The effects of crystallographic orientation on fatigue crack initiation behavior in Ti-6Al-4V

The influence of microstructure on crack initiation behavior of Ti-6Al-4V was investigated by using atomic force microscope (AFM) and electron backscattered diffraction (EBSD). This research considers the effects of both the Schmid factor (SF) value and the slip direction of the grain on fatigue crack initiation sites. The result shows that fatigue cracks tend to form basal slips in primary alpha grains. In addition, these cracks are generated from primary alpha grains with relatively high basal SF values. However, it was found that fatigue cracks do not necessarily originate from basal planes of primary alpha grain with the maximum SF value. Finally, a new parameter that combines SF and the slip angle Omega (slip angle Omega is the angle between the specimen surface and the slip direction) was suggested and that parameter enables to predict fatigue crack initiation sites, since it was revealed that fatigue cracks initiated from primary alpha grains with high SFsin Omega values.