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Influence of successive thermal cycling on microstructure evolution of EBM-manufactured alloy 718 in track-by-track and layer-by-layer design
Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT). (PTW)ORCID-id: 0000-0001-6610-1486
Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT). (PTW)ORCID-id: 0000-0002-7663-9631
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Luleå, 971 87, Sweden.
Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT). Powder Materials & Additive Manufacturing, Swerea KIMAB AB, Kista, 164 40, Sweden. (PTW)
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2018 (Engelska)Ingår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 160, s. 427-441Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Successive thermal cycling (STC) during multi-track and multi-layer manufacturing of Alloy 718 using electron beam melting (EBM) process leads to a microstructure with a high degree of complexity. In the present study, a detailed microstructural study of EBM-manufactured Alloy 718 was conducted by producing samples in shapes from one single track and single wall to 3D samples with maximum 10 longitudinal tracks and 50 vertical layers. The relationship between STC, solidification microstructure, interdendritic segregation, phase precipitation (MC, δ-phase), and hardness was investigated. Cooling rates (liquid-to-solid and solid-to-solid state) was estimated by measuring primary dendrite arm spacing (PDAS) and showed an increased cooling rate at the bottom compared to the top of the multi-layer samples. Thus, microstructure gradient was identified along the build direction. Moreover, extensive formation of solidification micro-constituents including MC-type carbides, induced by micro-segregation, was observed in all the samples. The electron backscatter diffraction (EBSD) technique showed a high textured structure in 〈001〉 direction with a few grains misoriented at the surface of all samples. Finer microstructure and possibility of more γ″ phase precipitation at the bottom of the samples resulted in slightly higher (~11%) hardness values compared to top of the samples. © 2018 Elsevier Ltd

Ort, förlag, år, upplaga, sidor
2018. Vol. 160, s. 427-441
Nyckelord [en]
3D printers; Carbides; Cooling; Electron beam melting; Electron beams; Hardness; Segregation (metallography); Solidification; Thermal cycling, Alloy 718; Electron backscatter diffraction technique; Interdendritic segregation; Layer by layer; Micro-structure evolutions; Primary dendrite arm spacings; Solidification microstructures; Track by track, Microstructure
Nationell ämneskategori
Bearbetnings-, yt- och fogningsteknik Metallurgi och metalliska material
Forskningsämne
TEKNIK, Produktions- och materialteknik; Produktionsteknik
Identifikatorer
URN: urn:nbn:se:hv:diva-13042DOI: 10.1016/j.matdes.2018.09.038ISI: 000453008100040Scopus ID: 2-s2.0-85053828514OAI: oai:DiVA.org:hv-13042DiVA, id: diva2:1259268
Forskningsfinansiär
KK-stiftelsen
Anmärkning

Funders: Simulation and Control of Material affecting Processes (SiCoMap); "SUMAN-Next"

Tillgänglig från: 2018-10-29 Skapad: 2018-10-29 Senast uppdaterad: 2019-05-28Bibliografiskt granskad
Ingår i avhandling
1. Electron beam melting of Alloy 718: Influence of process parameters on the microstructure
Öppna denna publikation i ny flik eller fönster >>Electron beam melting of Alloy 718: Influence of process parameters on the microstructure
2018 (Engelska)Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Additive manufacturing (AM) is the name given to the technology of building 3D parts by adding layer-by-layer of materials, including metals, plastics, concrete, etc. Of the different types of AM techniques, electron beam melting (EBM), as a powder bed fusion technology, has been used in this study. EBM is used to build parts by melting metallic powders by using a highly intense electron beam as the energy source. Compared to a conventional process, EBM offers enhanced efficiency for the production of customized and specific parts in aerospace, space, and medical fields. In addition, the EBM process is used to produce complex parts for which other technologies would be either expensive or difficult to apply. This thesis has been divided into three sections, starting from a wider window and proceeding to a smaller one. The first section reveals how the position-related parameters (distance between samples, height from build plate, and sample location on build plate) can affect the microstructural characteristics. It has been found that the gap between the samples and the height from the build plate can have significant effects on the defect content and niobium-rich phase fraction. In the second section, through a deeper investigation, the behavior of Alloy 718 during the EBM process as a function of different geometry-related parameters is examined by building single tracks adjacent to each other (track-by-track) andsingle-wall samples (single tracks on top of each other). In this section, the main focus is to understand the effect of successive thermal cycling on microstructural evolution. In the final section, the correlations between the main machine-related parameters (scanning speed, beam current, and focus offset) and the geometrical (melt pool width, track height, re-melted depth, and contact angle) and microstructural (grain structure, niobium-rich phase fraction, and primary dendrite arm spacing) characteristics of a single track of Alloy 718 have been investigated. It has been found that the most influential machine-related parameters are scanning speed and beam current, which have significant effects on the geometry and the microstructure of the single-melted tracks.

Ort, förlag, år, upplaga, sidor
Trollhättan: University West, 2018. s. 65
Serie
Licentiate Thesis: University West ; 22
Nyckelord
Additive manufacturing; Powder bed fusion; Electron beam melting; Part’s orientation; Microstructure development; Single track; Energy input; Focus offset; Geometrical features, Alloy 718
Nationell ämneskategori
Bearbetnings-, yt- och fogningsteknik
Forskningsämne
TEKNIK, Produktions- och materialteknik; Produktionsteknik
Identifikatorer
urn:nbn:se:hv:diva-13140 (URN)978-91-88847-08-9 (ISBN)978-91-88847-07-2 (ISBN)
Presentation
2018-11-21, C120, Högskolan Väst, Trollhättan, 10:00 (Engelska)
Handledare
Tillgänglig från: 2018-11-21 Skapad: 2018-11-19 Senast uppdaterad: 2018-11-19

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