Mechanisms of neutron irradiation hardening in impurity-doped ferritic alloys

Nishiyama, Yutaka ; Liu, X.*; Kameda, Jun*

Mechanisms of neutron-irradiation hardening in phosphorus (P), sulfur (S) and/or copper (Cu) doped ferritic alloys have been studied by applying a rate theory to temperature dependence of the yield strength. In P-doped alloys, neutron irradiation below 563 K brings about a remarkable increase in the athermal stress and activation energy due to more extensive dispersion of fine (1.7 nm) P-rich precipitates than Cu-rich precipitates. During neutron irradiation above 668 K, precipitation hardening occurs to some extent in Cu-doped and S-doped alloys, compared to small or negligible hardening in the P-doped alloys. In alloys with low to moderate contents of various dissolved impurities subjected to the high-temperature irradiation, the formation of kink pairs becomes considerably difficult. Differing dynamic interactions of dissolved and precipitated impurities with the nucleation and growth of dislocations are discussed, giving rise to irradiation hardening.