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

摘要

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 phosphorus segregation than sulfur segregation. Irradiation-induced phosphorus segregation became more prominent with decreasing bulk phosphorus content. Intergranular carbon segregation remained small in all the as-irradiated alloys, which was enhanced by the ETA except for the high phosphorus-containing alloy. A PIA study has shown that the phosphorus segregation in phosphorus-doped alloys subjected to lower temperature PIA proceeds via mobile phosphorus-interstitial complexes, whereas the sulfur segregation, which occurs over a wide PIA temperature range, 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. Copyright (C) 2001 John Wiley & Sons, Ltd. [References: 35]