Effects of neutron irradiation on mechanical properties and microstructures of dispersion and precipitation hardened copper alloys

Tensile specimens of Cu-Al2O3, CuCrZr and CuNiBe alloys were irradiated with fission neutrons to fluences of 5 x 10(22), 5 x 10(23) and 1 x 10(24) n/m(2) (E > 1 MeV) at 47 degrees C. Tensile properties and Vickers hardness were determined at 22 degrees C. Microstructures of irradiated as well as unirradiated specimens were examined using a transmission electron microscope and the fractured surfaces were investigated in a scanning electron microscope, The most significant effect of irradiation is a drastic decrease in the ductility of copper alloys at a dose level as low as 0.2 dpa. The loss of ductility appears to be related to the intrinsic hardness of the grain interior and not to the grain boundary embrittlement. It is suggested that the irradiation-induced hardening and the lack of uniform elongation may be understood in terms of difficulty in dislocation generation due to pinning of grown-in dislocation by defect clusters (loops) and/or impurity atoms.