Abstract: Understanding the long-term corrosion behavior of neutron absorber materials in H₃BO₃ solution is crucial for the materials applications in spent fuel storage. In this paper, long-term corrosion evolution for 180 d in relation to the structural heterogeneities of an Fe-based amorphous coating (AMC) in H₃BO₃ solution at various temperatures was systematically investigated. Results indicate that the coating corrosion could be divided into three distinct stages. Initially, the corrosion resistance increased owing to the thickening and composition evolution of the passive films. Subsequently, the corrosion rate was kept almost constant in the second stage, which connected with the steady state of the passive film. Finally, the corrosion resistance of coating reduced gradually owing to the initiation and penetration of localized corrosion. Interestingly, it was revealed that the localized corrosion was initiated at the relatively Cr-depleted amorphous matrix in the deep pores of the coating. This could be attributed to the synergy of Cr-depletion and occlusive effect in the deep pores during long-term immersion. With the elevation of temperature, the localized corrosion was enhanced due to the accumulation of the H⁺ in the pores to swiftly reach the critical conditions for passive film breakdown. This work provides insights into the long-term corrosion mechanism of Fe-based AMCs in H₃BO₃ solution and offers meaningful contributions to the design of new corrosion resistant neutron absorbing coatings for spent fuel storage applications.

Key words: AMC, Boric acid, EIS, Long-term corrosion, Temperature