Evaluation of high cycle fatigue behaviour of alloy 617M at 973 K: Haigh diagram and associated mechanisms

Microstructural damage assessment in alloy 617M near high cycle fatigue threshold at elevated temperature

“…Similar features were also observed in an earlier study on the material. 7 Figure 3D shows stage III of stable propagation of fatigue crack. This stage is dominantly characterized by striations typical of a fatigue fracture.…”

“…Apart from being oxidation and hot‐corrosion resistant, the alloy also exhibits exceptional high cycle fatigue (HCF) strength at high temperatures owing to the precipitation of ordered γ′ phase of Ni 3 (Al, Ti) intermetallic in the γ matrix and Cr‐ and Mo‐rich carbides of type M 23 C 6 /M 6 C 3. Besides, the matrix strengthening associated with the occurrence of dynamic strain aging (DSA) in the alloy also contributes to the strengthening of the alloy under cyclic loading at high temperatures causing an increase in the fatigue strength 7,8 …”

“…Numerous studies have tried to explore the association of low cycle fatigue loading 17–24 with the microstructural attributes of this alloy in past. However, only a few investigators have attempted to study the behavior under pure HCF loading 7–9,25,26 . Karnati et al 7 studied the performance of alloy 617M at different R‐ratios at 973 K under HCF and reported a significant increment in the fatigue strength for the life contours of 10 5 , 10 6 , and 10 7 cycles.…”

“…Apart from being oxidation and hot-corrosion resistant, the alloy also exhibits exceptional high cycle fatigue (HCF) strength at high temperatures owing to the precipitation of ordered γ 0 phase of Ni 3 (Al, Ti) intermetallic in the γ matrix and Cr-and Mo-rich carbides of type M 23 C 6 /M 6 C.3 Besides, the matrix strengthening associated with the occurrence of dynamic strain aging (DSA) in the alloy also contributes to the strengthening of the alloy under cyclic loading at high temperatures causing an increase in the fatigue strength. 7,8 In a previous study, 9 the authors reported that the alloy can sustain a fatigue life of 10 7 cycles at 320 MPa at 973 K. However, a marginal increase of the alternating stress (σ a ) to 322.5 MPa causes the material to fail around 10 5 cycles. Thus, a mere 1% increase in the stress amplitude causes a drastic reduction in the cyclic life.…”

“…However, only a few investigators have attempted to study the behavior under pure HCF loading. [7][8][9]25,26 Karnati et al 7 studied the performance of alloy 617M at different R-ratios at 973 K under HCF and reported a significant increment in the fatigue strength for the life contours of 10 5 , 10 6 , and 10 7 cycles. The authors attributed this superior performance under HCF to the DSA occurring in this regime.…”