Deciphering the orientation-dependent growth of the internal oxide precipitates in Fe-9Cr alloy exposed to supercritical water via advanced characterization and atomic simulation

Advanced characterization techniques and atomic simulations, including density functional theory calculation and molecular dynamics simulation, are performed to reveal the orientation-dependent growth mechanism of Cr-rich oxide precipitates in the internal oxide layer of Fe-9Cr steel under supercritical water environment. A new Fe/Cr/O/H reactive force field is constructed to address the limitations of existing empirical potentials in accurately describing the corrosion mechanism of FeCr alloy. The high-resolution characterization reveals the growth mechanism of needle-like FeCr2O4 precipitates in the <1 0 0> direction of the matrix. Atomic simulation demonstrate that the directed growth is thermodynamically preferred than the isotropic growth. The vacancies generated by the outward diffusion of metal atoms enhancing the diffusion of Cr atoms, and O promote the aggregation of Cr atoms along the <1 0 0> direction.