Phase decomposition of oxide film of flow accelerated corroded F82H steel under high-temperature iron irradiation

The purpose of the present study is to clarify the phase stability of the corroded layer in reduced activation ferritic/martensitic steels under irradiation. The oxide film of F82H steel was subjected to ion irradiation using 2.8 MeV-Fe ²⁺ at 573 K. For post-irradiation experiments, grazing incident X-ray diffraction (GIXRD) and Raman analysis were conducted to clarify the features of the oxide layer with the variation of the irradiation dose. The dominant phase of the oxide film was identified as FeCr ₂O ₄ , which co-existed with up to ∼30% of the residual matrix phase. The fraction of the residual matrix decreased as the irradiation dose increased, the phase transformation from FeCr ₂O ₄ to Fe ₃O ₄ was confirmed. The hypothesis for the phase transformation of FeCr ₂O ₄ to Fe ₃O ₄ under irradiation was proposed based on the experimental results. Specifically, the FeCr ₂O ₄ phase is unstable under irradiation, and tends to become stable after absorbing Fe atoms from the residual matrix in the corrosion layer. As a result, the Fe concentration in the oxide layer increased under irradiation, the phase transformation of FeCr ₂O ₄ to Fe ₃O ₄ is presumed under irradiation. However, concerns about the mechanism of the instability of FeCr ₂O ₄ under irradiation, and better stability of Fe ₃O ₄ phase relative to FeCr ₂O ₄ phase have to be further considered to achieve a better understanding.