Low-cycle Fatigue Behavior of a Cast Ni-based Superalloy K4169 at 650℃
The low cycle fatigue behavior of nickel based cast superalloy K4169 at 650℃ was stud-ied,while its microstructure variation before and after test was assessed by means of SEM and TEM.The results show that the fatigue life of the alloy gradually decreases with the increasing strain.When the strain is 0.5％ and 0.6％,the alloy experiences strain hardening within the early 2～200 cycles,followed by cyclic stability and cyclic softening,respectively;When the strain is 0.8％ and 1.0％,the alloy exhibits con-tinuous cyclic softening behavior;Initial cyclic hardening is related to the hindering effect of y"strengthen-ing phases on the movement of dislocations,while cyclic softening is attributed to dislocations shearing y"phases repeatedly.The Coffin-Manson equation for the relationship between the plastic strain amplitude and the reverse number of fatigue failure of the alloy exhibits a bilinear relationship.Observation of the microstructure shows that the cyclic deformation mode of the alloy at high and low strains is all disloca-tions shearing y"phase and slip,and the fatigue failure of the alloy under different strains all exhibits transgranular fracture.Therefore,the reason for the bilinear behavior of the alloy may be the transforma-tion of deformation uniformity,and the non-Masing characteristic exhibited by the alloy also demonstrate the transformation of deformation uniformity.
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