Development of polyvinylsilazane-derived ceramic matrix composites based on Tyranno SA3 fibers

Abstract

A damage tolerant weak matrix SiC fiber reinforced composite was developed by utilising a polyvinylsilazane in the polymer infiltration and pyrolysis (PIP) process. The polysilazane was infiltrated via resin transfer moulding in a layup of SA3 fabrics, thermally cured and pyrolyzed. This process was repeated until a residual open porosity of below 5% was reached. During pyrolysis the polyvinylsilazane converts to an amorphous SiCN matrix. In combination with the high modulus Tyranno SA3 SiC fibers a weak matrix composite is created. To protect the composite in oxidative environment at high temperatures, an exterior SiC coating by means of chemical vapour deposition was applied. The polyvinylsilazane was investigated in terms of differential scanning calorimetry and measurement of viscosity to find the ideal temperatures for the polymer infiltration step. Specimens of the precursor were cured and pyrolyzed. The densification during pyrolysis was investigated in terms of He gas pycnometry and X-ray diffraction. The composite was characterized by SEM, μCT and mercury intrusion porosimetry. To determine the suitability of the SiC/SiCN composite for high temperature applications, samples were oxidized and tested by means of 3-point bending.