Copper precipitation in Fe–Cu alloys under electron and neutron irradiation

Precipitation of copper-rich clusters is a contribution to in-service hardening of some reactor pressure vessel ferritic steels. At temperatures less than 300 °C the precipitates are observed to be about 2 nm in diameter and not to coarsen, at least in the dose range from ∼10−3 to 10−2 dpa. As a result the hardening is close to a maximum. This phenomenon is studied here by computer simulations based on the “mean-field” approach for describing microstructural evolution in a binary Fe–Cu alloy. It is shown that the experimental data obtained from electron irradiated material and reactor-neutron irradiated steels have a stage of precipitate evolution intermediate between growth and coarsening. During this stage the size distribution of precipitates broadens while the number density and the mean size remain constant, which explains the observations. The role interstitial atom clusters produced in displacement cascades may have on the kinetics of copper precipitate coarsening is discussed.