An investigation of nucleation sites for the formation of solute clusters in ferrite Fe

Abstract

The hardening and embrittlement of reactor pressure vessel steels source from the formation of Cu-enriched precipitates (CRPs) and Mn-Ni-Si precipitates (MNSPs). Recent studies of atom probe tomography indicated that the formation of CRPs and MNSPs may have similar mechanisms, and the major difference may be the nucleation site. Cu clusters and Cu-vacancy complexes may act as the nucleation sites for CRPs, whereas the nucleation sites for MNSPs are unknown. In this work, vacancy clusters of different sizes were analyzed by first-principles calculations for their possibility to act as the nucleation sites for MNSPs. The results were compared with that of Cu clusters and Cu-vacancy complexes in CRPs. Cluster size effects were also discussed. It has been found that Ni was attracted by both Cu cluster and vacancy cluster. Si was not much attracted by Cu cluster but was highly attracted by vacancy cluster, and it was the vacancy in Cu-V complex that attracted Si. In all the configurations calculated, the Mn atoms in antiferromagnetic state would stabilize the configurations and lead to positive binding energy with the clusters. The magnetic state of Mn could be correlated with its atomic volume in bcc-Fe.