This fiber is similar in size and microstructure to boron.
The fibres are produced on both tungsten and carbon cores.
These fibres are relativity stiff due to thicker diameter of the fibres. The diameter of the fibres is about 140 .
The fibres have strength in the range of 3.4 – 4.0 GPa.
Failure strain is in the range of 0.8 - 1%.
The Young’s modulus is about 430 GPa.
The fibres show high structural stability and strength retention even at temperatures above 1000 .
The CVD with as the reactant, SiC is deposited on the core as follows:
The SiC fibres produced on a tungsten core with a diameter about 12 . It shows a thin interfacial layer between the SiC mantle and the tungsten core. In case, when carbon fibre is used the fibre diameter of the carbon fibres is about 33 .
Both type of SiC fibre have smoother surfaces than a boron fibre. This is because there is a deposition of small columnar grains as compared to conical nodules in boron fibres.
The SiC fibres produced with carbon core are used in light reinforced alloys. These fibres are produced with a surface coating. The composition of this coating varies from carbon rich from inner surface to silicon carbide at the outer surface.
The fibres that are used to reinforce the titanium have a protective layer which varies from a carbon rich to silicon rich and again to a composition which is rich in carbon at the surface. The outer surface acts as a protective surface and when it comes in contact with molten and highly reactive titanium. The fibres are made by Specialty Materials Inc. under the trade name SCS-6. The coating increases the fibres diameter by 6 .
The fibre has low failure stresses due to surface flaws.
The higher strength of fibre is due to the controlled defects at the core-mantle interface.
The strength of SiC fibres produced using CVD is seen to be anisotropic. The radial strength is significantly lower than longitudinal tensile strength.
When the fibres are heated to above 800 ºC in air for a long period, they lose their strength due to oxidation of the carbon rich outer layers.
The CVD for SiC fibres is shown in Figure 1.9.
Figure 1.9: Schematic of reactors for silicon carbide fibres by Chemical Vapour Deposition