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Publications (10 of 13) Show all publications
Goel, S., Ahlfors, M., Bahbou, F. & Joshi, S. V. (2019). Effect of Different Post-treatments on the Microstructure of EBM-Built Alloy 718. Journal of materials engineering and performance (Print), 28(2), 673-680
Open this publication in new window or tab >>Effect of Different Post-treatments on the Microstructure of EBM-Built Alloy 718
2019 (English)In: Journal of materials engineering and performance (Print), ISSN 1059-9495, E-ISSN 1544-1024, Vol. 28, no 2, p. 673-680Article in journal (Refereed) Published
Abstract [en]

Electron beam melting (EBM) of Alloy 718 is of rapidly growing interest as it allows cost-effective production of complex components. However, the inherent flaws in the component in as-built state are of concern in view of the severe working conditions in which Alloy 718 components typically operate. The present work entails an investigation of changes in microstructure that accompany some post-treatments that are being widely considered to address defects in EBM processed Alloy 718. The effect of two different post-treatments, namely hot isostatic pressing (HIP) and a combined HIP + heat treatment (HT) carried out inside the HIP vessel, have been studied and results from as-built and post-treated specimens were compared in terms of porosity/lack-of-fusion, microstructure, phase constitution (NbC content, ÎŽ-phase) and micro-hardness. Post-treatment resulted in reduction in defect content by more than an order of magnitude. HIPing led to complete dissolution of ÎŽ phase. In comparison to as-built material, HIPed specimens exhibited significant drop in hardness. However, a sharp ‘recovery’ of hardness to yield values higher than in as-built condition was observed after HIP + HT and can be attributed to precipitation of γ′′ phase. © 2018, The Author(s).

Keywords
3D printers, Cost effectiveness, Defects, Electron beam melting, Electron beams, Hardness, Heat treatment, Hot isostatic pressing, Microhardness, Microstructure, Alloy 718, Complete dissolution, Complex components, Cost-effective production, Defect contents, Phase constitution, Post treatment, Yield value, Niobium compounds
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-13133 (URN)10.1007/s11665-018-3712-0 (DOI)000458782100012 ()2-s2.0-85055983075 (Scopus ID)
Funder
Knowledge Foundation, 20160281
Note

First Online: 29 October 2018

Available from: 2018-11-19 Created: 2018-11-19 Last updated: 2019-06-12Bibliographically approved
Goel, S., Sittiho, A., Charit, I., Klement, U. & Joshi, S. V. (2019). Effect of post-treatments under hot isostatic pressure on microstructural characteristics of EBM-built Alloy 718. Additive Manufacturing, 28, 727-737
Open this publication in new window or tab >>Effect of post-treatments under hot isostatic pressure on microstructural characteristics of EBM-built Alloy 718
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2019 (English)In: Additive Manufacturing, ISSN 2214-8604, Vol. 28, p. 727-737Article in journal (Refereed) Published
Abstract [en]

Electron beam melting (EBM) has emerged as an important additive manufacturing technique. In this study, Alloy 718 produced by EBM was investigated in as-built and post-treated conditions for microstructural characteristics and hardness. The post-treatments investigated were hot isostatic pressing (HIP) and combined HIP + heat treatment (HIP + HT) carried out as a single cycle inside the HIP vessel. Both the post-treatments resulted in significant decrease in defects inevitably present in the as-built material. The columnar grain structure of the as-built material was found to be maintained after post-treatment, with some sporadic localized grain coarsening noted. Although HIP led to complete dissolution of δ and γ′′ phase, stable NbC and TiN (occasionally present) particles were observed in the post-treated specimens. Significant precipitation of γ′′ phase was observed after HIP + HT, which was attributed to the two-step aging heat treatment carried out during HIP + HT. The presence of γ′′ phase or otherwise was correlated to the hardness of the material. While the HIP treatment resulted in drop in hardness, HIP + HT led to 'recovery' of the hardness to values exceeding those exhibited by the as-built material. © 2019 Elsevier B.V.

