Effect of boron on the hydrogen-induced grain boundary embrittlement in α-Fe

The influence of interstitial impurities such as B and C on the H-induced Fe Σ5(310) symmetrical tilt grain boundary embrittlement was investigated using the projector augmented-wave method. It was shown that in contrast to hydrogen, both boron and carbon decrease the grain boundary energy more significantly than the surface one. This results in an increase in the Griffith work, i.e. the grain boundary strengthening. The strengthening of grain boundary is more pronounced with increased number of B atoms whereas the increase of H concentration makes the process of intergranular brittle cleavage fracture easier. The grain boundary energy is lowered with an increased number of B atoms indicating a strong driving force for segregation. Our estimations of the Griffith work for the Fe Σ5(310) grain boundary containing both B and H atoms show an increase in comparison with the undoped grain boundary. It is revealed that improved cohesion of Fe Σ5(310) grain boundary due to B is mainly a chemical effect, whereas both elastic and chemical contributions to the Griffith work in case of H are negative, i.e. they are embrittling contributions.