Fiber-reinforced ceramic matrix composites using alumina nanoparticles

Sapphire, SiC, carbon and Kevlar (R) fibers have been dip-coated in aqueous solutions of Ca-, La- and Y-doped carboxylate-alumoxane nanoparticles and fired to form uniform, conformal and contiguous, aluminate coatings; CaAl12O19, LaAl11O18, and Y3Al5O12, respectively. Optimum solvent, dip/dry cycles, and firing sequences were determined for the formation of crack-free coatings. Coatings produced were stable to thermal cycling under air at temperatures of 1400 degreesC. The ability of the carboxylate-alumoxanes to provide crack infiltration and repair is demonstrated. Fiber-reinforced ceramic matrix composites (CMCs) have been prepared with Ca- and La-aluminate interphase layers. Microscopy and fiber push-out data confirm that the Ca- and La-hexaluminate coatings provide a means for controlling failure properties at the fiber-matrix interface with no detrimental chemical or physical reaction. However, CMCs containing YAG-coated fibers failed catastrophically before interfacial debonding and/or sliding occurred. Results from 3-point bend tests for carbon/Kevlar (R) fabric-reinforced CMCs and carbon fiber-reinforced CMCs were within the ranges observed for previously reported CMCs of similar composition.