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Towards more sustainable approaches for protecting surfaces against wear
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. (KAMPT)ORCID iD: 0000-0001-8404-8180
2023 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

WC-Co coatings, with and without chromium additives, are widely used in the industry for severe tribological applications. However, concerns about cobalt supply and its environmental and health impacts have led industries to explore sustainable binder alternatives. As a deposition technique, high velocity air-fuel(HVAF) spraying technology offers a promising solution by producing dense WC-based coatings with minimal material degradation during spraying. Moreover, the combination of high velocity and low flame temperature in HVAF enables the deposition of finer powders, which are more susceptible to thermal damage, with minimal decarburization. This results in denser coatings with improved properties compared to conventional spraying techniques. Therefore, this thesis aims to evaluate more sustainable approaches to depositing WC-based wear resistant coatings involving (a) HVAF as a less energy-intensive technique compared to other methods like high velocity oxy-fuel (HVOF), (b) alternative Co-lean/free binders, and (c) fabrication of thin ('flash') coatings from finer feedstock powders.

In HVAF spraying, particles’ in-flight temperature and velocity can be influenced by the process variables including nozzle configuration as well as feedstock particle size distribution. On the other hand, the chemistry of metallic binder can also play a key role in determining both properties and performance of these coatings. In this thesis, characteristics and tribological behaviour of HVAF sprayed WC-CoCr coatings were investigated by spraying feedstock powders with varying particle sizes (ultra fine: 15/5, fine: 20/5, medium: 30/5 and coarse: 45/5um) employing different nozzle configurations (various lengths and divergence convergence configurations). Additionally, different WC-based feedstocks, comprising alternative binders to traditionally used CoCr (namely NiMoCrFeCo, FeNiCrMoCu and FeCrAl) were investigated. Results showed that the HVAF spraying excelled in processing WC-based powders with various size distributions, enabling the deposition of thinner coatings from fine powders ('flash' coatings) with similar properties/performance as thick coatings. This leads to reduced material usage while offering potential for considerable component life extension, both of which are important elements of sustainability. Additionally, it was concluded that the Co-lean/Co-free binders demonstrated comparable, and in some cases superior performance than the reference Co-based binder under various wear conditions. All of these together can represent a significant step forward towards more sustainable approaches for protecting surfaces against wear.

Abstract [sv]

WC-Co-beläggningar, med och utan kromtillsatser, används i stor utsträckning inom industrin i slitagekrävande applikationer. Oron för koboltförsörjningen och kobolts miljö- och hälsoeffekter har dock fått industrin att leta efter mer hållbara alternativ. Höghastighetsflamsprutning med luft (HVAF) är en lovande sprutteknik för att producera täta WC-baserade beläggningar med minimal materialpåverkan. Den låga temperaturen och den höga kinetiska energin hos partiklarna i lågan som sprutas med HVAF, kan möjliggöra användning av finare pulver, vilket potentiellt kan resultera i tätare och tunnare beläggningar med förbättrade prestanda. HVAF tekniken skulle även kunna vara en potentiell teknik för att åstadkomma koboltfria beläggningar. Slitageegenskaperna hos WC beläggningar som är koboltfria och som sprutas med HVAF är dock okänt. HVAF teknikens potential för att kunna ersätta hög hastighetsflamsprutning med syre (HVOF), som är den teknik som dominerar på marknaden idag vid sprutning av täta slitagebeständiga beläggningar är även okänt. HVAF är ett intressant alternativ till HVOF eftersom metoden kräver mindre energi jämfört med HVOF. Vid sprutning med HVAF kan partiklarnas temperatur och hastighet i lågan påverkas med hjälp av processvariabler, munstyckskonfiguration och genom att variera tillsatsmaterialets storleksfördelning. Partiklarnas hastighet och temperatur i lågan påverkar i sin tur den sprutade beläggningens mikrostruktur som i sin tur påverkar beläggningarnas egenskaper. Även den kemiska sammansättningen hos tillsatsmaterialet kan spela en stor roll för beläggningsegenskaperna.

I detta arbete utvärderas slitageegenskaper hos HVAF-sprutade WC-CoCr beläggningar där tillsatsmaterialet har olika storleksfördelning och olika munstyckskonfigurationer. Slitageegenskaperna jämförs med beläggningar som sprutats med tillsatsmaterial som saknar kobolt (NiMoCrFeCo, FeNiCrMoCu och FeCrAl).

