Phenomenology of fracture and fracture mechanisms under slow-crack-growth/creep regimes in high-purity Si{sub 3}N{sub 4} and its SiC-platelet composite

Journal Article · Sat Apr 01 04:00:00 EST 1995 · Acta Metallurgica et Materialia

DOI:https://doi.org/10.1016/0956-7151(94)00372-O· OSTI ID:39836

Pezzotti, G; Sakai, M ^[1]; Okamoto, Y; Nishida, T ^[2]

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1. Toyohashi Univ. of Technology (Japan). Dept. of Materials Science
2. Kyoto Inst. of Tech. (Japan). Dept. of Materials Engineering

The mechanical behaviors and the microfracture mechanisms of a high-purity dense Si{sub 3}N{sub 4} material and its 25 vol.% SiC-platelet composite have been investigated in the range of temperature 1,400--1,520 C by means of extensive mechanical testing coupled to transmission (TEM) and scanning (SEM) electron microscopy. Creep fracture was not observed even after several hundred hours exposure at high temperature and the slow (subcritical) crack growth (SCG) from a single, most critical pre-existing flaw was the dominant failure mechanism. Phenomenological crack-growth laws were discussed and compared with a theoretical model for diffusive crack propagation. Marked lifetime elongations and increased flaw crack tolerance were found in the composite material due to shielding mechanisms operated by the SiC platelets in the wake of the intergranular SCG crack. These positive effects, diminishing substantially with increasing the temperature, were well explained by an algorithm incorporating into the mechanical driving force acting on the crack tip, the closure-field contribution due to the rising R-curve behavior of the material.

• OSTI ID: 39836
• Journal Information: Acta Metallurgica et Materialia, Journal Name: Acta Metallurgica et Materialia Journal Issue: 4 Vol. 43; ISSN 0956-7151; ISSN AMATEB
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
COMPOSITE MATERIALS
CRACK PROPAGATION
CRACKS
CREEP
DEFECTS
FRACTURE MECHANICS
FRACTURE PROPERTIES
SILICON CARBIDES
SILICON NITRIDES