Investigation of Cu-enriched precipitates in thermally aged Fe-Cu and Fe-Cu-Ni model alloys

To better understand the mechanisms of thermally aged and embrittled reactor pressure vessel steels, the hardening behavior and microstructure evolution of different Fe-Cu and Fe-Cu-Ni model alloys were investigated using transmission electron microscopy (TEM) and small-angle neutron scattering (SANS) analysis methods. The effects of different aging conditions and alloy composition on the formation and growth of Cu-enriched precipitates were discussed. The results showed that the hardness of the Fe-Cu model alloys with low copper content continuously increased with aging, increasing to peak hardness and then decreasing for the Fe-Cu model alloys with high copper content. The aging time to reach peak hardness was greatly reduced due to the addition of Ni in the Fe-Cu model alloys. The TEM results showed that with increased aging temperature and copper content, the Cu-enriched precipitates with a B2 structure precipitated in the ferritic matrix following a direct relationship. Therefore, Ni addition led to relatively higher precipitation nucleation and growth, and the size distribution of the Cu-enriched precipitates derived from the SANS was in overall good agreement with the TEM observations for 6-25 nm regions. Therefore, small-angle scattering could provide better details when analyzing smaller, nano-sized precipitates.(c) 2022 Elsevier B.V. All rights reserved.

Automated summary

Through the use of transmission electron microscopy (TEM) and small-angle neutron scattering (SANS) analysis methods, the hardening behavior and microstructure evolution of thermally aged and embrittled reactor pressure vessel steels were investigated. The results showed that the addition of nickel led to faster precipitation nucleation and growth, resulting in higher peak hardness. The small-angle scattering method provided detailed information on the size distribution of nano-sized precipitates.