The necessity of both plasticity and brittleness in the fracture thresholds of iron

TLDR

The study aims to explain discontinuous brittle cracking in hydrogen‑laden materials through single‑crystal and crack/dislocation simulations. A computational scheme calculates the local stress tensor near a crack in anisotropic iron, modeling a load perpendicular to the {100} cleavage plane, growth along 〈010〉, and a stress intensity of 16 MPa m⁻¹ᐟ². The analysis shows that stresses shift ~23 nm from the crack tip, reaching ~20 000 MPa and concentrating hydrogen to nearly one per iron atom, which initiates decohesion over ~1 µm regions, matching experimental observations.

Abstract

Abstract In order to explain discontinuous brittle cracking in materials subjected to hydrogen, single-crystal and crack/dislocation simulation studies have been made. The computational scheme allows the local stress tensor near a crack in an anisotropic elastic solid with shielding dislocations to be determined. The model system is iron with a load axis perpendicular to the {100} cleavage plane, growth in the macroscopic 〈010〉 direction, and an applied stress intensity of 16 M Pa m1/2. The result is that the elastic stress distribution is translated out from the crack tip by about 23 nm and that large stresses, although not of a singular nature, still exist. These stresses near 20 000 M Pa are sufficient to concentrate dilute solutions of hydrogen to nearly one hydrogen for every iron atom. Such stresses, combined with these extremely high hydrogen concentrations are proposed for the initiation of decohesion which grows locally over 1 μm size areas, as observed experimentally.