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Seeded Grain Growth for Textured Silicon Carbide and Mullite.

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Final Technical rept. 1 Sep 94-31 Aug 97

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Textured fibers and bulk samples were fabricated using seeded grain growth. For bulk SiC samples, small amounts of SiC platelets were incorporated with preferred orientation during green-state processing of powder compacts. Upon heat treatment, the platelet seeds grew with preferred orientation by consuming the fine grains of the surrounding sintered SiC matrix. The volume fraction, size, and morphology of the in-situ grown plate-like grains could be controlled through variables such as heat-treatment temperature, matrix particle size, seed concentration, additive type, etc. Samples prepared with aluminayttria additives were used to prepare In-situ toughened SiC bulk samples. SiC fibers were prepared using organosilicon polymer precursors. Textured fibers were fabricated using SiC whiskers or platelets as seed crystals, but these fibers had relatively low strengths because the seeds and large grains formed during heat treatment acted as strength- degrading flaws. Unseeded SIC fibers with textured boron nitride BN coatings were formed by an in-situ reaction method. These fibers had high tensile strength and excellent creep resistance. Textured Si3N4 fibrous monoliths were fabricated using extruded, powder-derived fibers which contained Si3N4 whiskers as seeds. The textured Si3N4 showed fracture toughness anisotropy.

Subject Categories:

  • Inorganic Chemistry
  • Textiles
  • Properties of Metals and Alloys

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