Regulation mechanism of Re doping on high-temperature oxidation resistance of TaWNb-based refractory high-entropy alloys: First-Principles prediction and experimental verification

The mechanism of the effect of Re doping on the antioxidant properties of (TaWNb) 100-x Re x (x= 0, 2, 4, 6) refractory alloys was systematically investigated using a combination of high-temperature antioxidant experiments and first-principles calculations. The alloys were prepared using arc melting and subjected to thermogravimetric and static oxidation tests. It was found that the overall antioxidant properties decreased with increasing Re content, with the mass change rate can reach -86.3% at x=6. Using VASP simulation, it was found that with the increase of Re content, although the surface oxygen adsorption energy of the alloy gradually decreased (as low as 0.26 eV at x=6), while the anti-oxygen penetration performance was significantly improved (the total surface-to-subsurface diffusion energy barriers reached 8.21 eV and 11.01 eV, respectively, at x=6), the continuity of the dense oxide layer was severely inhibited, leading to a surge of the porosity of the oxide film. Electronic structure analysis shows that Ta, W, and Nb atoms hybridize with the orbitals of O to form stable covalent bonds, but Re doping weakens the metal-oxygen bond strength and promotes the tendency of adsorbed oxygen to metal ionization. It is shown that although the introduction of Re enhances the ability to inhibit oxygen adsorption and diffusion thermodynamically, its negative effect on the structural integrity of the oxide layer and the interfacial bonding strength dominates, which ultimately leads to the deterioration of the antioxidant properties. The results provide a key theoretical basis for the design of antioxidant components of high-entropy refractory alloys.