Fracture mechanisms in monolithic structural ceramics and ceramic composites
The fracture of three structurally distinct materials was characterized at test temperatures ranging from 20 through 1400{degree}C. Two monolithic, polycrystalline ceramic materials, one a high-purity transparent MgAl{sub 2}O{sub 4} spinel and the other a sintered Si{sub 3}N{sub 4} containing a grain-boundary, second-phase, sintering additive, provided for a comparison of the fracture mechanisms as they are governed by the differing microstructures. The third, a SiC whisker-reinforced, polycrystalline Al{sub 2}O{sub 3} matrix composite offered the added mechanism of a high-strength, high-modulus load-carrying element, not available in conventional, monolithic ceramic microstructures. The high-purity MgAl{sub 2}O{sub 4} spinel was found to maintain a constant fracture toughness of approximately 1.7 MPa{center dot}m{sup {1/2}} through 600{degree}C and then experienced only a slight decrease above this temperature to about 1.3 MPa{center dot}{sup {1/2}}. By comparison, the fracture toughness of the Si{sub 3}N{sub 4} decreased from nearly 8.0 MPa{center dot}m{sup {1/2}} at room temperature, to below 2.0 MPa{center dot}{sup {1/2}} 1400{degree}C, as governed by the character of the grain boundary glass phase. The SiC whisker/Al{sub 2}O{sub 3} composite was characterized by a fracture toughness value of about 6.8 MPa{center dot}{sup 1/2} throughout the test temperature range.
- Research Organization:
- Washington Univ., Seattle, WA (USA)
- OSTI ID:
- 5247268
- Country of Publication:
- United States
- Language:
- English
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ALKALINE EARTH METAL COMPOUNDS
ALUMINATES
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CARBIDES
CARBON COMPOUNDS
CERAMICS
CHALCOGENIDES
COMPOSITE MATERIALS
CRYSTALS
FRACTURE PROPERTIES
HIGH TEMPERATURE
MAGNESIUM COMPOUNDS
MAGNESIUM OXIDES
MATERIALS
MECHANICAL PROPERTIES
MINERALS
MONOCRYSTALS
NITRIDES
NITROGEN COMPOUNDS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PNICTIDES
POLYCRYSTALS
SILICON CARBIDES
SILICON COMPOUNDS
SILICON NITRIDES
SPINELS
VERY HIGH TEMPERATURE
WHISKERS