First-principles investigation of hydrogen interaction with TiC precipitates inα-Fe

Abstract

A correct description of hydrogen diffusion and trapping is the prerequisite for an understanding of the phenomenon of hydrogen embrittlement. In this study, we carried out extensive first-principles calculations based on density functional theory to investigate the interaction of H with TiC precipitates that are assumed to be efficient trapping agents mitigating HE in advanced high-strength steels. We found that there exists a large variety of possible trapping sites for H associated with different types of interfaces between the TiC particle and the Fe matrix, with misfit dislocations and other defects at these interfaces, and with carbon vacancies in TiC. The most efficient trapping by more than 1 eV occurs at carbon vacancies in the interior of TiC particles. However, these traps are difficult to populate at ambient temperatures since the energy barrier for H entering the particles is high. H trapping at the semicoherent interfaces between the TiC particles and the Fe matrix is moderate, ranging from 0.3 to 0.5 eV. However, a sufficiently large concentration of the carbide particles can significantly reduce the amount of H segregated at dislocation cores in the Fe matrix. A systematic comparison of the obtained theoretical results with available experimental observations reveals a consistent picture of hydrogen trapping at the TiC particles that is expected to be qualitatively valid also for other carbide precipitates with the rock-salt crystal structure.

The Role of κ-Carbides as Hydrogen Traps in High-Mn Steels

“…This was later confirmed by first-principles calculations [10], which further demonstrated that H accumulation can weaken the interface, resulting in hydrogen-enhanced decohesion and subsequent fracture formation.…”

“…Another possible scenario can be the formation of percolating networks of C vacancies which act as energetically favored pathways for hydrogen to diffuse from the interface to the bulk of the carbide, as observed for TiC [10]. We can further define the hydrogen-vacancy complex formation energy as the sum of the C vacancy formation energy and the H trapping energy within this vacancy.…”

“…In the case of Fe, the relevance of substitutional transition-metal atoms [18], vacancies [19], grain boundaries [20] and some precipitate phases [10] have been discussed. To the best of our knowledge, however, the hydrogen trapping by κ-phases has not been explicitly addressed theoretically.…”

Effect of Submicron‐Scale MnS Inclusions on Hydrogen Trapping and HIC Susceptibility of X70 Pipeline Steels

“…In particular, there is the largest hydrogen dissolution energy at the hollow site, showing the strongest solution effect of hydrogen locally . Other than the dissolution energy in the top site of S–Fe, the dissolution energies of hydrogen at other sites are above 1 eV, which is greater than the dissolution energy of hydrogen in semi‐coherent α ‐Fe/TiC interfaces (0.32–0.5 eV) by Stefano et al, and that of hydrogen at oriented grain boundaries of α ‐Fe (0.1–0.5 eV) by Mirzaev et al Thus, the dissolution (or trapping) of hydrogen at MnS inclusions is more stable than other sites such as lattice. As a result, the H atoms tend to be irreversibly trapped at numerous small inclusions with limited amount at each site, limiting the hydrogen pressure that can be developed locally and improving the resistance of the steel to HIC.…”

Ab initio study of energetics and structures of heterophase interfaces: From coherent to semicoherent interfaces

“…In particular, in low carbon steels, such as high-strength low-alloy (HSLA) steels, homogeneously distributed nano-sized MX precipitates significantly increase the yield stress. In order to exploit the benefits of the MX precipitates in steels, i.e., precipitation strengthening, grain refinement, and enhancing resistance to hydrogen embrittlement by trapping hydrogen [1][2][3], etc., a detailed characterization of the structures and energetics of the phase interfaces is required. For example, prevention of precipitate coarsening by Ostwald ripening during subsequent processing is crucial to realizing a sufficient precipitation hardening effect in the final product.…”