Page 100 - Fiber Fracture

FRACTURE PROCESSES IN FINE SILICON CARBIDE FIBRES 85

t

-t- Sylramic + Hi-Nicalon
-0- Tyranno

0 500 Type s 1000 1500
Temperature /"C
Fig. 12. The strength retention of the near-stoichiometric fibres is superior to that of earlier generations.

1400°C
1, E-04

h
8 1 ,E-05
7
v
+
Q)
2 1 ,E-06
c
.-
03
b 1 ,E-07
v)
1, E-08
0,1 1 ,o 10,o
Applied stress (GPa)
Fig. 13. The creep rates of the Nicalon Type S fibres are lower than the other near-stoichiometric fibres
which contain sintering aids.

A comparison of the creep behaviour between the Tyranno LOX-E fibre which contains
5 wt% of oxygen and the Hi-Nicalon fibre which contains 0.5 wt% of oxygen shows the
lower creep rates at high temperatures of the latter fibre, as can be seen in Fig. 1 1.
The Young moduli of the near-stoichiometric fibres are 375 GPa for the Hi-Nicalon
Type S, 330 GPa for the Tyranno SA and 390 GPa for the Sylramic fibre. Fig. 12 shows
that they retain their strengths to higher temperatures than the earlier generations of
fibres. The Hi-Nicalon Type S fibre shows little or no loss of strength even at 1400°C.
As can be seen from Fig. 13 the creep rate of the Hi-Nicalon Type S fibre is one
order of magnitude lower than that of the other two near-stoichiometric fibres because
of the lack of sintering aids which facilitate creep at high temperatures. Growth of a