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Karimi Neghlani, PariaORCID iD iconorcid.org/0000-0001-6610-1486
Publications (10 of 19) Show all publications
Karimi Neghlani, P., Sadeghi, E., Ålgårdh, J., Keshavarzkermani, A., Esmaeilizadeh, R., Toyserkani, E. & Andersson, J. (2021). Columnar-to-equiaxed grain transition in powder bed fusion via mimicking casting solidification and promoting in situ recrystallization. Additive Manufacturing, 46, Article ID 102086.
Open this publication in new window or tab >>Columnar-to-equiaxed grain transition in powder bed fusion via mimicking casting solidification and promoting in situ recrystallization
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2021 (English)In: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 46, article id 102086Article in journal (Refereed) Published
Abstract [en]

Columnar grain structure typically formed along the build direction in the electron beam-powder bed fusion (EBPBF) technique leads to anisotropic physical and mechanical properties. In this study, casting solidification condition was mimicked, and in situ recrystallization was promoted in EB-PBF to facilitate columnar-to-equiaxed grain structure transition in Alloy 718. This is achieved via a unique linear melting strategy coupled with a specific selection of process parameters in EB-PBF. It was found that site-specific melting using line order number (LON) function affected the cooling rate and temperature gradient, which controlled grain morphology and texture. A high LON resulted in a large equiaxed grain zone with a random texture, whereas a fixed LON with a high areal energy density led to a strong texture. The main driving force in the formation of cracks and shrinkage defects during the transition was investigated. A high LON at a fixed areal energy density reduced the average total shrinkage defects and crack length. The hardness was decreased through the transition, which was linked to the reduction in the size of the gamma ‘’ precipitates.

Place, publisher, year, edition, pages
ELSEVIER, 2021
Keywords
Additive manufacturing; Electron beam-powder bed fusion; Alloy 718; In situ recrystallization; Grain structure
National Category
Manufacturing, Surface and Joining Technology Metallurgy and Metallic Materials
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-17560 (URN)10.1016/j.addma.2021.102086 (DOI)000697020200002 ()2-s2.0-85110462749 (Scopus ID)
Note

Funding from the European Regional Development Fund, the Simulation and Control of Material affecting Processes (SiCoMap) and the Sustainable Manufacturing Through Next-Generation Additive Process (SUMAN-Next) projects with funding from the KK Foundation, are highly acknowledged.

Available from: 2021-11-08 Created: 2021-11-08 Last updated: 2022-03-31
Sadeghi, E., Asala, G., Karimi Neghlani, P., Deng, D., Moverare, J. & Hansson, T. (2021). Fatigue crack initiation and propagation in Alloy 718 with a bimodal grain morphology built via electron beam-powder bed fusion. Materials Science & Engineering: A, 827, Article ID 142051.
Open this publication in new window or tab >>Fatigue crack initiation and propagation in Alloy 718 with a bimodal grain morphology built via electron beam-powder bed fusion
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2021 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 827, article id 142051Article in journal (Refereed) Published
Abstract [en]

A unique melting strategy was implemented in electron beam-powder bed fusion (EB-PBF) of Alloy 718, resulting in the formation of a bimodal grain morphology consisting of fine equiaxed and columnar grains. The microstructure was preserved following various thermal post-treatments. The post-treated specimens were exposed to low cycle fatigue (LCF), and fatigue crack growth (FCG) tests in ambient air at 600 °C under pure and dwell-time (120 s) fatigue cycles. Clustered inclusions spanned a region of 100-600 µm in length acted as the crack initiation site, reducing the specimens' total fatigue life. When compared to pure fatigue cycles, dwell-time fatigue cycles reduced LCF life by approximately 35%, regardless of the thermal post-treatments. Due to a high fraction of grain boundary area in the as-built EB-PBF specimens, oxygen diffusion across the grain boundaries was enhanced. The intergranular fracture mode was favored in the plastic zone ahead of the crack tip, leading to rapid crack growth. No unbroken ligaments behind the crack front were found by high-resolution X-ray computed tomography, which was consistent with a large crack opening displacement linked to severe deformation around the crack tip. 

