Very high cycle fatigue (VHCF) properties of notched Ni-based single crystal specimens have been studied at 20 kHz and 1000°C. A new specimen geometry with a stress concentrator is presented alongside the experimental setup used for testing.

Crack initiation modes observed under pure fatigue (R = -1) loading are shown and discussed. Most tested specimens failed from a crack initiating on a casting pore. However, several specimens’ fatal cracks originated from the surface. For all the specimens with lives over 2*10^7 cycles, surface cracking can be observed.

An approach based on local stress without considering the existence of casting pores allowed to greatly reduce lifetime scatter.