Nanoscale defect formation in fcc Ni and low-Fe content NixFe1−x single crystals induced by self-ion irradiation†
Abstract
Fcc NixFe1−x single crystal alloys serve as model systems to study defect evolution under self-ion irradiation at room temperature across fluences from 4 × 1013 to 2 × 1015 cm−2. Defect characterization was performed using Rutherford backscattering spectrometry/channeling (RBS/C) and transmission electron microscopy (TEM) to distinguish defect types and calculate damage kinetics via a Multi-Step Damage Accumulation Model. Complementary molecular dynamics simulations of overlapping collision cascades revealed defect formation mechanisms at low irradiation doses. The simulations indicated that an A15 Frank-Kasper phase forms within the {111} plane in pure Ni, Ni0.88Fe0.12, and Ni0.77Fe0.23 up to a fluence of 2 × 1014 cm−2, which underlies Frank loop nucleation. This provided insight into the role of Fe atoms in influencing dislocation nucleation and evolution. The combination of TEM observations, and RBS/C analysis using Monte Carlo-based McChasy simulations revealed that point defects – interstitials, dumbbells, vacancies, and A15 phase – dominate in all compositions up to 2 × 1014 cm−2. At higher fluences of 2 × 1015 cm−2, these defects transform into complex structures such as dislocation loops and stacking fault tetrahedra. Notably, in Ni0.77Fe0.23, compact 3D precipitates form but remain too small to evolve into Frank loops, despite significant Fe decoration.