Synthesis of In Situ TiB_2/TiN Ceramic Matrix Composites from Dense BN-Ti and BN-Ti-Ni Powder Blends

摘要

In the present research, near-net-shape in situ TiB_2/TiN and TiB_2/TiN/Ni composites were fabricated from cold-sintered BN/Ti and BN/Ti/Ni powder blends by pressureless displacement reaction synthesis or thermal explosion under pressure. In both approaches, the processing or preheating temperatures (≤ 1200℃) were considerably lower than those typical of current methods used for the processing/consolidation of ceramic matrix composites. Microstructural characterization of the materials obtained was performed using X-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Mechanical properties were evaluated by measuring mi-crohardness, fracture toughness, and three-point bending strength. Application of a moderate external pressure (≤ 250 MPa) during self-propagating synthesis (SHS) synthesis was shown to be sufficient to ensure full density of the TiB_2/TiN/Ni composite. The entire procedure of thermal explosion under pressure could be performed in open air without noticeable oxidation damage to the final product. The high fracture toughness of the in situ synthesized TiB_2/TiN/Ni composite (20.5 MPam~(1/2)) indicated that the finely dispersed ductile Ni phase was effective in dissipating the energy of cracks propagating in the ceramic matrix.