Analysis of the various processes downstream cathodic hydrogen charging, V : Dissolved hydrogen, dislocations and dislocation drag

Abstract

The new views issued from corrosion on the mandatory replacement of the atomic hydrogen H by a proton H + are first reminded for metallurgist, as well as the evolution of the physical approach to the metallic state, its consequences on the understanding of ab initio calculations (e.g. incompatibility between nuclear and conventional applications), and the reciprocal hydrogen-dislocation interactions. In an edge dislocation, especially, and for relieving the involvement of lattice elasticity on the expanded and contracted sides of the slip plane, a flat and extended cluster of repulsive protons progressively replaces the missing half-plane, and a symmetrical proton depletion dampens the additional half-plane. But when becoming too broad, flat proton clusters can also turn to incipient decohesions, which explains the systematic morphology of cleavage-like cracking in yet ductile steels. The illusion of the thermodynamic of irreversible processes is then reminded in the prospect of a possible hydrogen diffusion under stress gradient. The dislocation drag of hydrogen is finally shown to be a convective transport, which results in an unexpected exponential enrichment at the arrival, explaining both SSC and SOHIC. The propensity of protons to form flat clusters also explains the characteristic morphologies of cleavage-like or intergranular cracking in HE and corrosion fatigue.