Keywords
3D printers; Additives; Coarsening; Electron beam melting; Electron beams; Hardness; Heat treatment; Hot isostatic pressing; Sintering; Titanium nitride, Alloy 718; Columnar grain structure; Complete dissolution; Grain coarsening; Hot isostatic pressure; Manufacturing techniques; Micro-structural characteristics; Post treatment, Niobium compounds
National Category
Manufacturing, Surface and Joining Technology Metallurgy and Metallic Materials
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-14457 (URN)10.1016/j.addma.2019.06.002 (DOI)2-s2.0-85067846675 (Scopus ID)
Funder
Knowledge Foundation, 20160281
Available from: 2019-10-02 Created: 2019-10-02 Last updated: 2019-11-01Bibliographically approved
Gopal, V., Goel, S., Manivasagam, G. & Joshi, S. V. (2019). Performance of Hybrid Powder-Suspension Axial Plasma Sprayed Al2O3-YSZ Coatings in Bovine Serum Solution. Materials, 12(12), Article ID E1922.
Open this publication in new window or tab >>Performance of Hybrid Powder-Suspension Axial Plasma Sprayed Al2O3-YSZ Coatings in Bovine Serum Solution
2019 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 12, no 12, article id E1922Article in journal (Refereed) Published
Abstract [en]

Ceramic coatings on metallic implants are a promising alternative to conventional implants due to their ability to offer superior wear resistance. The present work investigates the sliding wear behavior under bovine serum solution and indentation crack growth resistance of four coatings, namely (1) conventional powder-derived alumina coating (Ap), (2) suspension-derived alumina coating (As), (3) composite Al2O3-20wt % Yittria stabilized Zirconia (YSZ) coating (AsYs) deposited using a mixed suspension, and (4) powder Al2O3-suspension YSZ hybrid composite coating ApYs developed by axial feeding plasma spraying, respectively. The indentation crack growth resistance of the hybrid coating was superior due to the inclusion of distributed fine YSZ particles along with coarser alumina splats. Enhanced wear resistance was observed for the powder derived Ap and the hybrid ApYs coatings, whereas the suspension sprayed As and AsYs coatings significantly deteriorated due to extensive pitting.

Keywords
axial feeding, bovine serum solution, hybrid plasma spray coating, indentation, sliding wear
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-14435 (URN)10.3390/ma12121922 (DOI)000473759400041 ()31207880 (PubMedID)2-s2.0-85067995972 (Scopus ID)
Available from: 2019-10-02 Created: 2019-10-02 Last updated: 2019-10-16
Goel, S. (2019). Post-treatment of Alloy 718 produced by electron beam melting. (Licentiate dissertation). Trollhättan: University West
Open this publication in new window or tab >>Post-treatment of Alloy 718 produced by electron beam melting
2019 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Electron beam melting (EBM), a metal additive manufacturing (AM) process, has received considerable industrial attention for near net shape manufacture of complex geometries with traditionally difficult-to-machine materials. This has fuelled considerable academic interest in investigating EBM of Alloy 718, a nickel ironbased superalloy possessing an exciting combination of good mechanical behaviour and cost effectiveness. EBM production of Alloy 718 is particularly promising for aerospace and other sectors which value rapid production of components with large scope for design flexibility. The EBM builds are characterized by presence of inevitable defects and, anisotropy within a build is also a concern. Consequently, as-built Alloy 718 has to be subjected to post-build thermal-treatments (post-treatments) to ensure that the parts eventually meet the critical service requirements. Not withstanding the above, limited knowledge is available about optimal post-treatments for EBM-built Alloy 718. Therefore, the main focus of the work presented in this thesis was to systematically investigate the response of EBM-built material to post-treatments, which include hotisostatic pressing (HIPing), solution treatment (ST), and aging.

HIPing of EBM-built Alloy 718 led to more than an order of magnitude reduction in defect content, which was reduced from as high as 17% to < 0.2% in samples built with intentionally introduced porosity to investigate limits of defect closure achievable through HIPing. In addition, HIPing also caused complete dissolution of δ and γ" phases present in the as-built condition, with the latter causing dropin hardness of the material. HIPing had no effect on the carbides and inclusions such as TiN, Al2O3 present in the built material. The evolution of microstructure during ST and aging was systematically investigated. Growth of potentially beneficial grain boundary δ phase precipitates was found to cease after a certain duration of ST, with samples subjected to prior-HIPing exhibiting lesser precipitation of the δ phase during ST. While the specimen hardness increased onaging, it was observed to plateau after a duration significantly shorted than the specified ASTM 'standard' aging cycle. Therefore, prima facie there are promising prospects for shortening the overall heat treatment duration. A combination of HIPing, ST, and aging treatments in a single uninterrupted cycle was also explored. Future work involving incorporation of a shortened heat treatment schedule in a combined cycle can have significant industrial implications.

