction in stress intensity at the crack tip, suggesting that valid high-temperature toughness values cannot be obtained in an air environment. The increase in strength due to crack healing by oxidation can be achieved without compromising the fatigue properties of the silicon nitride ceramic.
Document ID
19920050272
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Choi, S. R.
(Cleveland State University OH, United States)
Tikare, V.
(NASA Lewis Research Center Cleveland, OH, United States)
Date Acquired
August 15, 2013
Publication Date
April 15, 1992
Publication Information
Publication: Scripta Metallurgica et Materialia
Volume: 26
ISSN: 0956-716X
Subject Category
Nonmetallic Materials
Accession Number
92A32896
Funding Number(s)
CONTRACT_GRANT: DE-AI05-87OR-21749
Distribution Limits
Public
Copyright
Other

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