Surface segregation of ternary alloys

Abstract

Ternary alloys have been developed for a wide range of applications and surface segregation of ternary alloys has a decisive impact on their performance. Different from binary alloys, in which surface energy is usually the dominant factor, the interaction between solute elements has a noticeable effect on the surface segregation behavior of ternary alloys. As a practical example, Pd-based ternary alloys have been proposed as promising candidates for hydrogen separation membranes due to their excellent permeability and selectivity. In the present work, surface segregation of Pd-Cu-Ag and Pd-Cu-Mo ternary alloys in both vacuum and hydrogen atmosphere is investigated. X-ray photoelectron spectroscopy and low energy ion scattering spectroscopy analyses reveal that the segregation trend of the outermost atomic layer is not always the same as that of the near-surface region. A thermodynamic model is developed to describe the surface segregation of ternary alloys. The results of the model are in good qualitative agreement with experimental results. Furthermore, calculations for other ternary alloy systems confirm that the model provides a simple but universal method for surface segregation in ternary alloys. The results can also be considered as basic guidelines to design novel ternary alloys for various applications.