Effects of Loading Waveform and Stress Field on High Temperature Fatigue Crack Growth of Alloy 718

Heuler, P.; Affeldt, E.; Wanhill, R.J.H.

doi:10.1002/mawe.200300663

Cited by 21 publications

(13 citation statements)

References 9 publications

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“…Previous studies [3][4][5] have shown that Inconel 718 mainly cracks transgranularly during cyclic testing in the lower temperature range and intergranularly during fatigue at higher temperatures and with dwell times. The same behaviour has been observed in other superalloys such as Waspalloy [6].…”

Section: Introductionmentioning

confidence: 93%

Influence of overloads on dwell time fatigue crack growth in Inconel 718

Saarimäki

Moverare

Eriksson

et al. 2014

Materials Science and Engineering: A

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Inconel 718 is one of the most commonly used superalloys for high temperature applications in gasturbines and aeroengines and is for example used for components such as turbine discs. Turbine discs can be subjected to temperatures up to ∼ 700 • C towards the outer radius of the disc. During service, the discs might start to develop cracks due to fatigue and long dwell times. Additionally, temperature variations during use can lead to large thermal transients during start-up and shutdown which can lead to overload peaks in the normal dwell time cycle. In this study, tests at 550 • C with an overload prior to the start of each dwell time, have been performed. The aim of the investigation was to get a better understanding of the effects of overloads on the microstructure and crack mechanisms. The microstructure was studied using electron channelling contrast imaging (ECCI). The image analysis toolbox in Matlab was used on cross sections of the cracks to quantify: crack length, branch length, and the number of braches in each crack. * jonas.saarimaki@liu.se +46 13 28 11 93Preprint submitted to Material Science & Engineering A June 2, 2014It was found that the amount of crack branching increases with an increasing overload and that the branch length decreases with an increasing overload.When the higher overloads were applied, the dwell time effect was almost cancelled out. There is a strong tendency for an increased roughness of the crack path with an increasing crack growth rate.

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Section: Introductionmentioning

confidence: 93%

Influence of overloads on dwell time fatigue crack growth in Inconel 718

Saarimäki

Moverare

Eriksson

et al. 2014

Materials Science and Engineering: A

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“…[1, 2,[5][6][7][8][9][10][11][12][13][14], which all show that hold times at high temperature can have a devastating effect on the crack growth rate. The modelling of hold time effects has also been studied by a number of different authors, often by use of additive models based on Paris law [15,16] with a cyclic part, based on pure cyclic crack growth, and a time dependent part, based on pure time dependent crack growth, see e.g.…”

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confidence: 99%

“…These hold times can greatly increase the fatigue crack growth rate, and it has been shown that this behaviour is due to material damage near the crack tip, causing the crack to grow by intergranular fracture, see e.g. [1][2][3]. Between hold times different types of loading can occur, e.g.…”

mentioning

confidence: 99%

A load history dependent model for fatigue crack propagation in Inconel 718 under hold time conditions

Lundström

Simonsson

Gustafsson

et al. 2014

Engineering Fracture Mechanics

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Modelling of high temperature fatigue crack growth in Inconel 718 under the interaction of fast cyclic loading and hold times at maximum load has been conducted. A model, based on the concept of a damaged zone in front of the crack tip has been applied for three different temperatures, 550, 600 and 650• C, with good agreement for both calibration and validation tests. A statistical evaluation of 22 tests in total was also conducted, which shows that the developed model gives a reasonable scatter factor at a probability of failure of 0.1 %.

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“…The mechanism is better described as nano scaled dynamic embrittlement (DE), where oxygen diffuses into highly stressed grain boundaries at the crack tip and mainspring decohesion [55,56]. Previous studies [41,57,58] have shown that Inconel 718 mainly cracks transgranularly during cyclic testing in the lower temperature range and intergranularly during fatigue and dwell-fatigue at higher temperatures. The same behaviour has been perceived in other superalloys such as Waspalloy [43].…”

Section: Dynamic Embrittlementmentioning

confidence: 99%

Effect of Dwell-times on Crack Propagation in Superalloys

Saarimäki¹

2015

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Linköping 2016Front page image: The general crack growth behaviour of Inconel 718 run at 550 ○ C, subjected to a 2160 s dwell-time, with a 15 % overload at the beginning of the dwell-time.During the course of research underlying this thesis, Jonas Saarimäki was enrolled in Agora Materiae, a multidiciplinary doctoral program at Linköping University, Sweden. Printed by LiU-Tryck 2015 © Jonas Saarimäki AbstractGas turbines are widely used in industry for power generation and as a power source at "hard to reach" locations where other possibilities for electrical supply are insufficient. There is a strong need for greener energy, considering the effect that pollution has had on global warming, and we need to come up with ways of producing cleaner electricity. A way to achieve this is by increasing the combustion temperature in gas turbines. This increases the demand on the high temperature performance of the materials used e.g. superalloys in the turbine. These high combustion temperatures can lead to detrimental degradation of critical components. These components are commonly subjected to cyclic loading of different types e.g. combined with dwell-times and overloads at elevated temperatures, which influence the crack growth. Dwell-times have shown to accelerate crack growth and change the cracking behaviour in both Inconel 718 and Haynes 282. Overloads at the beginning of the dwell-time cycle have shown to retard the dwell time effect on crack growth in Inconel 718. To understand these effects more microstructural investigations are needed.The work presented in this licentiate thesis was conducted under the umbrella of the research program Turbo Power; "High temperature fatigue crack propagation in nickel-based superalloys", concentrating on fatigue crack growth mechanisms in superalloys during dwell-times, which have shown to have a devastating effect on the crack propagation behaviour. Mechanical testing was performed under operation-like conditions in order to achieve representative microstructures and material data for the subsequent microstructural work. The microstructures were microscopically investigated in a scanning electron microscope (SEM) using electron channeling contrast imaging (ECCI) as well as using light optical microscopy.The outcome of this work has shown that there is a significant increase in crack growth rate when dwell-times are introduced at the maximum load (0% overload) in the fatigue cycle. With the introduction of a dwell-time there is also a shift from transgranular to intergranular crack growth for both Inconel 718 iii iv and Haynes 282. When an overload is applied prior to the dwell-time, the crack growth rate decreases with increasing overload levels in Inconel 718. At high temperature crack growth in Inconel 718 took place as intergranular crack growth along grain boundaries due to oxidation and the creation of nanometric voids. Another observed growth mechanism was crack advance along δ phase boundaries with subsequent severe oxidation of the δ phase.This thesis comprises two pa...

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Effects of Loading Waveform and Stress Field on High Temperature Fatigue Crack Growth of Alloy 718

Cited by 21 publications

References 9 publications

Influence of overloads on dwell time fatigue crack growth in Inconel 718

Influence of overloads on dwell time fatigue crack growth in Inconel 718

A load history dependent model for fatigue crack propagation in Inconel 718 under hold time conditions

Effect of Dwell-times on Crack Propagation in Superalloys

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