Resultaten visar att HVAF-tekniken fungerar mycket väl för sprutning av WC baserade tillsatsmaterial med olika storleksfördelningar, vilket möjliggör produktion av tätare och tunnare beläggningar jämfört med de beläggningar som produceras industriellt idag. Resultaten visar även att koboltfria beläggningar som sprutats med HVAF ger jämförbara, och i vissa fall, överlägsna prestanda avseende slitagebeständighet. Både HVAF tekniken och utnyttjandet av koboltfria material är sålunda möjliga alternativ för att åstadkomma mer hållbara lösningar för slitagekrävande industriapplikationer.

Place, publisher, year, edition, pages
Trollhättan: University West , 2023. , p. 49
Series
PhD Thesis: University West ; 59
Keywords [en]
Wear; HVAF spraying; WC-Based Coatings; Sustainability; Binder Chemistry
Keywords [sv]
Slitage; HVAF; WC-baserade beläggningar; Hållbar produktion; Bindemedelskemi
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
URN: urn:nbn:se:hv:diva-20914ISBN: 978-91-89325-60-9 (print)ISBN: 978-91-89325-59-3 (electronic)OAI: oai:DiVA.org:hv-20914DiVA, id: diva2:1810792
Public defence
2023-11-28, F131, Gustava Melins gata, Trollhättan, 10:00 (English)
Opponent
Supervisors
Note

Paper F is not included in the digital thesis due to the copyright.

Available from: 2023-11-09 Created: 2023-11-09 Last updated: 2024-01-15Bibliographically approved
List of papers
1. Advances in Thermally Sprayed WC-Based Wear-Resistant Coatings: Co-free Binders, Processing Routes and Tribological Behavior
Open this publication in new window or tab >>Advances in Thermally Sprayed WC-Based Wear-Resistant Coatings: Co-free Binders, Processing Routes and Tribological Behavior
2022 (English)In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 31, no 3, p. 342-377Article in journal (Refereed) Published
Abstract [en]

A growing understanding of wear behavior of various thermally sprayed ceramic–metallic matrix coatings has occurred over recent years. This has resulted from the continuous evolution in spraying methods as well as material feedstock, and the corresponding new aspects of the field that have been thoroughly explored. This paper aims to review recent developments in thermally sprayed tungsten carbide-based coatings, with specific emphasis on evaluating alternative binders, processing routes and tribological behavior of the coatings. A comprehensive evaluation of various compositions as binders for WC-based coatings, considering environmental concerns and market requirements has been carried out. The properties and performance of various potential alternatives for cobalt as a conventional binder for these coatings have been assessed. Moreover, different thermal spray methods have been reviewed, particularly highlighting the role of processing parameters, phase change and feedstock characteristics in the high-velocity oxy-fuel (HVOF) and high-velocity air fuel (HVAF) techniques. A comparison is made between HVAF and HVOF coatings in terms of their performance under different wear environments. Finally, various scenarios of material removal in HVAF and HVOF coatings, under various wear conditions, have also been reviewed.

Keywords
Co-free binders, HVAF, HVOF, tribology, WC-based coatings, wear mechanisms
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-20916 (URN)10.1007/s11666-022-01358-4 (DOI)000763240100001 ()2-s2.0-85125521489 (Scopus ID)
Note

CC BY 4.0

Available from: 2023-11-09 Created: 2023-11-09 Last updated: 2023-11-09
2. Influence of Test Conditions on Sliding Wear Performance of High Velocity Air Fuel-Sprayed WC–CoCr Coatings
Open this publication in new window or tab >>Influence of Test Conditions on Sliding Wear Performance of High Velocity Air Fuel-Sprayed WC–CoCr Coatings
2021 (English)In: Materials, E-ISSN 1996-1944, Vol. 14, no 11, article id 3074Article in journal (Refereed) Published
Abstract [en]

