Depth of intergranular oxygen diffusion during environment-dependent fatigue crack growth in alloy 718

Ghonem, H.; Zheng, Dongfang

doi:10.1016/0921-5093(92)90107-c

Cited by 103 publications

(73 citation statements)

References 8 publications

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“…As shown in [12], under applied external stress, the thickness of oxide layers increased significantly at 900°C when compared to that at 600°C. For alloy 718, the fatigue crack growth rate increased about two orders when the temperature was raised from 550°C to 650°C at low frequencies where the oxidation-fatigue interaction prevails [6]. Similar behavior was also observed in [14] for the study of fatigue crack growth in nickel alloy RR1000 at 650°C and 725°C, where long dwell periods imposed at peak loads was shown to promote oxidation-fatigue interaction.…”

Section: Introductionsupporting

confidence: 57%

“…The detrimental effects of environmental factors, in particular oxygen, on high-temperature fatigue crack growth resistance in nickel alloys have been clearly demonstrated by experimental results and well documented in the literature [1][2][3][4][5][6][7][8][9][10][11]. For polycrystalline nickel superalloys, environmental effects were frequently observed to modify the fracture morphology from transgranular to intergranular during crack growth, as well as to increase the crack growth rates significantly for a given stress intensity factor [5,6,8,9].…”

Section: Introductionmentioning

confidence: 73%

“…For polycrystalline nickel superalloys, environmental effects were frequently observed to modify the fracture morphology from transgranular to intergranular during crack growth, as well as to increase the crack growth rates significantly for a given stress intensity factor [5,6,8,9]. Considerable effort has been made to understand the crack tip oxidation mechanisms in order to provide a basis for the development of quantitative models that predict crack growth under operational temperatures and loading conditions.…”

Section: Introductionmentioning

confidence: 99%

“…A number of mechanisms have been proposed including oxide formation (Ni, Nb, Al, Cr) [5,8,9], vacancy injection [1], gas bubble formation (CO or CO 2 ) [2] and releasing of embrittling alloy elements [3] at the grain boundaries. As a result, several life prediction models have been developed for nickel alloys based on different perspectives of the fatigue-oxidation interaction process, such as the oxide-depth based model [6], the oxide-passivation based model [4] and the multiplicative mechanical-environmental damage model [7].…”

Section: Introductionmentioning

confidence: 99%

“…Temperature is one of the major factors identified in the study of fatigue-oxidation interaction, and oxidation-assisted fatigue crack growth can be several orders faster with the increase of temperature due to the enhanced coupling of fatigue and oxidation [e.g., 6,12,14]. For nickel alloys, the majority studies were carried out between 500°C and 900°C, such as the study of creep-fatigue-oxidation microcrack propagation at 500°C for alloy MAR-M247 [7], fatigue crack growth at 550°C [6], 650°C [5,6,9] and 700°C [10,11] for alloy 718, and stressassisted oxidation kinetics at 600°C and 900°C [12] for Ni-20Cr alloys. As shown in [12], under applied external stress, the thickness of oxide layers increased significantly at 900°C when compared to that at 600°C.…”

Section: Introductionmentioning

confidence: 99%

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Prediction of crack growth in a nickel-based superalloy under fatigue-oxidation conditions

Tong

Hardy

2010

Engineering Fracture Mechanics

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• This is the author's version of a work that was accepted for publication in the journal Engineering Fracture Mechanics. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication.A definitive version was subsequently pub- AbstractPrediction of oxidation-assisted crack growth has been carried out for a nickel-based superalloy at elevated temperature based on finite element analyses of oxygen diffusion, coupled with viscoplastic deformation, near a fatigue crack tip. The material constitutive behaviour, implemented in the finite element code ABAQUS via a user-defined material subroutine (UMAT), was described by a unified viscoplastic model with non-linear kinematic and isotropic hardening rules. Diffusion of oxygen was assumed to be controlled by two parameters, the oxygen diffusivity and deformation-assisted oxygen mobility. Low frequencies and superimposed hold periods at peak loads significantly enhanced oxygen concentration near the crack tip. Evaluations of near-tip deformation and oxygen concentration were performed, which led to the construction of a failure envelop for crack growth based on the consideration of both oxygen concentration and accumulated inelastic strain near the crack tip. The failure envelop was then utilised to predict crack growth rates in a compact tension (CT) specimen under fatigue-oxidation conditions for selected loading ranges, frequencies and dwell periods. The predictions from the fatigue-oxidation failure envelop compared well with the experimental results for triangular and dwell loading waveforms, with marked improvements 2 achieved over those predicted from the viscoplastic model alone. The fatigue-oxidation predictions also agree well with the experimental results for slow-fast loading waveforms, but not for fast-slow waveforms where the effect of oxidation is much reduced.

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Section: Introductionsupporting

confidence: 57%

Section: Introductionmentioning

confidence: 73%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Prediction of crack growth in a nickel-based superalloy under fatigue-oxidation conditions

Tong

Hardy

2010

Engineering Fracture Mechanics

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Oxidation of Superalloys in Extreme Environments

Pint¹,

Dryepondt²,

Unocic³

2010

Superalloy 718 and Derivatives

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With the current interest in increased efficiency and reduced emissions, materials in power generation systems are increasingly exposed to more aggressive environments and higher temperatures. It is important to understand how these environments can increase corrosion rates, possibly reducing performance and likely shortening component lifetimes. Superalloys like 718 and its derivatives primarily rely on the formation of an external Cr-rich oxide layer or scale for environmental protection at typical application temperatures (≤700°C). While many laboratory oxidation and creep experiments are conducted in ambient air, the application environment for these alloys often involves combustion products, such as H 2 O and CO-CO 2 . The effect of these environments is not completely understood, especially the impact of long-term exposures, typically required of superalloy components in turbines. Air and fuel impurities, especially S and Na, can result in accelerated degradation such as the well known hot corrosion attack. While the effect of environment on crack growth has been studied, less information is available on the effect of environment on creep and fatigue properties. Initial work is being conducted to better understand the role of environment on creep properties, eventually including in-situ testing. Examples are given from steam and wet air environments and comparisons of different superalloy compositions with cast versus wrought microstructures.

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Intergranular Fatigue

2011

Grain Boundaries and Crystalline Plasticity

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Depth of intergranular oxygen diffusion during environment-dependent fatigue crack growth in alloy 718

Cited by 103 publications

References 8 publications

Prediction of crack growth in a nickel-based superalloy under fatigue-oxidation conditions

Prediction of crack growth in a nickel-based superalloy under fatigue-oxidation conditions

Oxidation of Superalloys in Extreme Environments

Intergranular Fatigue

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