Novel α/β SiC-(Ti, Nb)B2 toughened (Ti, Nb)C-based composites with enhanced mechanical properties fabricated by in situ reactions sintering at low temperature

A novel alpha/beta SiC-(Ti, Nb)B-2 toughened (Ti, Nb)C-based composites was fabricated by reactive hot pressing with TiC, NbB2 and Si powders at 1500 degrees C and 1600 degrees C, respectively. The influence of NbB2, Si content, and sintering temperature on the microstructure and mechanical properties of the composite was investigated. The intermediate product NbC reacts with Si to form NbSi2 and beta-SiC phases. With addition of 10 mol% NbB2, a toughening phase alpha-SiC was formed. During the reaction process, insufficient diffusion of Nb atoms in TiC leads to the formation of a specific "core-shell" microstructure, which improves the flexural strength of the composite ceramics. The (Ti, Nb)C has a specific crystallographic orientation relationship with NbSi2 and alpha-SiC. The high-density stacking faults and ordered structures in beta-SiC crystals enhances its hardness. The rod-shaped alpha-SiC and plate-like (Ti, Nb)B-2 by in situ reactions effectively improve the fracture toughness of the composites. TiC-32 mol% Si-10 mol% NbB2 (raw powder composition) sintered at 1600 degrees C has excellent comprehensive mechanical properties, with fracture toughness, flexural strength, and Vickers hardness of 5.45 MPa<middle dot>m(1/2), 665 MPa, and 22 GPa, respectively, which provide a new insight into the optimization strength and toughness of TiC-based composites. In addition, under high temperature oxidation of 1000 similar to 1200 degrees C, the 30NB (54 mol% TiC-16 mol% Si-30 mol% NbB2) sample has better high-temperature oxidation resistance than the 30ZB (54 mol% TiC-16 mol% Si-30 mol% ZrB2) sample.