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Abstract

Structural materials such as steels are frequently processed under stress and strain conditions; in such systems, C and H have been shown to strongly affect the mechanical properties of Fe. Therefore, it is of interest to understand the coupling between segregation phenomena and mechanical response. In this work, we study the cohesion behaviour of a Σ5(310)[001] symmetrical tilt grain boundary (STGB) in body centred cubic (bcc) Fe with C as an interstitial alloying element and H as an impurity. Using first-principles calculations, the solution and segregation energies are obtained for varying mechanical load and GB coverage of the segregating atoms, either for fixed concentration or fixed chemical potential. Thus, the maximum concentration of C and H is calculated. We discuss that the concept of strain, or displacement, in ab initio tensile tests that include structural relaxations is ill-defined due to the release of elastic energy, which causes the calculated total energies to depend on the system size. The proposed procedure is to obtain the solution energies as a function of the stress instead of the displacement (or strain), assuming that the stress distributes equally among crystallographic planes in the supercell.