The fourth generation single crystal superalloy DD15 with [001]

[011] and [111] orientations was cast using seed method in the directionally solidified furnace. The high cycle fatigue properties of the alloy with different orientation were investigated at 800℃ . The microstructure

fracture surface and fatigue ruptured microstructure of the alloy with different orientation were studied. The results show that the alloy with different orientation has obviously various ascast dendritic structure and heat treated γ′ phase on the section perpendicular to the solidified direction. The high cycle fatigue properties of alloy at 800℃ has anisotropy and fatigue limit of the alloy decreases with the sequence of [111]

[001] and [011] orientation. The high cycle fatigue of alloy with different orientation breaks along the plane. The angle between the fracture plane and the stress axis of the sample is different and decreases with the sequence of [011]

[001] and [111] orientation. The high cycle fatigue fracture characteristics are basically the same. Fatigue source zone

crack propagation zone and transient fracture zone can be seen on the fracture surface of the alloy with different orientation. The fatigue crack initiated at or near the surface and propagated along {111} planes. The river pattern and fatigue striation can be seen in the crack propagation zone. The cleavage step and tear ridge can be seen in the transient fracture zone. The fracture mechanism is all quasi-cleavage fracture. The γ′ phase morphology still maintained cubic after fracture because of lower test temperature.