Enhancing the corrosion resistance of austenitic steels in molten solar salt at 700 °C using gradient eutectic Fe-Ni-Mo alloy coatings

In this study, molybdenum (Mo) coatings were deposited on 304 stainless steel (304SS) plates using magnetron sputtering. Subsequently, the samples were annealed at 800 °C under vacuum for varying durations to enhance adhesion strength and thermal stability. Immersion tests were conducted at 700 °C for up to 800 h. After 200 h of immersion, the weight loss of the annealed Mo-coated 304SS was significantly reduced from approximately 11 mg/cm 2 to about 0.44 mg/cm 2 . The Mo-enriched layer effectively suppressed the outward diffusion of alloy elements and facilitated the formation of Cr 2 O 3 by trapping Cr in the interdiffusion layer. Additionally, the Mo 3 Fe 3 O phase formed on the coating surface via diffusion reaction exhibited certain corrosion-resistant properties. Obvious interfaces emerged within the interdiffusion layer, and their formation mechanisms were analyzed. After four thermal cycles (with a 200-h interval), partial delamination of the Mo-enriched layer in the annealed Mo-coated 304SS was observed. This may have resulted from the substantial growth stress of Cr 2 O 3 and the significant mismatch in thermal expansion coefficient between Mo coating and 304SS.