Development and Characterization of Continuous SiC Fiber‐Reinforced HfB 2 ‐Based UHTC Matrix Composites Using Polymer Impregnation and Slurry Infiltration Techniques

This paper discusses the development of continuous SiC fiber‐reinforced HfB 2 ‐SiC composite laminates. A range of techniques, based on resin‐based precursors and slurries, for infiltrating porous SiC preforms with HfB 2 powder were developed. While resin‐based precursors proved to be ineffective due to low HfB 2 yield and poor adhesion, the slurry infiltration techniques were effective to varying degrees. The greatest pore filling and composite densities were achieved using pressure and vibration‐assisted pressure infiltration techniques. SiC f /HfB 2 ‐SiC laminates were subsequently developed via lamination, cure and pyrolysis of fabrics using a HfB 2 ‐loaded polymeric SiC precursor, followed by HfB 2 slurry infiltration and preceramic polymer infiltration and pyrolysis ( PIP ). Repeated PIP processing, for 6–10 cycles, resulted in density increases, from the 3.03–3.22 g/cm 3 range after HfB 2 slurry infiltration, to 3.97–4.03 g/cm 3 after PIP processing. Correspondingly, there was a decrease in open porosity from approximately 52% to less than 11%. The matrix consisted of discreet, lightly sintered HfB 2 particles dispersed in SiC. The PIP SiC matrix was primarily nanocrystalline after 1300°C pyrolysis, but experienced grain growth with further heat treatment at 1600°C.