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The Effect of Location and Post-treatment on the Microstructure of EBM-Built Alloy 718
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. (PTW)ORCID iD: 0000-0001-5676-7903
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. (PTW)ORCID iD: 0000-0003-0462-0912
Quintus Technologies AB, Västerås, Sweden.
Chalmers University of Technology, Department of Industrial and Materials Science, Gothenburg, Sweden.
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2018 (English)In: Proceedings of the 9th International Symposium on Superalloy 718 & Derivatives: Energy, Aerospace, and Industrial Applications / [ed] Ott, E., Liu, X., Andersson, J., Bi, Z., Bockenstedt, K., Dempster, I., Groh, J., Heck, K., Jablonski, P., Kaplan, M., Nagahama, D. and Sudbrack, C., Springer, 2018, p. 115-129Conference paper, Published paper (Refereed)
Abstract [en]

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 post-treatments on minor phase distributions (δ, 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 δ 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.

Place, publisher, year, edition, pages
Springer, 2018. p. 115-129
Series
The Minerals, Metals & Materials Series, ISSN 2367-1181, E-ISSN 2367-1696
Keywords [en]
Additive manufacturing, Electron beam melting, Alloy 718, HIP, Heat treatment, Microstructure, XRD, Hardness, δ, γ″, Carbide
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
URN: urn:nbn:se:hv:diva-12346DOI: 10.1007/978-3-319-89480-5_6ISBN: 978-3-319-89479-9 (print)ISBN: 978-3-319-89480-5 (electronic)OAI: oai:DiVA.org:hv-12346DiVA, id: diva2:1259025
Conference
9th International Symposium on Superalloy 718 & Derivatives, Energy, Aerospace, and Industrial Applications, Pittsburgh, Pennsylvania, USA, 3-6 June, 2018
Available from: 2018-10-26 Created: 2018-10-26 Last updated: 2019-02-18Bibliographically approved
In thesis
1. Post-treatment of Alloy 718 produced by electron beam melting
Open this publication in new window or tab >>Post-treatment of Alloy 718 produced by electron beam melting
2019 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Electron beam melting (EBM), a metal additive manufacturing (AM) process, has received considerable industrial attention for near net shape manufacture of complex geometries with traditionally difficult-to-machine materials. This has fuelled considerable academic interest in investigating EBM of Alloy 718, a nickel ironbased superalloy possessing an exciting combination of good mechanical behaviour and cost effectiveness. EBM production of Alloy 718 is particularly promising for aerospace and other sectors which value rapid production of components with large scope for design flexibility. The EBM builds are characterized by presence of inevitable defects and, anisotropy within a build is also a concern. Consequently, as-built Alloy 718 has to be subjected to post-build thermal-treatments (post-treatments) to ensure that the parts eventually meet the critical service requirements. Not withstanding the above, limited knowledge is available about optimal post-treatments for EBM-built Alloy 718. Therefore, the main focus of the work presented in this thesis was to systematically investigate the response of EBM-built material to post-treatments, which include hotisostatic pressing (HIPing), solution treatment (ST), and aging.

HIPing of EBM-built Alloy 718 led to more than an order of magnitude reduction in defect content, which was reduced from as high as 17% to < 0.2% in samples built with intentionally introduced porosity to investigate limits of defect closure achievable through HIPing. In addition, HIPing also caused complete dissolution of δ and γ" phases present in the as-built condition, with the latter causing dropin hardness of the material. HIPing had no effect on the carbides and inclusions such as TiN, Al2O3 present in the built material. The evolution of microstructure during ST and aging was systematically investigated. Growth of potentially beneficial grain boundary δ phase precipitates was found to cease after a certain duration of ST, with samples subjected to prior-HIPing exhibiting lesser precipitation of the δ phase during ST. While the specimen hardness increased onaging, it was observed to plateau after a duration significantly shorted than the specified ASTM 'standard' aging cycle. Therefore, prima facie there are promising prospects for shortening the overall heat treatment duration. A combination of HIPing, ST, and aging treatments in a single uninterrupted cycle was also explored. Future work involving incorporation of a shortened heat treatment schedule in a combined cycle can have significant industrial implications.

Place, publisher, year, edition, pages
Trollhättan: University West, 2019. p. 73
Series
Licentiate Thesis: University West
Keywords
Additive Manufacturing, Electron Beam Melting; Alloy 718; HIP; Heat Treatment; Solutionizing; Aging; HIP+HT; Microstructure; γ"; δ
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-13547 (URN)978-91-88847-25-6 (ISBN)978-91-88847-24-9 (ISBN)
Presentation
2019-02-18, F206, University West, Trollhättan, 10:00 (English)
Supervisors
Note

Articles submitted to journals and unpublished manuscripts are not included in this registration

Available from: 2019-02-18 Created: 2019-02-18 Last updated: 2019-02-18Bibliographically approved

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Goel, SnehaOlsson, JonasJoshi, Shrikant V.

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