PRESSURE INFILTRATION OF SOL GEL PROCESSED SHORT-FIBER CERAMIC-MATRIXCOMPOSITES/

Using pressure infiltration short fibre-reinforced ceramic matrix comp osites with uniform and dense microstructure can be made. Based upon t his processing technique, composites composed of silica sol, alumina p articles, and alumina short fibres were fabricated. The related proces sing parameters studied in this work include infiltration rate, fibre volume fraction V-f, particle size, and infiltrate viscosity. An optim al infiltration rate was 4 mm min(-1), at which rate the composite wit h V-f of 8.1% and particle size of 3 mu m has the highest green densit y. An equilibrium between particle packing strength and applied load m ust be obtained during the infiltration to obtain high green density a nd composite strength. The influence of fibre volume fraction and part icle size on composite green density is in a synergistic manner becaus e it involves particle-fibre interactions, fibre-fibre interactions, a nd sedimentation. Furthermore, the increase of sol viscosity results i n more sedimentation in the infiltrate and lower composite green densi ty. The fracture toughness of composites is 38% higher than that of mo nolithic alumina. (C) 1998 Chapman & Hall.