Construction and analysis of surface phase diagrams to describe segregation and dissolution behavior of Al and Ca in Mg alloys

Abstract

Segregation and dissolution behavior of Mg alloyed with Ca and Al are studied by performing density functional theory calculations considering an extensive set of surface structures and compositions. Combining ab initio surface science approaches with cluster expansion for ordered surface structures we construct surface phase diagrams for these alloys. We utilize these diagrams to study segregation phenomena and chemical trends for surfaces in contact with a dry environment or with an aqueous electrolyte. We show that the presence of water dramatically impacts the stability and chemical composition of the considered metallic surfaces. We furthermore find that the two alloying elements behave qualitatively different: whereas Ca strongly segregates to the surface and becomes dissolved upon exposure of the surface to water, Al shows an anti-segregation behavior, i.e., it remains in Mg bulk. These findings provide an explanation for the experimentally observed increase/decrease in corrosion rates when alloying Mg with Al/Ca.

arXiv comment12 pages, 9 figures, submitted to Phys. Rev. Materials

References in corpus (7)

• Implicit solvation model for density-functional study of nanocrystal surfaces and reaction pathways
• Composition, structure and stability of RuO_2(110) as a function of oxygen pressure
• The Alloy Theoretic Automated Toolkit: A User Guide
• Surface energies, work functions, and surface relaxations of low index metallic surfaces from first-principles
• The Effect of the Environment on alpha-Al_2O_3 (0001) Surface Structures
• Clean and As-covered zinc-blende GaN (001) surfaces: Novel surface structures and surfactant behavior
• Theory of alkali metal adsorption on close-packed metal surfaces

Cited by in corpus (1)

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