EVALUATION OF A POROUS FIBER COATING IN SIC-SI3N4 MINICOMPOSITE

A porous and discontinuous Si3N4-based fiber coating was evaluated in SiC/Si3N4 minicomposites by fiber push-out and fractography for debond capabilities following high temperature exposures. The exposures cons isted of 500 h annealing at 1350 degrees C, and 25-100 h oxidation in wafer form at 1200-1400 degrees C. In spite of considerable microstruc tural coarsening and/or oxidation of the coating, fiber debond and sli ding were achieved in all cases, and at stress levels comparable to th ose reported for tough, as-fabricated SiC/Si3N4 composites with a carb on or boron nitride interphase. Therefore, the porous coating is expec ted to perform better than C or BN in applications where oxidation is inevitable. The role of porosity in accommodating and mitigating the e ffects of oxidation is thought to be important.