Cavitation mechanisms during tensile creep of an advanced silicon nitride

Conference · Tue Dec 31 04:00:00 EST 1996

OSTI ID:518611

Lofaj, F; Okada, A ^[1]; Usami, H ^[2]

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1. Japan Fine Ceramics Center, Nagoya (Japan)
2. Meijo Univ., Nagoya (Japan); and others

Creep cavitation was investigated by electron microscopic methods after tensile creep tests of a self-reinforced silicon nitride conducted at temperatures ranging from 1250 to 1400{degrees}C. Fast and intensive cavitation in the amorphous secondary phase and slow growth of cavities inside the large silicon nitride grains were observed. Two basic types of cavities in glassy boundary phase were found; rounded cavities on the facets of large grains and irregular cavities in pockets among the matrix grains. A driving force for cavitation in boundary phase on large grain facets is concluded to be local tensile stress on local irregularities of facets produced on the interfaces between large grains and finer matrix grains during grain boundary sliding (GBS). Dilatant hydrostatic tensile stresses generated in a matrix due to GBS were thought to be responsible for cavitation in multigrain junctions. Small cavities formed on the facets and large cavities penetrating through the whole large grains of silicon nitride were found after long-term tests. The stresses transferred from matrix to large grains are suggested as a driving force for slow growth of small cavities on the facets and their later penetration inside the large silicon nitride grains. Basic cavitation mechanisms in amorphous phase are thought to be GBS and viscous flow while solution-precipitation is responsible for cavity growth in large silicon nitride grains.

• OSTI ID: 518611
• Report Number(s): CONF-960367--
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CERAMICS
CREEP
GRAIN SIZE
INTERFACES
SILICON NITRIDES
STRESSES
TENSILE PROPERTIES