Atomistic study of Al partitioning and its influence on nanoscale precipitation of Cu-rich nanocluster-strengthened steels

The intrinsic partitioning behavior of Al and its influence on the nanoscale precipitation of Cu-rich nanocluster-strengthened steels were investigated by using atom probe tomography (APT) and first-principles calculations. The APT results reveal that Al partitions to Cu-rich nanoclusters, which results in a slight decrease in the volume fraction of the nanoclusters. The first-principles calculations indicate that the Al substitution in body-centered cubic (bcc) Cu is more energetically favorable as compared with that in bcc Fe. In addition, the Al partitioning has no significant influence on the chemical driving force and interfacial energy but slightly increases the strain energy for nucleation, thereby increasing the critical energy for the formation of Cu-rich nanoclusters. As a result, the nanoscale Cu precipitation is slightly inhibited in the Al-containing ferritic steels. In addition, the effects of Al on the precipitation strengthening response were quantitatively evaluated, and the results indicate that the degree of precipitation strengthening depends majorly on the combined effect of cluster size and inter-cluster spacing.