Place, publisher, year, edition, pages
Elsevier Ltd, 2021
Keywords
3D printers; Additives; Computerized tomography; Crack tips; Electron beams; Fatigue of materials; Grain boundaries; Morphology; Superalloys; Textures, Alloy 718; Bimodal grains; Dwell time; Electron-beam; Fatigue crack initiation; Fatigue cycles; Grain morphologies; Grain-boundaries; Powder bed; Thermal post-treatments, Fatigue crack propagation
National Category
Manufacturing, Surface and Joining Technology Metallurgy and Metallic Materials
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-17513 (URN)10.1016/j.msea.2021.142051 (DOI)000713681600001 ()2-s2.0-85115023272 (Scopus ID)
Note

Financial supports of the Knowledge Foundation for the SupREme project (2018-0203) and Åforsk for the SCC-SUMAN project (18-296) are highly acknowledged. The authors would like to express their gratitude to Mr. Johannes Gårdstam from Quintus Technologies AB for performing the thermal post-treatment on the specimens. Mr. Mats Högström and Mr. Håkan Bäckström of University West deserve special recognition for their significant contributions to the room temperature LCF experiments. Chalmers Materials Analysis Laboratory (CMAL) at the Chalmers University of Technology is appreciated for the assistance with the EBSD/SEM analysis. Dr. Nitesh Raj Jaladurgam of Chalmers University of Technology and Mr. Vui Mai Nguyen of Red River College are greatly acknowledged for the analysis of the EBSD and X-ray CT results, respectively. The authors would like to thank Dr. Niklas Israelsson (Arcam-EBM), and Dr. James Shipley (Quintus Technologies AB), and Mr. Ron Morford (MetCut) for their significant contribution to the specimen manufacturing and post-processing.

Available from: 2021-09-30 Created: 2021-09-30 Last updated: 2022-03-31Bibliographically approved
Karimi Neghlani, P., Sadeghi, E., Ålgårdh, J., Olsson, J., Hörnqvist Colliander, M., Harlin, P., . . . Andersson, J. (2021). Tailored grain morphology via a unique melting strategy in electron beam-powder bed fusion. Materials Science & Engineering: A, 824, Article ID 141820.
Open this publication in new window or tab >>Tailored grain morphology via a unique melting strategy in electron beam-powder bed fusion
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2021 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 824, article id 141820Article in journal (Refereed) Published
Abstract [en]

This study presents a unique melting strategy in electron beam-powder bed fusion of Alloy 718 to tailor the grain morphology from the typical columnar to equiaxed morphology. For this transition, a specific combination of certain process parameters, including low scanning speeds (400-800 mm/s), wide line offsets (300-500 mu m) and a high number of line order (#10) was selected to control local solidification conditions in each melt pool during the process. In addition, secondary melting of each layer with a 90. rotation with respect to primary melting induced more vigorous motions within the melt pools and extensive changes in thermal gradient direction, facilitating grain morphology tailoring. Four different types of microstructures were classified according to the produced grain morphology depending on the overlap zone between two adjacent melt pools, i.e., fully-columnar (overlap above 40 %), fully-equiaxed (overlap below 15 %), mixed columnar-equiaxed grains, and hemispherical melt pools containing mixed columnar-equiaxed grains (overlap similar to 20-25 %). The typical texture was <001>; however, the texture was reduced significantly through the transition from the columnar to equiaxed grain morphology. Along with all four different microstructures, shrinkage defects and cracks were also identified which amount of them reduced by a reduction in areal energy input. The hardness was increased through the transition, which was linked to the growth of the.” precipitates and high grain boundary density in the fully-equiaxed grain morphology.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2021
Keywords
Additive manufacturing; Electron beam-powder-bed fusion; Melting strategy; Grain structure; Alloy 718
National Category
Manufacturing, Surface and Joining Technology Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hv:diva-17450 (URN)10.1016/j.msea.2021.141820 (DOI)000689220800002 ()2-s2.0-85111856337 (Scopus ID)
Note

Funding from the “European Regional Development Fund,” the “Simulation and Control of Material affecting Processes” (SiCoMap), and the “Sustainable Manufacturing Through Next-Generation Additive Process” (SUMAN-Next) projects, with funding from the KK foundation, are highly acknowledged

Available from: 2021-10-18 Created: 2021-10-18 Last updated: 2022-04-04
Karimi Neghlani, P., Schnur, C., Sadeghi, E. & Andersson, J. (2020). Contour design to improve topographical and microstructural characteristics of Alloy 718 manufactured by electron beam-powder bed fusion technique. Additive Manufacturing, 32, Article ID 101014.
Open this publication in new window or tab >>Contour design to improve topographical and microstructural characteristics of Alloy 718 manufactured by electron beam-powder bed fusion technique
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.

