The incorporation of Cr in enhancing the corrosion resistance, mechanical property and thermal stability of NbMoTaCr_x coatings

Refractory high-entropy alloy (RHEA) coatings with superior corrosion, mechanical properties and thermal stability are promising for complex environments such as high-temperature and multi-factor coupled corrosion conditions. The effects of Cr (Chromium) on the corrosion and thermal stability of NbMoTaCr_x coatings are investigated. Results demonstrates that NbMoTaCr_1.4 coating has the optimal corrosion performance, with the highest corrosion potential of −0.16 V and lowest corrosion current density of 0.01 μA cm⁻². The passive film of NbMoTaCr_1.4 coating is relatively more stable due to its higher reduction potential and lower semiconductor Fermi level. BCC (body-centered cubic) solid solution structures are retained even annealed at 800 °C, revealing good thermal stability of NbMoTaCr_x coatings. 400 °C-annealed NbMoTaCr_1.4 coating with fine grain sizes has a higher hardness of 11.4 GPa. Solid solution strengthening effects are dominated by modulus distortion of all NbMoTaCr_x coatings, and smallest atomic size distortion exhibits in equiatomic NbMoTaCr coating. In conclusion, the incorporation of Cr significantly enhances the corrosion and mechanical properties, and the NbMoTaCr_x coatings possesses excellent thermal stability.