Lukasz Kurpaska

Ion irradiation modifies the nanoscale initiation of plasticity in ferritic Fe-Cr alloys through the formation and evolution of irradiation-induced defects. Here, the deformation behaviour of a Fe-9Cr-NiSiP model alloy irradiated to 5 dpa at room temperature and 300°C is examined. Nanoindentation reveals systematic changes in pop-in behaviour, indicating a transition from nucleation-controlled plastic initiation in the pristine material to defect-controlled deformation after irradiation. Room-temperature irradiation produces a high density of fine defect structures that promote heterogeneous dislocation nucleation while restricting dislocation motion. In contrast, irradiation at 300°C leads to defect coarsening and solute segregation of Cr, Ni, Si and P, forming more stable defect complexes that delay plastic initiation. Correlative microscopy reveals distinct subsurface deformation morphologies consistent with the mechanical response. These results show that irradiation temperature controls defect evolution, which in turn governs the nanoscale onset of plasticity in Fe-Cr alloys.