Atomic-size effect in hydrogen-induced amorphization

Abstract

The microscopic mechanism of hydrogen-induced amorphization (HIA) in C15 Laves phases of AB₂ compounds is studied. Experimentally, compounds in which the AA internuclear distance is reduced and BB internuclear distance expanded compared to pure crystals show hydrogen-induced amorphization which suggests that the relative atomic size is the controlling factor. We investigate the role of the size effect by static and molecular dynamics methods using Lennard–Jones potentials. Our simulations show that in such a compound, the bulk modulus is remarkably reduced by hydrogenation compared to the isotropic tensile load, so that elastic instability is facilitated. This situation is caused by the negative increase of the pressure-fluctuation contribution in the elastic constant. We also report the fracture process under isotropic tensile loading. An elastic analysis at sublattice level shows that one of the sublattices is less stable in the HIA material.