Irradiation hardening in copper and nickel

Abstract

The lattice and dislocation components of irradiation hardening have been measured in polycrystalline copper and nickel as a function of 1. (a) testing temperature and 2. (b) neutron dose. The results are compared with Seeger's theory of lattice hardening, which is based on dislocations cutting through a forest of obstacles under the action of both stress and thermal activation. The observed temperature dependence of the lattice hardening in both metals is in excellent agreement with the theory in the as-irradiated condition. Mild annealing treatments greatly reduce the temperature sensitivity however and the theory is no longer obeyed. From the results it is concluded that the obstacles do not have a constant activation energy as assumed by Seeger and theories of the temperature dependence should include this factor. It is shown that the dose dependence of lattice hardening may be described by the new formula σ i = A(1 − e −Bφ) 1 2 which is derived by combining the theoretically predicted dependence on φ 1 2 with a saturation effect. The existence of obstacles of various sizes is also indicated from measurements of the temperature dependence of the constants in this equation. No definite conclusions as to the mechanism of formation of the obstacles can be made at present. The dislocation hardening component is shown to be independent of testing temperature in copper but not in nickel.