The Fe addition as an effective treatment for improving the radiation resistance of fcc Ni_xFe_1-x single-crystal alloys

In this work, five different compositions of fcc Ni and Ni_xFe_1-x single crystal alloys namely Ni, Ni_0.88Fe_0.12, Ni_0.77Fe_0.23, Ni_0.62Fe_0.38, Ni_0.38Fe_0.62 were irradiated by 1.5 MeV ⁵⁸Ni ions at room temperature in a wide fluence range (4 × 10¹³ to 4 × 10¹⁵ ions/cm²). The role of Fe addition on the radiation resistance of the Ni_xFe_1-x single crystals was studied by transmission electron microscopy (TEM), ion channeling technique (RBS/C) and nanoindentation techniques. The Multi-Step Damage Accumulation analysis revealed the cross-sections for damage formation significantly decreases for Ni_0.38Fe_0.62 and Ni_0.62Fe_0.38 as compared to that in pure Ni single crystal, which is consistent with RBS/C and TEM results. The results of nanoindentation show that Ni_0.62Fe_0.38 alloy possesses the highest hardness (2.96 GPa) among the other compositions in a pristine state. To interpret this result, hybrid Monte Carlo/ Molecular dynamics simulations were used to check the presence of the ordered crystal phase structure for Ni_xFe_1-x binary alloys. The simulation results have shown that depending on the iron content, we deal with different amounts of FeNi₃ (L1₂) phase. This result revealed that in Ni_0.62Fe_0.38 alloy, nanoprecipitate FeNi₃ (L1₂) phase (around 20%) is formed inside the disordered matrix, which could be one of the main reasons for the high hardness of this alloy before irradiation. Additionally, we have found adding iron reduced the number and size of the defects (as a result of ion irradiation) in Ni_xFe_1-x because the Fe element is more stable than Ni, which results from the electron configuration of both elements in the excited state. Therefore, the more iron in the material, the fewer defects are created.