Oxidation resistance in air of 1-D SiC (Hi-nicalon) fibre reinforced silicon nitride ceramic matrix composite

The oxidation behaviour of a Si3N4 matrix reinforced with SiC fibres (Hi-Nicalon) precoated with a 400 nm thick pyrolytic carbon layer has been investigated in dry air in the temperature range 800-1500 degrees C. The same study was performed for individual constituents of the composite (fibre and matrix), Two phenomena are: observed in the oxidation behaviour of the composite. Al low temperature (T<1200 degrees C), the matrix oxidation is negligible, only the carbon interphase was oxidised creating an annular space between the fibres and the matrix throughout the sample. Ar high temperature (T greater than or equal to 1300 degrees C) the rate of formation of the oxidation products of the matrix is rapid and a sealing effect is observed, While at these temperatures the interphase is protected in the bulk of the material, the time needed to seal the gap between the fibre and the matrix is too long to prevent its oxidation to a significant depth from tile surface, Finally, preliminary results are presented where the consumption of the interphase is completely prevented by applying an external coating which gives oxidation protection from low to high temperature.