Behavior of Fe-Based Alloys in a Liquid Lead-Bismuth Environment under Simultaneous Proton Irradiation and Corrosion

The performance and longevity of nuclear reactors are significantly influenced by the behavior of their structural materials, particularly under conditions of corrosion and irradiation. This study investigates the combined effects of corrosion and irradiation on three alloys: Fe-Ni-Cr-Al-Nb, Fe-Cr-Al-Y, and Fe-12Cr-2Si, exposed to a liquid Pb-4wt% Bi mixture at 675°C for 4 hours. 3 MeV proton irradiation was employed to understand the simultaneous effects of irradiation on the corrosion behavior of these alloys. When exposed to liquid lead-bismuth at 675°C for 4 hours, the Fe-Cr-Al-Y and Fe-12Cr-2Si alloys exhibited superior corrosion resistance compared to the Fe-Ni-Cr-Al-Nb alloy. Conversely, the Fe-Ni-Cr-Al-Nb alloy demonstrated significant Pb-Bi penetration, which was further accelerated by proton irradiation, resulting in increased penetration depth. This revealed that irradiation-induced damage can accelerate the corrosion rate of Fe-Ni-Cr-Al-Nb steel in lead-bismuth environments. Microstructural analysis using SEM/EDX, STEM, and diffraction patterns uncovered complex alloy interactions and potential chemical transformations in the irradiated Fe-Ni-Cr-Al-Nb alloy. This included the presence of lamellar or rod-like structures near Pb-Bi penetration sites and the selective retention of nickel by aluminum. In contrast, the Fe-12Cr-2Si alloy exhibited effective corrosion resistance attributed to a uniform distribution of elements and the formation of a protective Si-rich oxide layer. The Fe-Cr-Al-Y alloy developed distinct oxide layers, with chromium oxide predominating and a slight aluminum oxide layer, indicating the critical role of chromium oxide as a protective barrier.