Place, publisher, year, edition, pages
Trollhättan: University West, 2019. p. 73
Series
Licentiate Thesis: University West
Keywords
Additive Manufacturing, Electron Beam Melting; Alloy 718; HIP; Heat Treatment; Solutionizing; Aging; HIP+HT; Microstructure; γ"; δ
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-13547 (URN)978-91-88847-25-6 (ISBN)978-91-88847-24-9 (ISBN)
Presentation
2019-02-18, F206, University West, Trollhättan, 10:00 (English)
Supervisors
Note

Articles submitted to journals and unpublished manuscripts are not included in this registration

Available from: 2019-02-18 Created: 2019-02-18 Last updated: 2019-02-18Bibliographically approved
Björklund, S., Goel, S. & Joshi, S. V. (2018). Function-dependent coating architectures by hybrid powder-suspension plasma spraying: Injector design, processing and concept validation. Materials & design, 142, 56-65
Open this publication in new window or tab >>Function-dependent coating architectures by hybrid powder-suspension plasma spraying: Injector design, processing and concept validation
2018 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 142, p. 56-65Article in journal (Refereed) Published
Abstract [en]

The attractive properties achieved by Suspension Plasma Spraying (SPS), combined with the availability of high throughput capable plasma spray systems that permit axial feeding, provide encouragement to explore use of suspensions for next generation functional applications. This paper deals with realization of coatings with various pre-determined function-dependent architectures by employing a hybrid powder-suspension feedstock. Some illustrative application-relevant coating architecture designs are discussed, along with the specific benefits that can accrue by deploying a multi-scale powder-suspension feedstock combination. An elegant feedstock delivery arrangement to enable either simultaneous or sequential feeding of powders and suspensions to enable convenient processing of coatings with desired architectures is presented. As proof-of-concept, deposition of layered, composite and functionally graded coatings using the above system is also demonstrated using appropriate case studies

Keywords
Suspension, Hybrid feedstock, Layered, Composite, Functionally graded, Coatings
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-11993 (URN)10.1016/j.matdes.2018.01.002 (DOI)000425878200006 ()2-s2.0-85040645081 (Scopus ID)
Note

Available online 4 January 2018

Available from: 2018-01-16 Created: 2018-01-16 Last updated: 2019-02-18Bibliographically approved
Kanhed, S., Awasthi, S., Midha, S., Nair, J., Nisar, A., Patel, A. K., . . . Balani, K. (2018). Microporous Hydroxyapatite Ceramic Composites as Tissue Engineering Scaffolds: An Experimental and Computational Study. Advanced Engineering Materials, 20(7), Article ID 1701062.
Open this publication in new window or tab >>Microporous Hydroxyapatite Ceramic Composites as Tissue Engineering Scaffolds: An Experimental and Computational Study
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2018 (English)In: Advanced Engineering Materials, ISSN 1438-1656, E-ISSN 1527-2648, Vol. 20, no 7, article id 1701062Article in journal (Refereed) Published
Abstract [en]

Bone‐tissue engineering mandates the development of multi‐functional bioactive porous hydroxyapatite (HAp) scaffolds. Herein, microwave sintered HAp/ZnO and HAp/Ag composite scaffolds with ≈5–19% porosity are developed using 0–30 vol% graphite as a porogen. The mechanical properties of the porous scaffold are analyzed in detail, revealing that even being more porous, the reinforcement of ZnO (9% porosity, hardness of 2.8 GPa, and toughness of 3.5 MPa.m1/2) has shown to have better hardness and fracture toughness when compared to Ag (5% porosity, hardness of 1.6 GPa, and toughness of 2.6 MPa.m1/2). The flexural strength obtained experimentally are complemented with a finite‐element technique that adopts microstructural features in visualizing the effect of porosity on stress distribution. The antibacterial efficacy and cytocompatibility of these composites are validated by increased metabolic activity and conspicuous cell‐matrix interactions. The anticipation of the results reveal that HAp/ZnO (9% porosity) and HAp/Ag (5% porosity) composites can be used as a potential multi‐functional bone implant scaffolds.

Keywords
Antibacterial, Cytocompatibility, Diametrical Compression Test, Hydroxyapatite, Object‐Oriented Finite Element Modeling (OOF2), Porosity, Silver, Zinc Oxide
National Category
Manufacturing, Surface and Joining Technology Biomaterials Science Metallurgy and Metallic Materials
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-12249 (URN)10.1002/adem.201701062 (DOI)000439735800012 ()2-s2.0-85044234392 (Scopus ID)
Note

Funders: Ministry of Human Resource Development, India.

