As a newly synthesized two-dimensional carbon material, the stability study of monolayer fullerene networks or quasi-hexagonal phase fullerenes (qhp-C₆₀) is timely desirable. We have investigated the stabilities of qhp-C₆₀, including thermal, structural, mechanical, and thermodynamic stabilities, as well as the bonding characteristics, ductility, and mechanical properties, via first-principles calculations. The results show that qhp-C₆₀ is energetically, mechanically, and thermodynamically stable. The thermodynamic stability of qhp-C₆₀ at 300 K and 600 K is verified. The bonding characteristics of qhp-C₆₀ are analyzed from the bond length, and it has sp² and sp³ hybridization. The Pugh ratio (B/G) and Poisson’s ratio (v) indicate similar ductility with graphite and graphene. We also found that qhp-C₆₀ has the lowest hardness and the anisotropy of the material. In addition, the electronic characteristics, including electron localization function (ELF), crystal orbital Hamiltonian population (COHP), and density of states (DOS) at different temperatures, are analyzed to verify the thermal stability of the material. Our results might be helpful in the material design of qhp-C₆₀-related applications.

Hydrogen embrittlement poses a significant threat to the structural integrity of high-strength steels. Although vanadium carbide (VC) precipitates are recognized as effective traps for mitigating hydrogen-induced damage, the precise mechanisms of hydrogen trapping and diffusion within VC remain controversial. In this study, we employ first-principles calculations to investigate the influence of carbon vacancies on hydrogen trapping and diffusion behavior at the coherent α-Fe/VC interface. Our results reveal that interfacial carbon vacancies facilitate hydrogen approach along the xy-plane, while interconnected vacancy networks enable hydrogen to diffuse from the α-Fe matrix into the VC bulk. Notably, hydrogen ingress into VC occurs preferentially through nearest-neighbor carbon vacancies. The calculated activation energies for hydrogen escape from interfacial and internal VC vacancies are 67.5 kJ mol⁻¹ and 82.2–83.9 kJ mol⁻¹, respectively, in good agreement with experimental values. These findings underscore the critical role of interfacial and connected carbon vacancies in mediating hydrogen diffusion and trapping within VC, providing atomistic insights for designing hydrogen-resistant steels.

Enhancing the utilisation of internal carbon (C) vacancies in vanadium carbide (VC) precipitates through the doping of chromium (Cr) atoms is crucial for mitigating hydrogen embrittlement in high-strength steels.

Hydrogen trapping at carbide/matrix interfaces is important for improving the resistance of steels to hydrogen embrittlement. In this work, the segregation behavior of hydrogen at the coherent α-Fe/V₄C₃ interface was investigated by first-principles calculations. Representative hydrogen sites were considered systematically, including interstitial sites in the near-interface region, interfacial sites, and carbon-vacancy sites in V₄C₃. All of the sites examined are energetically favorable for hydrogen trapping, but the carbon vacancy inside V₄C₃ exhibits the strongest trapping tendency. Charge density, Bader charge, and density-of-states analyses indicate that hydrogen at this site gains more electrons and forms stronger interactions with neighboring V atoms, leading to enhanced stability. The behavior of H₂ at the internal carbon vacancy was also evaluated. After structural relaxation, the H₂ molecule dissociated into two separate H atoms, indicating that hydrogen is more stably trapped in atomic rather than molecular form. These findings reveal the crucial role of carbon vacancies in regulating hydrogen trapping at the α-Fe/V₄C₃ interface and provide atomic-scale insight into the hydrogen trapping mechanism of vanadium carbide precipitates in steels.