Accession Number : ADA304266

Title :   Mullite Fiber Reinforced Reaction Bonded Si3N4 Composites,

Corporate Author : MASSACHUSETTS INST OF TECH CAMBRIDGE

Personal Author(s) : Saleh, T. ; Lightfoot, A. ; Haggerty, J. ; Sayir, A.

PDF Url : ADA304266

Report Date : JAN 1996

Pagination or Media Count : 8

Abstract : Fracture toughnesses of brittle ceramic materials have been improved by introducing reinforcements and carefully tailored interface layers. Silicon carbide and Si3N4 have been emphasized as matrices of structural composites intended for high temperature service because they combine excellent mechanical, chemical, thermal and physical properties. Both matrices have been successfully toughened with SiC fibers, whiskers and particles for ceramic matrix composite (CMC) parts made by sintering, hot pressing or reaction forming processes. These SiC reinforced CMCs have exhibited significantly improved toughnesses at low and intermediate temperature levels, as well as retention of properties at high temperatures for selected exposures; however, they are vulnerable to attack from elevated temperature dry and wet oxidizing atmospheres after the matrix has cracked. Property degradation results from oxidation of interface layers and/or reinforcements. The problem is particularly acute for small diameter (-20 tim) polymer derived SiC fibers used for weavable toes. This research explored opportunities for reinforcing Si3N4 matrices with fibers having improved environmental stability; the findings should also be applicable to SiC matrix CMCs. (MM)

Descriptors :   *CERAMIC MATRIX COMPOSITES, *FIBER REINFORCED COMPOSITES, *CERAMIC MATERIALS, THERMAL PROPERTIES, STABILITY, DEGRADATION, HIGH TEMPERATURE, HOT PRESSING, TOUGHNESS, MOISTURE CONTENT, FRACTURE(MECHANICS), BRITTLENESS, OXIDATION, THERMAL EXPANSION, SILICON CARBIDES, SINTERING, WHISKER COMPOSITES, MATERIAL FORMING.

Subject Categories : Ceramics, Refractories and Glass
      Laminates and Composite Materials

Distribution Statement : APPROVED FOR PUBLIC RELEASE