Available from: 2018-04-10 Created: 2018-04-10 Last updated: 2019-01-25Bibliographically approved
Goel, S., Olsson, J., Ahlfors, M., Klement, U. & Joshi, S. V. (2018). The Effect of Location and Post-treatment on the Microstructure of EBM-Built Alloy 718. In: Ott, E., Liu, X., Andersson, J., Bi, Z., Bockenstedt, K., Dempster, I., Groh, J., Heck, K., Jablonski, P., Kaplan, M., Nagahama, D. and Sudbrack, C. (Ed.), Proceedings of the 9th International Symposium on Superalloy 718 & Derivatives: Energy, Aerospace, and Industrial Applications. Paper presented at 9th International Symposium on Superalloy 718 & Derivatives, Energy, Aerospace, and Industrial Applications, Pittsburgh, Pennsylvania, USA, 3-6 June, 2018 (pp. 115-129). Springer
Open this publication in new window or tab >>The Effect of Location and Post-treatment on the Microstructure of EBM-Built Alloy 718
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2018 (English)In: Proceedings of the 9th International Symposium on Superalloy 718 & Derivatives: Energy, Aerospace, and Industrial Applications / [ed] Ott, E., Liu, X., Andersson, J., Bi, Z., Bockenstedt, K., Dempster, I., Groh, J., Heck, K., Jablonski, P., Kaplan, M., Nagahama, D. and Sudbrack, C., Springer, 2018, p. 115-129Conference paper, Published paper (Refereed)
Abstract [en]

Additive manufacturing (AM) of Ni-based superalloys such as Alloy 718 may obviate the need for difficult machining and welding operations associated with geometrically intricate parts, thus potentially expanding design possibilities and facilitating cost-effective manufacture of complex components. However, processing AM builds completely free from defects, which may impair mechanical properties such as fatigue and ductility, is challenging. Anisotropic properties, microstructural heterogeneities and local formation of undesired phases are additional concerns that have motivated post-treatment of AM builds. This work investigates the microstructural changes associated with post-treatment of Alloy 718 specimens produced by Electron Beam Melting (EBM) for as-built microstructures at 3 build heights: near base plate, in the middle of build and near the top of the build. Two different post-treatment conditions, hot isostatic pressing (HIP) alone and a combined HIP with solutionising and two-step aging were examined and compared to the results for the as-built condition. The influence of various post-treatments on minor phase distributions (δ, γ″, carbides), overall porosity, longitudinal grain widths and Vickers microhardness was considered. The HIP treatment led to significant reduction in overall porosity and dissolution of δ phase, which led to appreciable grain growth for both post-treatment conditions. The variation in hardness noted as a function of build height for the as-built specimens was eliminated after post-treatment. Overall, the hardness was found to decrease after HIP and increase after the full HIP, solutionising and aging treatment, which was attributed to dissolution of γ″ during HIP and its re-precipitation in subsequent heat treatment steps.

Place, publisher, year, edition, pages
Springer, 2018
Series
The Minerals, Metals & Materials Series, ISSN 2367-1181, E-ISSN 2367-1696
Keywords
Additive manufacturing, Electron beam melting, Alloy 718, HIP, Heat treatment, Microstructure, XRD, Hardness, δ, γ″, Carbide
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-12346 (URN)10.1007/978-3-319-89480-5_6 (DOI)978-3-319-89479-9 (ISBN)978-3-319-89480-5 (ISBN)
Conference
9th International Symposium on Superalloy 718 & Derivatives, Energy, Aerospace, and Industrial Applications, Pittsburgh, Pennsylvania, USA, 3-6 June, 2018
Available from: 2018-10-26 Created: 2018-10-26 Last updated: 2019-02-18Bibliographically approved
Goel, S., Björklund, S., Curry, N., Wiklund, U. & Joshi, S. V. (2017). Axial suspension plasma spraying of Al2O3 coatings for superior tribological properties. Surface & Coatings Technology, 315, 80-87
Open this publication in new window or tab >>Axial suspension plasma spraying of Al2O3 coatings for superior tribological properties
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2017 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 315, p. 80-87Article in journal (Refereed) Published
Abstract [en]

Suspension plasma spray is a relatively new thermal spray technique which enables feeding of fine powder to produce advanced coatings for varied applications. This work investigates the difference in structure and performance of Al2O3 coatings manufactured using conventional micron-sized powder feedstock and a suspension of sub-micron to few micron sized powder. Axial injection was implemented for deposition in both cases. The effect of feedstock size and processing on the tribological performance of the two coatings was of specific interest. The coatings were characterized by Optical and Scanning Electron Microscopy, micro-hardness and scratch resistance testing, and their dry sliding wear performance evaluated. The suspension sprayed coatings yielded significantly higher scratch resistance, lower friction coefficient and reduced wear rate compared to conventional coatings. The improved tribological behaviour of the former is attributable to finer porosity, smaller splat sizes, and improved interlamellar bonding. (C) 2017 Elsevier B.V. All rights reserved.

