ABSTRACT
In-situ fatigue experiments within a scanning electron microscope (SEM) have been carried out to study initiation and growth of short cracks in a nickel-based single crystal superalloy. Load-controlled tension fatigue tests were conducted for notched specimens with two different crystallographic orientations, e.g., [001] and [111], in a vacuum environment. Crack initiation was associated with shear deformation along activated slip systems. Following the initiation of cracks, continuous development of slip traces was observed ahead of the crack tip and acted as nuclei for early-stage crack growth. These slip traces were a direct result of accumulated shear deformation of activated octahedral slip systems, which were identified from crystallographic analyses. Based on in situ imaging, the crack-growth rates were calculated and correlated with the range of stress intensity factor, showing the anomaly of slip-controlled short-crack growth behaviour.
