Effect of TiB2 addition on grain orientation of porous Si3N4-TiB2 composites by magnetic field alignment technology

Textured porous Si3N4-TiB2 composites were prepared by gel-casting-assisted magnetic field alignment technology and subsequent pressureless sintering in the N-2 atmosphere. The effects of TiB2 content on grain orientation and properties of composites were studied. Results showed that using the magnetic field of 6T, Si3N4 grains exhibited a high a- or b-axis orientation and TiB2 grains exhibited a high c-axis orientation. In textured green bodies, the increase in TiB2 content from 0 to 20 wt%, the degree of texture of Si3N4 grains showed a slight decrease from 0.78 to 0.71. However, the degree of texture of TiB2 grains was maintained at about 0.98 regardless of TiB2 content. After sintering, except for the Si3N4 and TiB2 phases, new TiN and BN phases also appeared in the samples. Additionally, the sintering process promotes grain orientation of Si3N4 and TiB2. Herein, the degree of texture of TiB2 reached to about 1 regardless of TiB2 content, meaning that the complete grain orientation formed for TiB2. Owing to the reconstruction reaction between TiB2 and N-2, new TiN and BN phases did not form the orientation. The increase in TiB2 contents gradually increased the apparent porosity of the textured samples from 27.9% to 39.4%, thereby leading to the decrease in bending strength from 126.8 +/- 18.8 MPa to 60.3 +/- 11.2 MPa and from 105.3 +/- 19.8 MPa to 53.6 +/- 13.0 MPa in two directions, respectively.