Crack initiation sensitivity of wrought direct aged alloy 718 in the very high cycle fatigue regime: the role of non-metallic inclusions

Texier, Damien; Cormier, Jonathan; Villechaise, Patrick; Stinville, J.C.; Torbet, Chris; Pierret, Stéphane; Pollock, Tresa M.

doi:10.1016/j.msea.2016.09.098

Cited by 105 publications

(45 citation statements)

References 48 publications

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“…The fracture mode and nucleation source of the secondary fractures on the fatigue fracture profiles of the two states were the same as those of the fatigue source fractures (Figure 7). The average SF of the grains where the secondary fracture source was located was lower than that of the surrounding grains, and the intragranular SF changed more (Figures 8 and 9), which is different from the fatigue surface fracture features observed by Texier et al [12]. There were more low angle grain boundaries near the secondary fracture of the ST state than that of the ST + A state, and the distribution was more uniform, indicating that the local plastic deformation of the cyclic ST state was more uniform than that of the ST + A state, and the degree of stress concentration was relatively low.…”

Section: Analysis Of the High Cycle Fatigue Fracture Of The Inconel 7contrasting

confidence: 67%

“…The laser scanning confocal diagrams for the vertical sections of the ST and ST + A fatigue fractures are shown in Figure 7. In Figure 7a, the plane of the ST state fatigue fracture source is 45 • to the stress axis, indicating that the fatigue fracture initiated on the <111> slip plane [34]; this fracture mechanism is different from the room temperature ultrahigh cycle fatigue surface fracture of the aged state Inconel 718 alloy, which initiated at the twin boundaries of the coarse grains [12]. The bumpy morphology of the main fracture shows plastic fracture features.…”

Section: Fatigue Fracture Profilementioning

confidence: 95%

“…Therefore, the research on fatigue performance of the Inconel 718 alloy has been widely concerned. According to the specific service environment temperature and load of the parts, it can be roughly divided into several aspects: high temperature [2]/medium temperature [3]/room temperature [4,5] low cycle fatigue, high temperature [6,7]/room temperature [8]/low temperature [9,10] high cycle fatigue, and ultra-high cycle fatigue [11,12] performance. Fournier et al [13] found that the Inconel 718 alloy in the solution treated and aged (ST + A) state had cyclic softening while in the direct aged (DA) state [14] had cyclic hardening under high temperature.…”

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confidence: 99%

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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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Section: Analysis Of the High Cycle Fatigue Fracture Of The Inconel 7contrasting

confidence: 67%

Section: Fatigue Fracture Profilementioning

confidence: 95%

mentioning

confidence: 99%

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

Liqiong

Liang

et al. 2018

Metals

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“…10 and Table 2). Twins, and more precisely twin boundaries, were found particularly prone to crack initiation in high twin containing superalloys subjected to fatigue loading, either in VHCF or LCF loading conditions where strain amplitudes are low [2,3,36]. Due to relatively high elastic anisotropy at the grain level in Ni-based superalloys, intense strain/stress localization in the elastic domain raises near grain boundaries and even more near twin boundaries [32].…”

Section: Strain Localization In Polycrystalline and Twinned Materialsmentioning

confidence: 99%

In-plane and out-of-plane deformation at the sub-grain scale in polycrystalline materials assessed by confocal microscopy

et al. 2019

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a b s t r a c tHigh-resolution digital image correlation (HR-DIC) techniques have become essential in material mechanics to assess strain measurements at the scale of the elementary mechanisms responsible of the deformation in polycrystalline materials. The purpose of this study is to demonstrate the use of laser scanning confocal microscopy (LSCM) coupled with DIC techniques to deepen knowledge on the deformation process of a polycrystalline nickel-based superalloy at room temperature. The LSCM technique is capable of detecting both in-plane and out-of-plane strain localization within slip bands at the sub-grain level. The LSCM observations are consistent with previous in-situ scanning electron microscopy (SEM) studies: The onset of crystal plasticity occurs primarily near S3 twin boundaries with macroscopic loading in the elastic domain (macroscopic stress as low as 80% of the 0.2% offset yield strength (Y.S. 0.2% )). This intense irreversible strain localization occurs with either a high Schmid factor (m > 0.43) or a significant elastic modulus difference between the pair of twins (DЕ > 100 GPa). In the plastic deformation domain, transgranular slip activity following slip systems with the highest Schmid factor is mostly responsible for the deformation at the grain level, thus leading to strain percolation. The simultaneous in-plane and out-of-plane deformation assessment via the HR-LSCM-DIC technique was found to be essential for the identification of active slip systems. Finally, the HR-LSCM-DIC technique enabled the quantification of the glide amplitude involved in the three-dimensional shearing process at the grain level that solely in-plane measurements cannot provide.

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“…In general, the failure of Ni-based superalloy material originates from the sites of stress concentration. The main cause of stress concentration is the presence of defects in the material, including, MC, holes, precipitates phase and so on [9,10]. Figure 4a,b showed the two different morphology, rod and block shape, of carbide inclusions after tensile failure for PWA1483 Ni-based superalloy at 900 °C.…”

Section: Failure Modes Caused By Inclusionsmentioning

confidence: 99%

In-Situ SEM Deformation Testing of Ni-Based Superalloy Heated by the Joule Heat

Wang

Liang

2018

The 18th International Conference on Experimental Mechanics

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Studying the deformation and microstructure evolution for Ni-based single crystal alloys at high temperature has important effects on the design of turbine blades and disks. However, in-situ high temperature tests under scanning environment pose an important challenge for the current experimental conditions. In this paper, the resistance heating system was introduced into the high temperature fatigue experimental apparatus. The in-situ tensile test of 900 °C was successfully carried out. The experimental results showed that the crack initiation was mainly caused by inclusion debonding. The fracture mode was mainly characterized by the connection of micro holes.

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Crack initiation sensitivity of wrought direct aged alloy 718 in the very high cycle fatigue regime: the role of non-metallic inclusions

Cited by 105 publications

References 48 publications

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

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

In-plane and out-of-plane deformation at the sub-grain scale in polycrystalline materials assessed by confocal microscopy

In-Situ SEM Deformation Testing of Ni-Based Superalloy Heated by the Joule Heat

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