Fabrication and Characterization of Barium Aluminum Silicate-Silicon Nitride Composites

The barium aluminum silicate-silicon nitride (BAS-Si3N4) matrix-ceramic composite was fabricated using pressureless sintering, at temperatures ranging from 1720 degrees C, which is below the melting point of BAS, to 1850 degrees C. The effect of processing conditions on sinterability, crystalline structure, microstructure and mechanical properties was evaluated. It was demonstrated the BAS glass-ceramic served as an effective liquid-phase-sintering aid, to attain high densities and completed the alpha-Si3N4-beta-Si3N4 phase transformation, and remained as a structural matrix that was reinforced by the rod-like beta-Si3N4 grains. Si3N4 grains nucleated and grow in random directions in an almost completely crystallized matrix of hexacelsian bAS. High flexural strength (665 +/- 40 MPa) and fracture toughness (7.74 MPa.m(1/2)) could be obtained from 30wt%BAS-70wt%Si3N4 samples that have been sintered at 1800 degrees C for 120 min with a fine-grained microstructure.