Effect of Ta addition on the microstructures and mechanical properties of in situ bi-phase (TiB2-TiCxNy)/(Ni-Ta) cermets

In this work, in situ bi-phase (TiB2-TiCxNy)/(Ni-Ta) cermets were fabricated via a combined combustion synthesis and hot-pressing (CSHP) method in a Ni-Ti-BN-B4C-Ta system. The effects of Ta addition on the reaction process, phase constituents, microstructures and mechanical properties of the (TiB2-TiCxNy)/(Ni-Ta) cermets were studied. Ta is shown to dilute the system and lead to a small number of intermediate phases (Ni20Ti3B6 and Ni3Ti) that are retained in the products. Furthermore, the addition of Ta can markedly refine the ceramic particles and decrease the size and quantity of voids. The evaluation of the mechanical properties revealed that an increase in the Ta content resulted in increases in the compression strength (sigma(UCS)) and hardness and that the fracture strain (epsilon(f)) increased first and then decreased. The cermet with the optimal addition of 5 wt % Ta possessed the best mechanical properties without decreasing the value of epsilon(f) (2.9%). The addition of 5 wt% Ta resulted in a compressive strength of 3.37 GPa and the highest hardness of 1909 Hv, which is an increase of similar to 16% and similar to 22%, respectively, compared to cermets without added Ta.