Dense in situ TiB2/TiN and TiB2/TiC ceramic matrix composites: reactive synthesis and properties

In the present research, near-fully dense in situ composites were fabricated from cold sintered B4C–3Ti and 2BN–3Ti powder blends with and without the addition of Ni. Two reactive synthesis techniques were employed: combustion consolidation (pressure-assisted thermal explosion) and reactive hot pressing (displacement reaction under pressure) RHP. In both approaches, the processing or preheating temperature (≤1100°C) was considerably lower than those typical of current methods used for the processing/consolidation of ceramic matrix composites. Microstructure characterization of the materials obtained was performed using X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive analysis (EDS). Mechanical properties were evaluated by measuring microhardness, fracture toughness and three-point bending strength. Full conversion of reagents into products was achieved in B4C–3Ti, B4C–3Ti–1.5Ni and 2BN–3Ti–1.5Ni blends during combustion consolidation, and a moderate external pressure of 150 MPa was sufficient to ensure full density of the final products. Unlike this, no thermal explosion occurred in 2BN–3Ti samples at 1100°C under pressure. The entire procedure of thermal explosion under pressure could be performed in open air without noticeable oxidation damage to the final product. The RHP processing route yielded dense materials with finer microstructures, however full conversion of reagents into products has not been achieved. The addition of Ni to the powder blends was shown to enhance densification, as well as improve the fracture toughness of the composites synthesized.