Study on the Partitioning of Alloying Elements Between bcc-Fe Matrix and bcc-Cu Precipitates and the Corresponding Effects on the Precipitation Interface

During aging of Fe-Cu-based ferritic steels when the nano-sized Cu-rich particles precipitate, the partitioning trends of the alloying elements in the bcc Fe/bcc Cu system and the corresponding effects on the interface are of crucial importance for understanding the evolution of the composition, morphology and transformation of Cu-rich particles. The formation energies and partitioning energies of the alloying elements,i.e.,Al, Si, Ti, V, Cr, Mn, Co, Ni, Nb and Mo, in the system of bcc Fe matrix/bcc Cu precipitates and the effects of the alloying elements on the interfacial energy and bonding strength were systematically investigated based on the first-principles calculations. The results reveal that all the alloying elements prefer to partition to the bcc Fe matrix, although the formation energies of Al, Si, Ti and Ni are negative in the bcc Cu phase. Among the investigated alloying elements, Al, Si, Ti, Mn, Ni and Nb exhibit preferences to segregate to the bcc Fe/bcc Cu interface, while the effects of these six alloying elements on the interfacial energy and Griffith work of the interface are different. The segregation of Al increases the interfacial energy while those of Si, Ti, Mn, Ni and Nb exhibit the opposite effect. Furthermore, Al, Ti, Mn, Ni and Nb at their favorable segregation sites increase the Griffith work of the interface while Si plays an opposite role.