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Contour design to improve topographical and microstructural characteristics of Alloy 718 manufactured by electron beam-powder bed fusion technique
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. (PTW)ORCID iD: 0000-0001-6610-1486
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. (PTW)
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. (PTW)ORCID iD: 0000-0002-7663-9631
University West, Department of Engineering Science, Division of Welding Technology. (PTW)ORCID iD: 0000-0001-9065-0741
2020 (English)In: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 32, article id 101014Article in journal (Refereed) Published
Abstract [en]

Additive manufacturing (AM) processes are being frequently used in industry as they allow the manufacture ofcomplex parts with reduced lead times. Electron beam-powder bed fusion (EB-PBF) as an AM technology isknown for its near-net-shape production capacity with low residual stress. However, the surface quality andgeometrical accuracy of the manufactured parts are major obstacles for the wider industrial adoption of thistechnology, especially when enhanced mechanical performance is taken into consideration. Identifying theorigins of surface features such as satellite particles and sharp valleys on the parts manufactured by EB-PBF isimportant for a better understanding of the process and its capability. Moreover, understanding the influence ofthe contour melting strategy, by altering process parameters, on the surface roughness of the parts and thenumber of near-surface defects is highly critical. In this study, processing parameters of the EB-PBF techniquesuch as scanning speed, beam current, focus offset, and number of contours (one or two) with the linear meltingstrategy were investigated. A sample manufactured using Arcam-recommended process parameters (threecontours with the spot melting strategy) was used as a reference. For the samples with one contour, the scanningspeed had the greatest effect on the arithmetical mean height (Sa), and for the samples with two contours, thebeam current and focus offset had the greatest effect. For the samples with two contours, a lower focus offset andlower scan speed (at a higher beam current) resulted in a lower Sa; however, increasing the scan speed for thesamples with one contour decreased Sa. In general, the samples with two contours provided a lower Sa (∼22 %)but with slightly higher porosity (∼8 %) compared to the samples with one contour. Fewer defects were detected with a lower scanning speed and higher beam current. The number of defects and the Sa value for thesamples with two contours manufactured using the linear melting strategy were ∼85 % and 16 %, respectively,lower than those of the reference samples manufactured using the spot melting strategy.

Place, publisher, year, edition, pages
2020. Vol. 32, article id 101014
Keywords [en]
3D printers; Additives; Electron beams; Scanning; Speed; Surface defects; Surface properties; Surface roughness, Alloy 718; Geometrical accuracy; Linear and spot melting strategies; Mechanical performance; Micro-structural characteristics; Near-surface defects; Powder bed; Processing parameters, Melting
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
URN: urn:nbn:se:hv:diva-14993DOI: 10.1016/j.addma.2019.101014ISI: 000522928600020Scopus ID: 2-s2.0-85078915522OAI: oai:DiVA.org:hv-14993DiVA, id: diva2:1395747
Available from: 2020-02-24 Created: 2020-02-24 Last updated: 2021-06-11Bibliographically approved
In thesis
1. Electron beam-powder bed fusion of Alloy 718: Effect of process parameters on microstructure evolution
Open this publication in new window or tab >>Electron beam-powder bed fusion of Alloy 718: Effect of process parameters on microstructure evolution
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Additive manufacturing (AM) is the technology of building 3D parts through layer-by-layer addition of material. Of the different types of AM techniques, electron beam-powder bed fusion (EB-PBF) has been used in this study. EB-PBF can build parts by melting metallic powders using an electron beam as the energy source. Compared to conventional manufacturing processes, EB-PBF offers a convenient approach and enhanced efficiency in producing customized and specific parts in the aerospace, space, automotive, and medical fields. In addition, the EB-PBF process is used to produce complex parts with less residual stress due to the high-temperature environment within the process.

This thesis has been divided into four stages. In the first stage, the behavior of Alloy 718 during the EB-PBF process as a function of different geometry-related parameters is examined by building single tracks adjacent to each other (track-by track) and single tracks on top of each other (single-wall samples). In this stage,the focus is on understanding the effect of successive thermal cycling on microstructural evolution. In the second stage, the effect of the position-related parameters–including the distance or gap between samples, height from the build plate (in the Z direction), and sample location on the build plate (in the X–Y plane) –on the microstructural characteristics, are revealed. These three position related parameters can have significant effects on the defect content and niobium rich phase fraction. In the third stage, the correlations between the main machinerelated parameters, geometric (melt pool width, track height, remelted depth, and contact angle), and microstructural (grain structure, niobium-rich phase fraction,and primary dendrite arm spacing) characteristics of a single track are delineated.

The results obtained in stages one to three were used as a guideline for the reduction of the internal–external defects and columnar-to-equiaxed transition(CET) in the grain structure of a typical cubic part. The final stage reveals two different strategies that were developed using machine-related parameters (scanning speed, beam current, focus offset, line offset, and line order number) to tailor the grain structures. All investigated parameters with respect to the proper selection of the processing window played a critical role in the solidification parameters (thermal gradient, growth rate, and cooling rate) on the solidification front, which could induce formation of more fine equiaxed grains.

Place, publisher, year, edition, pages
Trollhättan: University West, 2020. p. 75
Series
PhD Thesis: University West ; 2020:37
Keywords
Additive manufacturing; Electron beam-powder bed fusion; Microstructure evolution; Microstructure tailoring; Process understanding; Alloy 718
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-16013 (URN)978-91-88847-65-2 (ISBN)978-91-88847-64-5 (ISBN)
Public defence
2020-12-01, F131, Trollhättan, 10:00 (English)
Opponent
Supervisors
Available from: 2020-11-10 Created: 2020-11-10 Last updated: 2020-11-10Bibliographically approved

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Karimi Neghlani, PariaSadeghi, EsmaeilAndersson, Joel

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