Keywords
Atmospheric plasma spray; Suspension plasma spray; Axial injection; Alumina; Coating; Microstructure; Micro-hardness; Scratch; Wear
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-10931 (URN)10.1016/j.surfcoat.2017.02.025 (DOI)000399268100009 ()2-s2.0-85013027004 (Scopus ID)
Available from: 2017-09-20 Created: 2017-09-20 Last updated: 2019-05-23Bibliographically approved
Joshi, S. V., Goel, S., Björklund, S. & Wiklund, U. (2017). Hybrid powder-suspension Al2O3-ZrO2 coatings by axial plasma spraying: Processing, characteristics & tribological behavior. In: : . Paper presented at International Thermal Spray Conference & Exposition, ITSC 2017, Düsseldorf, Germany, June 7-9, 2017.
Open this publication in new window or tab >>Hybrid powder-suspension Al2O3-ZrO2 coatings by axial plasma spraying: Processing, characteristics & tribological behavior
2017 (English)Conference paper, Oral presentation only (Other academic)
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-11965 (URN)
Conference
International Thermal Spray Conference & Exposition, ITSC 2017, Düsseldorf, Germany, June 7-9, 2017
Available from: 2017-12-29 Created: 2017-12-29 Last updated: 2018-08-12Bibliographically approved
Goel, S., Björklund, S., Wiklund, U. & Joshi, S. V. (2017). Hybrid powder-suspension Al2O3-ZrO2 coatings by axial plasma spraying: Processing, characteristics & tribological behaviour. In: Proceedings of the International Thermal Spray Conference & Exposition: . Paper presented at International Thermal Spray Conference and Exposition, ITSC 2017, Dusseldorf, Germany, 7-9 June, 2017 (pp. 374-379). New York: Curran Associates, Inc, 1
Open this publication in new window or tab >>Hybrid powder-suspension Al2O3-ZrO2 coatings by axial plasma spraying: Processing, characteristics & tribological behaviour
2017 (English)In: Proceedings of the International Thermal Spray Conference & Exposition, New York: Curran Associates, Inc , 2017, Vol. 1, p. 374-379Conference paper, Published paper (Refereed)
Abstract [en]

The ability of suspension plasma spraying (SPS) to overcome difficulties associated with feeding of fine (submicron or nano-sized) powders and achieve more refined microstructures than possible in atmospheric plasma spraying (APS) is well established. In recent times, the use of axial injection plasma spray systems has yielded substantial enhancement in deposition rates/efficiencies due to improved thermal exchange between the plasma plume and injected feedstock. The present paper describes utilization of both the above advances in plasma spraying to create various function-dependent coating architectures through simultaneous and/or sequential spraying of hybrid powder-suspension feedstock. A specific variant of such hybrid axial plasma spraying that enables deposition of composite coatings by simultaneous injection of a powder and a suspension is discussed in particular detail. Results obtained using an Al2O3-ZrO2 material system as a case study reveal that composite coatings combining the micron-size features arising from the spray-grade Al2O3 powder and submicron or nano-sized features attributable to the ZrO2 suspension can be conveniently realized. The surface morphology, microstructure, and composition of these coatings, as well as their tribological behaviour determined using scratch and ball-on-disc tests, are presented herein. The utility of this method to develop a wide array of composite coatings is also discussed. 

Place, publisher, year, edition, pages
New York: Curran Associates, Inc, 2017
Keywords
Alumina; Aluminum oxide; Deposition rates; Feedstocks; Microstructure; Plasma jets; Plasma spraying; Powder coatings; Tribology; Zirconia, Atmospheric plasma spraying; Ball-on-disc tests; Nano-sized features; Refined microstructure; Simultaneous injections; Suspension plasma spraying; Tribological behaviour; Various functions, Composite coatings
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-12908 (URN)2-s2.0-85047507789 (Scopus ID)9781510858220 (ISBN)
Conference
International Thermal Spray Conference and Exposition, ITSC 2017, Dusseldorf, Germany, 7-9 June, 2017
Available from: 2018-09-17 Created: 2018-09-17 Last updated: 2019-01-10Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-5676-7903

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