Update on SiC Fiber/[MoSi₂-Matrix/Si₃N₄ Particle] Composites

A report presents updated information on the developments described in "MoSi2-Based Composite Materials for Aircraft Engines" (LEW-16617),NASA Tech Briefs, Vol. 22, No. 9 (September 1998), page 62. To recapitulate: Hybrid composites of (1) SiC-based fibers within (2) matrices that are, themselves, composites of MoSi2 containing 30 to 50 volume percent of Si3N4particles are candidate high-temperature-resistant materials for use in advanced aircraft engines. The addition of the Si3N4 particles (1) results in the formation of an Si2ON2 protective scale that increases resistance to low-temperature accelerated oxidation, which otherwise causes catastrophic "pest failure" of MoSi2; (2) increases high-temperature creep strength to almost 105 times that of neat MoSi2; (3) doubles room-temperature toughness; and (4) decreases the coefficient of thermal expansion to such an extent as to eliminate matrix cracking in the presence of SiC-based fiber reinforcement, even after thermal cycling.