Dislocation mechanism of hydrogen embrittlement of metals and alloys with HCP and FCC crystal structure

Abstract

The results of the experimental study of the mechanism of hydrogen embrittlement were generalized on the basis of a theory of thermally activated (quasi-brittle) fracture, developed by the authors to predict the nature of gradual quasi-brittle transition of Me-H solid solutions. It was established that development of hydrogen brittleness for polycrystals appeared to be controlled at low (cryogenic) temperature by thermally activated sliding screening dislocations overcoming segregated H atoms at the microcrack tips with activation energy of 0.05-0.07 eV at the critical (hard-activated) stage of fracture propagation. If the concentration of excess (hydrogen- and deformation-induced) vacancies of 2–3 orders exceeds that for thermal equilibrium vacancies, the structure's clusterization of Me-H solid solutions was observed within the thermally activated area of dynamic deformational aging (in the host metal and at the boundaries). Hereby the formation of strong “H atom-excess vacancy” clusters with a binding energy of 0.2-0.5 eV, being large in comparison with “H atom-screening dislocation” binding energy, prevent the H atom's segregation at the structure defects. The methods for elimination of hydrogen brittleness, restoration of plasticity and strength properties of Me-H systems are suggested on the basis of the formation of the new barriers for propagating microcracks—the disoriented cellular structures in clusterized solid solutions with large numbers of active sliding systems of screening dislocations. TiH, ZrH and AlH or superdisperse granular structures in superplastic and plastic states of clusterized substitution alloys with a lack of active sliding systems of screening dislocations (MgBaH, BeCoH).