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Balachandramurthi, Arun RamanathanORCID iD iconorcid.org/0000-0002-8664-4573
Publications (5 of 5) Show all publications
Balachandramurthi, A. R., Moverare, J., Dixit, N., Deng, D. & Pederson, R. (2019). Microstructural influence on fatigue crack propagation during high cycle fatigue testing of additively manufactured Alloy 718. Materials Characterization, 149, 82-94
Open this publication in new window or tab >>Microstructural influence on fatigue crack propagation during high cycle fatigue testing of additively manufactured Alloy 718
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2019 (English)In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 149, p. 82-94Article in journal (Refereed) Published
Abstract [en]

A study of the microstructure of additively manufactured Alloy 718 was performed in order to better understand the parameters that have an influence on the fatigue properties of the material. The specimens were manufactured using two powder bed fusion techniques – Electron Beam Melting (EBM) and Selective Laser Melting (SLM). Four point bending fatigue tests were performed at room temperature with a stress ratio of R = 0.1 and 20 Hz frequency, on material that was either in hot isostatically pressed (HIP) and solution treated and aged (STA) condition or in STA condition without a prior HIP treatment. The grains in the SLM material in the HIP + STA condition have grown considerably both in the hatch and the contour regions; EBM material, in contrast, shows grain growth only in the contour region. Fractographic analysis of the specimens in HIP + STA condition showed a faceted appearance while the specimens in STA condition showed a more planar crack appearance. The crack propagation occurred in a transgranular mode and it was found that precipitatessuch as NbC, TiN or δ-phase, when present, did not affect the crack path. The areas with larger grains corresponded to the faceted appearance of the fracture surface. This could be attributed to the plastic zone ahead of the crack tip being confined within one grain, in case of the larger grains, which promotes single shear crack growth mode

Keywords
Electron beam melting, Selective laser melting, Alloy 718, Fatigue crack propagation, Microstructure, Hot isostatic pressing
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-13460 (URN)10.1016/j.matchar.2019.01.018 (DOI)000475837800008 ()2-s2.0-85060346504 (Scopus ID)
Funder
Knowledge Foundation, 20160281
Available from: 2019-02-04 Created: 2019-02-04 Last updated: 2019-10-16Bibliographically approved
Balachandramurthi, A. R. & Olsson, J. (2019). Microstructure tailoring in Electron Beam Powder Bed Fusion Additive Manufacturing and its potential consequences. Results in Materials, 1
Open this publication in new window or tab >>Microstructure tailoring in Electron Beam Powder Bed Fusion Additive Manufacturing and its potential consequences
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2019 (English)In: Results in Materials, ISSN 2590-048X, Vol. 1Article in journal (Refereed) Published
Abstract [en]

Electron Beam Powder Bed Fusion process for Alloy 718 was investigated, in the sense of microstructural evolution with varying process conditions. The existence of a geometric relationship between the melt front and the processing parameters was observed. By understanding and capitalizing on this relationship, it was possible to obtain columnar, equiaxed or bimodal microstructure.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Alloy 718, Texture, Microstructure, Additive manufacturing, Powder bed fusion
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-14331 (URN)10.1016/j.rinma.2019.100017 (DOI)
Available from: 2019-08-26 Created: 2019-08-26 Last updated: 2019-12-12Bibliographically approved
Balachandramurthi Ramanathan, A., Moverare, J., Mahade, S. & Pederson, R. (2018). Additive Manufacturing of Alloy 718 via Electron Beam Melting: Effect of Post-Treatment on the Microstructure and the Mechanical Properties.. Materials, 12(1), Article ID E68.
Open this publication in new window or tab >>Additive Manufacturing of Alloy 718 via Electron Beam Melting: Effect of Post-Treatment on the Microstructure and the Mechanical Properties.
2018 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 12, no 1, article id E68Article in journal (Refereed) Published
Abstract [en]

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.

Keywords
Alloy 718, electron beam melting, fatigue properties, microstructure, tensile properties, texture
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-13364 (URN)10.3390/ma12010068 (DOI)000456410200068 ()30585242 (PubMedID)2-s2.0-85059182911 (Scopus ID)
Funder
Knowledge Foundation, 20160281
Available from: 2019-01-08 Created: 2019-01-08 Last updated: 2019-05-27Bibliographically approved
Balachandramurthi, A. R. (2018). Fatigue Properties of Additively Manufactured Alloy 718. (Licentiate dissertation). Trollhättan: University West
Open this publication in new window or tab >>Fatigue Properties of Additively Manufactured Alloy 718
2018 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Additive Manufacturing (AM), commonly known as 3D Printing, is a disruptive modern manufacturing process, in which parts are manufactured in a layer-wise fashion. Among the metal AM processes, Powder Bed Fusion (PBF) technology has opened up a design space that was not formerly accessible with conventional manufacturing processes. It is, now, possible to manufacture complex geometries, such as topology-optimized structures, lattice structures and intricate internal channels, with relative ease. PBF is comprised of Electron Beam Melting (EBM) and Selective Laser Melting (SLM) processes.

