Revisiting hydrogen embrittlement models and hydrogen-induced homogeneous nucleation of dislocations

Models explaining hydrogen embrittlement as caused by enhanced local plasticity are discussed in the light of a novel concept describing solute–defect interaction in a thermodynamic framework. Solute atoms segregating at defects with an excess Γ are called defactants because they lower the defect formation energy of defects γ, analagous to the action of surfactants with surfaces. The corresponding decrease is given by dγ = −Γdμ, where μ is the chemical potential of the defactant. This equation is applied to recent nanoindentation results, and reveals a lower energy barrier for the generation of dislocation loops in the presence of hydrogen.