Nano-scale failure in steel: Interace decohesion at iron/precipitate interfaces

Multiphase alloys such as advanced high strength steels show limited ductility due to interface decohesion at internal boundaries. This interface decohesion is caused by dislocations that pile-up at interfaces in the material, where they cause a stress concentration. This stress concentration in turn can lead to interface decohesion, resulting in the formation of voids, which, when they coalesce, can form a macroscopic crack. In order to understand the process of interface decohesion and the factors facilitating this, in this thesis interface decohesion at interfaces between the soft iron matrix of steel and hard precipitates is studied at the nano-scale with molecular dynamics simulations. From the nano-scale simulations cohesive laws are derived that relate the tractions at the interface to the separations at the interface. These cohesive laws can be used to describe interface decohesion in material models at the next larger length scale (micro-scale), such as discrete dislocation plasticity.