The behavior of short fatigue cracks during Very High Cycle (VHCF) Fatigue of duplex stainless steel

• Phase and grain boundaries are barriers to VHCF crack propagation.
• Barrier efficiency depends on slip geometry of neighboring grains.
• The first barrier decides if duplex stainless steel exhibits a real fatigue limit.
• Barrier efficiencies can be implemented in the finite element method.

During VHCF loading of duplex steels fatigue damage starts within the softer austenite phase. Depending on the spatial mismatch between the slip systems of neighboring grains, intergranular or transgranular fatigue cracks are initiated. If these cracks can propagate or are blocked depends on the interactions with the local microstructure. These interactions have been studied by ultrasonic fatigue testing in combination with electron microscopy and synchrotron diffraction experiments. It was found that the strength of the first microstructural barrier is decisive for VHCF life. The barrier strength as a function of the microstructural arrangement has been implemented in a micromechanical finite element approach that shall be used to predict the VHCF life or the existence of a fatigue limit for given microstructure parameters.