Effect of Strain Range on the Low Cycle Fatigue in Alloy 617 at High Temperature

Abstract

Abstract:The aim of this study is to investigate the fully-reversed low cycle fatigue properties of Alloy 617 in the air at 950 • C; these tests were conducted at total strain ranges from 0.9% to 1.5% with a constant strain rate of 10 −3 /s. The result of the fatigue tests showed a decrease in fatigue resistance with an increasing total strain range. The reduction of fatigue resistance was due to the effect of the total strain range and microstructure evolution during high temperature, such as brittle oxides cracking. At all testing conditions, the cyclic softening mechanism was observed as a function of the total strain range in the current high temperature condition. An analysis of low cycle fatigue resistance was performed using the Coffin-Manson relationship and the total strain energy density; it was found that Alloy 617 followed these relationships well. In addition, this study compared well with previous work reported in the literature for a similar testing condition. Post-fracture analysis on the fracture surfaces of failed specimens revealed a more severe damage cracking at the periphery of specimens due to the increase in the total strain range. The surface connected grain boundary cracks induced by oxidation were obvious at low strain range. Thus, the primary crack propagation occurred in transgranular mode from persistent slip bands.

High-Temperature Creep-Fatigue Behavior of Alloy 617

“…However, additional testing should be implemented to further study the saturation effect at longer tensile hold time for weldments. 1 Cycle number was determined from a 20% drop in the stress ratio. Figure 6 shows the maximum/minimum stresses as a function of cycle number.…”

“…Based on this behavior it can be assumed that there would be creep deformation at high temperature [10,19]. 1 Cycle number was determined from a 20% drop in the stress ratio. Figure 6 shows the maximum/minimum stresses as a function of cycle number.…”

“…The very-high-temperature reactor (VHTR) of Generation-IV type systems is being developed as a nuclear system with helium as the primary coolant, and is designed to produce an effective heat for hydrogen generation and electricity production [1,2]. The conceptual design reaches a maximum expected outlet temperature of about 950 • C to satisfy the efficient generation of hydrogen [3][4][5].…”

“…For mechanical structures, welds are critical considerations in the engineering design because they are the weakest links in the components and may have several inherent defects. Experience with nickel alloy weldments in structural applications suggests that most cases of high-temperature fatigue failures occurred in the weld metal part; see [1,2]. Literature reviews on Alloy 617 [3][4][5][6][7][8][9][10]15,16] have suggested that this alloy was sensitive to tensile hold time.…”

Low Cycle Fatigue Behaviour of DP Steels: Micromechanical Modelling vs. Validation

“…Several researchers have developed correlation models to predict the cyclic deformation behavior of steels from monotonic tensile properties and hardness [42][43][44][45]. Smith et al [46] discovered the correlation between the hardening or softening behavior and the ratio of ultimate tensile strength to yield strength (S u /S y ) from sixteen materials including steel, aluminium and titanium alloys.…”