Dispersoid stability in ion irradiated oxide-dispersion-strengthened alloy

The radiation response of oxide dispersoids in a Hf-doped oxide-dispersion-strengthened (ODS) alloy was studied by using 3.5 MeV Fe2+ self-ion irradiation at 475 °C. The size changes of coherent and incoherent dispersoids were studied as a function of depth. Although there was up to 2.6 times difference in local displacements-per-atom (dpa) rate at different characterization depths, the sizes of coherent and incoherent dispersoids did not show a noticeable dependence on dpa rate at depths up to the peak dpa position. In order to explain the experimental observations, the diffusion of solute atoms (dissolved from dispersoids) must take into consideration defect-assisted-diffusion mechanisms. A high dpa rate results in enhanced dispersoid dissolution. On the other hand, dispersoid recovery is increased due to defect-assisted diffusion. Therefore, the two effects are balanced, leading to a relative insensitivity of dispersoid size to dpa rate. The study further shows that both coherent and incoherent dispersoids shrink during irradiation but the final equilibrium sizes of coherent dispersoids are smaller than that of incoherent dispersoids, arising primarily from a difference of their interfacial energies. Incoherent dispersoids undergo more significant volume reduction under irradiation than do coherent dispersoids.