The Effect of Ti-Si-Fe Addition and N₂ Pressure on Microstructure and Mechanical Properties of BN/SiC/Si₃N₄ Composite Ceramics

BN/SiC/Si₃N₄ composite ceramics were prepared through in-situ nitridation reaction sintering with BN, Si, SiC powders, Ti-Si-Fe alloys and phenolic resin (PFF) as raw materials and B₂O₃ as sintering aid. Mechanical properties of the samples, depending on the content of Ti-Si-Fe alloys to partially replace silicon powder and nitrogen pressure, were evaluated and discussed. The presence of Fe, Mn and other elements in the Ti-Si-Fe alloy promoted the nitridation of silicon and the growth of silicon nitride whiskers. All the nitridized products were filled into the pores and hence improved densification of the sample, so that mechanical properties of the materials were enhanced. When the content of Ti-Si-Fe alloy is 1.5 wt. %, the sample has the lowest apparent porosity (25.3%) and the highest bulk density (1.97 g·cm^-3), meanwhile the highest bending strength is 33.8 MPa at ambient pressure. At gas pressure of 43.4 MPa, the corresponding lowest apparent porosity is 20.8% and the highest bulk density is 2.15 g·cm^-3. After sintering at gas pressure of 2 MPa, the growth of fiber-like Si₃N₄ crystals might be significantly suppressed, while that of columnar Si₃N₄ crystals was significantly boosted.