At present

study on low cycle fatigue of DD6 superalloy focuses on the high temperature range. In order to explore the orientation correlation

cyclic stress response

and fracture mechanism of low cycle fatigue of DD6 nickel based single crystal superalloy at a moderate temperature of 850 ℃

the low cycle fatigue tests of smooth round rod specimens of DD6 nickel based single crystal superalloy with different orientations at 850 ℃ is studied via Instron 8801 hydraulic servo high temperature fatigue testing machine

the microstructure characteristics near the fracture via scanning electron microscopy (SEM) and optical microscopy (OM) is analyzed. The results indicate that considering the strain and stress range

the fatigue performance of DD6 nickel based single crystal superalloy with [011] orientation is the best; the overall trend is that the larger the orientation deviation

the lower the fatigue life. Under the same orientation

the higher strain amplitudes intensify the initial cyclic hardening

shorten the stress saturation stage

and reduce the fatigue life. After the initiation of low cycle fatigue crack in DD6 single crystal superalloy

the initial crack propagates along different crystal orientations and slip systems

and along the {111} slip plane until the specimen fractures. The cross-section belongs to the quasi cleavage type; a persistent slip band is observed near the fracture

and its direction is related to the direction of crack propagation