Evaluating Use of Boron- and Hafnium-Modified Polysilazanes for Ceramic Matrix Minicomposites

In this study, the potential of polymer-derived ceramic matrix composites (CMCs) is demonstrated by the addition of thin ceramic coatings on carbon fiber (CF) bundles. Boron- and hafnium-modified polysilazane liquid precursors were synthesized and used to infiltrate the fiber bundles of CF to fabricate lab-scale Si­(B)­CN/CF and Si­(Hf)­CN/CF CMC minicomposites, respectively by crosslinking and then pyrolysis at 800 °C. The crosslinked precursor to ceramic yield was observed to be as high as 90% when the procedure was carried out in inert environment. The Si­(B)­CN/CF contained Si–N and B–N bonds, while Si–N and Hf–O–Si bonds were observed for the Si­(Hf)­CN/CF sample with uniform and dense surfaces. Room-temperature tensile tests showed that the Si­(Hf)­CN/CF sample could reach a tensile strength of ∼790 MPa and an elastic modulus of 66.88 GPa among the composites. An oxidation study of the Si­(Hf)­CN/CF minicomposites showed higher stability compared to SiCN/CF and Si­(B)­CN/CF minicomposites up to 1500 °C.