Effect of Irradiation Parameters on Nickel-Ion Damage in Nickel

Void and dislocation structures have been studied in high-purity nickel which had been irradiated with 2.8 MeV³⁸ Ni⁺ ions. The irradiation conditions included specimen temperatures between 325 and 725°C, calculated peak damage densities from 4 to 130 displacements per atom (dpa), and calculated peak displacement rates of 7 × 10^-2 dpa/s and 7 × 10^-4 dpa/s. For the irradiations at 7 × 10^-2 dpa/s, voids were formed in specimens irradiated between 525 and 725°C. The maximum swelling at a damage level of 13 dpa was ΔV/V = 1.2 percent, observed in a specimen irradiated at 625°C. Irradiation of the same material to 13 dpa at 7 × 10^-4 dpa/s shifted the void formation temperatures approximately 100°C lower and produced a maximum swelling of 2.3 percent at 550°C. For specimens irradiated at a displacement rate of 7 × 10^-2 and a irradiation temperature of 575°C, the material was found to swell at a relatively rapid rate to a value of ΔV/V = 0.9 percent at 13 dpa. Above 13 dpa, the swelling rate was lower, and a value of ΔV/V = 2.2 percent was reached at 130 dpa. The results of analyses of these data by void nucleation and growth models are discussed.