High temperature low cycle fatigue behavior of a directionally solidified Ni-base superalloy DZ951

Total strain-controlled low cycle fatigue (LCF) tests were performed at a temperature range from 700 to 900 °C in ambient air condition on a directionally solidified Ni-base superalloy DZ951. The fatigue life of DZ951 alloy does not monotonously decrease with increasing temperature, but exhibits a strong dependence on the total strain range. The dislocation characteristics and failed surface observation were evaluated through transmission electron microscopy and scanning electron microscopy. The alloy exhibits cyclic hardening, softening or cyclic stability as a whole, which is dependent on the testing temperature and total strain range. At 700 °C, the cyclic plastic deformation process is the main cause of fatigue failure. At 900 °C, the failure mostly results from combined fatigue and creep damage under total strain range from 0.6 to 1.2% and the reduction in fatigue life can be taken as the cause of oxidation, creep and cyclic plastic deformation under total strain range of 0.5%.