Models explaining hydrogen embrittlement as caused by enhanced local plasticity were 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 were called defactants because they lower the defect formation energy of defects γ, analogous to the action of surfactants with surfaces. The corresponding decrease was given by dγ = −Γdμ, where μ was the chemical potential of the defactant. This equation was applied to recent nano-indentation results, and reveals a lower energy barrier for the generation of dislocation loops in the presence of hydrogen.

Revisiting Hydrogen Embrittlement Models and Hydrogen-Induced Homogeneous Nucleation of Dislocations. R.Kirchheim: Scripta Materialia, 2010, 62[2], 67-70