Page 102 - Fiber Fracture

FRACTURE PROCESSES IN FINE SILICON CARBIDE FIBRES 87

CONCLUSION

The fracture morphologies of the fine silicon carbide fibres made from polymer
precursors reveal the nature of their microstructures of the fibres. Successive generations
of fibres have been created with reduced oxygen contents so producing better controlled
microstructures and eliminating the presence of amorphous intergranular phases which
limit mechanical behaviour at high temperatures. As a consequence the Sic grains have
become larger and the Young moduli have increased. Whereas the earliest Sic fibres had
Young moduli of around 200 GPa and showed glassy fracture morphologies because of
their nanometric grain structure, the latest, near-stoichiometric fibres have moduli of up
to 400 Gpa and fail with a granular fracture morphology reflecting the large Sic grains
of their structures.

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