First-principles study of Suzuki segregation at stacking faults in disordered face-centered cubic Co-Ni alloys

Abstract

The formation of stacking faults (SFs) observed in various metallic materials, such as Co-, and Ni-based alloys, influence the plastic deformation and strain-induced phase transformations. One possible explanation for the propensity of SF formation is Suzuki segregation, which is the localized segregation of solute to SFs. Through first-principles calculations, we investigate the driving force of Suzuki segregation in the disordered face-centered cubic Co-Ni binary system and quantitatively predict the resulting temperature- and composition-dependent stacking fault energies (SFEs). We predict the segregation of Co to the stacking fault region in the disordered face-centered cubic Co-Ni binary alloy system utilizing a combination of cluster expansions and Monte Carlo simulations. We find that configurational and vibrational effects aid in stabilizing the SFs through segregation of Co to the two innermost (111) planes in the SFs and predict a reduction of segregation with increasing temperature. We further emphasize that the experimentally determined SFE is strongly related to Co segregation and vibrational free energy contributions. The method developed herein could be leveraged to inform alloy design strategies and predict segregation in other interfacial problems such as grain boundaries and heterointerfaces.