Study of the effect of α irradiation on the microstructure and mechanical properties of nanocrystalline Ni

The effect of irradiation damage on the microstructure evolution and mechanical properties in nanocrystalline (nc) Ni with an average grain size of ∼60 nm was studied. Samples were irradiated at doses of 1.6 × 1015, 2.3 × 1015, 5 × 1015 and 2.3 × 1016 He2+ cm−2 by 12 MeV He ions at room temperature. Microstructural parameters like domain size and microstrain were studied in detail using the X-ray diffraction (XRD) technique with the simplified breadth method and Williamson–Hall analysis. The average domain size was found to decrease systematically with the increase in irradiation dose. Microscopic observations made with transmission electron microscopy showed dislocation loops and dislocation networks within the grain interior of the irradiated sample. In addition, irradiation at a higher dose showed small amounts of the sand-like black dots inside some grains, which could be due to the accumulation of point defects. Tensile tests performed on the irradiated sample were compared with unirradiated samples. The irradiated sample showed higher ultimate tensile strength and average work-hardening rate as compared to the unirradiated sample. Nanoindentation studies were performed to study the effect of irradiation on deformation parameters like strain rate sensitivity (m) and activation volume (V*). The value of m was found to increase whereas V* was found to decrease with increase in irradiation dose. Fracture surfaces of the tensile sample were investigated by SEM. The fracture morphology of the unirradiated sample showed dimpled rupture with much large dimple diameter and depth. The irradiated sample also showed dimple rupture but with much finer dimple diameter with wide size distribution and shallow depths.