Evaluation of Porous ZrO ₂ ‐SiO ₂ and Monazite Coatings Using Nextel ^TM 720‐Fiber‐Reinforced Blackglas™ Minicomposites

Abstract

A procedure was developed to fabricate oxide‐fiber‐reinforced minicomposites with a dense matrix and evaluate two oxidation‐resistant interface coatings, porous oxide (zirconia‐silica mixture) and monazite. The coatings were evaluated using Nextel TM 720‐fiber‐reinforced Blackglas TM ‐matrix minicomposites. Boron nitride (BN) coated and uncoated fibers were used as controls for comparison. The evaluation was based on ultimate failure strengths, fractography, and fiber pushin tests. All the composites that used fiber coatings had ultimate strengths significantly better than the control that used uncoated fibers. In addition, porous‐oxide‐coated fibers were found to be similar to BN‐coated fibers in strength, fractography, and fiber pushin behavior. Monazite‐coated fibers resulted in similar ultimate strengths but showed no appreciable fiber pullout. Fiber pushin tests showed that monazite debonds readily but frictional resistance is higher than for BN or porous oxide fiber coatings.