Fatigue behavior and microstructural evolution of additively manufactured Inconel 718 under cyclic loading at elevated temperature

Johnson, Alexander S.; Nezhadfar, P.D.

doi:10.1016/j.ijfatigue.2020.105598

Cited by 68 publications

(30 citation statements)

References 22 publications

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“…For both the printing directions, the crack propagation featured smooth facets, onto which striations lines can be clearly identified, as shown in Figures 6C-E and 7C-E. The presence of these features indicates that the crack propagation is mainly transgranular, as reported in a recent work by Nezhadfar et al 32 In 1960, Forsyth and Ryder 46 demonstrated that the spacing between striation lines calculated at different crack lengths correlates well with the macroscopic crack propagation curve. This methodology was later applied in previous studies, 47,48 showing a good correlation between the macroscopic crack propagation curve and the crack speed computed from striation spacing for different materials.…”

Section: Analysis Of the Fracture Surfacessupporting

confidence: 72%

“…The effect of elevated environmental temperature on fatigue strength of Inconel718 was investigated in previous studies. 31,32 The impact of different layer orientations on the fatigue strength of Inconel718 AM at 650 C was investigated in Kirka et al 31 The conclusion of this work was that the material with the columnar grains oriented parallel to the main loading direction showed a longer fatigue life than the other orientations. Moreover, it was demonstrated that the overall fatigue life of Inconel718 produced using AM was comparable with its wrought material counterpart.…”

Section: Introductionmentioning

confidence: 91%

“…The fatigue properties of Inconel718 produced using laser beam directed energy deposition (LB-DED) under high-temperature conditions were investigated in a recent work by Nezhadfar et al 32 In this paper, it was found that the fatigue resistance of AM Inconel718 at high temperature was lower than that at room temperature. This was found to be due to the formation of more δ and Laves phases during fatigue testing at high temperatures; because these phases are brittle, they break under high-strain conditions, accelerating crack advancement.…”

Section: Introductionmentioning

confidence: 97%

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Anisotropic mechanical and fatigue behaviour of Inconel718 produced by SLM in LCF and high‐temperature conditions

Sausto

Marchese

Bassini

et al. 2020

Fatigue Fract Eng Mat Struct

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Additive manufacturing (AM) is one of the processes with the most potential for producing components used in internal combustion engines and features high efficiency due to the possibility of building very complex shapes. Several drawbacks of parts produced using AM are still unresolved, like poor surface quality, the presence of internal defects and anisotropic mechanical behaviour, which all contribute to decreasing the fatigue strength compared with the material produced using conventional processes. The effect of building direction on both the macroscopic mechanical behaviour and the crack propagation mechanism of Ni-base superalloy Inconel718 produced using AM was investigated under the combined effect of low cycle fatigue (LCF) and high temperature. The different crack growth mechanisms investigated using compact tension (CT) specimens, tested at high temperature, showed a significant difference between the two building directions. The LCF fatigue experiments also showed a significant difference in the ε-N curves from the two directions together with a high level of scatter due to the dispersion of the defect size at the fracture origin. The dimensions of the defects (as measured using the ffiffiffiffiffiffiffiffiffi area p parameter) were analysed by means of extreme value statistics and showed a significant difference between the two orientations investigated. The aim of this work is to propose a simplified approach (based on ΔJ eff concepts) to estimate the fatigue life of a component produced using AM that takes into account the material variability due to the combined effect of mechanical anisotropic behaviour and the presence of defects at high-temperature conditions.

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Section: Analysis Of the Fracture Surfacessupporting

confidence: 72%

Section: Introductionmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 97%

See 1 more Smart Citation

Anisotropic mechanical and fatigue behaviour of Inconel718 produced by SLM in LCF and high‐temperature conditions

Sausto

Marchese

Bassini

et al. 2020

Fatigue Fract Eng Mat Struct

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“…In high-temperature fatigue of Inconel 718, some researchers are attributing the high fatigue strength and the retardation of short crack growth to the formation of oxide films at the crack tip, which suppresses slipping. [43][44][45][46][47] Assuming that the AB surfaces are "precracked" due to the defects in the surface region, the initiation of crack growth might be suppressed by the oxide film. In addition to this, the oxide films could be "blunting" the defects so that an oxide layer covers their initial sharp radius.…”

Section: Failure Locationsmentioning

confidence: 99%

Fatigue assessment of as‐built and heat‐treated Inconel 718 specimens produced by additive manufacturing including notch effects

Solberg

Wan

2020

Fatigue Fract Eng Mat Struct

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The fatigue behaviour of notched and unnotched specimens produced by additively manufactured Inconel 718 were analysed in the as‐built and heat‐treated conditions. The surfaces display high roughness and defects acting as fatigue initiation sites. In the as‐built condition, fine subgrains were found, while in in the heat‐treated state, the subgrains were removed and the dislocation density recovered. SN‐curves are predicted based on tensile properties, hardness and defects obtained by fractography, using the area‐method.

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“…Limited studies exist regarding the effect of microstructure and defects on the fatigue behavior at elevated temperature, especially in the very-high-cycle fatigue (VHCF) regime. Nezhadfar et al investigated the low cycle fatigue resistance of SLM IN718 at RT and 650 °C and found that SLM specimens possessed slightly lower fatigue resistance at RT but exhibited a comparable fatigue strength at elevated temperature [ 12 ]. They ascribed the similar fatigue behavior at 650 °C to the same initiation sites of surface oxide films formed during the fatigue testing, which could retard the growth of the microstructurally short cracks.…”

Section: Introductionmentioning

confidence: 99%

Very-High-Cycle Fatigue Behavior of Inconel 718 Alloy Fabricated by Selective Laser Melting at Elevated Temperature

et al. 2021

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This study investigates the very-high-cycle fatigue (VHCF) behavior at elevated temperature (650 °C) of the Inconel 718 alloy fabricated by selective laser melting (SLM). The results are compared with those of the wrought alloy. Large columnar grain with a cellular structure in the grain interior and Laves/δ phases precipitated along the grain boundaries were exhibited in the SLM alloy, while fine equiaxed grains were present in the wrought alloy. The elevated temperature had a minor effect on the fatigue resistance in the regime below 108 cycles for the SLM alloy but significantly reduced the fatigue strength in the VHCF regime above 108 cycles. Both the SLM and wrought specimens exhibited similar fatigue resistance in the fatigue life regime of fewer than 107–108 cycles at elevated temperature, and the surface initiation mechanism was dominant in both alloys. In a VHCF regime above 107–108 cycles at elevated temperature, the wrought material exhibited slightly better fatigue resistance than the SLM alloy. All fatigue cracks are initiated from the internal defects or the microstructure discontinuities. The precipitation of Laves and δ phases is examined after fatigue tests at high temperatures, and the effect of microstructure on the formation and the propagation of the microstructural small cracks is also discussed.

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Fatigue behavior and microstructural evolution of additively manufactured Inconel 718 under cyclic loading at elevated temperature

Cited by 68 publications

References 22 publications

Anisotropic mechanical and fatigue behaviour of Inconel718 produced by SLM in LCF and high‐temperature conditions

Anisotropic mechanical and fatigue behaviour of Inconel718 produced by SLM in LCF and high‐temperature conditions

Fatigue assessment of as‐built and heat‐treated Inconel 718 specimens produced by additive manufacturing including notch effects

Very-High-Cycle Fatigue Behavior of Inconel 718 Alloy Fabricated by Selective Laser Melting at Elevated Temperature

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