First-principles study on segregation anisotropy of grain boundaries in Pt–Au alloys

Gold (Au) segregation at Pt grain boundaries (GBs) plays an important role in the properties of Pt-based alloys. It was reported that close-packed GBs and open GBs exhibit different segregation behaviors, and their origin is still unclear. Based on the density functional theory as implemented in the exact muffin-tin orbitals method and the full charge density technique, we investigate the impact of bulk composition and temperature on the segregation behaviors of the Σ3(111)[11¯0], Σ5(310)[001], and Σ9(221)[11¯0] symmetric tilt GBs in Pt–Au alloys. It is revealed that the segregation driving forces are correlated with the large local volume near the GB and the miscibility gap in Pt–Au alloys. At finite temperatures when the configurational entropy is considered, a competition between the chemical driving force and the configurational entropy is responsible for the segregation anisotropy in Pt–Au alloys. The bulk composition has a small effect on the segregation energy but strongly impacts the equilibrium concentration profiles at finite temperatures. The present study provides a theoretical analysis for the segregation anisotropy, and the methodology utilized in this work can be generalized to other binary or multi-component dilute or concentrated alloys while the composition variation is involved.