Atom probe study of irradiation-enhanced α precipitation in neutron-irradiated Fe-Cr model alloys

Atom probe tomography (APT) was performed to study the effects of Cr concentrations, irradiation doses and irradiation temperatures on α phase formation in Fe-Cr model alloys (10-16 at.%) irradiated at 300 and 450 °C to 0.01, 0.1 and 1 dpa. For 1 dpa specimens, α precipitates with an average radius of 1.0-1.3 nm were observed. The precipitate density varied significantly from 1.1 × 10²³ to 2.7 × 10²⁴ 1/m³, depending on Cr concentrations and irradiation temperatures. The volume fraction of α phase in 1 dpa specimens qualitatively agreed with the phase diagram prediction. For 0.01 dpa and 0.1 dpa, frequency distribution analysis detected slight Cr segregation in high-Cr specimens, but not in Fe-10Cr specimens. Proximity histogram analysis showed that the radial Cr concentration was highest at the center of α precipitates. For most precipitates, the Cr contents were significantly lower than that predicted by the phase diagram. The Cr concentration at precipitate center increased with increasing precipitate size.