Effect of Ti and Si Additions on Microstructure, Fracture Toughness and Oxidation Resistance of Nb-Mo₅SiB₂ Composite

Nb-Mo₅SiB₂ (T2)-based composites with Ti and Si additions were prepared by mechanical alloying followed by hot pressing. The phase analysis revealed that element additions induced the phase composition change. In the Ti-added Nb-T2 composite, Ti was distributed in the grain boundary as sub-micron Ti-rich oxide particles due to insufficient oxidation. The addition of Si turned the Nb-T2 into a complete intermetallic composite by forming Nb-silicide. The mechanical properties showed that Ti- and Si-co-added Nb-T2 composite had the highest hardness (1939 HV) and compressive strength (3445 MPa), while the Ti-added Nb-T2 composite exhibited the best toughening effect, and the fracture toughness reached 13.37 MPa m^1/2, which were about 31% and 300% higher than that of Nb-T2 and pure polycrystalline T2, respectively. Although the Nb and Ti had excellent toughening effect on the T2 phase, it worsened the oxidation resistance of the composites.