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Goel, S., Bourreau, K., Olsson, J., Klement, U. & Joshi, S. V. (2020). Can Appropriate Thermal Post-Treatment Make Defect Content in as-Built Electron Beam Additively Manufactured Alloy 718 Irrelevant?. Materials, 13(3), Article ID 536.
Open this publication in new window or tab >>Can Appropriate Thermal Post-Treatment Make Defect Content in as-Built Electron Beam Additively Manufactured Alloy 718 Irrelevant?
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2020 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 13, no 3, article id 536Article in journal (Refereed) Published
Abstract [en]

Electron beam melting (EBM) is gaining rapid popularity for production of complex customized parts. For strategic applications involving materials like superalloys (e.g., Alloy 718), post-treatments including hot isostatic pressing (HIPing) to eliminate defects, and solutionizing and aging to achieve the desired phase constitution are often practiced. The present study specifically explores the ability of the combination of the above post-treatments to render the as-built defect content in EBM Alloy 718 irrelevant. Results show that HIPing can reduce defect content from as high as 17% in as-built samples (intentionally generated employing increased processing speeds in this illustrative proof-of-concept study) to <0.3%, with the small amount of remnant defects being mainly associated with oxide inclusions. The subsequent solution and aging treatments are also found to yield virtually identical phase distribution and hardness values in samples with vastly varying as-built defect contents. This can have considerable implications in contributing to minimizing elaborate process optimization efforts as well as slightly enhancing production speeds to promote industrialization of EBM for applications that demand the above post-treatments.

Keywords
additive manufacturing, electron beam melting, defects, microstructure, hardness, alloy 718, hot isostatic pressing, post-treatment
National Category
Manufacturing, Surface and Joining Technology
Identifiers
urn:nbn:se:hv:diva-14926 (URN)10.3390/ma13030536 (DOI)
Available from: 2020-01-30 Created: 2020-01-30 Last updated: 2020-01-30
Sreekanth, S., Hurtig, K., Joshi, S. V., Andersson, J. & Ghassemali, E. (2020). Effect of Direct Energy Deposition Process Parameters on Single-Track Deposits of Alloy 718. Metals, 10(1), 01-16, Article ID 96.
Open this publication in new window or tab >>Effect of Direct Energy Deposition Process Parameters on Single-Track Deposits of Alloy 718
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2020 (English)In: Metals, E-ISSN 2075-4701, Vol. 10, no 1, p. 01-16, article id 96Article in journal (Refereed) Published
Abstract [en]

The effect of three important process parameters, namely laser power, scanning speed and laser stand-off distance on the deposit geometry, microstructure and segregation characteristics in direct energy deposited alloy 718 specimens has been studied. Laser power and laser stand-off distance were found to notably affect the width and depth of the deposit, while the scanning speed influenced the deposit height. An increase in specific energy conditions (between 0.5 J/mm2 and 1.0 J/mm2) increased the total area of deposit yielding varied grain morphologies and precipitation behaviors which were comprehensively analyzed. A deposit comprising three distinct zones, namely the top, middle and bottom regions, categorized based on the distinct microstructural features formed on account of variation in local solidification conditions. Nb-rich eutectics preferentially segregated in the top region of the deposit (5.4–9.6% area fraction, Af) which predominantly consisted of an equiaxed grain structure, as compared to the middle (1.5–5.7% Af) and the bottom regions (2.6–4.5% Af), where columnar dendritic morphology was observed. High scan speed was more effective in reducing the area fraction of Nb-rich phases in the top and middle regions of the deposit. The <100> crystallographic direction was observed to be the preferred growth direction of columnar grains while equiaxed grains had a random orientation.

Place, publisher, year, edition, pages
Basel, Switzerland: , 2020
Keywords
laser metal deposition (LMD); columnar dendritic morphology; constitutional supercooling; columnar to equiaxed transition (CET); high deposition rate
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-14922 (URN)10.3390/met10010096 (DOI)
Available from: 2020-01-29 Created: 2020-01-29 Last updated: 2020-01-29Bibliographically approved
Ganvir, A., Björklund, S., Yao, Y., Vadali, S. V. .., Klement, U. & Joshi, S. V. (2019). A facile approach to deposit graphenaceous composite coatings by suspension plasma spraying. Coatings, 9(3), Article ID 171.
Open this publication in new window or tab >>A facile approach to deposit graphenaceous composite coatings by suspension plasma spraying
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2019 (English)In: Coatings, ISSN 2079-6412, Vol. 9, no 3, article id 171Article in journal (Refereed) Published
Abstract [en]

This paper demonstrates, for the first time ever, the deposition of graphenaceous composite coatings using an easy, yet robust, suspension plasma spraying (SPS) process. As a case study, a composite coating comprising 8 wt.% of yttria-stabilized-zirconia (8YSZ) and reinforced with graphene oxide (GO) was deposited on a steel substrate. The coatings were sprayed using an 8YSZ-GO mixed suspension with varied plasma spray parameters. Establishing the possibility of retaining the graphene in a ceramic matrix using SPS was of specific interest. Electron microscopy and Raman spectroscopy confirmed the presence of graphenaceous material distributed throughout the coating in the 8YSZ matrix. The experimental results discussed in this work confirm that SPS is an immensely attractive pathway to incorporate a graphenaceous material into virtually any matrix material and can potentially have major implications in enabling the deposition of large-area graphene-containing coatings for diverse functional applications. © 2019 by the authors.

