Influence of high temperature hold times on the fatigue crack propagation in Inconel 718

Gustafsson, David; Moverare, Johan; Johansson, Sten; Simonsson, Kjell; Hörnqvist, Magnus; Månsson, Tomas; Sjöström, Sören

doi:10.1016/j.ijfatigue.2011.05.011

Cited by 58 publications

(54 citation statements)

References 15 publications

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“…[6][7][8] where it was shown that the crack growth per cycle during unloading-reloading is much higher after a dwell time period compared to pure cyclic loading. Similar observations has been reported to occur during thermomechanical fatigue crack growth tests [9].…”

Section: Introductionmentioning

confidence: 99%

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: 99%

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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“…The same behaviour has been perceived in other superalloys such as Waspalloy [74]. Grain boundary embrittlement has been studied in [64,74,75] where it was shown that the crack growth per cycle during unloading-reloading is much higher after a dwell-time period compared to pure cyclic loading. Similar observations during thermomechanical fatigue crack growth tests have been reported in [73].…”

Section: Dynamic Embrittlementsupporting

confidence: 58%

“…A life prediction model for the overload tests microstructurally investigated in Paper I [7] was developed by Gustafsson et al [70]. The other test series leading up to it are discussed in many articles [70,[72][73][74][75][76][77][78][79][80][81][82][83] where models for fatigue crack propagation were modified to handle load ratios R, stress-intensity factors K, threshold values and environmental effects, which are vital to accurately enable life prediction. Modeling is of course important, but more so is the understanding and possibility to explain the leading mechanisms behind the crack propagation during fatigue.…”

Section: Crack Propagation Mechanismsmentioning

confidence: 99%

Cracks in superalloys

Saarimäki¹

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Linköping 2018Cover image: An orientation imaging map illustrating the general crack propagation behaviour of a 2160 s dwell-time tested Inconel 718 bar run at 550 ○ C, with a 15 % superimposed 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 2018 © 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 power supplies are insufficient. New ways of producing greener energy is needed to reduce emission levels. This can be achieved by increasing the combustion temperature of gas turbines. High combustion temperatures can be detrimental and degrade critical components. This raises the demands on the high temperature performance of the superalloys used in gas turbine components. These components are frequently subjected to different cyclic loads combined with for example dwell-times and overloads at elevated temperatures, which can influence the crack growth. Dwell-times have been shown to accelerate crack growth and change cracking behaviour in both Inconel 718, Haynes 282 and Hastelloy X. On the other hand, overloads at the beginning of a dwell-time cycle have been shown to retard the dwell-time effect on crack growth in Inconel 718. More experiments and microstructural investigations are needed to better understand these effects.The work presented in this thesis was conducted under the umbrella of the research program Turbo Power; "High temperature fatigue crack propagation in nickel-based superalloys", where I have mainly looked at fatigue crack growth mechanisms in superalloys subjected to dwell-fatigue, which can have a devastating effect on crack propagation behaviour. Mechanical testing was performed under operation-like cycles in order to achieve representative microstructures and material data for the subsequent microstructural work. Microstructures were investigated using light optical microscopy and scanning electron microscopy (SEM) techniques such as electron channeling contrast imaging (ECCI) and electron backscatter diffraction (EBSD).The outcome of this work has shown that there is a significant increase in crack growth rate when dwell-times are introduced at 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 and Haynes 282. The crack growth rate decreases with increasing overload levels in Inconel 718 when iii iv an overload is applied prior to the dwell-time. At high temperature, intergranular crack growth was observed in Inconel 718 as a result of oxidation and the creation of nanometric voids. Another observed growth mechanism was crack advance along δ-phase boundaries with subsequent oxidation of the δ phase.This thesis comprises two parts. Part I gives an introducti...

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“…[56]. These results have been made available for this second phase of the programme (2012 to 2015), which has given a significantly larger population of tests to use for model development.…”

Section: Materials Batchesmentioning

confidence: 99%

High Temperature Fatigue Crack Growth in a Ni-based Superalloy : Modelling Including the Interaction of Dwell Times

Storgärds¹

2015

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Safe life of gas turbines is always of major concern for manufacturers in order to ensure passenger safety and stable continuous power output. An increasing amount of resources have been put into research and development to assure that all safety aspects are covered in the design of new turbines and to ensure that enough frequent service intervals are scheduled to avoid complications. Many of these issues require good knowledge of material properties and of how to use these in the design process. Some of these relate to fatigue which is of major concern in all parts of a development programme. However, while some fatigue problems have been extensively studied, some have not. One example is crack growth with influence of dwell times at elevated temperature in combination with cyclic loading. Such loading conditions have been shown to give a different cracking behaviour compared to rapid cyclic loading, increasing the growth rate significantly with respect to the number of load cycles. Improved models for predicting this behaviour is therefore of major interest for gas turbine manufacturers, and could substantially increase the reliability. As a result, more research is needed in order solve these problems. The work presented in this dissertation has focused on how to predict life under the above-mentioned circumstances. The materials used in high temperature gas turbine applications are often nickel-based superalloys, and in this work the most common one, Inconel 718, has been studied. Mechanical experiments have been performed under operation like conditions in order to receive material data for the subsequent modelling work. The modelling approach was chosen such that the underlying physics of the dwell time cracking have been incorporated on a phenomenological basis, creating a model which can be physically motivated as well as used for industrial applications. The main feature of the modelling work has been to track material damage which is received from dwell times, how this interacts with cyclic loading and how it affects the crack growth rate, thus creating a load history dependent model. The outcome of this work has resulted in a model which is both easy to use and which has shown to give good correlation to available experimental data. Key components such as calibration for cheap and easy parameter determination, validation on complex engine spectra loadings, three dimensional crack growth, overload influences, material scatter, thermo-mechanical fatigue crack growth and the impact of high cycle fatigue loadings, are all covered in the presented work, both as experimental findings and as continuous development of the modelling concept. The dissertation consists of two parts. In the first an introduction with the theory and background to crack growth with dwell times is given, while the second part consists of 10 papers

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Influence of high temperature hold times on the fatigue crack propagation in Inconel 718

Cited by 58 publications

References 15 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

Cracks in superalloys

High Temperature Fatigue Crack Growth in a Ni-based Superalloy : Modelling Including the Interaction of Dwell Times

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