Microstructural Features Controlling the Variability in Low-Cycle Fatigue Properties of Alloy Inconel 718DA at Intermediate Temperature

Texier, Damien; Gomez, Ana C.; Pierret, Stéphane; Franchet, Jean‐Michel; Pollock, Tresa M.; Villechaise, Patrick; Cormier, Jonathan

doi:10.1007/s11661-015-3291-8

Cited by 66 publications

(50 citation statements)

References 39 publications

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“…These parts are generally obtained by hot-forging. Since it represents approximately one third of the weight of current aircraft engines, Inconel 718 is one of the most important Nickel-based superalloys (Texier et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Discrimination of dynamically and post‐dynamically recrystallized grains based on EBSD data: application to Inconel 718

Nicolaÿ

Franchet

Cormier

et al. 2018

Journal of Microscopy

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Summary The importance of angular resolution in EBSD analyses is discussed based on an Inconel 718 sample containing several populations of recrystallized grains, with subtle differences in dislocation contents. Classical EBSD analyses (with angular resolution in the range of 0.5–1°) do not allow for distinguishing recrystallized grains grown dynamically or post‐dynamically. The angular resolution of EBSD orientation and misorientation data can be significantly improved (down to about 0.1–0.2°) either using more sophisticated Kikuchi pattern indexing methods and/or using the recently proposed LLASS denoising filter (Local Linear Automatic Smoothing Splines). Then the coexistence of both dynamically and post‐dynamically recrystallized grains in the sample can be confirmed and quantified. ECCI images unambiguously confirm the conclusions drawn from the analysis of improved angular resolution EBSD data, and furthermore reveal the presence of thermal stress induced dislocations with typical patterns in water quenched Inconel 718 recrystallized grains. Lay Description EBSD is widely used to study recrystallization phenomena. Conventional EBSD is nevertheless not able to distinguish dynamic recrystallized grains from post‐dynamic recrystallized grains which differ by subtitle differences in dislocation contents. In this paper, we show that improving the orientation precision of EBSD data by means of different methods allows distinguishing these two recrystallized grains populations. Analyses and discussion are based on an Inconel 718, a famous Nickel‐based superalloy in aeronautic.

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Section: Introductionmentioning

confidence: 99%

Discrimination of dynamically and post‐dynamically recrystallized grains based on EBSD data: application to Inconel 718

Nicolaÿ

Franchet

Cormier

et al. 2018

Journal of Microscopy

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“…Metals 2019, 9,13 2 of 14 by the United States in the 1950s [1]. In the aging treatment process, the γ" phase, which is coherent with the matrix γ phase (Ni 3 Nb, body-centered tetragonal DO 22 structure), and the γ' phase, which is semicoherent with the γ phase (face-centered cubic LI 2 structure), disperses precipitation and hinders dislocation motion, not only giving the Inconel 718 alloy a higher room temperature strength but also allowing this alloy to maintain a comparatively high strength at high temperatures under 650 • C. Thus, this alloy is widely used in the manufacture of turbine discs and blades for aircraft engines and other key parts and components exposed to high temperatures and fasteners not exposed to high temperatures. The high-frequency vibrations of an aircraft engine during operation generate disturbance stress effects on the nearby parts and components, requiring the Inconel 718 alloy to have not only good static strength and creep performance but also good fatigue performance.…”

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confidence: 99%

High Cycle Fatigue Performance of Inconel 718 Alloys with Different Strengths at Room Temperature

Liqiong

Liang

et al. 2018

Metals

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In this paper, the high cycle fatigue performance of solid solution state and aged Inconel 718 superalloys was studied at room temperature. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to analyze the original structural features and fatigue deformation features of two kinds of alloys. SEM, laser scanning confocal microscopy, and electron backscatter diffraction (EBSD) were used to analyze the secondary fracture features of the fatigue fracture morphology and fatigue fracture profile. The results showed that the aging treatment significantly affected the strength and plasticity of the alloy, which in turn affected the fatigue performance of the alloy. After the aging treatment, the yield strength σ s and the tensile strength σ b of the Inconel 718 alloy increased by 152% and 65.9%, respectively, compared with those of the solid solution state, but the rate of elongation δ and rate of contraction in the cross-section area ϕ decreased by 63.7% and 52.3%, respectively. The fatigue limit of the aged state was lower than that of the solid solution state by 6.3%. The quadratic function relationship between the high cycle fatigue limit σ −1 and the tensile strength σ b of the Inconel 718 superalloy at room temperature was σ −1 = σ b · (0.869−3.67 × 10 −4 · σ b ). An analysis of the fatigue fracture mechanism showed that the fatigue fractures before and after aging were all initiated in the grains oriented relatively unfavorably on the surface of the sample, with a mixture of intergranular and transgranular propagation after the transgranular propagation of several grains. The higher plasticity of the solid solution state Inconel 718 alloy resulted in a large number of slip deformation zones under high cycle fatigue loads, and the plastic deformation was relatively uniform. The lengths of the secondary fractures were as high as 120 µm, which formed the single-source plastic fatigue fracture that promoted an increase in the fatigue limit. After aging treatment, the higher strength of the Inconel 718 alloy made dislocation slip difficult under high cycle fatigue loads, and the plasticity compatible deformation capability was poor. When local dislocations slipped to the intragranular γ" phase, γ' phase, or interfaces with nonmetallic compounds (NMCs), plugging occurred. The degree of stress concentration increased, causing the initiation of fatigue fracture; the secondary fracture was approximately 20 µm. Brittle cleavage due to multiple sources significantly reduced the fatigue limit.

