Non-equilibrium intergranular segregation and embrittlement in neutron-irradiated ferritic alloys

Kameda, Jun*; Nishiyama, Yutaka ; Bloomer, T. E.*

This study describes intergranular segregation and embrittlement in several model ferritic alloys doped with Mn, P, S and/or Cu subjected to neutron irradiation, irradiation-equivalent thermal ageing (ETA) and post-irradiation annealing (PIA). Neutron irradiation produced a larger amount of intergranular P segregation than S segregation. Intergranular C segregation remained small in all the as-irradiated alloys. A PIA study has shown that the P segregation in P-doped alloys subjected to lower temperature PIA proceeds via mobile P-interstitial complexes while the S segregation is controlled by vacancy-enhanced diffusion. The mechanisms of non-equilibrium intergranular segregation induced by neutron irradiation are discussed in light of coupled fluxes of point defects and impurities, and changes in the segregation capacity of grain boundaries. Small punch tests demonstrated how the impurity segregation or desegregation and hardening or softening induced by the irradiation, ETA and PIA influence intergranular embrittlement in the various ferritic alloys.