Keywords
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:nbn:se:hv:diva-14993 (URN)10.1016/j.addma.2019.101014 (DOI)000522928600020 ()2-s2.0-85078915522 (Scopus ID)
Available from: 2020-02-24 Created: 2020-02-24 Last updated: 2021-06-11Bibliographically approved
Karimi Neghlani, P., Sadeghi, E., Ålgårdh, J., Harlin, P. & Andersson, J. (2020). Effect of build location on microstructural characteristics and corrosion behavior of EB-PBF built Alloy 718. The International Journal of Advanced Manufacturing Technology, 106(7-8), 3597-3607
Open this publication in new window or tab >>Effect of build location on microstructural characteristics and corrosion behavior of EB-PBF built Alloy 718
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2020 (English)In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 106, no 7-8, p. 3597-3607Article in journal (Refereed) Published
Abstract [en]

Electron beam-powder bed fusion (EB-PBF), a high-temperature additive manufacturing (AM) technique, shows great promise in the production of high-quality metallic parts in different applications such as the aerospace industry. To achieve a higher build efficiency, it is ideal to build multiple parts together with as low spacing as possible between the respective parts. In the EB-PBF technique, there are many unknown variations in microstructural characteristics and functional performance that could be induced as a result of the location of the parts on the build plate, gaps between the parts and part geometry, etc. In the present study, the variations in the microstructure and corrosion performance as a function of the parts location on the build plate in the EB-PBF process were investigated. The microstructural features were correlated with the thermal history of the samples built in different locations on the build plate, including exterior (the outermost), middle (between the outermost and innermost), and interior (the innermost) regions. The cubic coupons located in the exterior regions showed increased level (~ 20 %) of defects (mainly in the form of shrinkage pores) and lower level (~ 30-35 %) of Nb-rich phase fraction due to their higher cooling rates compared to the interior and middle samples. Electrochemical investigations showed that the location indirectly had a substantial influence on the corrosion behavior, verified by a significant increase in polarization resistance (Rp) from the exterior (2.1 ± 0.3 kΩ.cm2) to interior regions (39.2 ± 4.1 kΩ.cm2). © 2020, The Author(s).

Keywords
3D printers; Additives; Aerospace industry; Corrosion; Corrosive effects; Electron beams; Hardness; High temperature applications, Alloy 718; Electrochemical investigations; Functional performance; Micro-structural characteristics; Micro-structural characterization; Microstructural features; Polarization resistances; Powder bed, Location
National Category
Manufacturing, Surface and Joining Technology
Identifiers
urn:nbn:se:hv:diva-15004 (URN)10.1007/s00170-019-04859-9 (DOI)000511506500069 ()2-s2.0-85077549789 (Scopus ID)
Funder
Knowledge FoundationEuropean Regional Development Fund (ERDF)
Available from: 2020-02-24 Created: 2020-02-24 Last updated: 2020-11-10
Alehojat, M., Jafari, R., Karimi Neghlani, P. & Sadeghi, E. (2020). Electron beam-powder bed fusion of Alloy 718: Effect of hot isostatic pressing and thermal spraying on microstructural characteristics and oxidation performance. Surface & Coatings Technology, 404, Article ID 126626.
Open this publication in new window or tab >>Electron beam-powder bed fusion of Alloy 718: Effect of hot isostatic pressing and thermal spraying on microstructural characteristics and oxidation performance
2020 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 404, article id 126626Article in journal (Refereed) Published
Abstract [en]

Alloy 718 manufactured via electron beam-powder bed fusion (EB-PBF) was coated with a thermally- sprayed NiCoCrAlY coating for enhanced oxidation protection. A high-velocity air fuel technique was used to deposit the coating. The specimens were then subjected to hot isostatic pressing (HIP). Oxidation of the specimens was undertaken in an ambient air environment at 650 and 800 °C for 168 h. The oxidation performance of EB-PBF-built Alloy 718 was improved after the deposition of the coating, particularly at 800 °C. In this temperature, a thick Cr-rich oxide scale was found on the uncoated Alloy 718 specimen, whereas a thin and stable Al-rich oxide scale was formed on the surface of the coated specimen. HIPing enhanced the oxidation resistance of uncoated Alloy 718; however, the oxidation behavior of coated Alloy 718 was negatively affected by HIPing. © 2020 The Authors

