SOL-GEL MULLITE MATRIX-SIC AND MULLITE 2D WOVEN FABRIC COMPOSITES WITH OR WITHOUT ZIRCONIA CONTAINING INTERPHASE - ELABORATION AND PROPERTIES

The properties of composites made with fabrics of Nicalon(R) NLM202 Si C or Nextel(R) 440 mullite fibers are reported. The method used to mak e composites is a three stages sol-gel process: (i) in situ gelation o f a mixture of alkoxides in a ceramic fiber fabric, (ii) the deposit o f a matrix precursor onto the impregnated fabrics and (iii) hot-pressi ng of the stacked fabrics in a carbon mold. The composites have been s tudied by SEM and TEM. Three point flexural strength has been measured at room temperature and at 900 degrees C in air. Local Young's modulu s, microhardness and interfacial shear stress have been determined at RT. Micro-Raman spectra and X-ray microanalysis have been used to stud y the fiber-interface reactions. Using a mixture of aluminium-silicon ester and tributylborate as interface precursor, we obtained a carbon film free SiC-mullite sliding interface. The use of a complementary Zr O2-GeO2 gel interface precursor allows us to obtain dense composites a t a low temperature exhibiting good mechanical properties (linear beha viour up to similar to 180 MPa, even after annealing in air). The effe cts of a zirconia interphase on the mechanical properties of mullite-m ullite composite are also discussed.