Page 97 - Fiber Fracture

82 A.R. Bunsell

Fig. 6. Fracture morphology of the Tyranno SA fibre broken in tension at room temperature.

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Fig. 7. Microstructure of the Tyranno SA fibre.

Fig. 6 shows the fracture morphology of a Tyranno SA fibre. The fibre has a diameter of
10 Fm. The fracture surface can be seen to be markedly granular in sharp contrast to the
earlier fibres.
An examination of the microstructure by TEM reveals that the Sic grains in the
Tyranno SA fibre are around 200 nm in size, as is shown in Fig. 7. Despite the claim
of near-stoichiometry there is considerable free carbon in the fibre and its concentration
increases near the centre of the fibre indicating incomplete removal during sintering.
The Sylramic fibre produced by Dow Corning uses a PCT precursor which is doped
with boron to aid sintering and to control grain growth during heating to around 1600°C.
The fibre has a diameter of 10 Wm and Sic grain sizes ranging from 0.1 to 0.5 km