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The microstructure of silicon carbide (Nicalon) fibre reinforced silicon carbide ceramic‐matrix composites heat treated in vacuo and in pure oxygen
Author(s) -
VINE W. J.,
STEEDS J. W.
Publication year - 1993
Publication title -
journal of microscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.569
H-Index - 111
eISSN - 1365-2818
pISSN - 0022-2720
DOI - 10.1111/j.1365-2818.1993.tb03296.x
Subject(s) - materials science , composite material , microstructure , silicon carbide , recrystallization (geology) , pyrolytic carbon , ceramic matrix composite , ceramic , electron microprobe , carbide , transmission electron microscopy , scanning electron microscope , metallurgy , pyrolysis , chemical engineering , nanotechnology , paleontology , engineering , biology
SUMMARY Silicon carbide (Nicalon) fibre reinforced SiC composites have been heat treated in vacuo and in pure oxygen environments at 1400°C for 100 h. The response of the microstructure and, in particular, of the interface between fibre, carbon interlayer and SiC matrix components has been studied. Microstructural modifications were observed by transmission electron microscopy, using imaging, electron energy‐loss spectroscopy and electron diffraction techniques, and fibre stoichiometries were determined using a scanning Auger microprobe. Recrystallization of Nicalon fibres within composites heat treated in vacuo was found to result from decomposition of the metastable silicon oxy‐carbide phase found in the fibres. No significant changes to the pyrolytic carbon interlayer were observed. Fibre recrystallization was considered to embrittle the composite. Samples heat treated in oxygen showed no appreciable fibre recrystallization. Study of interlayers in such aged samples often revealed decohesions, holes and narrow silica layers. In the most extreme cases, complete displacement of carbon by SiO 2 was found and such interfaces were identified as silica and α‐cristobalite. Interfacial modifications were considered to be responsible for the retention of the small β‐SiC grain size in Nicalon fibres and were also considered to be deleterious to the mechanical properties.