Enhancing the mechanical properties and oxidation resistance of NbC-Ni cermets via the formation of gradient (Nb,Ta)C grains

In this study, Coarse and fine TaC particles (from 0 to 13.05 wt.%) were used as additive in NbC-Ni cermets to improve the mechanical properties and oxidation resistance. The addition of TaC resulted in its dissolution into the NbC grains, yielding a gradient (Nb,Ta)C solid solution grains with an Nb-rich core and Ta-rich rim. The formation of gradient (Nb,Ta)C reduced the lattice mismatch between the NbC grains and Ni binder and improved the mechanical properties of the NbC-Ni cermets. Compared to that of the coarse TaC particles, the incorporation of fine TaC particles increased the TaC concentration in the NbC grains and reduced the residual TaC content in the NbC-Ni cermets. This can be attributed to the refinement in the size of the TaC particles, which accelerated the dissolution process resulting from the low solubility of TaC in Ni. The mechanical properties of the NbC-Ni cermets first increased and then decreased with the increase in TaC content. At fine TaC particle contents of 13.05 and 8.7 wt.%, the maximum Vickers hardness (HV₁₀) and transverse rupture strength (TRS) of the NbC-Ni cermets were obtained: 1452.6 kg/mm² and 1406.21 MPa, respectively. Similarly, the oxidation resistance of the NbC-Ni cermets increased with the increase in the TaC content. Compared to the other NbC-Ni cermets, those containing 13.05 wt.% fine TaC particles showed the thinnest oxide scales (approximately 23.1 μm) after oxidation at 600 °C for 1 h.