Regulating the grain boundaries (GBs) via solute segregation provides a viable pathway to design stable nanocrystalline metals. This study investigates the segregation tendencies of X (X = In, Cr, Ca, Co, Zn, Ag, Zr, and Sn) at the potential sites of Cu Σ11 [110](1 \(\overline{1}\) 3) GB, as well as the co-segregation behavior of Y (Y = Cr and Co) at the Zr- and Ca-segregated Cu GBs, using first-principles calculations. Our results indicate that Cr and Co lack a thermodynamic driving force for segregating to Cu GBs, unlike other elements possessing GB segregation tendencies. The co-segregation calculations show that the presence of Zr at Cu GB can induce the segregation of Cr and Co. In comparison to the single-solute segregation of Zr, Cr, and Co, Zr-Co and Zr-Cr co-segregations exhibit synergistic enhancing effect on the GB thermodynamic stability. Regarding to the enhancement of GB fracture strength, Zr-Co co-segregation shows antagonistic effect, whereas Zr-Cr co-segregation demonstrates synergistic action. This work sheds light on accurately regulating the GB stability and strength of nanograined Cu alloys based on GB segregation.
