Mechanisms and micromechanics of intergranular ductile fracture

The process of void nucleation, growth, and coalescence is among the dominant ductile failure modes in metallic alloys and can be transgranular as well as intergranular. In the latter case, the phenomenon of void growth and coalescence happens at grain boundaries due to intense intergranular plastic flow and is associated with fracture surfaces displaying intergranular facets covered in fine dimples. The present review gives a comprehensive summary of intergranular ductile fracture mechanisms based on available experimental evidence, allowing to distinguish precisely this failure mode from other related processes. Moreover, the metallic alloys of industrial significance that can exhibit intergranular ductile fracture are carefully outlined. Then, in order to lay bridges between material science and fracture micromechanics, an overview of the current development of the local approach to fracture applied to grain boundary ductile failure is presented. Emphasis is placed on the accounting of crystallographic effects. Finally, prospects for progress in intergranular ductile fracture modeling and simulation are detailed. In particular, it is foreseen that conflicting trends seen on fracture toughness could be reconciled thanks to physically-based approaches.