Improved corrosion resistance of reactive gas pulse sputtered (TiTaNbZrNi)N high entropy alloy coatings with a hybrid architecture of multilayered and compositionally graded structures

Abstract In an attempt to introduce a new coating structure design strategy to strengthen the high temperature water corrosion resistance or high temperature oxidation of the coating in the normal operation condition or event of a loss-of-coolant accident. (TiTaNbZrNi)N hybrid structure coatings with ν = 0.25, 0.5, 1, 2 sccm/min were prepared by the reactive gas pulse (RGP) sputtering technique. This hybrid structure consisted of a FCC (TiTaNbZrNi)N sublayer and an amorphous (TiTaNbZrNi)Nx sublayer with both N element concentration gradient, and .an amorphous TiTaNbZrNi sublayer. After autoclave test at a temperature of 360°C and a pressure of 18.6 MPa for 3, 14 and 50 days, the results indicated that the weight gain of the hybrid structure coating is approximately an order of magnitude lower than that of the uncoated N36 substrate, and it still has a stable FCC structure. The coating with ν = 2 sccm/min has a lower oxygen diffusion depth than the coating ν = 0.25, 2 sccm/min, which is due to the lower thickness of the (TiTaNbZrNi)Nx sublayer and the multilayer interface suppressing the diffusion of oxygen. Moreover, Corrosion resistance of the (TiTaNbZrNi)N hybrid coating can be well tuned by changing the undulation period number of N2 gas flow rate. Detailed analysis indicates that the corrosion resistance of hybrid structure coatings may be related to the combined effect of multilayer structure and composition gradient structures.