The thermally activated dislocation motion in neutron irradiated iron-nickel alloys

Abstract

Polycrystalline samples of iron-nickel alloys with various interstitial impurity levels were irradiated to a fluence of 1.6 × 1019 n/cm2 (E > 1 MeV). The temperature and strain rate dependence of the yield stress of the alloys have been investigated in the temperature range of 77 to 580°K. The activation parameters have also been evaluated and used to identify the rate controlling mechanisms of the dislocation motion. It was observed that above 300°K the thermally activated dislocation motion over the neutron-produced obstacles is the rate controlling mechanism for the irradiated samples. This observation is in agreement with a prediction made by Arsenault. The effect of post-irradiation annealing on the temperature dependence of the yield stress becomes significant above 400°K; therefore, by the single strain rate change tests there is no way to determine the athermal stress for the irradiated samples. The motion of double kinks in dislocations over the Peierls’ stress hill is the lower temperature rate controlling mechanism before and after neutron irradiation.