Microstructure and defect evolution in oxygen ion-irradiated pure nickel-Insights from experimental probes and molecular dynamics simulations

Pure nickel samples were irradiated to various doses by 160 MeV oxygen ions and the change in microstructure (domain size, microstrain, dislocation density etc.) were investigated with the help of X-ray diffraction (XRD) data from synchrotron source and Transmission electron microscopy (TEM). The coherent domain size decreased, whereas the microstrain and dislocation density increased in all irradiated samples as compared to the unirradiated one. However, these parameters showed saturation with increasing dose. The analysis reveals that there is an increase in the stacking fault probability with irradiation. TEM study confirmed the presence of stacking fault tetrahedra and dislocation loops in the irradiated samples. Microhardness measurements show an increase in the hardness with irradiation due to formation of defect clusters and dislocations. The effect of irradiation on the microstructure of the pure Ni has been simulated by molecular dynamics using overlapping simulation cascades of PKA generated by oxygen ion.