Microstructure Development in Electron Beam-Melted Inconel 718 and Associated Tensile Properties

Kirka, Michael M.; Unocic, Kinga A.; Raghavan, Narendran; Medina, Francisco; DeHoff, R. T.; Babu, S. S.

doi:10.1007/s11837-016-1812-6

Cited by 105 publications

(58 citation statements)

References 30 publications

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“…In their subsequent paper [75], anisotropic tensile properties were reported as due to the local agglomerate of porosities rather than the intrinsic properties. The anisotropic tensile properties were further confirmed by Kirka et al [77,186]: both the tensile strength and elongation are higher tested along the building direction that tested perpendicular to the building direction in the as-manufactured sample, and these anisotropic properties almost disappear after post heat-treatment. The microstructure gradient along the building direction was first reported by Unocic et al [187], and was attributed to the height-dependant thermal exposure experienced by different parts of the component [61].…”

Section: Ebm In718supporting

confidence: 54%

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Additively Manufactured Inconel 718 : Microstructures and Mechanical Properties

Deng

2018

Linköping Studies in Science and Technology. Licentiate Thesis

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Linköping 2018Cover image: A fracture surface of EBM IN718 after tensile test at room temperature.During the course of research underlying this thesis, Dunyong Deng was enrolled in Agora Materiae, a multidiciplinary doctoral program at Linköping University, Sweden. Printed by LiU-Tryck 2018 © Dunyong Deng AbstractAdditive manufacturing (AM), also known as 3D printing, has gained significant interest in aerospace, energy, automotive and medical industries due to its capabilities of manufacturing components that are either prohibitively costly or impossible to manufacture by conventional processes. Among the various additive manufacturing processes for metallic components, electron beam melting (EBM) and selective laser melting (SLM) are two of the most widely used powder bed based processes, and have shown great potential for manufacturing high-end critical components, such as turbine blades and customized medical implants. The futures of the EBM and SLM are doubtlessly promising, but to fully realize their potentials there are still many challenges to overcome.Inconel 718 (IN718) is a nickel-base superalloy and has impressive combination of good mechanical properties and low cost. Though IN718 is being mostly used as a turbine disk material now, the initial introduction of IN718 was to overcome the poor weldability of superalloys in 1960s, since sluggish precipitation of strengthening phases γ ′ /γ ′′ enables good resistance to strain-age cracking during welding or post weld heat treatment. Given the similarity between AM and welding processes, IN718 has been widely applied to the metallic AM field to facilitate the understandings of process-microstructure-property relationships.The work presented in this licentiate thesis aims to better understand microstructures and mechanical properties EBM and SLM IN718, which have not been systematically investigated. Microstructures of EBM and SLM IN718 have been characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM) and correlated with the process conditions. Monotonic mechanical properties (e.g., Vickers microhardness and tensile properties) have also been measured and rationalized with regards to the microstructure evolutions before and after heat treatments.For EBM IN718, the results show the microstructure is not homogeneous but dependant on the location in the components, and the anisotropic mechanical properties are probably attributed to alignment of porosities rather than texture.iii Post heat treatment can slightly increase the mechanical strength compared to the as-manufactured condition but does not alter the anisotropy. SLM IN718 shows significantly different microstructure and mechanical properties to EBM IN718. The as-manufactured SLM IN718 has very fine dendritic microstructure and Laves phases in the interdendrites, and is "work-hardened" by the residual strains and dislocations present in the material. Mechanical properties are different between horizontally and vertically built samples, and heat treatment can m...

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Section: Ebm In718supporting

confidence: 54%

“…Currently, the major EBM Ni-base superalloy research is focus on IN718 [53,[74][75][76][77][78] and IN625 [79,80] because of their weldabilities. However, the relatively high chamber temperature during process enables the possibility of manufacturing those γ ′ strengthened Ni-based superalloy.…”

Section: Materials Manufactured With Ebmmentioning

confidence: 99%

Additively Manufactured Inconel 718 : Microstructures and Mechanical Properties

Deng

2018

Linköping Studies in Science and Technology. Licentiate Thesis

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“…Therefore, a value of 2000 K/s was assumed for the simulation, which is in the range of the cooling rate values reported for EBM Alloy 718. [6] Periodic boundary conditions were assigned at the boundaries of the simulated domain.…”

Section: A Micress and The Governing Equationmentioning

confidence: 99%

“…Due to the inherent features of the layer-by-layer manufacturing approach, the microstructure of Alloy 718 after the EBM process exhibits a gradient along the build direction. [5,6] During the melting process, the powder material is melted and it then solidifies, thereby leading to the formation of different phases, as mentioned earlier. As the subsequent layers are built, the solidified structure gradually undergoes ''in situ'' heat treatment due to the elevated powder bed temperature (> 1000°C for Alloy 718) in the EBM process.…”

Section: Introductionmentioning

confidence: 99%

Predicting the Microstructural Evolution of Electron Beam Melting of Alloy 718 with Phase-Field Modeling

Kumara

Deng

Hanning

et al. 2019

Metall Mater Trans A

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Electron beam melting (EBM) is a powder bed additive manufacturing process where a powder material is melted selectively in a layer-by-layer approach using an electron beam. EBM has some unique features during the manufacture of components with high-performance superalloys that are commonly used in gas turbines such as Alloy 718. EBM has a high deposition rate due to its high beam energy and speed, comparatively low residual stresses, and limited problems with oxidation. However, due to the layer-by-layer melting approach and high powder bed temperature, the as-built EBM Alloy 718 exhibits a microstructural gradient starting from the top of the sample. In this study, we conducted modeling to obtain a deeper understanding of microstructural development during EBM and the homogenization that occurs during manufacturing with Alloy 718. A multicomponent phase-field modeling approach was combined with transformation kinetic modeling to predict the microstructural gradient and the results were compared with experimental observations. In particular, we investigated the segregation of elements during solidification and the subsequent ''in situ'' homogenization heat treatment at the elevated powder bed temperature. The predicted elemental composition was then used for thermodynamic modeling to predict the changes in the continuous cooling transformation and time-temperature transformation diagrams for Alloy 718, which helped to explain the observed phase evolution within the microstructure. The results indicate that the proposed approach can be employed as a valuable tool for understanding processes and for process development, including post-heat treatments.

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“…These dimensions are similar to those previously identified in AM Ni-based super alloys. [9, 20, 23–26]…”

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confidence: 99%

Homogenization kinetics of a nickel-based superalloy produced by powder bed fusion laser sintering

et al. 2017

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Additively manufactured (AM) metal components often exhibit fine dendritic microstructures and elemental segregation due to the initial rapid solidification and subsequent melting and cooling during the build process, which without homogenization would adversely affect materials performance. In this letter, we report in situ observation of the homogenization kinetics of an AM nickel-based superalloy using synchrotron small angle X-ray scattering. The identified kinetic time scale is in good agreement with thermodynamic diffusion simulation predictions using microstructural dimensions acquired by ex situ scanning electron microscopy. These findings could serve as a recipe for predicting, observing, and validating homogenization treatments in AM materials.

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Microstructure Development in Electron Beam-Melted Inconel 718 and Associated Tensile Properties

Cited by 105 publications

References 30 publications

Additively Manufactured Inconel 718 : Microstructures and Mechanical Properties

Additively Manufactured Inconel 718 : Microstructures and Mechanical Properties

Predicting the Microstructural Evolution of Electron Beam Melting of Alloy 718 with Phase-Field Modeling

Homogenization kinetics of a nickel-based superalloy produced by powder bed fusion laser sintering

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