Though AM processes offer several advantages, the suitability of these processes to replace conventional manufacturing processes must be studied in detail; for instance, the capability to produce components of consistent quality. Therefore, understanding the relationship between the AM process together with the post treatment used and the resulting microstructure and its influence on the mechanical properties is crucial, to enable manufacturing of high-performance components. In this regard, for AM built Alloy 718, only a limited amount of work has been performed compared to conventional processes such as casting and forging. The aim of this work, therefore, is to understand how the fatigue properties of EBM and SLM built Alloy 718, subjected to different thermal post-treatments, is affected by the microstructure. In addition, the effect of as-built surface roughness is also studied.

Defects can have a detrimental effect on fatigue life. Numerous factors such as the defect type, size, shape, location, distribution and nature determine the effect of defects on properties. Hot Isostatic Pressing (HIP) improves fatigue life as it leads to closure of most defects. Presence of oxides in the defects, however, hinders complete closure by HIP. Machining the as-built surface improves fatiguelife; however, for EBM manufactured material, the extent of improvement is dependent on the amount of material removed. The as-built surface roughness, which has numerous crack initiation sites, leads to lower scatter in fatigue life. In both SLM and EBM manufactured material, fatigue crack propagation is transgranular. Crack propagation is affected by grain size and texture of the material.

Place, publisher, year, edition, pages
Trollhättan: University West, 2018. p. 49
Series
Licentiate Thesis: University West ; 24
Keywords
Fatigue; Additive Manufacturing; Powder Bed Fusion; Superalloy; Microstructure; Surface roughness
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-13186 (URN)978-91-88847-13-3 (ISBN)978-91-88847-12-6 (ISBN)
Presentation
2018-12-05, University West, Trollhättan, 10:00 (English)
Supervisors
Available from: 2018-12-05 Created: 2018-12-05 Last updated: 2019-01-07Bibliographically approved
Balachandramurthi, A. R., Moverare, J., Dixit, N. & Pederson, R. (2018). Influence of defects and as-built surface roughness on fatigue properties of additively manufactured Alloy 718. Materials Science & Engineering: A, 735, 463-474
Open this publication in new window or tab >>Influence of defects and as-built surface roughness on fatigue properties of additively manufactured Alloy 718
2018 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 735, p. 463-474Article in journal (Refereed) Published
Abstract [en]

Electron beam melting (EBM) and Selective Laser Melting (SLM) are powder bed based additive manufacturing (AM) processes. These, relatively new, processes offer advantages such as near net shaping, manufacturing complex geometries with a design space that was previously not accessible with conventional manufacturing processes, part consolidation to reduce number of assemblies, shorter time to market etc. The aerospace and gas turbine industries have shown interest in the EBM and the SLM processes to enable topology-optimized designs, parts with lattice structures and part consolidation. However, to realize such advantages, factors affecting the mechanical properties must be well understood – especially the fatigue properties. In the context of fatigue performance, apart from the effect of different phases in the material, the effect of defects in terms of both the amount and distribution and the effect of “rough” as-built surface must be studied in detail. Fatigue properties of Alloy 718, a Ni-Fe based superalloy widely used in the aerospace engines is investigated in this study. Four point bending fatigue tests have been performed at 20 Hz in room temperature at different stress ranges to compare the performance of the EBM and the SLM material to the wrought material. The experiment aims to assess the differences in fatigue properties between the two powder bed AM processes as well as assess the effect of two post-treatment methods namely – machining and hot isostatic pressing (HIP). Fractography and metallography have been performed to explain the observed properties. Both HIPing and machining improve the fatigue performance; however, a large scatter is observed for machined specimens. Fatigue properties of SLM material approach that of wrought material while in EBM material defects severely affect the fatigue life. © 2018 Elsevier B.V.

Keywords
Additive manufacturing, Alloy 718, Fatigue, Surface roughness, Hot isostatic pressing, 3D printers, Bending tests, Binary alloys, Fatigue testing, Fighter aircraft, Fracture mechanics, Gas turbines, Hot isostatic pressing, Iron alloys, Mechanical properties, Melting, Nickel alloys, Sintering, Surface roughness, Alloy 718, Conventional manufacturing, Fatigue performance, Gas turbine industry, Lattice structures, Manufacturing complex, Post-treatment method, Selective laser melting, Fatigue of materials
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-12956 (URN)10.1016/j.msea.2018.08.072 (DOI)000447117300055 ()2-s2.0-85052655828 (Scopus ID)
Funder
Knowledge Foundation, 20160281
Note

Available online 23 August 2018

Available from: 2018-09-27 Created: 2018-09-27 Last updated: 2019-05-28Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-8664-4573

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