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

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Abstract
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 1.2×10−5 to 3.1×10−2 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 1.2×10−2 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 Dmix /K′=1.3×10−18 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 Cs showed no dependence on displacement rate but a considerable temperature dependence, e.g., Cs =2×10−6 at 850 K and Cs =2.5×10−7 at 950 K. The conditions for a stationary effective sink concentration in self-ion irradiated nickel are discussed.

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