Effect of the alfa content on the mechanical properties of Si3N4/BAS composite by spark plasma sintering

Barium-alumina-silicate- Si3N4 composite was successfully prepared by spark plasma sintering. Effects of alfa and beta-Si3N4 powders as raw materials and SPS temperature were investigated on the mechanical properties of this composite. X-ray diffraction patterns showed that the alfa-beta phase transformation was completed at 1650 and 1700 °C for the samples with 30 and 90 wt% of primary alfa phase, respectively. Higher amount of alfa phase in the initial powder led to the better mechanical properties due to the in-situ transformation of alfa-beta-Si3N4 with the aspect ratio of more than 4. Alfa-Si3N4 grains were dissolved in the barium-alumina-silicate liquid phase and in-situ transformed to beta-Si3N4 with rod-like morphology which was confirmed by scanning electron microscopy images. Higher alfa-Si3N4 led to the increasing of bending strength and fracture toughness from 352 MPa and 5.6 MPa m1/2 to 610 MPa and 6.2 MPa m1/2, respectively.