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“…However, when fatigue cracks are initiated at inclusions, whether the formed crack may grow and lead to a short fatigue life depends on the inclusion type, size, and distribution, as well as the residual stresses in the particles and matrix. Fractographic observations have revealed the crack initiation at surface and sub-surface non-metallic inclusions such as carbides, nitrides, and carbonitrides, when the alloy Inconel 718 is subjected to low-cycle fatigue with low-strain amplitude at intermediate temperatures [96]. Instead of inclusions, fatigue crack initiation at other metallurgical weak sites like porosities is also fairly common in cast alloys and powder-metallurgy alloys [97][98][99][100][101].…”

Section: Crack Initiationmentioning

confidence: 99%

Surface Integrity and Fatigue Performance of Nickel-based Superalloys

Chen¹

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Gas turbines are widely used in e.g., power generation, and aero-industries. Due to global warming, the demand for more efficient gas turbines has increased. A way to achieve this is by increasing the operating temperature of gas turbines. Therefore, nickel-based superalloys have been developed to withstand these extreme temperatures and loads, especially in the hot sections.Today, the way of operating land-based gas turbines is changing. Instead of running for long periods of time, the operation is becoming more flexible, with everincreasing cyclic loads and number of start and stop cycles. To handle the increased stress and cycles, component resistance to fatigue failure needs to be improved.Surface integrity is critical to fatigue performance, since fatigue cracks are normally initiated at surfaces. Nickel-based superalloys are difficult-to-machine materials, primarily due to their high strength, high tendency for work-hardening, and low thermal conductivity. The machining process changes the surface integrity of the alloys which can result in worse fatigue resistance.The work presented in this Ph.D. thesis was conducted in collaboration with Siemens Industrial Turbomachinery AB in Finspång, Sweden. Surface integrity changes which are induced during machining and their effects on fatigue performance have been studied on alloy Inconel 718. Inconel 718 is a widely-used nickel-based superalloy for high temperature applications in modern gas turbines.Broaching, milling, and wire electrical discharge machining, related to component manufacturing in turbo machinery industries, were included in this study. Surface irregularity and defects induced by machining provide preferential sites for fatigue crack initiation which influence the fatigue performance of the alloy. If compressive residual stresses are induced during machining, they benefit the fatigue life by retarding fatigue crack initiation away from surface regions. Shot peening was performed on machined Inconel 718, by which high compressive residual stresses are deliberately induced. It results in increased fatigue performance. The high iv temperatures in gas turbines generally deteriorate the surface integrity. For instance, recrystallization often occurs in the highly plastically-deformed surface layer. Microstructural degradation, in a form of α-Cr precipitates, have also been observed in the deformed surface and sub-surface microstructure when subjected to thermal exposure. Oxidation at elevated temperatures was found to degrade the surface integrity and thereby also the fatigue performance. Fatigue cracks are preferably initiated at oxidized surface carbides, if thermal exposure has been made prior to the test, and a reduced fatigue life is often obtained. It is even worse when high temperatures relax the beneficial compressive residual stresses induced by shotpeening and thereby lowering the fatigue resistance. This increases the interest for research regarding how to optimize the shot peening process in order to enhance the thermal stability o...

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Microstructural Features Controlling the Variability in Low-Cycle Fatigue Properties of Alloy Inconel 718DA at Intermediate Temperature

Cited by 66 publications

References 39 publications

Discrimination of dynamically and post‐dynamically recrystallized grains based on EBSD data: application to Inconel 718

Discrimination of dynamically and post‐dynamically recrystallized grains based on EBSD data: application to Inconel 718

High Cycle Fatigue Performance of Inconel 718 Alloys with Different Strengths at Room Temperature

Surface Integrity and Fatigue Performance of Nickel-based Superalloys

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