First–principles study on embrittlement behavior of gadolinium-doped nickel grain boundaries

Understanding the microstructure and mechanical properties of gadolinium (Gd) doped nickel grain boundaries (GBs) is essential to enhance the service performance of structural materials. The structural stability and mechanical properties of typical Σ3(111), Σ5(021), Σ9(221), and Σ11(113¯) GBs in Gd-doped nickel alloys were systematically calculated by a first-principles method. The results indicate that Gd has the capacity to segregate for all four GBs. Notably, its susceptibility to segregation is heightened at the Σ5 and Σ9 GBs. By analyzing the embrittlement through the Rice–Wang model, it is determined that Gd has a brittle effect on all four GBs, which originates from both mechanical and chemical components. The mechanical component arises from weakened bonding due to increased bond length. The chemical component intensifies embrittlement at the Σ3 and Σ11 GBs, while mitigating it at the Σ5 and Σ9 GBs, which is mainly due to covalent bond formation. First-principles tensile tests showed that Gd doping causes a decrease in GB fracture energy and theoretical tensile strength. This work elucidates the microscopic embrittlement mechanism influence of Gd on the GBs of nickel alloys, which can provide reliable theoretical guidance for design and optimization as well as structural modulation of highly stable nickel alloys.