A coexistent view of hydrogen effects on mechanical behavior of crystals: HELP and HEDE

The literature is now replete with publications extolling the virtues of hydrogen-enhanced localized plasticity (HELP) versus hydrogen-enhanced decohesion (HEDE). What this contribution desires to accomplish is separating the various stages of dislocation plasticity and fracture. To that end it is proposed that HELP almost always occurs but may have very different ramifications on the interpretation of dislocation nucleation and dislocation velocities. Similarly, whether or not decohesion or ductile rupture occurs in a given system cannot be divorced from the combinative effects of hydrogen on plasticity, except perhaps in rare cases. From a fracture mechanics viewpoint, a couple of plausible interactions of HELP and/or HEDE are described for hydrogen-enhanced cleavage, microvoid growth, or shear instability.