On the propensity of lath martensite intervariant boundaries to hydrogen absorption using molecular statics simulation

In the current study, the influence of boundary character (i.e., tilt, twist and mixed) on hydrogen absorption was, for the first time, investigated for lath martensite using molecular statics simulations. The energies of the martensitic intervariant boundaries varied widely from 306 to 1109 mJ/m2 depending on their character. The symmetric tilt and quasi-tilt boundaries revealed the lowest and highest boundary energies, respectively. This was, to some extent, reflected by distinct boundary unit structure/s and their complexity within a given intervariant boundary type. Interestingly, the intervariant boundary energy was not the main criteria to regulate the propensity of the boundary to hydrogen absorption. Rather, absorption depended on a distinct arrangement of unit structure/s within a given boundary plane, providing different interstitial sites for hydrogen. Indeed, the propensity for hydrogen atom/s was largely determined by the number of inequivalent interstitial sites, which resulted from the interaction of wide varieties of boundary unit structures. The intervariant boundary that consisted of regular arrangements of atoms with fewer boundary unit structure variety exhibited less tendency to H/H2 absorption (e.g., 60°/[111¯] symmetrical tilt boundary). On the contrary, the presence of a substantial number of diverse unit structures within the boundary plane significantly enhanced the tendency for hydrogen segregation (e.g., 51.73°/[116¯11] quasi-tilt and 10.53°/[01¯1¯] twist intervariant boundaries). The current findings provide a fundamental basis for the engineering of the intervariant boundary network within the martensitic microstructure to significantly enhance the hydrogen embrittlement resistance. This is critical for steels used in severe environments, such as hydrogen storage and pipelines for hydrogen transportation.