Low cycle fatigue behaviors and deformation mechanisms of the [011] oriented fourth-generation Nickel-based single crystal superalloy at 1000 °C

The fourth-generation single crystal superalloy has excellent service performance at high temperature. In this work, the low cycle fatigue behaviors and deformation mechanisms of the [011] oriented fourth-generation Ni-based single crystal superalloy was systematically investigated at 1000 °C. The alloy exhibited a cyclic stable behavior under strain amplitude of 0.5 %. However, under strain amplitude of 0.7 % and 0.8 %, the alloy exhibited a cycle hardening behavior. Afterwards, the crack initiation could be attributed to the exfoliation of the oxidation layers under strain amplitude of 0.5 %. As the strain amplitude increases to 0.7 % and 0.8 %, the crack initiation was mainly observed near the cast pores. Moreover, it could be seen that slip bands sheared both γ and γ′ phases in the vicinity of the fracture surface under different strain amplitudes. The cycle hardening behavior was attributed to the formation of SFs with different directions and inhomogeneous dislocation networks. In addition, the cycle softening behavior was attributed to the formation of bowing dislocations and super-dislocations. The phenomenon of dislocations movement led to the severe plastic deformation, thereby reducing the LCF life. This work and resulting experimental date guide the engineering application of the fourth-generation single crystal superalloy in the future.