Atomistic insights into the thermo-kinetic regulation of localised nanoindentation deformation in Fe ₃ O ₄

Understanding the local mechanical response of Fe3O4 is important for evaluating the mechanical stability of oxide scales formed on T91 steel in supercritical CO2 environments. In this work, molecular dynamics nanoindentation simulations were performed to investigate the effects of temperature and loading rate on the deformation behavior of Fe3O4. The load-depth behavior, peak load, residual indentation depth, apparent hardness, indentation modulus, atomic displacement and local shear strain were systematically analyzed. The results show that increasing temperature weakens the indentation resistance of Fe3O4, reduces its apparent hardness and indentation modulus, and promotes greater irreversible deformation after unloading. In contrast, increasing the loading rate raises the apparent indentation resistance and increases both the apparent hardness and indentation modulus, while suppressing residual deformation. Atomic-scale analysis further reveals that elevated temperature expands both the displacement-affected zone and the high-shear-strain region, whereas rapid loading confines deformation to a smaller subsurface volume and limits local structural accommodation. These findings demonstrate a clear thermo-kinetic competition in the nanoindentation response of Fe3O4 and provide atomistic insight into the local mechanical stability of oxide scales under contact loading.