Abstract: Directionallly solidified superalloy DZ125 is aged at 950 ℃ for 500 h, 1 000 h and 1 500 h, respectively. The ultra-high cycle fatigue property of alloy DZ125 is measured using an ultrasonic fatigue test machine. The microstructures and ultra-high cycle fatigue behaviors of DZ125 are investigated using scan electron microscopy, transmission electron microscopy and electron backscatter diffraction (EBSD) technique. The results show that the effect of long-term aging heat treatments on the microstructures of DZ125 is small, and the lattice misfit is reduced after long-term aging. With the increase of the aging time, γ' phases accumulate and grow obviously, but the topologically close packed(TCP)phase is not found. The effect of long-term aging heat treatments on the ultra-high cycle fatigue properties is small. With the increase of the aging time, the ultra-high cycle fatigue property shows a downward trend .The fatigue fracture surface is perpendicular to the stress axis/fatigue cracks initiate from the sample surface, and the grain rotation angle is small after ultra-high cycle fatigue tests.

Key words: directionally solidification, superalloy, long-term aging, ultra-high cycle fatigue, fatigue fracture, cracks