In situ fracture experiment on a duplex stainless steel

Abstract

Abstract Development of the dislocation structure in the plastic zone ahead of a propagating crack in a duplex stainless steel has been investigated using in situ fracture experiments in a scanning transmission electron microscope. These showed that the dislocation configuration and crack propagation modes were totally different in the two phases. In the α phase a broad plastic zone formed ahead of the crack owing to cross-slip of dislocations emitted by the crack tip. The crack advanced along a relatively straight path. In the austenite phase, dislocations were confined to a few thin ribbons in which they formed inverse pile-ups ahead of the crack tip. The main crack normally propagated in a zigzag manner. Owing to strong interaction of the crack with the interface, multiple slip originated from dislocation sources in the phase boundaries ahead of the crack. Dislocation activity in the austenite phase intensified when the crack approached the interface. One or two microcracks initiated in the α-γ boundary and propagated in a zigzag manner through the austenite phase before sudden rupture of the connecting ligament occurred. Detailed analysis has shown that the activation of the slip system ahead of the crack in the ferrite was mainly controlled by the crack tip Schmid factor, whereas in the γ phase the bulk Schmid factor was also important in controlling the activation of the slip systems.