Keywords
Air; Aluminum alloys; Aluminum coatings; Aluminum oxide; Chromium alloys; Chromium compounds; Cobalt alloys; Electron beams; Oxidation; Oxidation resistance; Scale (deposits); Sintering; Thermal spraying, Ambient air; High velocity air fuels; Micro-structural characteristics; NiCoCrAlY coatings; Oxidation behaviors; Oxidation protection; Oxide scale; Powder bed, Hot isostatic pressing
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-16101 (URN)10.1016/j.surfcoat.2020.126626 (DOI):000597889400063 ()2-s2.0-85096582818 (Scopus ID)
Funder
Knowledge Foundation, 2018-0203
Note

Funders:Åforsk [18-296]

Available from: 2020-12-09 Created: 2020-12-09 Last updated: 2022-01-19Bibliographically approved
Karimi Neghlani, P. (2020). Electron beam-powder bed fusion of Alloy 718: Effect of process parameters on microstructure evolution. (Doctoral dissertation). Trollhättan: University West
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
Sadeghi, E., Karimi Neghlani, P., Israelsson, N., Shipley, J., Månsson, T. & Hansson, T. (2020). Inclusion-induced fatigue crack initiation in powder bed fusion of Alloy 718. Additive Manufacturing, 36, Article ID 101670.
Open this publication in new window or tab >>Inclusion-induced fatigue crack initiation in powder bed fusion of Alloy 718
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2020 (English)In: Additive Manufacturing, ISSN 2214-8604, E-ISSN 2214-7810, Vol. 36, article id 101670Article in journal (Refereed) Published
Abstract [en]

Fatigue crack initiation of Alloy 718 additively manufactured via electron beam-powder bed fusion (EB-PBF) process was investigated. The melt parameters were chosen to achieve sufficient energy input and minimize process-induced defects. A line offset of 200 µm with enough line energy was used, leading to the formation of wide and deep melt pools. This strategy facilitated the formation of equiaxed grains at the melt pools bottom, and short columnar grains within the melt pools aligned parallel to the build direction. The mixed grain morphology and texture were retained after various thermal post-treatments, including heat treatment (HT), hot isostatic pressing (HIP), and HIP-HT. Micron-sized non-metallic inclusions in the feedstock powder, such as Al-rich oxide and titanium nitride clustered during the EB-PBF process, and remained intact during the post-treatments. Low cycle fatigue cracks mainly originated from the non-metallic inclusions found near the surface of the test specimens. HIPing was able to remove a portion of the internal defects, including round-shaped and shrinkage pores; therefore, a small fatigue life enhancement was observed in HIP-HT compared to HT.

Place, publisher, year, edition, pages
Elsevier B.V., 2020
Keywords
Electron beam-powder bed fusion, Grain morphology, Non-metallic inclusion, Thermal post-treatment, Low cycle fatigue
National Category
Manufacturing, Surface and Joining Technology Metallurgy and Metallic Materials
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-16102 (URN)10.1016/j.addma.2020.101670 (DOI)000600807800191 ()2-s2.0-85096566033 (Scopus ID)
Funder
Knowledge Foundation, 2018-0203
Note

Funders: Åforsk [18-296]

Available from: 2020-12-09 Created: 2020-12-09 Last updated: 2021-03-02Bibliographically approved
Sadeghi, E., Pant, P., Jafari, R., Peng, R. L. & Karimi Neghlani, P. (2020). Subsurface grain refinement in electron beam-powder bed fusion of Alloy 718: Surface texture and oxidation performance. Materials Characterization, 168
Open this publication in new window or tab >>Subsurface grain refinement in electron beam-powder bed fusion of Alloy 718: Surface texture and oxidation performance
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2020 (English)In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 168Article in journal (Refereed) Published
Abstract [en]

Subsurface grains of Alloy 718 additively manufactured via electron beam-powder bed fusion technique were refined using shot peening to improve the surface texture and oxidation performance. Oxidation of the specimens was performed at 650 and 800 degrees C in ambient air. Due to plastic deformation upon shot peening, compressive residual stress and high microstrain were generated in the subsurface region within a depth of approximately 50 mu m. The shot-peened specimen exhibited lower surface roughness, finer subsurface grains, and higher hardness compared to the as-built specimen. Shot peening, coupled with hot isostatic pressing and heat treatment (HIP-HT), yielded superior oxidation performance with substantially low oxidation kinetics at 800 degrees C. The smooth surface, as well as dense and refined subsurface microstructure resulting from shot peening, facilitated the formation of a continuous, protective, and adherent Cr-rich oxide scale.

