Effects of the Environment on the Crack Propagation Behavior of IN718 in the Temperature Range of the Dynamic Embrittlement

Wackermann, Ken; Krupp, Ulrich; Christ, Hans‐Jürgen; Saxena, Avadh; Doğan, Bilal; Dean, S. W.

doi:10.1520/jai103569

Cited by 9 publications

(11 citation statements)

References 24 publications

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“…The same behaviour has been perceived in other superalloys such as Waspalloy [43]. Grain boundary embrittlement has been studied in [43,44,54] 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 [42].…”

Section: Dynamic Embrittlementsupporting

confidence: 59%

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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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Section: Dynamic Embrittlementsupporting

confidence: 59%

“…It has been well established that time dependent intergranular cracking of nickel-base superalloys, under both sustained and cyclic loads, is dominated by environmental interactions with oxygen at the crack tip [53,54]. Intergranular cracking is not due to the formation of massive oxidation products along the grain boundaries.…”

Section: Dynamic Embrittlementmentioning

confidence: 99%

Effect of Dwell-times on Crack Propagation in Superalloys

Saarimäki¹

2015

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“…Such films, with penetration depths of around 1-10 µm ahead of the tip, have been observed in dedicated experiments in several Ni-based superalloys [67,93,94]. SAGBO as a crack propagation mechanism has been discussed and suggested as a possible crack propagation mechanism in several other papers [64,65,86,[95][96][97][98][99][100][101][102][103]. SAGBO is also supported by observations in Paper IV, Fig.…”

Section: Introductionsupporting

confidence: 70%

“…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%

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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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Grain Size Depending Dwell‐Fatigue Crack Growth in Inconel 718

2018

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Inconel 718 is a commonly used superalloy for turbine discs in the gas turbine industry. Turbine discs are normally subjected to dwell-fatigue as a result of long constant load cycles. Dwell-times have been shown to give rise to increased crack propagation rates in superalloys at elevated temperatures. Dwell-time crack propagation behavior in Inconel 718 has been tested at 550 C using Kb test samples with 2160 s dwell-times at maximum load and "pure fatigue" tests. The dwell-time effect has been studied for differently processed Inconel 718, that is, fine grained bar, grain enlarged bar, and cast material. This has been done in order to investigate the effect of grain size on crack propagation. Microstructure characterization is conducted using scanning electron microscopy techniques such as electron channeling contrast imaging and electron backscatter diffraction. Time dependent crack propagation rates are strongly affected by grain size. Propagation rates increase with decreasing grain size, whereas crack tip blunting increased with increasing grain size.

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Effects of the Environment on the Crack Propagation Behavior of IN718 in the Temperature Range of the Dynamic Embrittlement

Cited by 9 publications

References 24 publications

Effect of Dwell-times on Crack Propagation in Superalloys

Effect of Dwell-times on Crack Propagation in Superalloys

Cracks in superalloys

Grain Size Depending Dwell‐Fatigue Crack Growth in Inconel 718

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