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Interfacial chemistry-structure and fracture of ceramic composites

Conference ·
OSTI ID:5484371
The interfacial chemistry and structure of SiC/Si/sub 3/N/sub 4/ composites has been evaluated using TEM/STEM and AES. Nicalon SiC fiber reinforced hot-pressed Si/sub 3/N/sub 4/ and VLS single crystal SiC reinforced reaction-bonded silicon nitride (RBSN) have been evaluated. An amorphous carbon-graphite interface structure was observed in the Nicalon SiC fiber-reinforced material resulting from sizing used to assist fiber handling. Fiber pull-out occurred upon fracture of the composite material with the fracture apparently occurring between the amorphous and graphitic carbon layers. The flexure strength of the composite was about 1/3 that of the matrix with the degradation apparently resulting from the development of a glass phase in the grain boundaries of the Nicalon during hot pressing. The interfaces of Si/sub 3/N/sub 4/ matrix composites with C, BN, SiO/sub 2/ coated and untreated VLS whiskers were found to vary markedly. In the RBSN composites, the C was present in the form of a fibrous graphitic structure, the BN coating was nonexistent but large facets had formed on the whiskers while the SiO/sub 2/ coating was present as a discontinuous glass phase. The composite with the SiO/sub 2/ coated whiskers exhibited the highest fracture strength and toughness while the material made with BN-coated whiskers exhibited the lowest values. 4 figs., 1 tab.
Research Organization:
Pacific Northwest Lab., Richland, WA (USA); Los Alamos National Lab., NM (USA)
DOE Contract Number:
AC06-76RL01830
OSTI ID:
5484371
Report Number(s):
PNL-SA-15269; CONF-880118-1; ON: DE88005516
Country of Publication:
United States
Language:
English