The size, number density and composition of nm-sized defects responsible for the hardening and embrittlement in irradiated Fe-0.9wt%Cu and Fe-0.9Cu-1.0wt%Mn model reactor pressure vessel alloys were measured by using small-angle neutron scattering and positron annihilation spectroscopy. The alloys were irradiated at 290C to relatively low neutron fluences (E > 1MeV, 6.0 x 1020 to 4.0 x 1021/m2) in order to study the effect of Mn upon the nucleation and growth of Cu-rich precipitates and secondary defect features. It was found that Cu-rich precipitates were present in both alloys following irradiation. The effect of Mn was to reduce the size, and to increase the number density, of precipitates in the Fe-Cu-Mn alloy; relative to the Fe-Cu alloy. Vacancy clusters were observed in the Fe-Cu alloy, but not in the Fe-Cu-Mn alloy. The results suggested a strong effect of Mn upon vacancy diffusion and clustering.

Positron Annihilation Spectroscopy and Small-Angle Neutron Scattering Characterization of the Effect of Mn on the Nanostructural Features Formed in Irradiated Fe-Cu-Mn Alloys. S.C.Glade, B.D.Wirth, G.R.Odette, P.Asoka-Kumar, P.A.Sterne, R.H.Howell: Philosophical Magazine, 2005, 85[4-7], 629-39