Microstructures and Ultra-high Cycle Fatigue Behaviors of Directionally Solidified Superalloy DZ125 After Long-term Aging

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.