Journal ArticleDOI
Fatigue crack growth in nickel‐based superalloys at 500‐700°c. ii: direct‐aged alloy 718
TLDR
In this paper, the effects of cyclic frequency, hold time, and stress-intensity factor range (ΔK) on rates of fatigue crack growth in air at 500°C and 700°C have been studied for the direct-aged version of the nickel-based superalloy 718.Abstract:
— The effects of cyclic frequency, hold time, and stress-intensity factor range (ΔK) on rates of fatigue crack growth in air at 500°C and 700°C have been studied for the direct-aged version of the nickel-based superalloy 718. The main effects were similar to those observed for Waspaloy (Part I), namely: (i) small effects of cyclic frequency and hold time at 500°C, (ii) higher rates of crack growth at lower cyclic frequencies at high ΔK at 700°C, and (iii) lower rates of crack growth at low ΔK (and higher ΔK thresholds) for longer hold times at 700°C. For DA 718, there was no increase in crack growth rates with increasing hold times (0–60 s) at high ΔK at 700°C (unlike the large increases reported for standard processed Alloy 718). Metallographic and fractographic observations showed that crack growth was predominantly transgranular at 500°C, and predominantly intergranular at 700°C except at 2 Hz at high ΔK. The precise intergranular crack path, extent of branching, and fracture-surface appearance depended on ΔK, wave-form and cycle-period. The mechanisms responsible for the observed effects, and possible explanations for the different behaviour of DA 718 and standard processed Alloy 718, are discussed.read more
Citations
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Journal ArticleDOI
Oxygen-induced intergranular cracking of a Ni-base alloy at elevated temperatures-an example of dynamic embrittlement
TL;DR: In this paper, the authors studied the brittle intergranular cracking of Alloy 718 at temperatures between 550 and 650°C and at oxygen pressures from atmospheric to 10−5 torr.
Journal ArticleDOI
Modelling the optimum grain size on the low cycle fatigue life of a Ni based superalloy in the presence of two possible crack initiation sites
TL;DR: In this paper, a fatigue life prediction model including a transition in the crack initiation mechanism (particle/Stage I) is identified, based on Tanaka and Mura model for stage I initiation and Tomkins model for fatigue crack growth rate.
Journal ArticleDOI
Crack growth micro-mechanisms in the IN718 alloy under the combined influence of fatigue, creep and oxidation
TL;DR: In this article, a review of the different phenomena responsible for crack growth in the IN718 nickel-base superalloy under the combination of fatigue, creep and oxidation is presented.
Journal ArticleDOI
Short crack initiation and growth at 600 °C in notched specimens of Inconel718
TL;DR: In this paper, the authors studied the initiation and growth of short cracks in Inconel®718 U-notch specimens at 600 °C in air and conducted fatigue tests on specimens with as-broached and polished Unotches.
Journal ArticleDOI
Dynamic embrittlement - time-dependent quasi-brittle intergranular fracture at high temperatures
TL;DR: In this article, a failure mechanism for Ni-base superalloys at high temperatures is discussed that seems to be due to a generic phenomenon: dynamic embrittlement, where an embrittling species is moved into the grain boundaries by grain-boundary diffusion, giving rise to local decohesion ahead of an intergranular crack tip.
References
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Journal ArticleDOI
The effect of microstructure and environment on the crack growth behaviour of Inconel 718 alloy at 650 °C under fatigue, creep and combined loading
J.P. Pédron,André Pineau +1 more
TL;DR: In this paper, the crack growth properties of various microstructures developed in one heat of Inconel 718 alloy were investigated at 650 °C under air and vacuum environments.
Journal ArticleDOI
Frequency and wave-form effects on the fatigue crack growth behavior of alloy 718 at 298 K and 823 K
M. Clavel,André Pineau +1 more
TL;DR: In this paper, the authors measured the fatigue crack growth rate (FCGR) of Alloy 718 on CT type specimens at 298 and 823 K and found that a substantial increase in FCGR occurred at low stress intensity levels, as the temperature was increased from 298 to 823 k and as the frequency was decreased at 823k.
Journal ArticleDOI
The creep fracture of wrought nickel-base alloys by a fracture mechanics approach
TL;DR: In this article, a good correlation was found between the notch properties and the creep behavior of an unnotched sample loaded to the yield strength, but their differences were due primarily to material processing history and not to composition per se.
Journal ArticleDOI
Depth of intergranular oxygen diffusion during environment-dependent fatigue crack growth in alloy 718
Hamouda Ghonem,D. Zheng +1 more
TL;DR: In this article, an experimental program was carried out on compact tension specimens made of alloy 718 at 650 °C in which fatigue crack growth measurements were made for cyclic load conditions with and without hold time periods at minimum load level.
Proceedings ArticleDOI
The Development of Direct Age 718 for Gas Turbine Engine Disk Applications
TL;DR: Loria et al. as mentioned in this paper used Direct Age 718 as a commercial gas turbine aircraft engine disk material for disk applications and showed that the process window was suitable for production practice.
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