Toughening mechanisms in weak matrix ceramic composites
Tough behavior of ceramic matrix composites is closely related to the weak interface between fiber and matrix. The weak interfaces in composites were produced by reducing the chemical bonding and the residual thermal stresses between constituents. A new way to introduce the weak interface by induced porosity or damaged zones, porosity toughening or damage toughening respectively, was proposed to provide the rationale for guiding the development of oxide/oxide composites. The existence of porosity toughening was examined by qualitative theoretical consideration and experiments. Porous oxide/oxide composites were fabricated using alumino-silcate fibers (Nextel 440) and magnesium alumino-silicate matrix (1:1 mixture of kaolinite and talc), and sintered at 1100 and 1200 C. Both types of composites failed non-catastrophically in bending and tensile tests. The porous matrix composites showed the low ultimate strength of 12.7 +/- 3.4 MPa, but showed high work of fracture of 630 +/- 206 J/sq m for the specimens fired at 1100 C when tested in tension. Damaged zones or porous phases were introduced into the interface region of model composites and effects were determined using a single fiber pullout specimen or a single rod pullout specimen. Single fiber pullout specimens with a damaged zone (by the oxidation of SiC fiber in situ) produced higher frictional stress than debonding strength. Frictional stresses increased up to 6.4 +/- 3.4 MPa as pullout of the damaged fiber proceeded. The porous phase was produced by coating alumina rods with zirconia or alumino-silicates fired at various temperatures. Distinct changes in pullout behavior were observed in data for the specimens with an alumino-silicate coating fired at 1450 C. Magnitudes of frictional stress and debonding strength of the interface were both less than 2 MPa. Both coatings produced a gradual change of the pullout load during the pullout tests.
- Research Organization:
- Missouri Univ., Rolla, MO (United States)
- OSTI ID:
- 6839235
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360202 -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
360203* -- Ceramics
Cermets
& Refractories-- Mechanical Properties
ALKALINE EARTH METALS
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
ALUMINIUM SILICATES
BENDING
BONDING
CERAMICS
CHALCOGENIDES
COMPOSITE MATERIALS
DAMAGE
DEFORMATION
ELEMENTS
FABRICATION
FIBERS
INTERFACES
JOINING
KAOLINITE
MAGNESIUM
MATERIALS
MATRIX MATERIALS
MECHANICAL PROPERTIES
METALS
MINERALS
OXIDES
OXYGEN COMPOUNDS
POROSITY
RESIDUAL STRESSES
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SINTERED MATERIALS
STRESSES
TALC
TEMPERATURE RANGE
TEMPERATURE RANGE 1000-4000 K
TENSILE PROPERTIES
THERMAL STRESSES