WORK HARDENING OF NEUTRON-IRRADIATED COPPER SINGLE CRYSTALS. I. WORK HARDENING CURVES

A systematic investigation of the work hardening curve of neutron irradiated copper single crystals and its dependence of neutron dose, deformation temperature, and strain rate revealed that the work hardening behavior differs in different ranges of the irradiation dose. These differences were shown by different shapes of the shear stress vs. shear strain curves. The critical resolved shear stress, however, did not exhibit such differences dependent on irradiation dose. With increasing dose, four different types of curves were observed. The dose range, within which a transition from one type of curves to the next occurs depended on deformation temperature and strain rate. With increasing deformation temperature the transitions were shifted to lower neutron doses. All four types of work hardening curves may roughly be subdivided, similar to the work hardening curves of unirradiated crystals into three stages: a flat initial stage, which, apart from a very weak dose of irradiation, consists of yield point elongation zone with propagation of Luders bands; a rather steep intermediate stage; and a final stage with decreasing slope. Within these stages, particularly within the second stage, numerous substages with a slightly differing work hardening behavior were observed. (auth)