Polymer impregnation and pyrolysis (PIP) method for the preparation of laminated woven fabric/mullite matrix composites with pseudoductility

An ethylalcohol solution containing Si(OC2H5)(4) and Al(NO3)(3) with a composition of mullite, 3Al(2)O(3).SiO2, was infiltrated into a porous laminated woven fabric of 22-35 vol.% SiC or Al2O3-SiO2 fibers and 8-42 vol.% mullite powder (filler). The solution was then decomposed at 500 degreesC in air. This polymer impregnation and pyrolysis method (PIP) was repeated 20-23 times to produce a laminated mullite matrix composite of 73-79% density. The pseudoductility of the densified composite when tested in four-point bend was caused by delamination cracks. This mechanical property was enhanced by (1) good dispersion of the mullite filler in the filament yarn, (2) large amounts of dispersed filler, (3) formation of weak bonds in the filament yarn from the pyrolysis of the mullite precursor, and (4) lower amounts of mullite precursor-derived amorphous solid. The infiltration of the mullite filler dispersed electrosterically in an aqueous solution into the woven fabric offered significant pseudoductility, but infiltration of the filler dispersed in the ethylalcohol solution of the mullite precursor resulted in a brittle composite. (C) 2003 Elsevier Ltd. All rights reserved.