Mesoscopic model of hydrogen embrittlement in particle strengthened materials

This work focuses on the constitutive modelling of damage development in particle strengthened materials in the presence of hydrogen. We apply the model to an area at the interface of a dissimilar weld of 8630 steel/IN625 nickel alloy which is known as the 'featureless region'. This region contains an array of M7C3 carbides each measuring about 40 nm. Cleavage-like fracture has been observed only in the presence of hydrogen and it is attributed to a combination of two types of hydrogen embrittlement mechanisms: hydrogen-induced decohesion (HID) along the M7C3 -matrix interface of and a ductile-type fracture (Hydrogen Enhanced Local Plasticity, HELP). Modelling the constitutive behaviour of this region at a continuum level is not appropriate as the major role in the material response is the interaction of the carbide particles with dislocations which is captured at the mesoscopic level. Here we propose a constitutive model of the 'featureless zone' that accurately represents the effect of hydrogen on the constitutive response of the M7C3 region at the mesoscopic scale. Hydrogen enhances the evolution of dislocations around the M7C3 carbides, therefore the stress locally increases affecting the interfacial strength. The result is that, in the region of high hydrogen concentration, the material exhibits softening.