Segregation of bismuth and yttrium and their influence on the cohesive strength of copper grain boundaries: A first-principles study

Bismuth (Bi) is a harmful impurity in cooper (Cu) and Cu-based alloys, where its grain boundary (GB) segregation induces intergranular embrittlement. Alloying with rare-earth elements such as yttrium (Y) improves mechanical performance, yet the atomic-scale mechanisms remain unclear. Here, first-principles calculations were performed to investigate Bi and Y segregation at four representative symmetric tilt GBs in Cu—Σ3(111), Σ5(310), Σ5(210), and Σ7(415¯)—and their impact on GB cohesion. Segregation energies were evaluated for one-solute, two-solute and multi-solute models (corresponding to monolayer, bilayer, and multi-solute segregation configurations). Y generally exhibits more negative segregation energies than Bi, especially at the most stable sites, indicating a preference to substitute Bi at GBs. With increasing solute concentration, segregation becomes progressively less favorable due to solute–solute interactions, consistent with theoretical predictions and experimental observations. Computational tensile tests reveal that Bi reduces cohesion and promotes embrittlement, whereas Y can enhance GB cohesion by increasing the work of separation and producing more negative strengthening energies. Charge-density and bond-length analyses clarify the atomic origins of these effects. A linear relationship between segregation and strengthening energies, independent of GB structure or segregation mode, is established. These results demonstrate that Y effectively counteracts Bi-induced embrittlement and provide atomic-level insight into segregation–strengthening interactions, offering guidance for designing Cu-based alloys with improved properties.