Neutron irradiation-induced intergranular solute segregation in iron base alloys

The effect of neutron irradiation (9.4 × 10²² n/m² at 395°C) on solute segregation to grain or interfacial boundaries in several iron base alloys doped with P, Cu and/or C has been investigated using scanning Auger microscopy. It was found by fracture surface Auger analyses that while neutron irradiation enhanced intergranular segregation of S in a Cu-doped alloy with the absence of P segregation, it mitigated S segregation and promoted P segregation in P containing alloys. The quantity of segregated P was much greater for the irradiated alloys than for the thermally 1000 h aged alloys. The P-doped alloy showed a stronger effect of neutron irradiation on the enrichment of P segregation than the P-Cu-doped and P-C-doped alloys. Argon sputtering experiments indicated that the segregation profiles for S and P were more broadly and narrowly distributed during irradiation, respectively. A remarkable transition of the P segregation profile was observed near the interface of particles lying along grain boundaries where S was preferentially segregated because of the competitive segregation between S and P. The mechanism for neutron irradiation-induced solute segregation is discussed in light of inverse Kirkendall effects and the formation of defect-solute complexes arising from the dynamic interaction between solute and defect fluxes. The relationship of intergranular solute segregation to embrittlement is presented.