Low cycle fatigue properties and microstructure evolution at 760°C of a single crystal superalloy

Abstract

Low cycle fatigue (LCF) behavior of a single crystal superalloy was investigated at 760 1C. Microstructure evolution and fracture mechanism were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The results show that the fatigue data fluctuation was small and the fatigue parameters of the alloy had been determined. On increasing the cyclic number, the alloy initially showed slight cyclic softening at the early two or three cycles and slowly hardened to some extent afterwards, then kept stable for the most of the remaining fatigue life. The LCF of the alloy at 760 1C can be attributed to the main elastic damage in fatigue processing. The initiation site of fatigue crack was at or near the surface of the samples. Crack propagated perpendicularly to the loading direction at first and then along {111} octahedral slip planes. The fatigue fracture mechanism was quasi-cleavage fracture. The γ 0 phase morphology still maintained cubic shape after fracture. There were a number of slip bands shear the γ 0 precipitates and γ matrix near the fracture surface of the specimen. The inhomogeneous deformation microstructure was developed by dislocation motion of cross-slip and a limited γ 0 precipitate shearing by slip band, stacking faults or single dislocation was observed.

Influence of residual stress distribution and microstructural characteristics on fatigue failure mechanism in Ni‐based Superalloy

“…Hysteresis loop shows a downward shift of stress coordinate with an increasing number of cycles after testing at 1.4% strain in untreated and all treated conditions as a result of inelasticity. It represents the cyclic softening of the material as discussed by other researchers 20–22 . Cyclic softening occurred due to the dislocation recovery during the cyclic loading.…”

“…It represents the cyclic softening of the material as discussed by other researchers. [20][21][22] Cyclic softening occurred due to the dislocation recovery during the cyclic loading. During cyclic softening, residual stress combines with applied stress to cause local plastic yielding and to reduce local plastic mis-fit.…”

The porosity distribution of nickel‐base single‐crystal superalloy DD5 and its fatigue life property

“…Rai et al 7 investigated the dislocation and cyclic plastic deformation behavior of a nickel base superalloy through extensive scanning electron microscope (SEM) and transmission electron microscope (TEM) examinations. The low‐cycle fatigue behavior of NBSX at elevated temperature has been widely investigated experimentally 8–15 . Ravi Chandran 16,17 presented an S–N curve model employing the Gumbel distribution.…”

“…The low-cycle fatigue behavior of NBSX at elevated temperature has been widely investigated experimentally. [8][9][10][11][12][13][14][15] Ravi Chandran 16,17 presented an S-N curve model employing the Gumbel distribution. Vacchieri et al 18 used the safe life approach to estimate the fatigue life of a gas turbine first-stage blade.…”

Influence of Load Interaction between Creep and TMF on the Life of Single Crystal Nickel-based Superalloy

“…Research on the microstructure of the material under different kinds of loading is of positive significance to explaining the damage mechanism of the material and the macroscopic mechanical behavior. Ample research has been done on the evolution of the microstructure of SC superalloys under creep, isothermal low-cycle fatigue, and TMF conditions [9][10][11][12][13][14][15][16], and the main evolution mechanism of microstructure under those loading has been studied. However, the research on coupled failure mode mainly focused on the interaction of creep and isothermal low-cycle fatigue [17,18].…”