Evaluation of a porous fiber coating in SiC–Si₃N₄minicomposite

A porous and discontinuous Si₃N₄-based fiber coating was evaluated in SiC/Si₃N₄minicomposites by fiber push-out and fractography for debond capabilities following high temperature exposures. The exposures consisted of 500 h annealing at 1350 °C, and 25–100 h oxidation in wafer form at 1200–1400 °C. In spite of considerable microstructural coarsening and/or oxidation of the coating, fiber debond and sliding were achieved in all cases, and at stress levels comparable to those reported for tough, as-fabricated SiC/Si₃N₄composites with a carbon or boron nitride interphase. Therefore, the porous coating is expected to perform better than C or BN in applications where oxidation is inevitable. The role of porosity in accommodating and mitigating the effects of oxidation is thought to be important.