- Nanoindentation was used to measure the elastic modulus (E) and hardness (H) of the matrix materials of three ceramic composites reinforced with woven Nicalon fiber fabrics. The matrices included: (1) alumina produced by the Dimox process; (2) silicon carbide synthesized by chemical vapor infiltration; and (3) a SiC/BN material produced by polymer infiltration pyrolysis. The elastic moduli and hardnesses of the matrices of all three materials were found to be significantly lower than bulk ceramics of similar composition, probably due to porosity in the matrix and/or incomplete conversion of the infiltration materials to ceramic. Each of the composites was exposed to air at 750C for 64 h, and measurements of E and H were made. The silicon carbide matrix was essentially unaffected, but two other materials exhibited significant reductions in both E and H caused by thermal exposure.