FABRICATION OF NEAR NET SHAPE SIC/SIC COMPOSITES BY SILICON MELT INFILTRATION

THE OVERALL OBJECT OF THIS PROGRAM IS TO DEVELOP AN ECONOMIC PROCESS FOR THENEAR NET SHAPE FABRICATION OF SIC/SIC CERAMIC COMPOSITES BY LIQUID SILICON INFILTRATION OF POROUS SIC FIBER/CARBON MATRIX PERFORMS. THE PRIMARY OBJECTIVE OF THE PHASE I EFFORT IS TO DEMONSTRATE THAT A SILICON MELT INFILTRATION PROCESS CAN BE USED TO FABRICATE A DENSE COMPOSITE WITH CONTROLLED QUANTITIES OF FREE SILICON OR FREE CARBON IN THE MATRIX. A SECOND OBJECTIVE IS TO DEMONSTRATE A FIBER COATING SYSTEM THAT WILL GIVE THE COMPOSITE THE REQUIRED TOUGHNESS. SIC FIBER REINFORCED, PHENOLIC RESIN MATRIX, 2D LAMIATE PREFORMS WILL BE PREPARED BY CONVENTIONAL RESIN COMPOSITE TECHNOLOGY. THE FIBERS WILL HAVE A CARBON COATING TO PROTECT THEM AND TO PROMOTE WETTING BY THE INFILTRANT. VARIOUS MATRIX RESINS WILL BE USED SO THAT PYROLYSIS WILL YIELD POROUS PREFORMS WITH OPEN POROSITIES BETWEEN 15% AND 30%. THE PYROLYZED PREFORMS WILL BE MELT INFILTRATED WITH LIQUID SILICON TO CONVERT THE MATRIX CARBON TO SIC. THE FIBER COATING EFFORT WILL FOCUS ON THE USE OF BN OR CARBON AS THE WEAK FIBER/MATRIX INTERFACE AND BN OR SIO2 AS THE DIFFUSION BARRIER. BN AND CARBON FIBER COATINGS WILL BE APPLIED BY CHEMICAL VAPOR DEPOSITION (CVD). SIO2 DIFFUSION BARRIERS WILL BE FORMED IN SITU BY OXIDATION OF AN SIC OUTER FIBER COATING. THIS PROGRAM WILL DEMONSTRATE AN ECONOMIC NEAR NET SHAPE PROCESS FOR THE FABRICATION OF SIC/SIC CERAMIC COMPOSITES. ANTICIPATED BENEFITS/POTENTIAL COMMERCIAL APPLICATIONS - HIGH TEMPERATURE SIC/SIC COMPOSITES WOULD ALSO FIND USE IN A VARIETY OF INDUSTRIAL AND POWER SYSTEM APPLICATIONS, INCLUDING HEAT EXCHANGERS, GAS-FIRED RADIANT HEATERS, AND INDUSTRIAL AND VEHICULAR TURBINE ENGINES. KEY WORDS - CERAMIC COMPOSITE, SILICON CARBIDE