Sliding wear performance of thermal spray WC-based coatings has been widely studied. However, there is no systematic investigation on the influence of test conditions on wear behaviour of these coatings. In order to have a good understanding of the effect of test parameters on sliding wear test performance of HVAF-sprayed WC–CoCr coatings, ball-on-disc tests were conducted under varying test conditions, including different angular velocities, loads and sliding distances. Under normal load of 20 N and sliding distance of 5 km (used as ‘reference’ conditions), it was shown that, despite changes in angular velocity (from 1333 rpm up to 2400 rpm), specific wear rate values experienced no major variation. No major change was observed in specific wear rate values even upon increasing the load from 20 N to 40 N and sliding distance from 5 km to 10 km, and no significant change was noted in the prevailing wear mechanism, either. Results suggest that no dramatic changes in applicable wear regime occur over the window of test parameters investigated. Consequently, the findings of this study inspire confidence in utilizing test conditions within the above range to rank different WC-based coatings.

Place, publisher, year, edition, pages
Basel: MDPI, 2021
Keywords
Tests conditions, sliding wear, HVAF, WC–CoCr, ball-on-disk, wear mechanism
National Category
Manufacturing, Surface and Joining Technology
Identifiers
urn:nbn:se:hv:diva-16509 (URN)10.3390/ma14113074 (DOI)000660279500001 ()2-s2.0-85108228061 (Scopus ID)
Available from: 2021-06-10 Created: 2021-06-10 Last updated: 2024-01-12Bibliographically approved
3. Influence of nozzle configuration and particle size on characteristics and sliding wear behaviour of HVAF-sprayed WC-CoCr coatings
Open this publication in new window or tab >>Influence of nozzle configuration and particle size on characteristics and sliding wear behaviour of HVAF-sprayed WC-CoCr coatings
Show others...
2021 (English)In: Surface and Coatings Technology, ISSN 0257-8972, Vol. 423, p. 1-16, article id 127585Article in journal (Refereed) Published
Abstract [en]

In this study, effect of feedstock particle size and nozzle configuration on deposition, microstructural features, hardness and sliding wear behaviour of high velocity air fuel (HVAF)-sprayed WC-CoCr coatings was evaluated. Three different WC-CoCr powders with nominal particle sizes of 5/20 μm (fine), 5/30 μm (medium) and 15/45 μm (coarse) were sprayed employing a HVAF gun with four distinct DeLaval nozzle configurations involving different lengths and/or exit diameters. Microstructure, phase constitution and mechanical characteristics of the coatings were evaluated using SEM, EDS, XRD and micro indentation testing. Specific wear rate for all the samples was determined under sliding conditions and a comprehensive post wear analysis was conducted. X-ray diffraction analysis showed negligible decarburization in all the HVAF-sprayed coatings. It was shown that decrease in particle size of employed feedstock results in discernible changes in microstructural features of the coatings as well as considerable improvement in their performance. Also, notable changes in wear mechanisms were identified on reducing particle size from coarse to medium or fine. Fine and coarse feedstock powders were found to be sensitive to the type of nozzle used while no major difference was observed in coatings from powders with medium cut size sprayed with different nozzles.

Place, publisher, year, edition, pages
Elsevier, 2021
Keywords
Particle size, Nozzle configuration, HVAFWC-CoCr, Sliding wear
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-17483 (URN)10.1016/j.surfcoat.2021.127585 (DOI)000697566200017 ()2-s2.0-85108196054 (Scopus ID)
Available from: 2021-09-22 Created: 2021-09-22 Last updated: 2023-11-09Bibliographically approved
4. Tribological behavior of HVAF-sprayed WC-based coatings with alternative binders
Open this publication in new window or tab >>Tribological behavior of HVAF-sprayed WC-based coatings with alternative binders
Show others...
2022 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 436, article id 128296Article in journal (Refereed) Published
Abstract [en]

