Nickel-based superalloys are key structural materials for critical applications in extreme service environments, such as in aero-engines and nuclear reactors. However, under neutron irradiation, helium (He) is generated within the material via transmutation reactions. These helium atoms segregate and accumulate at defects like grain boundaries (GBs), leading to severe hardening and embrittlement (known as “helium embrittlement”), which significantly limits the material’s long-term service life.

To gain a deeper understanding of and mitigate helium embrittlement, this study employed first-principles calculations based on density functional theory (DFT) to systematically investigate the synergistic effects of four key alloying elements (Cr, Mo, Nb, Ti) and helium in four typical symmetric tilt grain boundaries (Σ3(111), Σ11(113), Σ5(210), and Σ5(310)) of nickel. Key thermodynamic parameters, such as segregation energy and strengthening/embrittling energy, were calculated. This was complemented by electronic structure analyses, including differential charge density and density of states, to elucidate, at the atomic and electronic levels, the influence of alloying elements on helium segregation behavior and the microscopic mechanisms by which they mitigate grain boundary embrittlement.

The segregation energy calculations show that both the alloying elements and helium atoms exhibit a tendency to segregate to the grain boundaries. A clear correlation exists between the segregation energies and the relative atomic excess volume, with larger excess volumes yielding more negative segregation energies. Interstitial helium possesses the largest relative atomic excess volume, resulting in the strongest segregation tendency. Although the introduction of alloying elements cannot completely prevent helium segregation, it can reduce its driving force for segregation.

Calculations of the strengthening energy indicate that when alloying elements like Cr, Mo, Nb, and Ti segregate to the grain boundaries, they generally reduce the embrittling energy of He. This mitigating effect is more pronounced at grain boundaries with higher formation energy, such as Σ5(310). Among the four elements, Mo exhibits the strongest and most stable inhibitory effect, reducing the embrittling energy of substitutional He by approximately 11% to 16% and that of interstitial He by 3% to 10%.

Electronic structure analysis reveals the underlying mechanism: The segregation of helium atoms causes electron depletion in the surrounding Ni-Ni bonds, weakening their bonding strength. In contrast, the alloying elements form strong chemical bonds with neighboring nickel atoms, increasing the electron density in the grain boundary region. This partially compensates for the electron depletion induced by helium, thereby protecting the grain boundary bonding and mitigating embrittlement.

This study clarifies the physical essence of how alloying elements inhibit helium embrittlement through an electronic compensation mechanism, providing an important theoretical basis for the compositional optimization and design of nickel-based superalloys with high resistance to irradiation and helium embrittlement.