Anisotropy effects during dwell-fatigue caused by δ-phase orientation in forged Inconel 718

Saarimäki, Jonas; Colliander, Magnus Hörnqvist; Moverare, Johan

doi:10.1016/j.msea.2017.03.063

Cited by 16 publications

(13 citation statements)

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“…The influence of the δ ‐phase on crack propagation has been pointed out in the work by Ponnelle et al and Saarimäki et al, where forged and rolled Inconel 718 disc material were investigated. Compact tension (CT) and Kb test samples were manufactured and subjected to various fatigue cycles at elevated temperatures.…”

Section: Introductionmentioning

confidence: 94%

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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Section: Introductionmentioning

confidence: 94%

Grain Size Depending Dwell‐Fatigue Crack Growth in Inconel 718

2018

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“…Morphology or anisotropy such as δ-phase orientation has also been shown to impact dwell-fatigue crack propagation rates as reported in Paper III [29] and shown in Fig. 2.7 (c).…”

Section: Dwell-timesmentioning

confidence: 67%

“…Generally, δ and η are observed as a plate like morphology. δ and η are not commonly regarded as strengthening phases but can in small quantities be used to refine grain size, and improve fatigue crack growth in certain directions [29].…”

Section: Phasesmentioning

confidence: 99%

“…The dashed circles and filled dots show where the cracks start to grow out of plane more than 10 ○ perpendicular to the loading direction, circles show the theoretical validity of the ∆K calculation according to ASTM E399-97. Data redrawn from [29]. Fig.…”

Section: Dwell-timesmentioning

confidence: 99%

“…[113]. (b) An OIM of a press-forged Inconel 718 turbine disc [29] Fatigue crack growth testing has been performed on Inconel 718 at 550 ○ C in Paper I with the purpose of investigating the effect of overloads on dwell-fatigue crack growth. In Paper II fatigue crack growth testing was performed on Haynes 282 at room temperature as well as at 650 ○ C and 700 ○ C under different loading conditions.…”

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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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On the Dwell-Fatigue Crack Propagation Behavior of a High-Strength Ni-Base Superalloy Manufactured by Selective Laser Melting

Deng

Eriksson

Peng

et al. 2019

Metall Mater Trans A

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This study focuses on the dwell-fatigue crack propagation behavior of IN718 manufactured via selective laser melting (SLM). The dwell-fatigue test condition is 823 K (550 $$^{\circ }$$∘C) with a long 2160-s dwell-holding period. Effects of heat treatment and loading direction on dwell-fatigue crack propagation rates are studied. A grain boundary $$\delta $$δ precipitate seems to be slightly beneficial to the dwell-fatigue cracking resistance of SLM IN718. A comparison has been made between SLM IN718 and forged counterparts at different temperatures, indicating that a creep damage mechanism is likely dominant for SLM IN718 under the present test condition. A general discussion of the inferior creep resistance of SLM IN718 is also included. The anisotropic dwell-fatigue cracking resistance has also been studied and rationalized with the effective stress intensity factor calculated from finite element modeling.

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Anisotropy effects during dwell-fatigue caused by δ-phase orientation in forged Inconel 718

Cited by 16 publications

References 38 publications

Grain Size Depending Dwell‐Fatigue Crack Growth in Inconel 718

Grain Size Depending Dwell‐Fatigue Crack Growth in Inconel 718

Cracks in superalloys

On the Dwell-Fatigue Crack Propagation Behavior of a High-Strength Ni-Base Superalloy Manufactured by Selective Laser Melting

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