Place, publisher, year, edition, pages
Elsevier, 2020
Keywords
Powder bed fusion; Alloy 718; Shot peening; Grain refinement; Surface texture; Surface characterization
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-17201 (URN)10.1016/j.matchar.2020.110567 (DOI)000571490200001 ()2-s2.0-85089745298 (Scopus ID)
Funder
Knowledge Foundation, 20180203
Note

Financial supports of the Knowledge Foundation for the SupREme project (Dnr 20180203) and Aforsk for the SCC-SUMAN project (18-296) are highly acknowledged. The authors would like to thank Mr. Jonas Olsson, Dr. Mahdi Eynian, and Prof. Joel Andersson for their valuable help and advice in processing and characterization of the specimens. The authors would like to thank Mr. Olle Widman from Curtiss-wright Surface Technologies for shot peening, Mr. Johannes Gardstam, and Mr. James Shipley from Quintus Technologies AB for HT-HIPing of the specimens. The authors are grateful to Venkataramanan Mohandass for the characterization of the specimens. Chalmers Materials Analysis Laboratory (CMAL) at the Chalmers University of Technology are appreciated for the help in the XRD/SEM analysis.

Available from: 2021-12-21 Created: 2021-12-21 Last updated: 2021-12-21
Karimi Neghlani, P., Sadeghi, E., Ålgårdh, J. & Andersson, J. (2019). EBM-manufactured single tracks of Alloy 718: Influence of energy input and focus offset on geometrical and microstructural characteristics. Materials Characterization, 148, 88-99
Open this publication in new window or tab >>EBM-manufactured single tracks of Alloy 718: Influence of energy input and focus offset on geometrical and microstructural characteristics
2019 (English)In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 148, p. 88-99Article in journal (Refereed) Published
Abstract [en]

Electron beam melting-powder bed fusion (EBM-PBF) is an additive manufacturing process, which is able to produce parts in layer-by-layer fashion from a 3D model data. Currently application of this technology in parts manufacturing with high geometrical complexity has acquired growing interest in industry. To recommend the EBM process into industry for manufacturing parts, improved mechanical properties of final part must be obtained. Such properties highly depend on individual single melted track and single layer. In EBM, interactions between the electron beam, powder, and solid underlying layer affect the geometrical (e.g., re-melt depth, track width, contact angle, and track height) and microstructural (e.g., grain structure, and primary dendrite arm spacing) characteristics of the melted tracks. The core of the present research was to explore the influence of linear energy input parameters in terms of beam scanning speed, beam current as well as focus offset and their interactions on the geometry and microstructure of EBM-manufactured single tracks of Alloy 718. Increased scanning speed led to lower linear energy input values (<0.9 J/mm) in an specific range of the focus offset (0–10 mA) which resulted in instability, and discontinuity of the single tracks as well as balling effect. Decreasing the scanning speed and increasing the beam current resulted in higher melt pool depth and width. By statistical evaluations, the most influencing parameters on the geometrical features were primarily the scanning speed, and secondly the beam current. Primary dendrite arm spacing (PDAS) slightly decreased by increasing the scanning speed using lower beam current values as the linear energy input decreased. By increasing the linear energy input, the chance of more equiaxed grain formation was high, however, at lower linear energy input, mainly columnar grains were observed. The lower focus offset values resulted in more uniform grains along the 〈001〉 crystallographic direction. © 2018 Elsevier Inc. 

Keywords
3D printers; Contact angle; Dendrites (metallography); Design of experiments; Electron beam melting; Electron beams; Scanning; Speed, Alloy 718; Geometrical characteristics; Powder bed; Single-tracks; Solidified microstructures, Geometry
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-13365 (URN)10.1016/j.matchar.2018.11.033 (DOI)000458228100011 ()2-s2.0-85058512738 (Scopus ID)
Funder
European Regional Development Fund (ERDF)Knowledge Foundation
Available from: 2019-01-08 Created: 2019-01-08 Last updated: 2020-11-10Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-6610-1486

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