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Radiation-induced heterogeneous damage is the single largest source of failures seen in structural components in nuclear power reactors. Single crystal materials without grain boundaries, show considerable promise for overcoming this problem. In this work, such heterogeneous damage was further overcome in Ni x Fe 1- x single crystal alloys via a simple strategy of fine-tuning the composition. [001] Ni x Fe 1- x ( x = 0, 0.38 and 0.62 at%) single crystals prepared using the Bridgman method were irradiated over a wide fluence range (4 × 10 13 to 4 × 10 15 ions per cm 2 ). The irradiation-induced defect evolution was studied using Rutherford backscattering/channeling spectrometry, Monte Carlo simulations, transmission electron microscopy and nanoindentation. The results indicate an increased radiation tolerance of Ni 0.38 Fe 0.62 compared to pure Ni and Ni 0.62 Fe 0.38 . The structural analysis performed by transmission electron microscopy revealed that defects tend to agglomerate at one place in Ni and Ni 0.62 Fe 0.38 , while in Ni 0.38 Fe 0.62 no defect accumulation zone (characteristic damage peak) has been captured either at low or high fluence. Moreover, we found that the hardness change with the increase of Fe content is due to different arrangements of Fe atoms in the crystal structure, which influences the obtained mechanical properties of Ni x Fe 1- x in the pristine state and after ion implantation.