A micromechanical image-based model for the featureless zone of a Fe-Ni dissimilar weld

This paper deals with the constitutive modelling of the 'featureless' region located on the Nickel side of a AISI8630/IN625 dissimilar weld interface. Fractography of failed weld interfaces show that cracks propagate in this carbides ()-rich region in the presence of hydrogen. In this paper, TEM images of the carbide-rich region are converted into a finite element mesh through an image-based mesh generation scheme. Simulations of the response of these structures show that in areas where the hydrogen content is high the matrix surrounding the carbides softens and plastic flow is localized. Moreover, the presence of hydrogen lowers the cohesive strength, giving rise to microcrack formation at the carbide-matrix interface. The amount of deformation then increases in a localized region adjacent to the region where (a) hydrogen content is high and (b) the carbide/matrix interface has debonded. As deformation proceeds the microcracks grow and link to form macrocracks, which generates the failure surface.