A novel NbTaW_0.5 (Mo₂C)_x refractory high-entropy alloy with excellent mechanical properties

In this study, a refractory high-entropy alloy (RHEA) NbTaW_0.5 was selected as the master alloy and carbide Mo₂C was added to prepare the NbTaW_0.5(Mo₂C)_x (x = 0–0.25) RHEAs. The effect of Mo₂C addition on the phase composition, microstructure evolution, and mechanical properties of the as-cast and annealed RHEA was investigated. The microstructure and mechanical properties of the as-cast and isothermally annealed (1673 K/12 h) NbTaW_0.5(Mo₂C)_x RHEAs were studied. The results showed that the as-cast RHEAs consisted of a disordered body-centered cubic solid solution phase and a second M₂C carbide phase with hexagonal close-packed (HCP) crystal structure. The HCP–M₂C carbides were enriched with Nb, Ta, and C elements and tended to achieve a similar eutectic morphology in the interdendritic regions. After isothermal annealing, orthorhombic carbides were formed near the primary carbides, which apparently depleted the carbon supersaturation of the matrix. The compression mechanical properties of as-cast alloys were determined at room temperature, 1473 K, and 1673 K. The yield strength of NbTaW_0.5(Mo₂C)_0.2 RHEA exceeded 1000 MPa at 1473 K, and even reached 697 MPa at 1673 K, far exceeding some of the currently reported RHEAs. These RHEAs had good plasticity and showed excellent application prospects.