National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-13737 (URN)10.3390/coatings9030171 (DOI)000465608700002 ()2-s2.0-85062495390 (Scopus ID)
Available from: 2019-03-21 Created: 2019-03-21 Last updated: 2020-02-04
Joshi, S. V. & Nylén, P. (2019). Advanced Coatings by Thermal Spray Processes. Technologies, 7(4), 1-14, Article ID 79.
Open this publication in new window or tab >>Advanced Coatings by Thermal Spray Processes
2019 (English)In: Technologies, E-ISSN  2227-7080, Vol. 7, no 4, p. 1-14, article id 79Article in journal (Refereed) Published
Abstract [en]

Coatings are pivotal in combating problems of premature component degradation in aggressive industrial environments and constitute a strategic area for continued development. Thermal spray (TS) coatings offer distinct advantages by combining versatility, cost-effectiveness, and the ability to coat complex geometries without constraints of other in-chamber processes. Consequently, TS techniques like high-velocity oxy-fuel (HVOF) and atmospheric plasma spray (APS) are industrially well-accepted. However, they have reached limits of their capabilities while expectations from coatings progressively increase in pursuit of enhanced efficiency and productivity. Two emerging TS variants, namely high-velocity air-fuel (HVAF) and liquid feedstock thermal spraying, offer attractive pathways to realize high-performance surfaces superior to those hitherto achievable. Supersonic HVAF spraying provides highly adherent coatings with negligible porosity and its low processing temperature also ensures insignificant thermal &lsquo;damage&rsquo; (oxidation, decarburization, etc.) to the starting material. On the other hand, liquid feedstock derived TS coatings, deposited using suspensions of fine particles (100 nm&ndash;5 &micro;m) or solution precursors, permits the production of coatings with novel microstructures and diverse application-specific architectures. The possibility of hybrid processing, combining liquid and powder feedstock, provides further opportunities to fine tune the properties of functional surfaces. These new approaches are discussed along with some illustrative examples.

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
coatings, high-velocity air-fuel, plasma spray, solution precursor, suspension
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-14702 (URN)10.3390/technologies7040079 (DOI)000506662500012 ()
Available from: 2019-11-15 Created: 2019-11-15 Last updated: 2020-01-29
Sadeghi, E., Markocsan, N. & Joshi, S. V. (2019). Advances in Corrosion-Resistant Thermal Spray Coatings for Renewable Energy Power Plants. Part I: Effect of Composition and Microstructure. Journal of thermal spray technology (Print), 28(8), 1749-1788
Open this publication in new window or tab >>Advances in Corrosion-Resistant Thermal Spray Coatings for Renewable Energy Power Plants. Part I: Effect of Composition and Microstructure
2019 (English)In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 28, no 8, p. 1749-1788Article in journal (Refereed) Published
Abstract [en]

Power generation from renewable resources has attracted increasing attention in recent years owing to the global implementation of clean energy policies. However, such power plants suffer from severe high-temperature corrosion of critical components such as water walls and superheater tubes. The corrosion is mainly triggered by aggressive gases like HCl, H2O, etc., often in combination with alkali and metal chlorides that are produced during fuel combustion. Employment of a dense defect-free adherent coating through thermal spray techniques is a promising approach to improving the performances of components as well as their lifetimes and, thus, significantly increasing the thermal/electrical efficiency of power plants. Notwithstanding the already widespread deployment of thermal spray coatings, a few intrinsic limitations, including the presence of pores and relatively weak intersplat bonding that lead to increased corrosion susceptibility, have restricted the benefits that can be derived from these coatings. Nonetheless, the field of thermal spraying has been continuously evolving, and concomitant advances have led to progressive improvements in coating quality; hence, a periodic critical assessment of our understanding of the efficacy of coatings in mitigating corrosion damage can be highly educative. The present paper seeks to comprehensively document the current state of the art, elaborating on the recent progress in thermal spray coatings for high-temperature corrosion applications, including the alloying effects, and the role of microstructural characteristics for understanding the behavior of corrosion-resistant coatings. In particular, this review comprises a substantive discussion on high-temperature corrosion mechanisms, novel coating compositions, and a succinct comparison of the corrosion-resistant coatings produced by diverse thermal spray techniques.

