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 SiC or Nextel(R) 440 mullite fibers are reported. The method used to make composites is a three stages sol-gel process: (i) in situ gelation of a mixture of alkoxides in a ceramic fiber fabric, (ii) the deposit of a matrix precursor onto the impregnated fabrics and (iii) hot-pressing of the stacked fabrics in a carbon mold. The composites have been studied by SEM and TEM. Three point flexural strength has been measured at room temperature and at 900 degrees C in air. Local Young's modulus, microhardness and interfacial shear stress have been determined at RT. Micro-Raman spectra and X-ray microanalysis have been used to study 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 ZrO2-GeO2 gel interface precursor allows us to obtain dense composites at a low temperature exhibiting good mechanical properties (linear behaviour up to similar to 180 MPa, even after annealing in air). The effects of a zirconia interphase on the mechanical properties of mullite-mullite composite are also discussed.