EFFECT OF PROCESSING AND FIBER COATING ON FIBER-MATRIX INTERACTION INMULLITE FIBER MULLITE MATRIX COMPOSITES

The fiber-matrix interaction in mullite fiber-mullite matrix composite s was investigated with the composites fabricated using a commercial m ullite powder and a mullite powder synthesized in our laboratory (via a diphasic gel route) as the matrix with uncoated and BN-coated fibers . Two different BN-coating thicknesses, 0.3 mum and 1 mum, were used. The composites made from the mullite powder synthesized in our laborat ory showed less interaction between the fiber and matrix as well as no fiber deformation owing to a lower processing temperature, compared w ith the composite made from the commercial mullite powder. However, th e fiber-matrix bonding in both the uncoated and even 0.3 mum BN-coated cases was still strong so that no fiber pullout was observed on the f racture surfaces. In the case of the 0.3 mum BN-coated fiber, the stro ng interfacial bonding resulted because the coating thickness was too thin to survive during processing. With 1 mum BN-coated fiber, however , extensive fiber pullout could be obtained because the coating surviv ed and prevented bonding between the fiber and matrix.