Keywords
architecture composition high-temperature, corrosion microstructure, renewable energy, power plants, thermal spray coatings
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-14700 (URN)10.1007/s11666-019-00938-1 (DOI):000495068400001 ()2-s2.0-85074849441 (Scopus ID)
Funder
Knowledge Foundation, (RUN 20160201Region Västra Götaland, RUN 2016-01489
Available from: 2019-11-15 Created: 2019-11-15 Last updated: 2020-01-29Bibliographically approved
Sadeghi, E., Markocsan, N. & Joshi, S. V. (2019). Advances in Corrosion-Resistant Thermal Spray Coatings for Renewable Energy Power Plants: Part II - Effect of Environment and Outlook. Journal of thermal spray technology (Print), 28(8), 1789-1850
Open this publication in new window or tab >>Advances in Corrosion-Resistant Thermal Spray Coatings for Renewable Energy Power Plants: Part II - Effect of Environment and Outlook
2019 (English)In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 28, no 8, p. 1789-1850Article in journal (Refereed) Published
Abstract [en]

High-temperature corrosion of critical components such as water walls and superheater tubes in biomass/waste-fired boilers is a major challenge. A dense and defect-free thermal spray coating has been shown to be promising to achieve a high electrical/thermal efficiency in power plants. The field of thermal spraying and quality of coatings have been progressively evolving; therefore, a critical assessment of our understanding of the efficacy of coatings in increasingly aggressive operating environments of the power plants can be highly educative. The effects of composition and microstructure on high-temperature corrosion behavior of the coatings were discussed in the first part of the review. The present paper that is the second part of the review covers the emerging research field of performance assessment of thermal spray coatings in harsh corrosion-prone environments and provides a comprehensive overview of the underlying high-temperature corrosion mechanisms that lead to the damage of exposed coatings. The application of contemporary analytical methods for better understanding of the behavior of corrosion-resistant coatings is also discussed. A discussion based on an exhaustive review of the literature provides an unbiased commentary on the advanced accomplishments and some outstanding issues in the field that warrant further research. An assessment of the current status of the field, the gaps in the scientific understanding, and the research needs for the expansion of thermal spray coatings for high-temperature corrosion applications is also provided. © 2019, The Author(s).

Keywords
Boiler corrosion; Corrosion resistance; Corrosive effects; Damage detection; High temperature applications; High temperature corrosion; Power plants; Sprayed coatings; Superheater tubes; Thermal spraying, Corrosion-resistant; Effect of environments; environments; High temperature corrosion mechanisms; Operating environment; Performance assessment; Renewable energy power; Thermal spray coatings, Corrosion resistant coatings
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-14836 (URN)10.1007/s11666-019-00939-0 (DOI)000496259400004 ()2-s2.0-85075211091 (Scopus ID)
Funder
Knowledge Foundation, RUN 20160201Region Västra Götaland, RUN 2016-01489)
Available from: 2020-01-29 Created: 2020-01-29 Last updated: 2020-01-29Bibliographically approved
Sadeghi, E. & Joshi, S. V. (2019). Chlorine-induced high-temperature corrosion and erosion-corrosion of HVAF and HVOF-sprayed amorphous Fe-based coatings. Surface & Coatings Technology, 371(S1), 20-35
Open this publication in new window or tab >>Chlorine-induced high-temperature corrosion and erosion-corrosion of HVAF and HVOF-sprayed amorphous Fe-based coatings
2019 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 371, no S1, p. 20-35Article in journal (Refereed) Published
Abstract [en]

Chlorine-induced high-temperature corrosion and erosion-corrosion behavior of amorphous Fe-based coatings sprayed by high velocity air-fuel (HVAF) and high velocity oxy-fuel (HVOF) techniques were investigated. The coated specimens were first exposed to isothermal high-temperature corrosion at 600 °C in ambient air with and without KCl. The exposed specimens were then subjected to alumina erodent. The as-sprayed HVAF coating showed a more compact and uniform microstructure with a higher hardness leading to higher corrosion and erosion-corrosion resistance. After erosion, all the coatings similarly exhibited a combined brittle/ductile damage to surface oxide scale that previously formed in the corrosive environment. The corrosion and erosion-corrosion behavior of the coatings primarily relied on the uniformity of coatings’ microstructure and distribution of alloying elements to form the protective oxide scale in the corrosive environment, which can resist against erodent in the erosive media. © 2019 Elsevier B.V.

