Point defect sinks in self-ion-irradiated nickel: A self-diffusion investigation

The diffusion coefficient of 63Ni in pure nickel after irradiation with 300 keV Ni ions has been measured directly using a secondary ion mass spectrometer. The calculated displacement rate for this irradiation ranged from 1.2 x 10/sup -5/ to 3.1 x 10/sup -2/ dpa/s, the dose from 0.2 to 102 dpa, and the temperatures from 293 to 950 K. Between 293 and 650 K the irradiation-induced diffusion coefficient is temperature independent for a displacement rate of 1.2 x 10/sup -2/ dpa/s. In this temperature range mass transport by atomic mixing prevails over diffusion via point defects (radiation-enhanced diffusion). Normalized to the displacement rate K' the diffusion coefficient describing atomic mixing attains a value of D/sub mix/ /K' = 1.3 x 10/sup -18/ m2 /dpa. The temperature and displacement rate dependence of the radiation-enhanced diffusion coefficient is discussed in the framework of a rate equation model. The analysis yields a production rate of freely migrating defects of about 1.5% of the calculated displacement rate. The effective concentration of point defect sinks was derived for nickel under heavy ion irradiation. This effective sink concentration C/sub s/ showed no dependence on displacement rate but a considerable temperature dependence, e.g., C/sub s/ = 2 x 10/sup -6/ at 850 K and C/sub s/ = 2.5 x 10/sup -7/ at 950 K. The conditions for a stationary effective sink concentration in self-ion irradiated nickel are discussed