Hydrogen-induced plasticity model

Figure 5-55. Schematization of adsorbed hydrogen induced plasticity model for CF cleavage-like cracking.

Other mechanisms have been proposed, particularly the hydrogen-induced plasticity model for precipitates containing materials such as Al-Zn-Mg alloys. This model is shown in Figure 19 [5]. 

Schematization of the hydrogen-induced plasticity model for CF cleavage like cracking. (From Lynch, S.P., Acta Metall, 36,2639,1988.)...

Hydrogen-induced plasticity. Another approach is related to the fact that hydrogen increases local plasticity. Two models have been proposed based on the adsorption and absorption of hydrogen. 

The specific role of stress and strain in hydrogen embrittlement and cracking mechanisms has been established in the case of only a few models such as hydrogen-induced decohesion (HIDE) and hydrogen-induced local plasticity (HELP). 

Several testable models for stress-corrosion cracking (SCC) of metals are discussed in terms of the main experimental variables stress, metallurgy, and environment. Slip-dissolution, film-induced cleavage, and hydrogen embrittlement models are all shown to be consistent with experimental data in particular systems. Other models that cite effects of corrosion (without a film) or adsorption on crack tip deformation, leading to microcleavage or plastic microfracture, are less easy to test. No model can be universal in view of the demonstrable multiplicity of mechanisms. In many cases the atomistic mechanism is unknown, yet cracking can be controlled or predicted via the localized corrosion process that precedes SCC. 

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