Effect of TiB ₂ addition on grain orientation of porous Si ₃ N ₄ ‐TiB ₂ composites by magnetic field alignment technology

Abstract Textured porous Si ₃ N ₄ ‐TiB ₂ composites were prepared by gel‐casting–assisted magnetic field alignment technology and subsequent pressureless sintering in the N ₂ atmosphere. The effects of TiB ₂ content on grain orientation and properties of composites were studied. Results showed that using the magnetic field of 6T, Si ₃ N ₄ grains exhibited a high a‐ or b‐axis orientation and TiB ₂ grains exhibited a high c‐axis orientation. In textured green bodies, the increase in TiB ₂ content from 0 to 20 wt%, the degree of texture of Si ₃ N ₄ grains showed a slight decrease from 0.78 to 0.71. However, the degree of texture of TiB ₂ grains was maintained at about 0.98 regardless of TiB ₂ content. After sintering, except for the Si ₃ N ₄ and TiB ₂ phases, new TiN and BN phases also appeared in the samples. Additionally, the sintering process promotes grain orientation of Si ₃ N ₄ and TiB ₂ . Herein, the degree of texture of TiB ₂ reached to about 1 regardless of TiB ₂ content, meaning that the complete grain orientation formed for TiB ₂ . Owing to the reconstruction reaction between TiB ₂ and N ₂ , new TiN and BN phases did not form the orientation. The increase in TiB ₂ 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.