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Effect of W and WC on the oxidation resistance of yttria-doped silicon nitrideThe effect of tungsten and tungsten carbide contamination on the oxidation and cracking in air of yttria-doped silicon nitride ceramics is investigated. Silicon nitride powder containing 8 wt % Y2O3 was doped with 2 wt % W, 4 wt % W, 2 wt % WC or left undoped, and sintered in order to simulate contamination during milling, and specimens were exposed in air to 500, 750 and 1350 C for various lengths of time. Scanning electron and optical microscopy and X-ray diffraction of the specimens in the as-sintered state reveals that the addition of W or WC does not affect the phase relationships in the system, composed of alpha and beta Si3N4, melilite and an amorphous phase. Catastrophic oxidation is observed at 750 C in specimens containing 2 and 4 wt % W, accompanied by the disappearance of alpha Si3N4 and melilite from the structure. At 1350 C, the formation of a protective glassy oxide layer was observed on all specimens without catastrophic oxidation, and it is found that pre-oxidation at 1350 C also improved the oxidation resistance at 750 C of bars doped with 4 wt % W. It is suggested that tungsten contamination from WC grinding balls may be the major cause of the intermediate-temperature cracking and instability frequently observed in Si3N4-8Y2O3.
Document ID
19800061929
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Schuon, S.
(NASA Lewis Research Center Cleveland, Ohio, United States)
Date Acquired
August 10, 2013
Publication Date
April 1, 1980
Subject Category
Nonmetallic Materials
Meeting Information
Meeting: Annual Meeting
Location: Chicago, IL
Start Date: April 28, 1980
End Date: April 30, 1980
Sponsors: American Ceramic Society
Accession Number
80A46099
Distribution Limits
Public
Copyright
Other

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