Crack healing behavior of hot pressed silicon nitride due to oxidation

Journal Article · Wed Apr 01 04:00:00 EST 1992 · Scripta Metallurgica et Materialia; (United States)

DOI:https://doi.org/10.1016/0956-716X(92)90574-X· OSTI ID:5071120

Choi, S R; Tikare, V ^[1]

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1. Cleveland State University, OH (United States) NASA, Lewis Research Center, Cleveland, OH (United States)

It 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. 17 refs.

• OSTI ID: 5071120
• Journal Information: Scripta Metallurgica et Materialia; (United States), Journal Name: Scripta Metallurgica et Materialia; (United States) Vol. 26; ISSN SCRME; ISSN 0956-716X
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360203* -- Ceramics
Cermets
& Refractories-- Mechanical Properties
360205 -- Ceramics
Cermets
& Refractories-- Corrosion & Erosion
ALKALINE EARTH METAL COMPOUNDS
CERAMICS
CHALCOGENIDES
CHEMICAL REACTIONS
CRACKS
FABRICATION
FRACTURE PROPERTIES
HOT PRESSING
MAGNESIUM COMPOUNDS
MAGNESIUM OXIDES
MATERIALS WORKING
MECHANICAL PROPERTIES
NITRIDES
NITROGEN COMPOUNDS
OXIDATION
OXIDES
OXYGEN COMPOUNDS
PNICTIDES
PRESSING
SILICON COMPOUNDS
SILICON NITRIDES
TEMPERATURE RANGE
TEMPERATURE RANGE 1000-4000 K