Effect of anisotropy and texture on the low cycle fatigue behavior of Inconel 718 processed via electron beam melting

Kirka, Michael M.; Greeley, Duncan A.; Hawkins, Charles; Dehoff, Ryan R.

doi:10.1016/j.ijfatigue.2017.08.021

Cited by 95 publications

(47 citation statements)

References 23 publications

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“…Generally, thermal post-treatment involves hot isostatic pressing (HIP) for closure and healing of defects, solution treatment for homogenization of the microstructure, and aging for precipitation of strengthening phase (c¢¢, Ni 3 Nb and c¢, Ni 3 (Al, Ti)). The specific interest in thermal post-treatment of EBMbuilt Alloy 718 is motivated by published results showing substantial improvement in mechanical performance after posttreatment (Ref [1][2][3].…”

Section: Introductionmentioning

confidence: 99%

Effect of Different Post-treatments on the Microstructure of EBM-Built Alloy 718

Goel

Ahlfors

Bahbou³

et al. 2018

J. of Materi Eng and Perform

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Electron beam melting (EBM) of Alloy 718 is of rapidly growing interest as it allows cost-effective production of complex components. However, the inherent flaws in the component in as-built state are of concern in view of the severe working conditions in which Alloy 718 components typically operate. The present work entails an investigation of changes in microstructure that accompany some post-treatments that are being widely considered to address defects in EBM processed Alloy 718. The effect of two different post-treatments, namely hot isostatic pressing (HIP) and a combined HIP + heat treatment (HT) carried out inside the HIP vessel, have been studied and results from as-built and post-treated specimens were compared in terms of porosity/lack-of-fusion, microstructure, phase constitution (NbC content, d-phase) and micro-hardness. Post-treatment resulted in reduction in defect content by more than an order of magnitude. HIPing led to complete dissolution of d phase. In comparison to as-built material, HIPed specimens exhibited significant drop in hardness. However, a sharp ÔrecoveryÕ of hardness to yield values higher than in as-built condition was observed after HIP + HT and can be attributed to precipitation of c¢¢ phase.

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Section: Introductionmentioning

confidence: 99%

Effect of Different Post-treatments on the Microstructure of EBM-Built Alloy 718

Goel

Ahlfors

Bahbou³

et al. 2018

J. of Materi Eng and Perform

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“…Previously published work on post-treatment of EBM-built Alloy 718 involved HIP for healing the defects by plastic flow, solution treatment (ST) to dissolve the secondary phases such as the δ phase, and aging to precipitate the desired strengthening phases like γ" [10]- [12]. Kirka et al have reported significant improvement in low cycle fatigue behaviour of EBM built Alloy 718 after post-treatment in comparison to the as-built material [16], presumably as a consequence of the above.…”

Section: Introductionmentioning

confidence: 99%

The Effect of Location and Post-treatment on the Microstructure of EBM-Built Alloy 718

Goel

Olsson

Ahlfors

et al. 2018

The Minerals, Metals &Amp; Materials Series

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Additive manufacturing (AM) of Ni-based superalloys such as Alloy 718 may obviate the need for difficult machining and welding operations associated with geometrically intricate parts, thus potentially expanding design possibilities and facilitating cost-effective manufacture of complex components. However, processing AM builds completely free from defects, which may impair mechanical properties such as fatigue and ductility, is challenging. Anisotropic properties, microstructural heterogeneities and local formation of undesired phases are additional concerns that have motivated post-treatment of AM builds. This work investigates the microstructural changes associated with post-treatment of Alloy 718 specimens produced by Electron Beam Melting (EBM) for as-built microstructures at 3 build heights: near base plate, in the middle of build and near the top of the build. Two different post-treatment conditions, hot isostatic pressing (HIP) alone and a combined HIP with solutionising and two-step aging were examined and compared to the results for the as-built condition. The influence of various posttreatments on minor phase distributions (, γ", carbides), overall porosity, longitudinal grain widths and Vickers microhardness was considered. The HIP treatment led to significant reduction in overall porosity and dissolution of  phase, which led to appreciable grain growth for both post-treatment conditions. The variation in hardness noted as a function of build height for the as-built specimens was eliminated after post-treatment. Overall, the hardness was found to decrease after HIP and increase after the full HIP, solutionising and aging treatment, which was attributed to dissolution of γ" during HIP and its re-precipitation in subsequent heat treatment steps.

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“…It is widely demonstrated that the specimen build orientation affects the microstructure in terms of texture in Inconel 718 processed by both LPBF and electron beam melting . According to these studies, the variation in the elastic and shear moduli from the weakest to the strongest orientation does not account for more than 10% and 50%, respectively.…”

Section: Resultsmentioning

confidence: 99%

“…It is widely demonstrated that the specimen build orientation affects the microstructure in terms of texture in Inconel 718 processed by both LPBF 21,22,24,29 and electron beam melting. 30 According to these studies, the variation in the elastic and shear moduli from the weakest to the strongest orientation does not account for more than 10% and 50%, respectively. Although for a polished sample with k t = 1 the variation of anisotropic properties is quite influential, these effects are considerably lower than the SCF impact that is shown to amplify the externally applies stress by 150% to 350% (k t = 1.5 to 3.5).…”

Section: High Cycle Fatigue Life Estimationmentioning

confidence: 92%

High cycle fatigue life estimation of materials processed by laser powder bed fusion

Hovig

Azar

Sunding

et al. 2019

Fatigue Fract Eng Mat Struct

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The fatigue life of metal components is known to depend on the surface topography. For components made by laser powder bed fusion, the roughness of the as‐built surfaces depends on the orientation of the component surface with respect to the build plate. Surface topographies of AlSi10Mg and Inconel 718 specimens built at 0° to 90° inclination, with 15° increments, were characterised by white light interferometry. Two methods for calculating the stress concentration factor using the surface roughness data are proposed, and the results of each approach are presented and compared. Moreover, a finite element model was developed, in order to analyse the stress field when subsurface porosity is present. The fatigue lifetime estimates suggest that the lifetime of components may differ up to two orders of magnitude, depending on the build orientation.

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Effect of anisotropy and texture on the low cycle fatigue behavior of Inconel 718 processed via electron beam melting

Cited by 95 publications

References 23 publications

Effect of Different Post-treatments on the Microstructure of EBM-Built Alloy 718

Effect of Different Post-treatments on the Microstructure of EBM-Built Alloy 718

The Effect of Location and Post-treatment on the Microstructure of EBM-Built Alloy 718

High cycle fatigue life estimation of materials processed by laser powder bed fusion

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