Keywords
Air, Alloying elements, Alumina, Aluminum oxide, Chlorine, Corrosion resistance, Corrosive effects, Erosion, Fuels, High temperature corrosion, HVOF thermal spraying, Microstructure, Potassium compounds, Scale (deposits), Sprayed coatings, Thermal spraying, Amorphous coating, Chlorine-induced high-temperature corrosion, Erosion - corrosions, HVAF, HVOF, Corrosion resistant coatings
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-13514 (URN)10.1016/j.surfcoat.2019.01.080 (DOI)000472694300004 ()2-s2.0-85060532855 (Scopus ID)
Funder
Knowledge Foundation, RUN 20160201Region Västra Götaland, 2016-01489
Available from: 2019-03-21 Created: 2019-03-21 Last updated: 2020-02-03Bibliographically approved
Aranke, O., Algenaid, W., Awe, S. & Joshi, S. V. (2019). Coatings for automotive gray cast iron brake discs: A review. Coatings, 9(9), Article ID 552.
Open this publication in new window or tab >>Coatings for automotive gray cast iron brake discs: A review
2019 (English)In: Coatings, ISSN 2079-6412, Vol. 9, no 9, article id 552Article in journal (Refereed) Published
Abstract [en]

Gray cast iron (GCI) is a popular automotive brake disc material by virtue of its high melting point as well as excellent heat storage and damping capability. GCI is also attractive because of its good castability and machinability, combined with its cost-effectiveness. Although several lightweight alloys have been explored as alternatives in an attempt to achieve weight reduction, their widespread use has been limited by low melting point and high inherent costs. Therefore, GCI is still the preferred material for brake discs due to its robust performance. However, poor corrosion resistance and excessive wear of brake disc material during service continue to be areas of concern, with the latter leading to brake emissions in the form of dust and particulate matter that have adverse effects on human health. With the exhaust emission norms becoming increasingly stringent, it is important to address the problem of brake disc wear without compromising the braking performance of the material. Surface treatment of GCI brake discs in the form of a suitable coating represents a promising solution to this problem. This paper reviews the different coating technologies and materials that have been traditionally used and examines the prospects of some emergent thermal spray technologies, along with the industrial implications of adopting them for brake disc applications. © 2019 by the authors.

National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear) Vehicle Engineering
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-14488 (URN)10.3390/coatings9090552 (DOI)000487973600064 ()2-s2.0-85072179966 (Scopus ID)
Funder
Swedish Energy Agency, 46393-1
Available from: 2019-10-01 Created: 2019-10-01 Last updated: 2020-01-30
Mahade, S., Curry, N., Björklund, S., Markocsan, N. & Joshi, S. V. (2019). Durability of Gadolinium Zirconate/YSZ Double-Layered Thermal Barrier Coatings under Different Thermal Cyclic Test Conditions. Materials, 12(14), Article ID E2238.
Open this publication in new window or tab >>Durability of Gadolinium Zirconate/YSZ Double-Layered Thermal Barrier Coatings under Different Thermal Cyclic Test Conditions
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2019 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 12, no 14, article id E2238Article in journal (Refereed) Published
Abstract [en]

Higher durability in thermal barrier coatings (TBCs) is constantly sought to enhance the service life of gas turbine engine components such as blades and vanes. In this study, three double layered gadolinium zirconate (GZ)-on-yttria stabilized zirconia (YSZ) TBC variants with varying individual layer thickness but identical total thickness produced by suspension plasma spray (SPS) process were evaluated. The objective was to investigate the role of YSZ layer thickness on the durability of GZ/YSZ double-layered TBCs under different thermal cyclic test conditions i.e., thermal cyclic fatigue (TCF) at 1100 °C and a burner rig test (BRT) at a surface temperature of 1400 °C, respectively. Microstructural characterization was performed using SEM (Scanning Electron Microscopy) and porosity content was measured using image analysis technique. Results reveal that the durability of double-layered TBCs decreased with YSZ thickness under both TCF and BRT test conditions. The TBCs were analyzed by SEM to investigate microstructural evolution as well as failure modes during TCF and BRT test conditions. It was observed that the failure modes varied with test conditions, with all the three double-layered TBC variants showing failure in the TGO (thermally grown oxide) during the TCF test and in the ceramic GZ top coat close to the GZ/YSZ interface during BRT. Furthermore, porosity analysis of the as-sprayed and TCF failed TBCs revealed differences in sintering behavior for GZ and YSZ. The findings from this work provide new insights into the mechanisms responsible for failure of SPS processed double-layered TBCs under different thermal cyclic test conditions.

Keywords
burner rig test, double-layered TBC, gadolinium zirconate, suspension plasma spray, thermal cyclic fatigue, yttria stabilized zirconia
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-14438 (URN)10.3390/ma12142238 (DOI)000480454300026 ()31336713 (PubMedID)2-s2.0-85070469165 (Scopus ID)
Funder
Knowledge Foundation, Dnr-20140130
Available from: 2019-10-02 Created: 2019-10-02 Last updated: 2020-02-03
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: 2020-02-04Bibliographically approved
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