Trends in Segregation Energies and their Application to Embrittlement and Creep

Interfacial segregation is one of the most fundamental and influential phenomena in surface science. In particular, segregation of impurities to metallic surfaces and grain boundaries is known to control most basic material properties, including influencing the mechanical, chemical, and transport behavior of solids. There is thus a large need to understand the thermodynamic origins of segregation in solids. Historically, segregation in metals has been posited to be driven by a combination of elastic, chemical, and bond-breaking effects. To this explore the origins of segregation, a large number of groups have been pursuing calculation of segregation energies, primarily with density functional theory (DFT). However, most of these studies have proceeded in isolation, and a global collation and investigation of segregation energies in solids has been lacking. In particular, several important questions remain to connect calculated DFT segregation energies to macroscopic behavior:

(1) Can we quantitatively verify the posited origins surface segregation energies in metals?

(2) What are the origins of surface segregation anisotropy, and is segregation relatively isotropic or anisotropic?

(3) Given the similarity in posited driving forces for grain boundary and surface segregation, what is the correlation between these two phenomena and what is its origin?

(4) As the difference in grain boundary and surface segregation energies yields the change in the ideal work of separation of a boundary, can the ideal work of separation be related to embrittlement? If so, are the origins of grain boundary embrittlement electronic, elastic, or cohesive in origin?

We have created a database of DFT-based GB and surface segregation energies to answer these questions, and present a quantitative assessment of said database. We connect our findings to embrittlement and creep of metals using examples from the literature, and present general guidelines for future alloy design to prevent unwanted failures.