Dose Dependence of the Dislocation Breakaway Stress in Neutron-Irradiated Copper as Measured by Amplitude-Dependent Internal Friction

Abstract

Measurements of the strain‐amplitude dependence of the internal friction in copper have been made at 100°C as a function of fast neutron dose. Although it is found that the Granato‐Lücke theory of amplitude‐dependent internal friction does not describe the results obtained, the dose dependence of the dislocation breakaway stress can be deduced by other means. After taking into account the variation with neutron dose of the mean free dislocation length, it is found that the breakaway stress is proportional to the cube root of the integrated flux in the dose range from 10¹¹ to 10¹⁴ neutrons/cm² (E>0.6 MeV). Extrapolation of the breakaway stress results to doses greater than 10¹⁹ neutrons/cm² shows essential agreement with earlier neutron‐hardening results. The results are discussed in terms of a source‐hardening mechanism.