The tribological performance of High Velocity Air-Fuel (HVAF) sprayed WC-based cermet coatings with binders containing no or very limited amount of cobalt was evaluated under dry sliding, erosion, and abrasion wear conditions. The wear and corrosion behaviors of WC-NiMoCrFeCo, WC-FeNiCrMoCu and WC-FeCrAl HVAF sprayed coatings were investigated and compared to standard WC-CoCr coatings as benchmark. Microstructure characterization along with XRD analysis was conducted on all powders as well as the corresponding coatings. Comprehensive post wear analysis was conducted on all coatings subjected to ball-on-disk, gas jet erosion and dry sand-rubber wheel abrasion tests. Moreover, all coatings were exposed to 3.5% (wt./vol.) NaCl aqueous solution to evaluate their corrosion performance through electrochemical testing. XRD results showed negligible phase transformation between the powders and the deposited coatings. The WC-NiMoCrFeCo coating exhibited the best sliding wear and electrochemical corrosion performance, with an average specific wear rate value of 3.1 x 10(-8) (mm(3).N-1.m(-1)) and a corrosion current density of 1.9 mu A/cm2. This coating also showed comparable abrasive wear resistance to the WC-CoCr coating. Under erosive wear conditions, too, the WC-FeNiCrMoCu and WC-FeCrAl coatings showed a comparable performance to the benchmark. Dominant wear mechanisms for the reference WC-CoCr coating, under sliding wear conditions, were abrasion (deep grooving) and surface fatigue (crack propagation and pitting). On the contrary, no pitting was observed in WC-NiMoCrFeCo and WC-FeCrAl coatings during the sliding wear test. No considerable difference was identified in the wear mechanisms of the different coatings under abrasion and erosion wear conditions. The results highlight the promise of some of the environment friendly binders studied to replace Co.

Place, publisher, year, edition, pages
Elsevier, 2022
Keywords
Sliding wear; Erosion; Abrasion; Electrochemical polarization; Cermet coatings; High Velocity Air-Fuel (HVAF)
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-18313 (URN)10.1016/j.surfcoat.2022.128296 (DOI)000779413000001 ()2-s2.0-85125519738 (Scopus ID)
Funder
Swedish Research Council, HiPerCOAT (Dnr. 20180197)
Available from: 2022-09-26 Created: 2022-09-26 Last updated: 2023-11-09Bibliographically approved
5. Tribological Performance of Thin HVAF-Sprayed WC-CoCr Coatings Fabricated Employing Fine Powder Feedstock
Open this publication in new window or tab >>Tribological Performance of Thin HVAF-Sprayed WC-CoCr Coatings Fabricated Employing Fine Powder Feedstock
2022 (English)In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016Article in journal (Refereed) Epub ahead of print
Abstract [en]

In this study, sliding and abrasion wear performance of WC-CoCr coatings deposited by high velocity air–fuel (HVAF) spraying with various thicknesses (i.e., 240, 150, 100, 50 and 30 µm), fabricated from fine feedstock powder (5–15 µm), were evaluated. The main aim was to investigate how thinner coatings (30 and 50 µm) perform compared to conventional thick coatings (> 100 µm), in an effort to address the supply and cost concerns associated with Co and W. The feedstock powder and deposited coatings were characterized in terms of microstructure. The hardness of the thin and thick coatings was measured using Vickers hardness method from both cross section and top-surface. It was found that, regardless of the thickness, extremely dense coatings with very high hardness ( 1500 HV) can be deposited employing HVAF and fine feedstock powder. Thin and thick coatings were found to perform similarly under sliding wear with a normal load of 10 N or lower as well as under abrasion wear conditions which highlights the possibility of employing thinner coatings for a majority of the real applications. The results suggest that peening effect does not have a considerable influence on the microstructure or performance of the deposited coatings. However, for sliding wear tests with a 20 N normal load, it was noticed that wear resistance of the coatings slightly declines with decreasing thickness of the coating beyond 150 µm. The main reason was identified to be the involvement of substrate effect when performing tests under severe Hertzian contact pressure.  

Place, publisher, year, edition, pages
Springer, 2022
Keywords
abrasion, coatings, HVAF, sliding wear, thickness, WC-CoCr
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-19505 (URN)10.1007/s11666-022-01506-w (DOI)000895619600001 ()2-s2.0-85143848781 (Scopus ID)
Note

 The authors would like to thank Arashk Memarpour, Oliver Lanz from Höganäs for supporting this study through helpful discussions and by providing feedstock powders. Thank to Magnus Sandberg for assistance in preparing the samples. Also, financial support of the Knowledge Foundation, Sweden, for project HiPerCOAT (Dnr. 20180197) is gratefully acknowledged.

Available from: 2023-01-23 Created: 2023-01-23 Last updated: 2023-11-09

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Torkashvand, Kaveh

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