A MODEL DESCRIBING NEUTRON IRRADIATION-INDUCED SEGREGATION TO GRAIN-BOUNDARIES IN DILUTE ALLOYS

A model describing neutron irradiation-induced grain boundary segregat ion at a given temperature is established for dilute alloys based on a complex diffusion mechanism and combined with McLean's equilibrium se gregation model. In the model, irradiation-enhanced solute diffusion i s taken into consideration. The diffusion equations are more rigorousl y solved than in earlier models, so that an accurate definition of the grain boundary solute concentration is given as a function of time. T he effect of the temperature dependence of dislocation density is acco mmodated and the estimation method for complex diffusion is reappraise d. Theoretical predictions are made for segregation of phosphorus in n eutron-irradiated alpha-Fe. There exists a transition temperature belo w which combined irradiation-induced nonequilibrium and irradiation-en hanced equilibrium segregation is dominant and above which thermal equ ilibrium segregation is dominant. The peaks in the temperature depende nce of segregation shift to lower temperatures with decreasing-neutron dose rate and/or increasing neutron dose. The combined radiation-indu ced nonequilibrium and radiation-enhanced equilibrium peak segregation temperature is about 150 degrees C for P grain boundary segregation i n neutron-irradiated alpha-Fe at dose rate = 10(-6) dpa/s and dose = 1 dpa. The thermal equilibrium segregation peak is around 550 degrees C for the same conditions. Comparison of some experimental and predicte d results shows that the predictions are generally consistent with the observations.