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Article

Additive Manufacturing of Alloy 718 via Electron Beam Melting: Effect of Post-Treatment on the Microstructure and the Mechanical Properties

1
Department of Engineering Science, University West, SE 461 86 Trollhättan, Sweden
2
Department of Management and Engineering, Linköping University, SE 581 83 Linköping, Sweden
*
Author to whom correspondence should be addressed.
Materials 2019, 12(1), 68; https://doi.org/10.3390/ma12010068
Received: 6 November 2018 / Revised: 19 December 2018 / Accepted: 21 December 2018 / Published: 25 December 2018
Alloy 718 finds application in gas turbine engine components, such as turbine disks, compressor blades and so forth, due to its excellent mechanical and corrosion properties at elevated temperatures. Electron beam melting (EBM) is a recent addition to the list of additive manufacturing processes and has shown the capability to produce components with unique microstructural features. In this work, Alloy 718 specimens were manufactured using the EBM process with a single batch of virgin plasma atomized powder. One set of as-built specimens was subjected to solution treatment and ageing (STA); another set of as-built specimens was subjected to hot isostatic pressing (HIP), followed by STA (and referred to as HIP+STA). Microstructural analysis of as-built specimens, STA specimens and HIP+STA specimens was carried out using optical microscopy and scanning electron microscopy. Typical columnar microstructure, which is a characteristic of the EBM manufactured alloy, was observed. Hardness evaluation of the as-built, STA and HIP+STA specimens showed that the post-treatments led to an increase in hardness in the range of ~50 HV1. Tensile properties of the three material conditions (as-built, STA and HIP+STA) were evaluated. Post-treatments lead to an increase in the yield strength (YS) and the ultimate tensile strength (UTS). HIP+STA led to improved elongation compared to STA due to the closure of defects but YS and UTS were comparable for the two post-treatment conditions. Fractographic analysis of the tensile tested specimens showed that the closure of shrinkage porosity and the partial healing of lack of fusion (LoF) defects were responsible for improved properties. Fatigue properties were evaluated in both STA and HIP+STA conditions. In addition, three surface conditions were also investigated, namely the ‘raw’ as-built surface, the machined surface with the contour region and the machined surface without the contour region. Machining off the contour region completely together with HIP+STA led to significant improvement in fatigue performance. View Full-Text
Keywords: Alloy 718; electron beam melting; fatigue properties; tensile properties; microstructure; texture Alloy 718; electron beam melting; fatigue properties; tensile properties; microstructure; texture
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MDPI and ACS Style

Balachandramurthi, A.R.; Moverare, J.; Mahade, S.; Pederson, R. Additive Manufacturing of Alloy 718 via Electron Beam Melting: Effect of Post-Treatment on the Microstructure and the Mechanical Properties. Materials 2019, 12, 68. https://doi.org/10.3390/ma12010068

AMA Style

Balachandramurthi AR, Moverare J, Mahade S, Pederson R. Additive Manufacturing of Alloy 718 via Electron Beam Melting: Effect of Post-Treatment on the Microstructure and the Mechanical Properties. Materials. 2019; 12(1):68. https://doi.org/10.3390/ma12010068

Chicago/Turabian Style

Balachandramurthi, Arun R.; Moverare, Johan; Mahade, Satyapal; Pederson, Robert. 2019. "Additive Manufacturing of Alloy 718 via Electron Beam Melting: Effect of Post-Treatment on the Microstructure and the Mechanical Properties" Materials 12, no. 1: 68. https://doi.org/10.3390/ma12010068

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