Effects of grain boundary misorientation on radiation-induced solute segregation in proton irradiated 304 stainless steels

This paper describes the effects of the grain boundary misorientation on the radiation induced segregation (RIS) in proton irradiated 304 stainless steels. Experimentally, four test conditions were used for the 304 stainless steel specimens: (1) As-received (AR) with enriched Cr at grain boundary, (2) AR + 1 dpa proton irradiated at 450degreesC, (3) Thermal sensitized (SEN), and (4) SEN + 1 dpa proton irradiated at 450degreesC. Compared with no pre-enrichment condition, a delayed Cr depletion was found at grain boundaries in AR + I dpa specimens. After irradiation, the Cr concentration profile across grain boundaries became narrower and deeper in SEN + I dpa specimens. The degree of grain boundary segregation was observed to be higher at random boundaries than special boundaries. In the case of SEN + I dpa specimens, the segregation cusps were observed at grain boundaries of Sigma3, Sigma9 and Sigma15, and the Cr segregation levels at special boundaries were increasing with Sigma for value up to Sigma = 15. Theoretically, a simple rate equation model with modified boundary conditions, which were related to the grain boundary diffusion of defects and the densities of the grain boundary dislocations, was developed for RIS at boundaries with different Sigma and Deltatheta. The model calculations showed that the RIS model with modified boundary conditions could predict clearly the same trend as that of experiments, in which the Cr depletion levels at special boundaries in irradiated 304 stainless steels were increasing with Sigma. The model calculations also showed that the widths of the segregation cusps were decreasing with increasing Sigma.