The microstructure and associated tensile properties of irradiated fcc and bcc metals

The differences and similarities of behaviour between fcc and bcc metals after irradiation have been investigated. For this purpose, fcc Cu, Pd and 304 stainless steel and bcc Fe, Mo and Mo–5% Re were irradiated with either neutrons or 590 MeV protons at temperatures below recovery stage V. It is shown that a dense population of defect clusters (up to 10 22–10 24 m −3) develops, the type of cluster formed depending apparently on the stacking fault energy. In the case of stacking fault tetrahedra formed in Cu, their size is independent of dose, while interstitial loops in stainless steel grow at neutron doses higher than 1 dpa. The defect microstructure is found to be independent of the recoil energy spectra in this temperature region, but shows a very strong dependence on the type of crystalline structure. The results of tensile testing indicate the presence of radiation hardening, starting at very low doses as an upper yield point develops followed by a (serrated) yield region. The main deformation mode observed is dislocation channeling. The hardening is modelled in terms of the initial dislocation locking by the irradiation-induced defects followed by the dispersed hardening induced by the global distribution of clusters in the matrix.